*^^iixw% 11.^3 #■ -tH. 'tj^ ' ».. ^^- •■^% ;*■■ j-"^*»^-* *«^ »'> (* THE PAINTER AND VARNISHER'S GUIDE; OR, BOTH IN THEORY AND PRACTICE, ON THE ART OF MAKING AND APPLYING VARNISHES ; ON THE DIFFERENT KINDS OF PAINTING j AND ON THE METHOD OF PREPARING COLOURS BOTH SIMPLE AND COMPOUND: WITH NEW OBSERVATION'S AND EXPERIMENTS ON COPAL; OW THE NATURE OK THE SUBSTANCES EMPLOYED IN THE COMPOSITION OF" VARNISHES AND OF COLOURS-, AND ON VARIOUS PROCESSES USED IN THE ART. BEDICATED TO THE SOCIETY AT GENEVA FOR THE ENCOURAGEMENT 0Î THE ARTS, AGRICULTURE, AND COMMERCE. BY P. F. TINGRY, PROrEJSOR OF CHEMISTRY, NATURAL HISTORY, AND MINERALOOT IN THE ACADEMY OF GENEVA. ILLUSTR.\TED WITH ENGRAVINGS. LONDON: PP.1NTED FOR G. KEARSLEY, FLEET-STREET, By J. Taylor, Black-Horse-Court. 1804. 5os- TC '4':^' ^ AUTHOR'S PREi^gfe.^^ The Society established at Geneva for the En- couragement of the Arts, Agriculture, and Com- merce, charged its Committee of. Chemistry to take into consideration those arts of which no methodical descriptions had been given by the Academy of Sciences at Paris. It was, indeed, intended by the Academy that the art of var- nishing should form a part of their collection ; and de Machy, one of the members, had, I believe, prepared some materials for that pur- pose, but on the publication of Watin's work in 1772 he seems to have abandoned his design. This art, which is of modern date in Europe, notwithstanding the assistance thus given to it by Watin, still required that the principles on which it is founded, and by which it can be carried to perfection, should be more fully ex- plained and illustrated. Every thing that re- lates to the history of the colouring parts, and to the operations which make them appear witli^ their true properties, has in that publication been either omitted or neglected. The Com- a2 74- IV AUTHOR S PREFACE. mittee of Chemistry, in consequence of some observations which I had made on the arts in my pubHc or private lectures, were of opinion that a new work on this subject would form a valuable and even necessary addition to that of Watin: they conceived also, that as this art is one of those wliich are entirely founded on chemistiy, it ought to be treated according to the modern system. I engaged to undertake this labour; and I now present the result of it to the public, with the approbation of the So- ciety to whom I have dedicated it. INTRODUCTION. 1 HOUGH it is commonly supposed that painting in oil was not known before the fourteenth century, it is probable ^hat the antients employed it for ornamenting their porticoes. The fragments of painting with which the fronts of some of the edifices discovered among the ruins of Hercvdaneum and Pompeia are still decorated, and which have escaped the ravages of time, and the impression of the volcanic ashes under which they were buried, appear to me sufficient au- thority for this observation. But the wars which hastened, and those which followed, the fall of the Roman empire j the almost general devasta- tion which was the result of them ; the conversion of po- lished nations, by a series of calamitous circumstances, into Goths and Vandals ; and the ages of barbarism which suc- ceeded, dissipated the last traces of industry and of the progress of civilization ; changed or corrupted every thing, and even the language of the subjected nations, which a state of oppressive servitude reduced and accustomed to the mere necessaries of life. Those accumulated scourges to which Europe was ex-r posed were, however, confined within certain limits, by that desire wJiich men have for peace when nothing more remains for them to destroy ; and by that peace itself^ which' gradually restores them to the use of their reason, and brings them back to the dignity of their nature.- Their physical strength is then employed in seconding the efiorts of the imao;ination and of genius. Their thou i>;hts are em- ployed on new objects ; discoveries are multiplied ; com- mercial intercourse is re-established between nations ; the wants of society are enlarged in proportion to the extent of a.3 AI INTRODUCTION. this communication^ and a desire of enjoyment increaseâ. All these effects, the result of a more settled state of go- vernment, soon tended to ameliorate agriculture j to im- prove the necessary arts ; to extend those which contribute to heighten the comforts of life; and to call forth those sciences which form the chief glory of nations. It is, no doubt, unfortunate that the scourges which, during the different convulsions among mankind, poison in this manner all the sources of public happiness ; which fall heavily on enlightened nations, and either disperse or en- tirely destroy them, should leave to their successors only fragments that have escaped the general devastation. Th» sciences disappear with men of talents. It then becomes necessary to open new routes on a degraded soil, and the genius which advances in the career of discovery often ar- rives, after much labour, at results of which anterior ages have left some faint traces. Every thing connected with the secrets of industry would, no doubt, have been saved, had the valuable discovery of those processes which consti- tute the art of printing preceded that of the mechanical arts. It appears almost certain, that the varnishes which have been made and employed for many centuries by the nations who inhabit the eastern parts of Asia were in part known also to the Romans. The ruins of Pompeia remove every doubt in regard to the use which these people made of oil painting to ornament their buildings. Some pieces of their copper coin, struck under the reign of Trajan, and dug up from antient ruins, are covered, as Count Caylus remarks, with a kind of resi'^ious varnish, similar to that which would result from a mixture of oil and black pitch*. If the * It is not possible to conceive what advantage could result from the ap- |/!icadM of a coarse varnish, which deprived the coin of iu metallic spleji- dour, and destroj^ed the relief of the impression, wlxicU displays the talents of the engraver, and gives an ideal value to coin». lîîTRODUCTION. yA antients were ignorant of the art of grinding, mixing up, and combining oil colours, which, however, there is no reason to suppose ; and if they did not carry to such an ex- tent as the moderns those mechanical processes which assist painting of the first kind (that of picturas), it cannot be doubted that the Greeks, in particular, were acquainted with the art of giving lustre to the colours which they em- ployed in their fine compositions, and also of preserving them. The names of a Timanthes, a Zeuxis, an Apollodorus, a Polygnotus, a Pausias, and a Parrhasius, who by their warm compositions added lustre to the ages of Pericles and of Socrates ; who combined grace of disposition with bright- ness of colouring ; boldness of design with mellowness of execution ; and who produced masterpieces which exist only in the descriptions transmitted to us, show how great were the losses which followed the destruction of liberty among the Grecian republics. Their means, without being so extensive as ours, were sufficient, according to the ex- pression of Parrhasius, to give their compositions as much solidity as enabled them to withstand the influence of the air. It is well known that oily or resinous matters were mnch employed amon-^ the Romans. The use of perfumes, sepulchral lights, and flambeaux, was very extensive In their public and private ceremonies. A resinous kind of cement was much employed also by these people in building. It is, there- fore, probable that the conflagrations by which Rome and so many other fine cities were destroyed, and the revolutions of which Italy was tliq theatre, may have been the real causes of that resinous incrustation ob- terved on some of the Roman copper coins dug up from antient ruins. It seems to be probable also, that similar accidents, by which various jnatters were mixed in confusion and buried for so many centuries, may have given rise to thzt patine so much esteemed by antiquaries, which they seek for on certain coins, and which seems to be merely a production of time. Thç decomposition of water, and the oxidation which is a certain result of it, are, no doubt, the principal causes of the formation of this crust, or smooth and sometimes shining paste, which is so gratifying to the eager eye of th#' antiquary. VIIl INTRODUCTION*. But were Apellcs, Protogcncs^ and Aristitles, who suc- ceeded to the glory of these early painters, and who in some things even surpassed them, better acquainted with the art of preparing colours, and the means of giving them more body and more solidity? — If the preservation of the colour- ing was owing to a varnish, or to substances capable of making a varnish, did thev mix them, as some modern painters do, with the colouring parts, even when distributed on the palette ? — or did they reserv'e them to be applied to the composition after it was finished ? There is no monument in existence which can enable us to resolve these jjuestions. The masterpieces of Apelies, and those of the painters who preceded him, disappeared with the generations who saw them produced. Gum water and wliite of egg, which are still employed for certam pieces of painting, v;erc not perhaps neglected. Being ill calculated, however, by their nature to resist the impression of moisture, and the vxashing rendered necessar)' in conse^ quence of their being dirtied by insects, they could not be any security to artists that their v.orks would be handed down unimpaired to posterity. The mixture of oils and resins, and that of resins with alcohol (spirit of ^^ine), which form real varnishes, are alone endowed with the va- luable property of checking the ravages of time. Since no trace of the compositions of the antient masters remains, there is reason to presume that our means were unknown to them; or that they employed processes less effectual; or that their works were condemned to the same fate as so many other productions of human industry, and were lost in the wreck of time. If we even suppose that the Greeks had acquired by their commercial intercourse some knowledge of the Chinese varnish, they could not apply it to their fine paintings, both on account of the consistence which that varnish is known INTRODUCTION. IX to possess, and of its colour, which must have presented an obstacle still more insurmountable. The same Greeks, however, were in possession of a kind of painting which was attended with the advantage of brav- ing the influence of the air and of the sun, and of not being subject to those reflections of light which render it neces- sary that oil paintings, to be seen with advantage, should be placed in a particular situation ; I here mean encaustic, or painting in wax, which was lost, and which was revived by two celebrated men in the last century. Vieu, a very ingenious painter, to whom the fine arts are under great obligations, made an attempt, under the au- spices of Count Caylus, to paint in this way a head of the Virgin, which was engraved in the chalk manner. En- caustic found a no less enlightened protector a few years ao-Q in Counsellor Rafelschtein. Some Italian artists, assist- ed by his advice, and by the encouragement which he gave them, executed several paintings of this kind, which ob- tained the approbation of connoisseurs. Encaustic painting possesses more strength than that in distemper. Its uniform mellowness produces more har- mony in the tones, which the spectator readily catches in every position. This method of painting does not adniit of any kind of varnish applied after the work is tinished. Wax, which is the essential basis of it, and which com- bines exceedingly well vvith the colours, becomes the causa of the consistence and pliablcness of the painting, vv'hen it )ias received from a pretty strong heat that inustion, which makes it penetra.te into the canvas. The canvas, v^hen it has thus imbibed the wax, exhibits a thin flexible stratum^ which is nevertheless susceptible of a very fine polish. Nothwithstanding all those kinds of degradation which, the fine arts experienced under the Lower empire, and par- ticularly towards its fall, Greece might, perhaps, still boast of masterpieces of encaustic, from the hands of Polygno- if INTRODUCTION. tus of Thasos, had they not, after nuie centuries of admira- tion, become a subject of envy or emulation to one of the- Rôman praetors, who caused them to be transported to the capital of the world, where they shared in the fate of so many other valuable monuments of antiquity. All the arts approach each other in more or fewer points, atid in a manner more or less perceptible. This affinity is more sensible in the mechanical arts, which are employed on objects of the first necessity, than in those the principles. of which depend on the progress of civilization, and which require a knowledge of combinations, and an intimate ac- quaintance with the materials which they consume or which Ihey modify. A knowledge of the analogies discovered be- tween certain resinous substances belongs to the analytical part of chemistry : it consequently comprehends a long series of processes ; and it docs not appear that this science, which led to the discovery of varnish, formed a part of the gérions occupations of the Greeks. The greater part of the mechanical, and we may even say of all the arts, began to be attended with conspicuous suc- cess onlv at that period when the facts relating to them were sufficiently connected to admit of their being formed into a theory. This assertion;, which might be generalized, is more particularly applicable to those arts which depend on the cffiects of chemical combinations. At every step ob- stacles occur ; every thing appears new and strange; and inconstancy in the results of experiments, often intrusted to chance, discourages in enterprises which the least know- ledge of theory vvould render successful. It may readily be believed that the discovery of varnish was the fruit of re- peated trials ; and though those who made them had conti- nually in their hands the essential materials, there was still wanting a motive, which was soon created among peaceable and industrious nations, by a taste for luxury, and by com- jDercial communication. 4 INTRODUCTION, XI Bat, if a knowledge of the theoiy which is now appHed to certain manipulations in the arts, founded on the em- ployment of chemical combinations, is deduced from a great number of leading facts, so intimately connected with these manipulations that they are a necessary and even expected result of them, the cause of them would, perhaps, have remained long unknown, without the influence of societies established for the purpose of exciting and calling forth the energies of the human mind. The public respect attached to these associations of learned men and artists distinguished by their merit, and still more the support of governments, which promote experiments and enterprises that require en- couragement, have contributed not a little towards those interesting discoveries for which the present period is cele- brated. In regard to painting, some of the happiest results arising from these associations were, that the study of history was facilitated to young artists ; that they were surrounded, jri some measure, with masterpieces of the old painters ; that their judgment was exercised with respect to chasteness of execution, propriety of arrangement, and correctness of design ; this was rendering them familiar with real beauty, and inspiring them, at length, with the genius of the Greeks. This genius, which among the Athenians in particular was exalted by the establishment of liberty, which was kept in full activity by commerce, and to which a spirit of enterprise was conmiunicated by prosperity, necessarily raised them above that simplicity of manners by which na- tions who apply to agriculture, to those arts which are purely mechanical, or to a pastoral life, are characterized. This genius was formed to direct taste, to create it even, and to soar to the sublime in all its great conceptions. This was the case at Athens by the intercourse which the Greeks kept up v/ith their neighbours j the latter were made to Xll INTRODUCTION, participate in their glory. The fine arts ha\'e their con- quests j and these conquests arc tlie more certain as they become minçïlcd with, and increase, our dearest enjoyments. They produce emulation; and conduct, by a sure path, to that taste for real heauty which announces the progress of civihzation. ^ In tracing out these grand effects, one is naturally led to inquire into the cause v\hich produced them. This cause we can look for only in that rational liberty which inspires men with the desire of employing all the resources of their talents; which, by an insensible gradation, raises one indivi- dual above another ; which induces them to divest them- selves of all envy on account of merit different from their own, or which surpasses it ; and which makes them seek happiness in a continued intercourse with virtuous citizens, Avhom the public opinion has invested with respect. Such v.as the use which Athens made of her liberty during the period of her splendour : it was in this manner that plain citizens, but distinguished by particular talents, concurred to produce those important results with vt'hich the interests of nations are so intimately connected; which raise them into notice, and which turn to the greatest benefit of man- kind the intercourse they maintain with others. The Greeks, in consequence of their republican institu- tions, were able to extend much further those advantages which we make to depend on difîerent learned societies, such as those established in Italy, in France, and in other countries, of Europe. Their progress, therefore, was much more rapid than ours, and their enterprises were more marked with grandeur. We are indebted to them for all the splendour displayed by the fine arts among us ; but im fortunately we do not yet possess all their riches. But, in matters of government, the best institutions are not sheltered from the instability attached to human affiiirs. The prosperity of the Greek republics \va5 soon blasted by their INTRODUCTION. • xKi intestine divisions. The fine arts laiigmshéd, and seemed to expire along with the flame of Ubcrty ; /and if the inter- course afterwards renewed between the na,tiGns of antient Greece, and those of Asia and India in particular, by the conquests of Alexander the Great, seemed to revive the arts in their antlent country ; if it seemed to recall the flourishing periods of a Pericles ; it was only, as we may say, to afford an opportunity of collecting those valuable ma- terials which Italy and other countries were afterwards, ia some measure, to naturalize and to improve. The Thebaid, the most remote part of Egypt, which is now a desert, notwithstanding the ravage of time, still attests the influence of the fine arts of Greece on the people of that country. It would appear, from the recent observa- tions of some travellers who visited the ruins of Thebes, that the antient inhabitants of this country were well versed in all the branches of design and of painting. If the fresh- ness which still characterizes some fragments discovered in antient galleries buried amidst ruins, seems to prove that the painters were then acquainted with the" same means, or others equivalent to them, v.hich the modern painters employ to preserve their works for posterity, — this circumstance must afford new motives for applauding the v/onderful discovery of the art of printing, which becomes the most certain safeguard to the productions of the human mind against that spirit of devastation by \Ahich all conquering nations are animated. I have already observed, that a state of peace in a nation which has been agitated by long convulsions has^ a much greater influence on the arts than any other circumstance depending on its particular genius. The Chinese, situated in the extremity of Asia, seem to form an exception to this remark, the justness of which in regard to the freer na- tions of Europe can be better appreciated. Among the former, the uninterrupted exercise of their arts is never ex- XIV INTRODUCTION. tended beyond habit and routine ; but it corrects^ to a cer- tain degree, the faults which arise from their aversion to imitation. They are never excited by a spirit of emulation. The son becomes the servile copyist of the works of his fa- ther : he has no idea of improvement ', and while manipu- lations are thought to be every thing, theory is neglected. This is clearly observed in the methods which the Chinese pursue in the application of their lakes -, in the style of their painting ; in the forms which they give to the difFerent ar- ticles of their manufacture, , and which appear to be as im- mutable as their empire. Their transparent varnish is com- posed of two substances only. The addition of common colours, without variation, constitutes their different lakes ; and the physical properties of these two substances contri- bute more than art to the solidity of their compositions. If the nations of Europe, and particularly the French, had found in their territories the natural production which sup- plies the Chinese with the principal ingredient of their var- nish, solidity combined wàth elegance of fonn ; highly finished painting, delicacy of design, and splendour of co- lours, would have soon made the art of the varnisher and painter be considered as one of the first sources of national riches, in consequence of the extent it would have given to various branches of commerce. But the spirit of imitation, strengthened by the know- ledge acquired in regard to chemical analysis, at length na- turalized in France an art which seemed to be confined to the remotest parts of Asia. The observations of the Jesuit missionaries on certain arts cultivated by the Chinese, and on some of the most important branches of their industry, excited a spirit of emulation among artists, and induced them to repeat the processes of their inventors ; to supply those deficiencies which might arise from want of suffi- cient inibrmation, in consequence of the reserve which forms a prominent feature in the character of these people ; INTIl)DDUCTION. XV and to correct those faults which might' proceed from a dif- ference in the substances employed*. The publicity of these observations marks out the period of Our enterprises and success in a new series of processes before unknown ; and the execution of them, whether servile imitations or modi- fied according to the ingenuity of the artists, seemed to be so much connected with our enjoyments, that there was rea- son to conclude the result w^ould be a suflkiency of mate- rials and information to enable artists to subject the. mecha- nical processes to correct principles, as well as invariable rules; and to add a new art to those already known. In the year 173/ such a spirit of emulation was excited among the French artists, in consequence of some models or varnished articles brought from China, and such an en- thusiasm for imitating this varnish, which was rqjrescnted as being unalterable in the fire, that people were almost dis- posed to prefer varnishe' to metallic vessels. The dreams of the credulous alchemists were not entirely useless to the chemists who succeeded them : in the same manner, this ephemeron enthusiasm was not lost to society. The imagination, when it dwells for a long time on one ob- ject, will at length arrive at some valuable discovery. These attempts to obtain an incombustible varnish gave birth at length to a new art, which was the more lucrative to France as it has not, like so many other objects, experienced the effects of the inconstancy of taste. I here allude to the art of making varnished paper snufi-boxes, &c. Among the artists employed in this new branch of in- dustry, there was one for whom it was reserved to extendits limits, by applying it to objects of luxury of the highest importance. The celebrated Martin, being furnished with good compositions of varnish, soon combined the two kinds * See Lettres édifiantes et cvricuses published by the Jesuits. The details of Father d'Incarville respecting the Cliijiese varaish may be found in the M/' mvires des Savons Mirangers, vol. iii. Xvi /•■' , /? INTRODUCTION. ." •^' ., ■ '-:-'^ cf.p,gnntihg. Ifft>talled in to his aid the art of the gilder, anid gàye ib^that importance which always arises from the wants of mé public. In a word, all the arts belonging to coach-making received from it an assistance the more cer- tain as thev all depend on an inexhaustible source, namely, a taste for show, to which the opulent sacrifice every thing. An art so fertile in resources could no longer be confined to external objects of luxury. A taste4"or the decorations applied to apartments, during this continued and progres- sive improvement, was extended from palaces to the habita- tions of the rich, and by the effect of imitation was trans- ferred thence to the humble abode of the citizen in easy circumstances. The processes, however, employed at this period were agreeable to the experience of artists who had been engaged, for the most part, in those simple operations used for paint- ing in distemper. The m.ost intelligent confined themselves to a series of processes for which they were indebted to par- ticular researches, or to communications from amateurs di- stinguished by their fortune or their knowledge, or w hich ihey obtained from venders of secrets, a kind of people who are very common in professions founded on chemical opera- tions. Each process, therefore, bore evident marks of the ignorance or inexperience of the artist. Hence the differ- ences obser\'ed in the colouring, brilliancy, consistence, tenacity, or dr\Tiess of the varnish employed. The operator, too easily satisfied with his first attempts, proceeded no further in the improvement of his art. The secret was the more strictly observed, as it seemed to secure a certain re- source to the industry and family of the possessor. Hence also that incoherence in the formulae which different works seemed to confirm, and which they extol as the properest for answering the intended purpose. Hence, also, that im- jnense collection of obscure recipes, said to be derived from the best sources, which artists of ability sooa condemn;^ INTRODUCTION.! because they find them at variance withX&^trué-^irii^fflles of the art. The works intitled Les Secretsn^^-ts<^ $Ie- tiers*. Le Dictionnaire des Arts, L'Art du Veritvs^^r, Le Parfait Vernisseurf and other small essays; of this kind, abound with faults, arising from the bad choice of the editors, and which deprive them of the merit attached to good elementary works, and to methodical descriptions of the arts. The interest of the practitionei*, therefore, raised a barrier which prevented the art from approaching towards theory. It wasj however, necessary that the latter should become the basis of all future researches, in order to throw light on the different processes, to ascertain the nature of the results by a rigorous comparison, and thus to establish the real principles of the art. This happy effect was, in part, pro- duced by the public spirit of an artist who was so generous as to disclose some processes which I here propose to ex- amine, presenting them in a new order of distribution, and adding the necessary observations. Watin, to whom I here allude, did not forget the interest of the artist when he intrusted his precepts to the writer charged with preparing them for the press. But while he reserved the secret of certain processes, which were his own, he did not observe that by contributing to reduce the art to certain principles, he at the same time prepared means for lessening its difficulties, and of enabling artists to arrive speedily at that happy period when all reserve becomes use- ' A work in four large volumes, %vlth the attracting title of Secrets emu- ctrnanr les -irts et Meiiers, was published a fewyears ago. It is a crude com- pilation of all the processes with which the different periods of the various arts On whicli it treats have been encumbered. The art of varnishing occupies 2 whole volume, which contains, without choice, every thing, good or bad, relating to it. One may ri-adily perceive that it is more calculated to mislead the arti§t amid?t a labyrinth of contradictory formula;, than to guiMe him ift Lis progrt-ss by a series of principles which might enable him to bUiupfe iVt^ry tiling foreign to the main ob;ect of his researches. less.- 6r ri^iailoug. Had he lard open all his processes, he would certainly have acted more consistent with those prin- cijiles by which he seemâ to have been guided. Notwithstanding his reserve, which displays in a striking manner the spirit by which e'v'en the most experienced artists tife influenced, his work will always form an epoch in the- art of \'amishing. He unites in the same point of view a series of practical precepts founded on long experience, and which have hitherto been followed by the most intelligent painters : but the greater part of those who in country place» exercise thiâ profes-sion are guided in their operations by a faulty routine. Whatever treatise may in future be written eft this ttsêful art, it can only clear the path, which this author has in some measure traced out, from the shackles which real theory always imposes on the artist who is i^ierel/ a manipulator; and no addition in this respect can :••; .mv manner lessen the favourable opinion with A\'hich Watin's work was received. With this spirit I undertook to review a subject which ha» been treated by various au- IhorSy coi\&ideriinfg it under its different aspects, combining iif with every thing reserved for it by the new chemistry, aftd with many other arts which seem to require from it a .new support. It is much to be wished that this devotion to the public .ihtercèt were more imitated by artists of every class; but l^artieidarly by tkose whose manipulations depend on che- mical mixtures or combinations, as in the manufacturing of printed cottons, the art of making paper hangings, in dyeing. Sec, the various formulae of which are scattered among the conductors of manufactories. These processes, which for the most part have been the fruit of some acci- dental circumstances, would soon experience, by the free concurrence of artists and chemists, advantageous modifi- «•ations which w^oyijd lead to new discoveries. Society would thus be writhed with good descriptions of the artsj INTRODUCTION. xix and thege would add to the great importance attached to those valuable collections published by the ci-devant Aca- demy of Sciences at Paris, in regard to objects which have a powerful influence on the happiness and prosperity of empires. It is not my intention to follow the art of the varnisher through all the details which may seem suited to those artists who are more particularly employed in the decoration of carriages and other objects of luxury. I shall more im- mediately confine myself to an illustration of the principles. These alone are applicable to all circumstances in which the painter and varnisher are interested. They will lose no- thing by being condensed: and if they conduct the pupil and amateur, ûy a sure path, to that eminence from which they can see the extent of the art, they cannot be foreign to those complete artists who, by their talents and their mas- terpieces, contribute to feed the luxury of large cities. My object is to place in a conspicuous point of view every thing that can assist the varnisher and painter in regard to matters which fall within the province of their profession ; and, in some measure, to conduct the amateur by the hand. The composition of varnish is connected with a particular ki^id of knowledge respecting the physical and chemical properties of the dry or liquid substances which form its constituent parts. The study of these objects must induce artists to follow them in the effects which arise from the extreme division they expeyience, wnen brought into con- tact, according to certain laws. The kind of chemical phse- nomenon which takes place in the latter case depends, then, on rules and precepts established by experience. The art is gradually enlarged by all those parts which seem to have a coincident, relation. Painting in distemper preceded the discovery of painting in oil ; and the latter was some years anterior, as appears, to the invention and application of. varnish. These three parts touch each other in inseparable b2 XX IXTÊODtTCTION. points; but thcy have each their distinct rules, and are suffici- ently rich inmattcrs to iustifv the appropriation of one divi- sion of the work to a particular description of then». I have, therefore, been induced to divide this treatise into two parts. The first comprehends an historical account of the diy or liquid substaiices which concur towards the composition of varnish. The ingrredients employed in the different compositions of varnish arc (k'scribi d, in general, in works which form no part of the libraries of pupils or of artists.' I there- fore considered it mv duty to introduce this subject, to banish from it all tliose articles which are foreign to the art, and to subjoin sucli ol^servationJ as I thought iiseful, be- cause tliey appeared to me proper to excite a taste for study, to facilitate insiructic i, and to concur in a direct manner to produce that body of inlormation which is expected in a methodical work. It was necessary that an examination of the dry substances should be followed by an account of the duTcrent fluids em- ployed as excipients or vehicies in these compositions. A mere nomsnclç'ture would not have excited that interest which the study of thein requires : the case, however, is different when they are exhibited under all those relations which tend to make knov. n their nature, their particular properties, and the modi lications resulting from the prelirai- narv preparations to v.hich they are subjected. I then proceed to genc^ral observations on varnishes j which are followed by 3 distribution of them into two classes. The latter of thtse, or that which I have here chietly in view, is subdivided mto five genera, each contiiin- jng a certain nuriiber of spcries, or particular kinds, whjch are admitted into these genera according to their nature, their consistence, and the properties of their component, pp.vts. INTRODUCTION. XXÎ - This division, which is well calculated to facilitate a. knowledge of them, is followed by an examination of gene- ral precepts in regard to the composition of varnish on a. large scale. The object I had here in view could have been answered onlv In an imperfect manner if, in following all the details of rhe manipulations, I had neglected the means of rectifyinç^ them, in such a manner as to secure artists from those serious accidents with which these operations are often accompanied. I conceived that the use of an alembic of a new form might facilitate that rotary motion \\hich must necessarily be given to the matters inclosed in it, and at the same time prevent those inconveniences which arise from the too sudden tumefaction or evaporation of the Inflamma- ble liquid. It was neccssar)', also, that I should communicate to artists some observations, which are still more particularly my own, in regard to the solution of copal in essence of turpentine, a fact contested by Watin, though it seemed to be proved by some experiments of Lehman. The secret cause of this difference of opinion deserves to be known, as well as every thing that can facilitate the use of copal varnish made with essence or with ether. If the first part of this treatise is destined to make known the substances which concur to the composition of varnish, as well as the processes by which artists are en^tbled to o;ive them the requisite properties, the second, which contains an examination of the colouring substances, and of every thing tliat relates to the different branches of common paint- in Sixth species of the same genus, for giving a gold tint to arti- cles of brass. No. 9 ibid. Seventh species of the same genus. Changing varnish, or varnish destined to change or to modify the colour of those bodies to which it is applied, No. 10 12^ XJi^es of it ibid. Varnish employed by the artists of Geneva for giving a gold colour to die heads of small nails, used for ornamentir.g watch-cases 123 Eight species of the same genus. Changing varnish whicîi may be emplo) ed to give a gold colour to watch-cases, watch-keys, and articles made of brass, No. 11 ibid. Comparison between varnishes of tlie first and second genera and those of the third and fourth •. . . . 129 •TiURD Gen'us of varaishes. Varnishes with essence of tur- - pontine 13d Colouring parts soluble hi alcohol and insoluble in essence . . 131 Superiority of v?,rnlshes made with eseence to those corn- posed with alcohol ibid. First species of variiish for valuiblf' paintings. No. 12 133 Observations on the varnl^hfe? .ipplicd to paintings 134 ■SX. TABLE OF CONTENTS, Methods of preserving and cleaning pictures ". 135 Second species of the same genus, for grinding colours. No. 13 13S Third species of the same genus. Varnish proper to be em- ployed in mixing up colours for gi-ounds, No. 1-1 139 Fourth species of the same genus. Changing varnish of a less dr)-ing quality than tlie species Nu. 10., and applicable to metal. No. 15. 140 E.Kplanation of the term changing varnisb, * 141 Process for var/ii\g, vithout confusion, tlie different tints of changing varnish 142 Fifth species of the same genus. Varnish distinguished by the name of mordant. No. l6 143 Uses to which mandants of this hind are applied ibid. Mixtures which are often used for mordants 144 New mordant , ibid. FouHTH Genus. Copal varnishes made with ether and es- sence of turpentine' 145 Observations on the nature of this genus compared witli that of the preceding ibid. First species. Copal varnish \\'ith etlier. No. 17 14/ Eemarks on ether ibid. Quaiitity of copal dissolved by etlaer 14S Second species. Copal varnish witli esseiice of turpentine. No. 18 149 Observations on this process, which gives a solid varnish ex- ceedingly beautiful when applied to nietnliic surfaces .... 150 Third species. Copal varnish made witli essence by means of au iatcrmedlate substance. No., I9 15] Method of making copal held in solution hi oil of lavender to pass into essence 152 Fourtli species. Copal varnish by an intermed.Jtc substance according to a mediod given in tiie Jorrnai de Physique, No. 20 I5i Observatloni on this method ibid- Fll'tîx species. Cop;.d varnish by the m.edium of cafr^phOi and eiieiulal oil of lavende? destined for article* which require TABLE OP CONTEN-TS. XXX\ durability, pliableness, and transparency ; such as the var- nished wire-gauze used in ships instead of gkiss. No. 21. 154^ Observations and experiments in regard to tlie influence -of intermediate substances, and particularly that of camphor on the solution of copal in idcohol 15(5 Singular effect of camphor on resins ibid. Repetition of Mr. Sheldrake's experiments 157 First experiment with essence ibid. Second experiment with alcohol ibid. Third experiment, Etfect of camphor in strong doses .... 158 Fourth experiment. Effects produced by the varieties of copal 150 Fifth experiment. Kind of elasticity given to copal l6Ô Sixth experiment 16"1 Seventh experiment ibid. Singular anomalies arising from the particular nature of the different specimens of copal l63 Description of a furnace destined for the liquefaction of copal and amber in order to render them more soluble 105 Method of conducting the operation 1(X) New properties of copal when treated according to the pro- posed method Ijro Sixth species. Copal vai'nish with essence of turpentine with- out any intermediate substance. No, 22. lyi New experiments and observations on copal iy:i Object of these experiments and conclusions deduced from " them 1 S j Essence better suited than alcohol to the composition of var- nish isg Observations on the varieties of copal, and the chemical pro- perties it exhibits , igi Fifth Genus. Fat varnishes 1q3 First species. Extracted from Watin's work. No. 23 195 Second species of the same genus, employed in the manfac- tories of Geneva for watch-cases in imitation of torfeoise- shell. No. 24 106 Third species. Amber varnish, No, 25 « . jo/ XSXlt TABLE OP COKTENTs^ Vessels employed for tlie liquefiiction of amber . .'". . ...... igB New preparation of amber to render it fitter for the composi- tion of varnish 200 Amber varnish with essence of turpentine 203 Fourth species. Fat amber or copal varnish. No. 26' 204 Fifth species of the same genus. Fat varnish of a gold co- lour. No. 27 206 Sixth species of the same genus. Fat varnish which may serve as a mordant to gold and at the same time to dark colours, No. 2S ibid. Se\enth species of the same genus. Caoutchouc varnish. No. 29 20r Another varnish which may belong to this genus, and wi''.ich is destined for nautical purposes 209 CHAPTER IV. Gsr.cral ohscrvulkmi and precepts respecting the preparation of var- nish on a large scale. Description of an alemlic 7t'ifli a lalneum maricc, the use of ivtù«h prevents all those accidents that fre- quently, accompany the making of varnish 210 Peculiar qualities which distinguish good varnishes 211 All resins not proper for this preparation 212 Origin of the art of making boxes and toys of papier mâché, gilt leather, &c 214 Advantage of essence of birpentine as a \ elude in the compo- sition of certain varnishes 215 Causes which assign certain limits to oils in the preparation of varnish ibid. Distinction to be made between the efi'ccts of chemical disso- lution and those arising from simple solution 21(5 Washing of resins before they are employed in the composi- tion of varni.:,h , 218 Oa the necessity of a reduction in the number of the formulae 219 Of the choice of the matters 220 Of the respective doses of the dry and liquid substances .... 221 Of the effects of mechanical division on resins which oppose the i-rep.test resistaiico to solution 223 TABLE OF CONTENTS. XXXÎil Of the use of pounded glass T7.V . . 7. . . 223 Of clarification 225 Of filtration through cotton 226 Of tlie preparation of varnishes in open vessels, and the pre- cautions they require 227 Description of an alembic proper for the preparation of var- nish 230 Method of conducting the operation with this varnish 234 CHAPTER V. Observations on the influence which the solar light has to render es- sence of turpentine pr&perfor the solution of copal, so as to com- pose a durable and colourless varnish ^ 239 Object of these researches founded on the difierence of opi- nion amCTig chemists and artists in regard to the solubility of copal in essence 240 Anomalies observed in the same essence in regard to the solu- bility of copal 242 Particular crystallizations observed in essence exposed to the sun in close vessels 244 Chemical characters of this salt re-dissolved in water 246 Conclusive experiments in regard to the influence of time and light on essence to render it fit for the solution of copal . . 250 Conjectures respecting the composition of copal 256 Comparative table showing the addition made to tlie specific gravity of essence^ and the degrees of the influence exer- cised by the solar light in the course of a year 2^5 Geaeral consequences and conclusion Q,6g XXXIV TAELE OF CON'TÊKxi, PART THE SECOND. CHAPTER I. Historical account of the colouring suh s tunc es used in painting, u'ith a description of the processes employed to extract them, and of the methods of preparing or modifying them 2/9 Bougival white,, nature of it 280 Cremnitz ^^'hite 281 . Composition of a white to which the author gives the name of Cremnitz white 285 Spanish white 28d (îypsum 28/ White of Moudon or of Morat 289 White lead. White oxide of lead by vinegar ibid. Method of preparing it 29O Precautions in regard to grinding it 292 Ceruse. Oxide of lead by vinegar ibid. Mixed with white clay in different doses 2g3 Rouen wJiite 294 AVhite of Troyes. White chalk. Carbonate of lime 295 Inconvenience which attends chalk when not twice washed 296 White of zinc. Sublimated oxide of zinc. Calx of zinc. Flowers of zinc , 297 StTpposed fault in consequence of its dryness. ............. 2Q9 Method of preparing it ibid. Azure. Enamel blue. SafFer blue. Saxon blue. Vitreous oxide of cobalt 300 Method of preparing it ibid. Smalt or coarse Saxon blue 302 Ultramarine ibid. Preparation of ultramarine according to Kunckel's method . . 305 Neumann's process 306 Metliod of ascertaining v^-hether ultramarine be adulterated. . 30/ Researches respecting tins mineral colour ..,,., 308 TABLE OF CONTENTS, XXXV New observations on it by G^iyton de Morveau 30^ Prussian blue. PjTissiate of iron ibrtL Method of preparing it 3 ià\ Cause of the sfrsenish tint observed in sonàe kinds of Prussian . "-- ■»' r , '.' ' blue .",.,.,.. I. . . 312 , Artificial Saxon blue made with prussiate of u-on ........... 313 Blue verditer 314'. Pelletiev's process for the preparation of it 31(5 . Green verditer 31/ Cinnabar. Vermilion, Red sulphurated oxide of mercury . . 3 IS Naples yellow. Yellow oxide of lead mixed with white oxide of antimony by nitre 319 Method of preparing it 320 Montpelier yellow. Yellow oxide of lead by the muriatic acid 322 Chaptal's mediod of preparing it . . ibid. Indigo 324 Easy method of pulverizing it . ; ; . . . ibid. Of lakes 326 Carmine, method of preparing it .............. 329 Carminated lake. No. 1., preparation of : . . . . ibid. Another method of preparing carminated lake by extracting the colouring part from scarlet clotli .....' 332 Rouge for the toilette •....." 333 False carminated lakes in which the colouring part is different from tliat of cochineal ......'..... 334 Carminated lake extracted from madder. No. 2 ibid. EiFect of acetite of lead and arseniate of potash'on madder lake. No. 3 336 Lake from Brasil wood. No. 4 ••..:... ibid. Another process. No. 5 . . , . , . 33jj7 Keason for preferring carbonate of soda to carbonate of potash, •• in preparing lakes by chemical decomposition .-...,- 33B New researches respecting the means of distinguishing real ■ carminated lakes from those of an irifèrlor quality ... ■ .33'9 Comparative table exliibiting the results of these researches ' 340 Oxides of lead. First degree of oxidation. Gray' oxide . . . . 343 Massicot'. Yellow oxide of lead. Second dégree-'ôf oxidafîdH' ^44 C2 yX3«yi TABLE OF CONTENTS. Minium. Red oxide of lead. Third degree of oxidation .T.. 344 I/itliargeof gold or of silver. Vitreous oxide of lead. Fourth degree of oxidation 345 Lamp black. Fat soot resulting from the decomposition of resins and oils by fire 34/ Particular kind of lamp black 348 Beech black. Beech charcoal ibid. Black from wine lees 34g Black from burnt peach stones ibid. Black from burnt vine twigs 350 Ivory black. Bone black ibid. Of ochres 351 Brown ochre ibid. Ochre de rue 352 Calcined ochre de rue ibid. Natural yellow ochres ibid. Red ochre ibid. English red. Reddish brown and dark red oxide of iron with- out raixtnre 354 Method of pulverizing it 355 Prussian red. How prepared 356 Litmus. Method of preparing it ibid. Orpiment. Yellow sulphurated oxide of arsenic 35/ Considerations on the use of it ibid. Realgar. Red sulphurated oxide of arsenic 358 Anatto. Charged extract of a colouring fecula ibid. Bastard saffron. Flowers of cartliamus 360 Spanish vermilion 36l Red sandal wood. Colouring part soluble in water and in alcohol, but insoluble in oils 362 Dutch pinks 363 Dutch pink from -woad ibid. Another kind of Dutch pink 364 Dutch pink from yellow berrries ibid. Brownish yellow Dutch pink by tlie decomposition of sul- phate of alumine (alum) 365 TABLE OF CONTENTS. XXxfA putch pink with Spanish wliite, or with ceruse, preferable for oil painting ,. 365 Umber earth 3(5/ Green earth of Saxony 308 Green earth of Verona 369 Terra mérita ibid. Verdigris. Green oxide of copper by vinegar 370 Purification of it. Distilled verdigris. Acetite of copper .. 372 Liquid verdigris for colouring maps 3/5 Sap green ibid. CHAPTER II. Philosophical account of the origin of colours, npplied to materiat colours, simple and compound; ivith a description of the processes wMch art employs to vary the number and richness of the tints re- sulting from a mixture of them , . 37/ Idea of Isaac Vossius respecting colours ibid. Theory of Newton 378 Observations on white and black, which the theory of optics does not admit as colours 37p Primitive material colours , , 3S0 Secondary colours ibid. General view of the etTect produced by the mixture of colour- ing bodies , SSI Of virgin tints 38$ Particular characters which render certain coloured bodies proper for painting 384 Composition of coloms 33/ Black ibid. Composition of brown applied to tobacco-boxes 388 White -380 Difference between whites destined for distemper and those reseiTed for varnish and oil painting ibid. Composition of colours in which ceruse pre4ominates 39I Light gray ibid. Means of destroying tlie smell of varnish made with essence ibid, 5 rXXiVlU TABLE OF CON'TENTS. Pearl gray 3g% Flaxen gray ibid. Colour of oak wood SgA Colour of walnut-tree wood ibid. Ydlow 395 Pure and modified yellows ibid. Naples and Montpelier yellow ibid. Jonquil ibid. Lemon yellow 396 Observations on the use of orpiment mixed with ceruse .... ibid. Golden yellpw colour 397 Chamois colour. Buff colour 398 Olive colour ibid. Blue ibid. Observations on the use of prussiate of iron and indigo .... 399 Blue made with Saxon blue 401 Green colour and its compounds '. 402 Sea green ibid. Sea green for distemper ibid. Sea green for varnish 403 Green colour for doors, shutters, iron or wooden railing, pali' sades, balustrades, and for all articles exposed to the air ... 404 Compound colours for rooms 405 Compound green ibid. Green colour for articles exposed to friction and blows, such as the wheels of carriages, &c 4Q&. Ked colour for the bodies of carriages, coach-wheels, kc. . . ibid. Red for buffets 408 Mixed reds ibid. Bright red ibid. Crimson. Rose colour 409 "Violet colour ibid. Chesnut coloiu- ihid. Precepts in regard to dark colours 410 TABLE OF CONTEXT^. XXxl* CHAFTER III. Of the extent which may le given to the use of the turpentine copal ' varnishes Nos. 18. and 22., ly impregnating them ivith various solid colouring parts, transparent and proper for ans?vering the purpose of glazing on metalliclaminœ, sinootkor ornamented; for imitating transparent enamel, nnd for repairing those accidents if hie h frequent I II happen to enamelled articles 412 Transparent green colour 415 Another green colour 417 Another green colour by composition 413 Blue colour • . v ibid. Superb liquid blue .-. . . 420 Yellow 42 1 Dark red . .' 422 Violet .' ibid. Observations on the application of turjxnrtine copal varnish to brilliant metaliic surfaces ". . 423 Application of copal varnish to the reparation of opake en- amel 425 Method of making the coloured pastes 426 White paste ' 42/ Black ibid. Yellow ibid. Blue ■ 428 Qreen. . ibid. Red ibid. Purple ibid. Brick red ibid. Chr.mois colour ; ibid. Violet 429 Pearl gray ibid. Flaxen gray "........ ibid. Remarks '. ibid. On the method of making coloured foil 430 First preparation ■ .' . 43 1 Second preparation ibid. Blue colour .,'...".,. 433 ''-'' : TABLE OP CONTENTS* .A iiéfhcr blu'e .'. . . i v é ..... . 432 (jieeri. \ ibid. lied ,, . 433 Violet ibid. I.ilac 434 r»uby colour ibid. Hose colouf ibid. Ponceau. Poppy red. 435 Prune colour and other browTis ibid. ObseiTations on the application of these colours ibid, CHAPTER IV. Precepts respecting the application of varnishes, coloured or not co- loured, which the artist or araateur ought always to keep in re- membrance. Of the different kinds of painting. Of varnished linen and silk 43/ Precepts respecting pulverization 43S Necessary relation between the nature of varnish and that of the bodies to which it is to be applied ibid. Advantages arising from the gi'eat division of colours 440 Metliods of knowing when a colour is properly ground .... 441 Quantity of matter which may be ground at one time 442 Consistence requisite in mixing up colours ibid. Precautions to be observed when colours are ground in essence 443 Application of the different kinds of varnish to particular pur- poses 444 Methods employed by painters in tlie application of varnish on a large scale 445 Reasons for preferring varnish of the third and fourth genera 44S Method of applying varnish 450 Comp^'ison between the European and Chinese method of varnishing 451 On the nature of Chinese varnish 45% Diiierent method of applying the European and Chinese var- nish 454 How to destroy the smell of vaiTiish 455 Metltod of cleanifig varnish 458 TABLE OF CONTENTl. - /^ ' ''! \ ^^ Method of cleaning clothes stained with oil ^ofê;irs. •C^; • >^'\Q0 How to preserve colours and brashes^ so thh^^iey n^^be2;_\ again fit for use .^^^^/.^^.^ ib|d. Of oil painting '►■vr^.v-^'461 Oils proper for painting articles exposed to the weather, and articles kept in apartments. . 402 Precepts in regard to oil painting ihid. Observations on tlie two kinds of oil panting 4G8 Polishing 46g Wax cloth or oil cloth 4/2 Common wax clotli or varnished cloth 4/4 Metliod of making the liciuid paste to be appHed to the clodi 475 Fine printed varnished clotlis 477 Comparison between the process employed for these clotlis and calico printing 4/3 Varnished siik ibid. Two kinds of it ibid. Apparatus for preparing it 4/9 Remnants of silk how employed to advantage 4S0 Another kind of varnished silk 482 Covul plaster ibid. Adulteration of it how detected 484 CHAPTER V. Of painting in distemper. Sizing. Composition of colours for di^ s temper. General precepts in regard to this Iranch of the art 485 Origin of distemper ibid. Différent kinds of glue proper for this purpose 486 Glue of the first quality. Fish glue 487 Consistence which glue ought to have for different purposes 488 Glue of the second quality) or that made from glovers' clip- ^ pings and parchment 489 Glue of the tliird quality, or common glue ibid. Sizing 4Q1 ("^ases which require size to be cold or warm 492 General precepts applicable to painting in distemper ibid. Three kinds of distemper 4(j4 XÎii TABLE OF CONTENTS. First kind. First example 4Q5 Second example. Painting in milk 49S Resinous painting in milk 500 Third example. Painting for the fire-places and hearths in kitchens, &c. Genevese method 501 Fourth example. Distemper for parquets or floors of inlaid work 503 Fifth example. Red for corridors and halls paved with tiles 504 Œconomical method of reddening new tiles 505 Sixth example. Distemper in badigeon 506 Genevese method of giving a new appearance to the walls of old edifices 50/ Second kind of distemper. Varnished distemper. Chipolin. . ibid. Imitation of Chipohn 511 Third kind of distemper. Royal white 513 Simple method of discovering whether chalk or Spanish white has been substituted in painting for ceruse 515 CHAPTER VI. Of the instruments necessary in the art of varnishing. Observations on the use of some of them 51/ Meaning attached to tiie term painter 518 Situation proper for the workshop of tlie varnisher 5I9 Of die laboratory, and instruments necessary for the labour 521 Of tlie different kinds of brushes 524 Report made to tlie committee of chemistry of tlie society at Gene\ a for the encouragement of the arts on this new trea- tise on the art '^f preparing varnishes, and of composing the colours mixed up with them. ByM, Senebier 527 PART THE FIRST, CONTAINING- AN ACCOUNT OF THE SUBSTANCES USED IN MAKING VARNISHES, AND THE METHOD OF PREPARING THEM. TREATISE ON VARNISHES, PART THE FIRST. CHAPTER I. Historical account of the nature and properties of the sul" stances which form the lasis of varnishes j and of the eX' ternal qualities by which the lest kinds, may he known. ASPHALTUM. AspHALTUM is a bituminous substance, which in some countries is very abundant. The Peruvians, and in particular the Egyptians, formed it into a paste, and filled with it the cavities of those dead bodies which they were desirous of embalming. They gave to it also, by the help of certain mixtures, the consistence of varnish, and dipped in it the cloth which they wrapped round these bodies after they had been embalmed. This substance is a kind of mineral pitch, susceptible of acquiring a certain degree of consistence. The prin- ciples of its composition appear to be different from those which distinguish certain artificial kinds of pitch, resulting from the spontaneous or accidental decompo- sidon of a vegetable substance of an ir flammable nature. Asphaltum seems to participate a little in animal matter, B s Treatise on varnishes. It is of a black colour, the tone of which is not uni- form. Sometimes the surface of the pieces exhibits a capuchin black, while the interior is darker and glos- sier. It is employed, under certain circumstances, by painters in oil-colours', though its application in this kind of painting has by some been condemned. In common painting it is admitted into the composition of black lakes, and mixtures destined for coloured grounds, and for representing articles of iron : it is, however, rarely mixed with other substances. When employed, it is dissolved over a slow fire^vith prepared cil, until the result is a pretty thick liquid, which, when a rod has been immersed in it, runs from it as oil would do, and not at intervals or in separate portions. It may be readily conceived that this circumstance will depend on the proper proportions v\'hich must be observed, in the respective quantities of the two ingredients. Asphaltum issues in a liquidi form from the bottom of the lake Asphaltis in Judsea ; and hence the name of Jew's pitch, -which is given to it. It rises to the sur- fiice of the water, where it is dried by the combined action of the sun and of the air. To be good, it ought to be solid and brittle ; to have a brilliant surface as if poHshed; and to be almost black. If fragments of asphaltum, formed into thin laminse, be held between the eye and the light of a candle, the colour of them appears to incline to red. When cold it einits very little smell ; but when inflamed it has a .strong, penetrating, bituminous odour. It is often adulterated with pisasphaltum, another kind of bitum<=n, lees solid, the odour of which holds a meaa rank between that of pitch and that of bitumen. BENJAMIN. ô BENJAMIN. Benjamin . is a hai'd, dry, brittle, inflammable sub- stance, of a resinous taste, and which v/hen thrown on burning coals emits a sweet penetrating odour. It results froiri .1 resinous sap, which distils by incision from a kind of hadamier very abundant in some parts of India ; on the Malabar coast, and particularly in Cochinchinaj and in the islands of Sumatra, Java, &c. When this resin is fresh it has the consistence of a balsam, such as it is seen in turpentine ; it then gradu- ally thickens, and forms white tears, which are com* bined with other tears more coloured, either by the im- pression of the light, or by mixture with some part of the bark of the tree, or with dust driven abaut by the winds. This mixture of white tears, which the brown- ness of the mass renders still more striking, makes the whole have the appearance of nougat*, containing portions of peeled almonds ; and hence the name of amygdaloid given to this benjamin in commerce, to distinguish it from a more common kind of a fawn- colour, which is mixed with saw-dust, seeds, and other impurities. By sublimation, without any intermediate substance, and even by simple ebullition in water, benjamin fur- nishes a salt which assumes the form of snowy flakes, in consec^uence of the union of small tufts of very ii:^^ht argentine needles, exceedingly odorous, which to the taste manifest a remarkable principle of acidity. * Nov^at is a kind of preparation made in France from almonds.-^T. » b2 4 TREATISE ON VARNISHES. This particular salt, which forms the essential cha- racter of balsams, is foreign to the composition of var- nish. Benjamin ought to be chosen with as little colour as possible ; and if purity be required in the varnish, it will be proper to employ only the v/hite tears. Benjamin readily dissolves in alcohol (spirit of wine), and forms a tincture charged with a reddish colour. This tincture, under the name of balsamic milk, makes part of the formidable apparatus of the toilette. Benjamin, when in this state of extreme division by means of alcohol, forms a varnish of an agreeable odour, which retains a considerable degree of tenacity, and belongs to those kinds which are slightly coloured*. CAMPHOR. Camphor is a light vegetable substance, in part friable, transparent, slightly unctuous, and of a very strong aromatic odour. It has a bitter and highly acrid taste, though it at the same time occasions a sensation of cold. It dissolves entirely and with great facility in alcohol (rectified spirit of wine). It combines with oils both fixed and volatile ; it readily inflames and burns even on water, over which the part liquefied by the heat ex- tends, in consequence of its great lightness, and form^ a kind of bason, or crater, the circular edge of which, being cooled by the water, remains solid. As this kind of circumvallation preserves the centre from immersion, the camphor continues to burn, even below the level of the water. The flame is accompanied with a fuligi- nous smoke. * See die second kindj No. / , in tlie First Part. CAMPHOR. 5 ît appeîirs that no certain opinion has yet been formed in regard to the rank which camphor ought to hold in the order of vegetable substances. Naturalists consider ii as a resin ; but most of the chemists class it among the essential oils. The arguments on both sides seem tvo rest on a pretty solid foundadon. In camphor, indeed, we find particular properdes, which facilitate a comparison, and which indicate, at the same tini.^, that it participates more in the nature of essendal oils than in that of resins. 1 St. Like essential oils, it is volatilized at a degree of heat superior to that of boiling water. 2d. It dissolves entirely in alcohol. It combines with oils, both fixed and volatile, without disengaging heat and without leaving any residuum. 3d. When v/ater is added to a spirituous solution of camphor, the whole of it, the aroma or odorous prin- ciple excepted, abandons the alcohol and floats on the surface. 4th. In burning, it disengages a fuliginous smoke, like essential oils, and leaves no residuum. 5th. Solution of camphor in alcohol gives, by disdl- lation, a very abundant aromatic principle. In this respect no resin can be compared to it. Resins are fixed in the iire ; they do not entirely dissolve in alcohol ; a solution of them, v/hen mixed with water, forms a sediment ', they burn more slowly, and leave a great deal of charcoal. Camphor then appears to be of an oily nature. It would form a particular concrete oil, the origin of which does not seem to be attached* to one kind of B 3 6 TREATISE ON VARNISHES. plants, since it is found in vegetable individuals of dif- ferent families. The camphor sold in the shops is extracted from a kind of laurel which grows in great abundance in the large islands of the East Indies, such as Sumatra, Bor- neo, Java, Japan, &c. This tree is distinguished by the name of the camphor laurel. The camphor of the island of Java is of the lirst quality. The knowledge v.e have acquired in regard to the process employed to obtain camphor has been commu- nicated to us by the Jesuit missionaries*. The camphor is dispersed over every part of the tree : it is even often found under the form of small concrete lartiinœ. The peasants have a simple method of ex- tracting it. They cut off the young shoots, branches, and roots of the camphor tree, and, having bruised them, boil them in v^^ater, taking care to beat the mixture with a Idnd of broom formed of small twigs. When they ob- serve that these twigs are covered with a sort of v.hite jelly, they conclude that the separation of the camphor- ous matter has been effcdted. They then take the ves- sel from the fire ; leave the matter at rest for twenty- four hours ; and at the end of tliat time separate the camphor, which is found coagulated into one mass. This mass is composed of small balls, or grains, ren- dered impure by being mixed with fragments of bark, wood, and other foreign substances, which ah^ays ac- company the first process on a large scale. The worI%,- men, however, have a very simple method of purifying * Lettres édifiantes et curieuses des Jésuites Miîsionaires a la Chine, 24ine recueil^ &c. CAMPHOR. Y it, by means of sublimation with a sixteenth part of quicklime : but this purification is very inferior to that • practised in Europe ; for the Dutch, who have made this article a considerable branch of commerce, subject to a new sublim.ation the purified camphor which they import from India. This substance readily evaporates, especially when in contact with the atmosphere. It is even volatilised in the close boxes in which it is contained. The upper part of these boxes becomes covered with a beautiful crystallization, which disappears and reappears accord- ing as the temperature of the atmosphere is higher or lower. Some have imagined that the contact of the air might be prevented by covering the camphor with flax- seed ; but this method does not answer the intended purpose. The quantity of camphor thus lost by neglect cannot be estimated, but it is certainly very great. There is only one method of effectually preventing this spon- taneous evaporation, which is, to put the camphor into wide-mouthed bottles well closed with cork stoppers. • The use of camphor for vamish is limited : too great a quantity would render it mealy. It possesses the property of facilitating the solution of certain resinSj which are exceedingly refractory to the dissolving action of their appropriate liquors. Its union with copal is not easily destroyed : in this combination camphor loses its volatility, and the copal its hardness and consistence : the result at length is a small flexible mass, which re- tains a long time its elasticity. Camphor, however, when united in proper doses to other resins, gives tough- ness to the varnish, and prevents it from crr.cking. The B 4 8 TREATISE ON VARNISHES. weight of half an ounce or from five-eighths to a pound of alcohol must not be exceeded. The latter proportion is that suited to essence of turpentine. This substance does not admit of any choice. It is circulated in commerce pure and without any mixture, and only requires to be carefully preserved. CAOUTCHOUC, ELASTIC RESIN. The physical and chemical properties of caoutchouc, or elastic resin, do not completely justify the latter ap- pellation. Nothing indeed has less resemblance to a resin in its chemical properties, since it resists alcohol (rectified spirit of wane) ; nor is it a gum, since it is not soluble in water. These considerations are sufficient to make us admit the denomination of caoutchouc^ which is given to this substance by the people who inhabit the banks of the river of the Amazons. It is extracted, by incision, from a large tree known under the name of the syringe-tree^ or seringat ; and v/hich appears to be very abundant in eveiT part of South x\merica. The Cy^aguas, one of those tribes who inhabit Popayan, form of the inspissated juice of this tree a kind of hollow elastic pears, which serve them as syringes. This circumstance explains the ety- mology of the generic name given by the Portuguese to the tree which furnishes the caoutchouc. Though this substance differs in a great many respects from the particular properties of resins, it participates with them in an cKiinent degree in that of being inflam- Unable. The American tiibes know how to turn this property to advantage by converting the caoutchouc CAOUTCHOUC. 9 into a kind of tapers, two feet in length, and of the size of the finger, the flame of which emits a strong light, and lasts a long time. This singular substance when taken from the tree is fluid. At first it is a white juice, susceptible of inspis- sation by exposure to the air, and particularly by a pro- cess peculiar to the inhabitants ot these countries. When it fias acquired a certain degree of consistence, they wrap it round wooden or baked earth moulds, and ex- pose the moulds, covered in this manner, to the impres- sion of a thick smoke. It is this smoke which commu- nicates that brown or blackish colour observed in the caoutchouc imported to us under the form of pears. A temperature of from 75 to 1 00 degrees of Fahren. facilitates the elasticity, which is one of the most distin- guishing characters of this substr»nce ; and indeed it is the most astonishing when we consider the extent of it. Attempts have been made to apply this elasticity to new purposes of the utmost utihty. Som*e have endeavoured to dissolve caoutchouc in certain liquids supposed to be fittest for that purpose j but though various processes have been employed to restore to it its former elasticity, after a careful evaporation, none of them has succeeded, except that of its solution in sul- phuric ether. Macquer is the first chemist who made re- searches with a view to extend the utility of caoutchouc. He found that when dissolved in ether it experienced no modification capable of altering its elastic property. This ethereous solution poured on water deposits and extends the substance of the caoutchouc under the form of a pellicle, which may be easily removed by evapo- 10 TREATISE ON VARNISHES. ratiiifr the cihsr. The elasticity of this caoutchouc is astonishing. If this pclhcle be stretched over moulds it is capabl 3 of assuming every form, and of acquiring that state of consistence in which it appears after it has been subjected to this process. By these means it might be converted into boots and caps impenetrable to v/ater, and Vv'hich wculd be more pliable than leather. But the utility of these articles seems to vanish v/hen the ex- pense attending such processes is considered. Many chemists, howevsr, have since that time repeated Macquer's experiments, but without success. Among this number is Berniard, who found means to charge with caoutchouc oil of lavender as well as oil of turpen- tine, and to dissolve it in oil of camphor and in ex- pressed oils. I repeated Macquei's experiments with more success, by suffering the caoutchouc to digest in ether for twenty- four hours, and then keeping the matrass in the heat of a balneum maris to evaporate the most subtile part of the eth::r. The solution of the caoutchouc did not take place till the ethe% had decreased nearly one half in volume. One of the cases to vdiich the great elasticity of this substance may be applied with the best success, is to afford relief in diseases of the bladder which re- quire the use of a catheter. The fabrication of hollow elastic catheters seems to be one of the most striking and best contrived objects of the discovery of* caout- chouc, considered under the view of its utihty to society. Draftsmen employ it to wipe out stains from paper, false strokes, and outlines done with a black-lead pencil. ISINGLASS. 11 Caoutchouc was employed in the composition of the varnish with which the first balloon launched at Paris was covered. The constructors of it endeavoured to unite strength with a certain degree of pliableness, ccn- didons which appear to be essentially neccessar)- in such machines 3 but this varnish is very long in drying. ISINGLASS, FISH GLUE. Isinglass, fish glue, or ichthyocolla, is extracted from the air-bladder of a large fish (sturgeon), which emi- grates from the Black sea into the Danube, and v/hich is ver)^ abundant in that river from autumn to the month of January. During the fishing season the fishermen employ themselves in the preparadon of this substance on a large scale. They first take out these bladders, and, having opened them^, remove, by means of weak lime water, all the viscid matter which adheres to them. They separate from them also the fine membrane by which they are covered, and then expose «-hem to the air to make them experience a commencemient of desic- cation ; after which they roll around each of them the membrane separated from it, in order to convert it into a kind of cord of the size of the finger. This cord is twisted into the form of a heart v/ith obtuse angles ; the two ends are brought together, and fastened in that manner by a small wooden peg, which prevents the se- paration of the laminrs during 'the rest of the desicca- tion. These rolls are hung up in the open air to dry. They have the shape of small handles, and are brought to us under this form. When it is necessary to extract the glue, these rolls 4 1*2 TREATISE ON VARNISHES. are bruissd ; and, being torn into small portions, arc boiled with a sufficient quantity of water. The mem- branaceous part, which remains insoluble, soon gives up its gelatin, or glue, which is separated by straining it through a piece of linen ; and in this state it forms^ at most, a 25th part of the whole matter employed for the decoction. Fish gelatin (fish glue) is much used for giving a lustre and stilfness to ribbons and gauzes. It is a kind of varnish ; ir is the basis of the English court plaster, the preparation of which is terminated by the applica- tion of a coating of balsam of Peru. In the art oi varnishing, it ts employed for defending cut-paper works, &c. from the attacks of the varnish applied to them. Without this precaution the varnish would be imbibed, and form spots. This gelatin, when baked with a little sugar, consti- tutes lip-glue. It is employed, on account of its visco- sity, for clarifying coffee and purifying wines : for the latter purpose, liowever, albumen or ivhiîe of egg is preferable, because it is not attended widi the fault of incorporating with the wine, and of remaining in it in a state of solution. COPAL. Copal is a r::r,inous substance which distils naturally from a large tree abundant in New Spain. Copal is produced also in the East Indies; but in that country it is rarer. It passes gradually from the consistence of oil to the state of solid resin. The injects, such ar. flies and ants, inclosed in it sufliciently prove that this mat-. COPAL. 13 ter has been liquid ; and that it is indebted for its soli- dity to two causes united : the contact of the air, which dissipates its volatile principles, and the action of the solar rays. Copal, such as exhibited to us in commerce, emits a strong- odour when burnt. It is hard, sohd, and trans- parent ; has a shining surface of a faint lemon colour, but sometimes inclining to orange. Of all those who, through taste or by profession, have employed themselves in the preparation of varnish, no one seems to have observed a very rem.arkable cha- racter of copal, v/hich is, that it form.s an intermediate line between the common resins and amber, in regard to their property of dissolving in spirituous liquors. Like amber, theii, it exhibits a pardcular substance. It resembles those? resins most commonly employed in var- nishes, by suffering itself, under certain circumstances, to be attacked by oily substances v/hich exercise no action on amber ; and it approaches the latter by the resistance it opposes to the action of spirituous liquors, Avhich readily lay hold of all the real resins. AVhen destined for the composidon of varnish it ought to be chosen pure. I have remarked that the copal which exhibits a very ambcry colour opposes less resistance tp solution than tlie purest and consequently the least coloured copal : the cause of this will be-ex- plained hereafter. It was first known under the name of gum copal ; but the phenomena it exhibits in the fire, a,nd the re- sistance it opposes to the action of water, have induced naturalists to distinguish it by the appellation of copal 14- TREATISE ON VARNISHES. resin. This name, however, is as improper as the for-^ mer, because alcohol (spirit of wine) does not exercise its action on copal with the same energy as it does on resins. These distinctions, which are more or less cor^ rect, show the necessity of admitting the specific name of copal, laying aside any expression that might tend to define its particular nature. The principal cheraical properties of copal are as follow : 1st, Copal is in part soluble in alcohol, when directly applied ; that is to say, without any intermediate sub- stance. Çd. It is wholly soluble in alcohol, when, bing very much divided, it is first subjected to the action of a fluid less aqueous than alcohol, and which becomes a medium that facilitates its union with it. This effect is obtained by beginning the solution in essence of la- vender. 3d. It is wholly soluble in essence of turpentine, and without any intermediate substance, after the latter has acquired from the solar light a state of density and a particular modification, which establish in it a sort of homogeneity wi;:h the principles of the copal ; or when the copal has undergone a particular modification from heat. 4th. It is wholly soluble in sulphuric ether, and with- out any intermediate substance, when that liquor is proved by its specific gravity to be in a state of great purity ; for it must not be imagined that every fluid called ether is proper for the particular case to which I here allude. It is then certain that alcohol cannot be considered as GUM TRAGACANTH. ---■•.,.: IJ a vehicle proper for the solution of copal. iThe author of The Complete Varnisher does not appear to be of the same opinion, since he introduces copal into several re- i:ipes for varnish composed with alcohol. I have, hov\^- ever, ascertained one fact, which proves that the addi- tion of copal to certain resins contributes to the durabi- lity and even to the splendour and brilliancy of the var- nish ; but when this mixture is used the copal ought to be ground in small quantities on a piece of porphyry, with strong dosas of resins readily soluble in alcohol. GUM ADRAGANTH, OR TRAGACANTH. This gum distils spontaneously, or by incisions, from a small shrub named tragacanlha, which is very abun- dant in the Levant, and particularly in the island of Candia. The gummy sap hardens into long filaments, or small ribbons, twisted in the form of worms. This gum, of a colour more or less white, is diy, inodorous, and has a sweetish insipid taste j a character which be-. longs to ail gummy juices. It ought to be chosen pure, white, and transparent : that which is yellow, black, or mixed wiih foreign bo- dies, must be rejected. When put to soak in water it swells up a great deal, and assumes the consistence of very thick mucilage. This mucilage is sometimes employed by miniature painters, when they are desirous of rendering the vel- lum on Y/hich they paint as smooth as a plate of ivory. For this purpose, they put the mucilage into a pi :ce of fine linen, tie it into a knot, and rub it over the vallum. In painting in distemper a solution of gum tragacanth is subsdtuted for aqueous solution of gum arable, in 16 Treatise on varnishes. mixing up colours of a saline nature. This mucilage, at least, is used with that beautiful liquid blue which admits into its composition concentrated muriatic acid (marine acid*). This mucilage has more body than that of gum arable. GUM ARABIC. This gum distils naturally from the fissures in the bark, and from incisions made in the trunk of the real Egyptian acacia, which abounds in Egypt, in Arabia, Senegal, and several places on the coast of Africa. This gummy juice is found in pieces of different sizes, some- times round, sometimes angular, and sometimes folded double. They are of a yellowish-white colour, brittle and brilliant. They communicate to v/ater in which they are dissolved a glutinous viscosity, and give it an insipid taste, but unaccompanied with any smell. This gum often exhibits a dark amber yellow colour : it is found even sometimes . reddish, and in globular fragments. The latter kind is more particularly known under the name of Senegal gum. The mucilage it pro- duces is more viscid, and dries with difficulty. The sur- face of preparations made with this gum often dries ra- pidly by the contact of the air, while the interior part assumes a softer consistence than it had before. In ge- neral, the mucilage resuldng from Senegal gum has not the same softness as that of gum arable : dry white gum arable then is, in all cases, preferable. When it is necessary to employ gum arable in mix- ing up colours, or to form a coating for the purpose * See this composition in the Second Part. GUM ARABIC. GUM LAC. l7 of preventing varnish from p' -netratiiig those articlvis to wltich it IS iippli-d, it will b-^ proper to select pieces which have the least colour ; \\-hich are driest, most friable, and in particular free irom any mixture of straw, bark, &c. Mucilage of gum arabic is never so thick as that produced by gum tragacanth. When the gum is good and well chosen, it is colourless, and as transparen ' as water. This mucilage, when a little diluted with water, forms one of thoce matters which ought to con- stitute the first class of varnishes, as we shall show in treating on the division of its compositions. It per- forms, indeed, in a certain degree, the office of a var- nish when water colours are employed ; but the appa- rently vitreous coating which it forms is subject to the impressions of moisture. It is however used for cover- ing delicate articles intended to be varnished, such as cut paper work, &c. This mucilage preserves the ground and the colours from being attacked by the varnish. GUM I.AC, SEED LAC. This substance, called improperly a gum, is the re- sult of the industry of a kind of winged and flying ants found in several parts of India, such as Bengal, the kingdoms of Pegu and Siam, 8:c. These ants deposit the resin on the branches of a kind of jujube, or on reeds and tvv'igs, which the iriha- bitants take care to plant in the earth, in order that they may turn to advantage the industry of these insects.' If the reddish and tuberous covering v/ith which these a}its surround certain parts of a twig be carefully c 18 TREATISE ON VARNISHES. examined, it will be found that each tubercle contains small cells, or alveoli, nearly similar to those in a honev- ^comb. They crver their cells on the outside with a thick; r coating than that in the inside, in order to de- fend from the rain the young generation contained in them. This substance, the resinous nature of which is proper for accomplishing the latter object, is of a dark red or lateritious colour, and is of a tolerable consist- ence. Each cell contains a small round, and as it were moulded, body. This body is of a beautiful red colour, and when bruised gives a powder as red as cochineal. These small bodies, which, no doubt, are the em- bryos of the insect, communicate their .colouring part to water, and to resinous or oily substances. It is this matter which gives to gum lac its peculiar colour. Lac is known in three states. Lac in sticks is that still attached to the extremities of the small twigs on which it has been deposited ; seed lac is the same after- it has been separated from these tv.igs ; and shell lac is also the same which has been melted and cast into thin laminse. I^ac is not a pure resin : it does not di&solve entirely in alcohol (spirit of wine). There remains an insoluble matter, which seems to participate in the nature of wax. Seed lac gives a tough strong varnish, \.hicli is em- ployed for musical instruments, such as violins, basses, ^c. For this purpose, it may be used in the state in which it comes from the shops, that is to say, in grains; but in this state it is deprived of its colouring parts,., which the Indians apply to their printed cottons^^so mucL SHELL LAC. MASTIC. 19 sought after in Europe on account of the fixity and brightness of their colours. The want of this colouring part may be supplied by an infusion of anatto, which increases the beauty of the varnish desdned for musical instruments. SHELL LAC. Shell lac is prepared with that separated from the twiffs td which it adheres. It is washed in water to carry off the colouring part ; it is then melted, and poured on a marble table, over which it is spread out to be formed into thin laminss : these laminse are then distinguished by the name of shell lac. Under this form it becomes one of the principal in- gredients of sealing wax, which is coloured with ver- milion to form red wax, or with lamp black to form black. This sealing wax is also made to have a shining and speckled appearance by mixing "the shell lac with small scales of mica or aventurine, or with laminas of orpiment ; but the latter mixture is noxious, and emits a bad smell. MASTIC. Mastic is a resin ; by which expression is understood a friable inflammable substance, more or less odorous, soluble in whole or in part in alcohol (spirit of wine), and insoluble in water. Such are the chemical charac- ters by which we are enabled to distinguish substances whose external appearance is sometimes nearly the same, though they are very different in regard to their compo- nent principles. Masdc is sold in small grains or transparent tears of c 2 'JO' . TRrATlSE ON VAP-NISHES. ■<\ lemon colour. It distils by incirion, or even without incision, from the bark of the lentiscus, a tree very îibund?Jit in the Levant. This resin readily melts over the fire ; it has a sweet and slightly aromatic smell, with a weak balsamic savo,ur. The purest mastic is found in the island of Chio ; but it is reserved for the. use of the Turkish ladies, w^ho chew it, as it has the. property of cleaning the teeth, sÉrengthening the gums, . and rendering the breath sweet. The distinction of m.ale and female mastic is void of foundation. That intended for varnish ought to possess all . the characters already mentioned. The mastic brought to us by the way of Marseilles is not always pu-;e: it is a mixture of bjautiful tears with grains dirtied and. adulterated bv fragments of the bark of the len- tiscLi;;. Varnish compositions admit only the purest mastic, as little coloured and as transparent as possible. Mastic is often confounded with »\vhich may be known by the extent of the trâ|»sp£^mit parts. GUM ELEMI. There are two sorts of gum elemi ; one of which comes from Ethiopia, and the other from America. That of Ethiopia is the real kind. It is brought to us by the way of Marseilles in small cylindric frag- ments, seven or eight inches in length, and nearly two pounds in weight. It emits a very agreeable odour of fennel : it is almost entirely soluble in alcohol (spirit of wine). It has a greenish colour, and is interspersed with some reddish veins or glands. It has a solid consist- ence, and yet is susceptible of becoming soft under the fingers. This sort is enveloped in the leaves of the palm tree, or of that kind of reed called the Indian cane. It is believed that this resin distils from a species of middle-sized wild olive tree. The gum elemi imported from Brasil and New Spain is far from exhibiting the same characters. It is brought to Europe in large, soft, glutinous masses, and becomes solid only in the course of time. It is yellowish, semi- transparent, and has a resemblance to gallipot or white incense. Its smell seems to give reason for suspecting that the latter substance is mixed with it. It is believed that the tree which produces it is a kind of balsam tree, and that it grows to the height of the beech. In regard to this point naturalists are still di- vided in their opinions. But whatever may be the origin of gum elemi, it is not proper, unless pure, for being introduced into the composition of varnish. The GUM ELEMI. GAÀIBOG'Jl^ 'J X >'MS elemi of Ethiopia ought therefore to be pj^?|j?rrë(i:;>o (^ of America, both on account of its consisteH^e, "v^cll is bt'tter suited to this composition, and of tTi^s^et smell wliich it communicates to varnished articles. Ba- sides, it gives to the composition a toughness and dura- bility, v.'hich it would be in vain to expect f.om that of America. GUM GUTT^, GAMBOGE. This substance forms one of the resinous gums ; but, as the resinous part predominates, it perhaps may not be improper to distinguish it by the name of resin. It is the dried product of a milky juice, extrac:ed by in- cision from the bark, the trunk, and the uncovered roots of a large tree, the species of which has mul- tiplied veiy much in the country of Gamboge, in part of the kingdom of Siam, and in China. The inhabi- tants of the country, according to the relation of tra- vellers, give to this tree the name of carcapi;!!!. This resin, in the state of desiccation in which it is imported, is dry, solid and compact, hard, opake and inflammable, and of a yellow colour inclining a little to red. Such are its physical quahties. A greater quantity of it is taken up by alcohol (spirit of wine) than by water. In both these fluids the insoluble part is preci- pitated : these are its principal chemical characters : It gives a very beautiful yellow colour, which ren- V - « ders it exceedingly proper for water colours. In this respect it is used for washing and for miniatures. It possesses a colouring principle, much sought after for giving a gold colour to the composidons of changing c 4 24 TREATISE ON VARNISHES. varnishes. It communicates to them also body and brilliancy. This substance is not susceptible of much choice. It ought to be smooth and brilliant on the fracture. It has a kind ofvitrcQus appearance. It may be proper here to observe that it is a violent purgative, and that a very small dose of it is capable of producing the most irri- tating effects. This observation is addressed to painters who iiave the bad practice of v/iping their brushes v.ith their mouth. SANDARAC, GUM SANDARAC. Gum sandarac is extracted from a large kind of ju- niper, which grows in varm countries, sucli as Italy, Spain, and in particular Africa. It distils from the tree naturally, or from incisions made in the trunk during the hot weather. It exhibits itself under the form or tears, sometimes elongated, sometimes round, and sometimes folded together. That most esteemed is in bright, shining, and transparent tears of a pale yellow colour. It has a balsamic odour, and its taste is some- what acrid. It is called also rcDii.r, because it was the iirst sulv stance emploved by the antients in the composition of varnish, to which it gives solidity. As a resin, it is soluble in alcoliol, in essential and fixed oils*, but less so than niastic. By this union, and particularly by that with alcohol and essence oi * However, when it is necessary toamite it to drying oils, tht: same process must be employed as that used for the preparntinii «if ciiv.ber mid copal varnish. CUM SANDARAC. DRAGON S BLnQD. 2.5 turpentine, it forms a varnish which possesses great spLndour ; but it is soft, and is easily scratched by the It-ast friction. The varni.-h, however, may be rend^ -.^d harder by mixinp- the sandarac with other resinous sub- Stances, not so dry, such as gum elemi and gum anima. It is one of the.principal bases of alcoholic varnishes. If this resin, when in the pulverulent state, be rubbed over scratched paper, it restores the surface. The paper may then be Vviitten upon v^'ithout the ink sinking. Though the exterior or physical characters of san- darac may be easily distinguished, there are numerous examples of other substances being fraudulently sub- stituted in its stead, to the great prejudice of the artists who employ it, and v» ho apply, in confluence, to fi'ag- mjnts of copal, processes proper only for sandarac. I have often been consulted on similar occasions respect- ing the inactivity of alcohol applied to supposed sanda- rac. Artists, therefore, before they purchase large quan- tities of • what is usually sold in the shops under the name of this substance, ought to trv a small portion of it, by which means they may save both time and money ; for it is not possible to trace back these adul- terations to their source, in" order to be mdemnihcd. dr-Agon's blood. DracTon's blood is a dry, fripb^e, imlammable resin, of a dark red and almost brown colour on the outside. When in large thin lamin :« it is transparent. It 'las nei- ther savour nor smell when cold ; but w^hen buj-nt it emits a balsamic odour. 26 TREATISE ON VARNISHES. This resin is produced by a tree very common in the Canaries, in Jamaica, and in the East Indies. This tree, called the dragon tree, rises to a considerable height : its trunk is smooth, like that of the palm tree. There are several kinds of dragon's blood. That most esteemed comes to us in small masses of the size of an olive, wrapped up in the leaves of a species of reed. Some enveloped in this manner is brought from India: no difference is observed but in the globular form given to it. In general, the dragon's blood sold under the globular form, or that of an olive, is of the fmest quality. Another kind is of a soft consistence, and requires some time to become solid. This sort is also of a good quality, but inferior to the former. There is even a third kind known in commerce, which is sold in the form of round cakes. It is of a dull red or brick colour ; and appears to be a compound of diffe- rent resins coloured by brickdust, or by Brasil wood, or with a portion of real dragon's blood. In the fire it does not inflame, but swells up. This kind is abso- lutely improper for the composition of varnish. Real dragon's blood readily unites M-ith alcohol and with essential and drying oils : it is, however, employed only for alcoholic varnishes, or those made wdth es* sences, and particularly in the case when it is required to make a chanc-incr varnish destined for foil or tinsel, or for gilt leather. YELLOW AMBER. 27 AMBER, KARABÉ, YELLOW AMBER. Amber, generally known under the name oij/cllow amber and harahe^ is one of those substances on which a great deal has been written. It has bc-en an object of the combined researches of mineralogists and chemists. The results of the chemical analysis of it were well cal- culated to excite their curiosity, and to induce them to continue their experiments. 1 he physical and chemical properties of amber, so different from thote of other resinous substances, and the places where it v/as found, indicated, in some measure, its real origiii, and inclined them to consider it as a particular substance. It does not, indeed, appear to have a direct afEnity to any of the pure resins. Copal, though essentially different, seems to be the only substance that ap- proaches nearest to the nature of amber, which has no- thing in common with resinous substances but the pro- perty of being very inflammable. These were sufficient motives to induce naturalists to attempt to discover its origin; but notwithstanding the numerous researches made on that subject, there are few substances respect- ing which so much uncertainty prevails. Laying aside, therefore, all conjectures which have appeared proba- ble to the different persons who have applied to this research, we shall confine ourselves to those facts best estabhshed, and most capable of giving us certain ideas in regard to its nature. Some philosophers believed, with Philemon, that amber originated from the earth, and did not depend on any particular organization. Some of our philcsc- 28 TREATISE ON VARNISHES. pliers, at prcsjnt, have revived this idea in regard to the oiigin of bitumen. Phny the naturalist adopted the opinion of the Greeks, by assigning to amber a vege- table origin. He considered it as the resin of the pine tree liardened by the autumnal cold. In these remote ages, comparative analyses, being unknown, could not contribute to rectify tliis idea. This instability of opinions required direct observa- tions, or the concurrence of various circumstances; which fortunately took place under the reign of Fre- deric William, king of Prussia. Ducal Prussia, of all the countries with v.-] 'ich we are acquainted, is that v/hich seems to be most favoured by nature in regard to mines of amber. This production afforded considerable exeixise to the national industry under the reign of that prince, as a strong taste pre- vailed at that time for ornaments and trinkets made of amber. 'At that period the resources of cliL'micid ana- lysis were sufficiently certiiin to inspire confidence in reg-ard to the result of them. The study of natural history, the success of which seemed to depend on that of chemistry, acquired then a consistence which gave the best hopes of its future advancement. Such was the state of circumstances which seemed most favour- able for fixing the opinion of naturalists in regard to the nature of amber. Hoffman, a celebrated chemist, required onl)' the in- vitadon of that prince to emplov himself in researches, which he had the better opportunity of bringing to a fortunate conclusion, as he was in the centre of a coun- try where this substance abounds, and is dug up ircru YELLOW AMBER. 2"9 a mine." It was of importance to examine the soil, which exhibits different strata ; but Hoiiman does not mention their thickness. The first is of sand ; the second of clay, fifteen or sixteen feet in thickness ; and the third is composed of trees impregnated with sul- phurets of iron (martial pyrites), bituminous, and as it w.-re burnt. These trees have no consistence : some of them are of a large diameter, and in a state of pretty good preservation. This stratum of mineralized wood is not of equal thickness : some travellers make it to be forty or fifty feet. Under tins collection of bituminous v/cod is found a stratum of sulphurets and of sulphate of iron (py- rites of iron, and vitriol of iron, or green copperas) ; and it is not uncommon to meet with pieces of amber still adhering to the lower part of the trunks of the trees. They appear there under the form of stalactites. This stratum of sulphurets and sulphate of iron rests on a bed of coarse sand. This sand is the reser^'oir of tlie amber, which is often found there in scattered fragments, but sometimes also in large masses. Under this bank of sand the argillaceous bank comniLLc^s, and prevents the amber from penetrating further. The large fragments of amber have always a pyra- midal form, which attests its distillation from the trees above, and removes every doubt in regard to its vegetable origin. The most conclusive argument, how- ever, is that deduced from the pieces of amber which partly penetrate into the sand, and still adhere by their upper extremity to the maternal stock. I'hls substance, being at first lir.uid, carried with ir. 4. so TREATISE ON VARNISHES. and enveloped difierent insects adhering to the bark of the tree, and, together with the vegetable mass, must have been buried by the efFect of one of those grand revolutions to which our earth has been subjected. Witli the period of these revolutions we are unac- quainted, but evident traces of them are still every wliere visible. Bernard de Jussieu, the object of whose ruling pas- sion was the sciences, and who applied to them with as much success as ardour, has remarked that the in- sects inclosed in amber do not belong to our continent. The schistous impressions found in our soil and in the neighbourhood of Toningen confirm this opinion, by the kind of plants the type of which they represent. As the obser\'ations of Hoffman have been fully confirmed by Neuman and later philosophers, a vege- table origin may be assigned to amber. It is probable that the impression of mineral waters, and the action of different gases developed by the intestine fermenta- - tion, which must take place in the mass of these bu- ried vegetables, are the causes of the principal differ- ences observed between an •"•er and resins, which have not been exposed to the same circumstances. However, when it is considered that copal in a cer- tain degree participates in some of its properties, one' might almost be induced to believe that the tree which produces amber is the same as that which furnishes copal, and which grows only in the torrid zone*. * If It be considered, on the other hand, that amber, besides the characters which distinguish it from other resins, possesses a pro- perty which st?ems to give it an affinity to certain resins or balsam» YELLOW AMBER. 51 Amber exhibits itself under various appearances. It is found white and opake, sometimes exceedingly trans- parent, and of a pale yellow colour; at other times of a beautiful dark golden colour. ït is described as a bituminous substance, dry, brittle, and inflammable. It is hard, and susceptible of a fine polish : it is easily worked in the lathe, and is then highly brilliant, and forms beautiful trinkets. When rubbed on a soft body, or piece of cloth, it exhibits an electric property, on which account it was called by the antients clccirum. Its other name, karal-e, is originally Persian: it signifies the at tractor ofstrcuus^ an effect arising from its electric virtue. Its specific gravity is very little superior to "that of pure v/ater. If the v/ater be mixed v. ith a saline body, or only slightly charged with sulphate of lime (selenite), as unboiled water often is, or if it be very near the term of congelation, it becomes equiponderable to amber. It is, no doubt, owing to one of these circumstances that we are indebted for the discovery of pieces of amber carried away by the rolling of the v/aves of the Baltic, which detach them from the deep mines where they are uncovered, and convev them to the shores. If amber be only rubbed, it has no smell ; but if ex- posed to a strong heat, it emits an odour far from being that furnish a volatile essential salt, have we not as mr.ch reason to think that the anibc-r-tree belongs to the lar-ily of the Iculamh'ts, some of which are tall, and furnish benjamin ? or to those large trees which give by incision balsam of Peru, a substance vvhich, as is mcU known, furnishes an acid aiid volatile esseniiiil sal: ? , 32 Treatise on varnishes. disagreeable : when melted over the fire it is in paiT decomposed, and exhales a strong, disagreeable, bitu- minous smell. Some chemists and certain artists, it is said, have found means to communicate to amber ductility and permanent elasticity, as well as dilierent colours, and to make it serve as a covering to various reptiles, with- out altering its nature, as a forced liquefaction would do. It is even said that certain miners have been able to r ender opake amber transparent, by subjecting it to ch jmical proc .'sses. All this may be true ; but it ap- pears certcdii ihat the pretended elastic amber was not so. By the addition of camphor to copal I obtained a small, fje:>vible, elastic mass, which has retained its ductility already six months*. Would the case be the same \^ith amber ? All the attempts hitherto made to modify its nature have had no other object than that of enhancing the price of it. No discovery the sole object of whi::h is avarice, exhibits motives sufn- ciently noble to induce the philosopher to employ himself in researches respecting it. The amber mines are not confined to Ducal Prussia, or to the Bakic sea, vvhich v/ashes its shores. It is found in many other countries, such as the march of Ancona, Sicily, Saxony, Poland, and Sweden. It is met with in several cantons of France ; but Prussia has the noble privilege of presenting it in large masses, and sufiiciently pure to form a very lucrative object to the national industrv. ■•• I shall enlarge furLker on this subjcQt in the article on copal vanii.^h. » YELLOW AMBER. 33 Amber formed into trinkets and various female or- naments maintained formerly a very important branch of commerce, the ramifications of which extended to eveiy part of Europe and to Asia. The use of precious stones, which acquired, a preference in consequence of their brilliancy, has very much abridged the advan- tages of this commerce, which is now confined to Persia, India, and China. The art of varnishing, however, has opened to it another channel of consumption in Europe. It forms the base of those beautiful varnishes, the splendour and durability of which have so much contributed to extend the reputation of the celebrated Martin. Amber does not unite indiscriminately with all spiri- tuous liquors, or with all the different oils usually em- ployed in the composition of varnishes. It would even, resist fat drying oils, if the preliminary preparations which convert it into varnish were neglected. Essential oils exercise very little action on amber ; and this is the case even with essential oil of lavender, which some authors suppose in this case to be suffi- ciently powerful. Ether, according to experiments which I made, effected a sort of division of this substance. It swelled up as cork does when placed on burning coals, and became pulverulent. But, notv/ithstanding this tumes- cence, which announces a division of parts, there was no solution. By evaporating the ether the amber re- sumes its original form and consistence. Alcohol (spirit of wine) distilled in a balneum mari£e over amber detaches a portion of it, which constitutes JO 34 TREATISE ON VARNISHE5. essence or tincture of amber, an article veiT much used in medicine. V\^hen the first pordons of the al- cohol distilled are re-disdlled several times over the powder contained in the balneum marise, the tinc- ture is sufficiently charged to form a kind of var- nish ; especially if a fourth part of the vehicle be sepa- rated from the filtered tincture by a new .distillation : but to succeed in this experiment the alcohol must be very pure*. This fact \dll appear directly contrary to the theory, of Watin, explained at full length in his critical notes on a work entitled Le Parfait Vernis^eur. " If am- ber," says he, " were kept a hundred years in a bal- neum marias under spirit of wine, it would always re- main the same.'* After the numerous and continued experiments of this kind which I made on amber, both in consequence of my situation, and with a view of rendering my re- searches applicable to the art of varnishing, I should not have hesitated to advise the union of amber with the different resins employed in the composition of var- nish, vvhen it is intended to give them more body^ had I not found in copal a substance somewhat more tractable than amber, and which possesses in the same degree the qualities sought for in the latter f. * I have no doiibt of the complete solution of amber in tartarized alcohol, as practised by, Hoffman ; but diis method, which might be usefiil for certain medical purposes, cannot be employed in tiie composition of Tarnish of iliis kind. In this process tlie alcohol.and the amber experience alterations which deprive them of the qua- lities essential to the nattire of varnish. f See tlie fust kind of varnish. No. 2j- Part I, TURPENTINE. Sâ Àmber destined for the composition of varnish must be chosen pure, transparent, and without any mixture of foreign bodies, which render it valuable only to the collectors of natural curiosities. TURPENTINE. Four kinds of resinous juice are denoted by the name turpentine*, though this denomination seems properly to belong only to the resinous fluid which distils from a tree called the turpentine tree, and from which it takes its name. Under this denomination indeed are comprehended, 1st, The turpentine of Chio, which on account of its bal- samic qualities is preferred to every other kind, and par- ticularly in medicine. 2d, Venice tur £■ tine. Sd, That of Strasburgh, or the German turpentine. 4th, The coarse or common turpentine, brought from the south- ern parts of France. These kinds of turpentine have physical qualities common to them all ; but it is observed that they are variously modified, and produce differences which give reason to believe that they are not all proper for the same uses. Turpentine has a consistence more or less. fluid. It is viscid and tenacious j has a strong aromiatic smeli in * In treating of turpentine I shall take a general view of all the substances of which it formis the basis^ such as pitch, resin, tar, &:c. I shall follow the order prescribed by the operations to whick it is subjected, as the best method of giving a detailed and con- nected history of this substance, which is singularly modified botli by nature and by particular processes. D 2 36 TREATISE ON VARNISHES. different degrees, and a bitter taste more or less acrid. It is produced by different resinous trees, which exhibit to the researches pf the naturalist différences in tlieir particular organization more remarkable than the che- mist finds in the resinous juice which is obtained from them. In many cases this substance is prepared by nature alons ; but for the most part her efibrts are assisted by long incisions made in the bark of the trees, and which, penetrate even to the soft part of the wood. The vis- cous juice, which flows from these incisions, is con- veyed into vessels placed at the bottom of the tree, by means of pieces of ba.rk bent into the form of a gutter. The product is imm^ediately removed, to prevent its being exposed to the influence of the air, which would occasion a change in its consistence. Time, and the difîerent changes produced in this juice by art, seem to extend or vary the degree of its utility, as applied to medicine, to the purposes of navigation, and to the arts. When this lioj^uid product is left to nature, the air and the sun exercise on it a speedy acdon. The vola- tile oily principle is dissipated, and nothing remains but a tenacious glutinous matter, which at first is called barras^ and v;hich is sold in the shops under the name of gallipot or white incense. It is distinguished from marbled incense by being cleaner and not so dry. But in whatever state exhibited, either by nature or by art, industi7 finds means to vary its properties by applying* it to different uses. CHIO AND VENICE TURPENTINE. 37 TURPENTINE OF CHIO. Turpentine of Chio, extracted by incision, or with- out incision, from a tree known under the name of the turpentine tree, has a firmer consistence than the other kinds of turpentine : but in tliis respect it varies. Some- times it has the hardness of honey ; is viscid and flex- ' ible ; and in this state is transparent. At other times it is friable, and breaks between the fingers into small fragments : its colour is then blueish- white, or inclining to green. It has a strong balsamic odour ; its taste is acrid and bitter. This kind of turpentine is the rarest and most esteemed. It may be employed in small quantities in the least drying kinds of varnish, that is to say, in those which admit the union of gum elemi, gum anima, &c. VENICE TURPENTINE. The turpentine of Chio, just mentioned, was long known under the name of Venice turpentine, because the Venetians, who got into their hands a great part of the Levant trade, sent to every part of Europe all the productions of these countries. At present, that di- stinguished by the name of Venice turpentine is pro- duced by a kind of larch tree very abundant in the Apennines, in part of the Alps of the Grisons, 'of Savoy, and even of the ci-devant Grenoble. It is fluid, limpid, glutinous, tenacious, and of a consist- ence between that of oil and that of honey. It has a yellowish^white colour,, and a strong penetrating yet agreeable smell, inclining somewhat to that of oranges. It possesses a more acrid and a bitterer taste than the tur- D 3 S8 TREATISE ON VARNISHES. pentine of Chio. This second kind is fit for tiie com- position of varnish. TURPENTINE OF STRASBURGH. The turpentine of Ahv.ce, or of Strasbiirgh, is pro- duced by a kind of silver fir, with leaves like those of the yew tree. When fresh it is liquid, and more trans- parent than that of Venice, but less viscid and tena- cious. Its smell is verv airreeable, and has more re- semblance to that of oranges than the smiell of the Venice turpentine. Jt has nearly the same taste as that of Chio. This turpentine, like that of Venice, takes its name firom the ciiy which carries on with it the greatest trade. It is extracted fi-om the firs which grow in great abun- dance in the northern parts of Germany, in Switzer- land, the ci-devant Lorraine, &c. There are formed on the bark of these trees vesicles filled with this re- sinous juice, which the peasants collect by means of a cornet of tin plate terminating in a very sharp point. This instrument serves for piercing the vesicles, and for receiving the juice which fiows from them. This turpentine also is exceedingly proper for var- nish ; but it gives less body to the composition than that of the larch. In general, the addition of turpen- tine to varnish contributes to give it a great deal of splendour, but does not render it more durable, COMMON TURPENTINE. The fourth kind of turpentine is reserved for less valuable purposes, and ought not to be employed iu COMMON TURPENTINE. S9 the composition of varnish. It is ' produced from the wild pine, and may be obtained either by or without mcisions. It has a viscous consistence, is white.^ ahnost opake, and more tenacious than those of Venice and Strasburgh. It has a stronger smeli than the other kinds of turpentine, and its taste is acrid., bitter, dis- agreeable and nauseous. It is a production of the southern departments of France, where these pines are found in great abundance. It'is called coarse turpen- tine and hijon. This turpentine, when it has acquired consistence by exposure to the air, forms what is called gallipot. All the resinous trees above mentioned, of whatever species, are a source of wealth to human industrv, which knows how to vary the employment of them,. On account of their great height, their lightness, and their pliability, they are exceedingly useful for ship- building. Their product, after it has experienced cer- tain modifications, distinguished by particular names, furnishes different substances which are highly useful in navigation, in medicine, and in the arts. The same substance, indeed, gives essence of tuipentine, ethere- ous essence of turpentine, colophonium, white incense, resin, white or Burgundy pitch, tar or liquid pitch, oil of cade, dry black pitch, naval pitch, and hmp black. These substances, the exterior characters of which seem to be so diilerent, and which indeed are applied to purposes which admit of no comparison, have all the same origin. They are all produced from turpen- tine, such as it is formed by nature, or modiLied by the D 4 40 TREATISE ON VARNISHES. air, or by the action of chemical processes ; and they all concur towards the composition of varnish, more or less valuable or useful. This consideration alone ren- ders it necessary to give a short description of each, in order that their nature and properties may be better known. ESSENTIAL OIL OF TURPENTINE. ESSENCE OF TURPENTINE. Turpentine extracted from the vesicles of the silver fir, after being mixed with a great deal of water and subjected to common distillation, gives for result a -light and highly volatile oil, which is sold in the shops under the name of essence of turpentine. In Switz- erland this oil is prepared from the cones of the silver fir, which are collected for that purpose in the month of June, a season when they are filled with liquid tur- pentine. They are cut into slices, and distilled v.ith water in large alembics. The oil is separated from the water, which passes over at the same time, by means of large glass funnels. This oil is light, colourless, of a penetrating smell, and has a singular influence on our organs ; for if a person only touch it, or inspire air impregnated with its effluvia, the urine acquires a strong smell of violets. By distillation with water this essence is always cxt ceedingly clear, limpid, and colourless : when disdlled without water, even in a strong heat, it is less fluid, and assumes a lemon colour : it is ako more oily an4 fatter. WHITE INCENSF.. GALLIPOT, 4*1 COLOPHONIUM. When turpentine is distilled with water, the solid re- sinous part, which cannot be volatilized, remains con- founded with the water of the bath, and constitutes what is known in the apothecaries* shops under the name of baked turpentine. It is separated from the water, and, being left to drain, is again melted before it is made an article of commerce, in which it is known by the names of colophonium, arcancon, hrai sec, poix Grecque, If the distillation has been effected without water, the colophonium is of a, darker colour ; it is red, and often reddish-brown. This colophonium is very much used, under the name of arcancon, in the composition of certain kinds of varnish. For this purpose, that which is most trans- parent and least coloured ought to be chosen. WHITE INCENSE. GALLIPOT. BARRAS. These different denominations express rather the state of purity and consistence of the resinous sub- stance furnished by the pine and the silver fir than any essential difference in its nature. The name barras expresses the soft resin which ad- heres to the bark of the tree, and which often contains fragments of it, as Vv-ell as dust and sand conveyed to it by the wind. It is sometimes seen resinified by the ;iction of the air and of the sun. The word gallipot denotes the same substance, but in a state of purity, in consequence of the care taken 42' Treatise on varnishes. when it distils to convey it into wooden troughs placed at the bottom of ths trees, or into pits lined with fat earth. This matter is viscous. What is called ivhite iiicense is gallipot resinified, and become friable by long exposure to the air. PINE RESIN. RESIN. A mixture of white incense and barras, exposed to a heat capable of rendering these substances liquid, without experiencing any alteration, and poured upon a kind of mats covered with straw, constitutes, after it has cooled, what is sold in the shops under the name of resin. ANOTHER METHOD OF PREPARING RESIN. The inhaL>"tants of the mountains of Switzerland are acquainted with another process for the preparation of this substance. They collect under sheds the old ti'unks of resinous trees, with which they surround a sort of hearth, and kindle a large fire on it. The heat, by penetrating these trees, melts the resin, which di- stils slowly into troughs fixed at the extremity of the trunks, and the flowing of the liquid is facilitated by the oblique position given to the trees. They then place over a fire all the different products, and form- them into cakes, which they sell in the neighbouring villages. The trunks from which the resin has been extracted are then split into fire- wood, and serve them for fuel in the winter. This resin is purer than that produced by a mixture of white incense and barras ; and is preferable, when the fire has not exercised on it too immediate an action» BURGUNDY AND WHITE PITCH. 4S White incense and resin are employed in the com- position of tht common varnish with which dark co- lours are mixed. EUP.GUNDY PITCH. WHITE PITCH. Turpentine extracted from the turpentine tree, from the larch and the silver fir, is exceedingly pure ; but that obtained from the pine and fi'om the spruce fir, picea or epicea, is impure, as well as less fluid, less balsiiniic, and less transparent. The Burgundy pitch sold in the shops is either natural or adulterated. A simple mixture of gallipot and barras, made with- out heat, is often sold under the name of Burgundy pitch ; but the mass resulting from this combinadoii soon becomes fri^la. It has neither the unctuosity, nor the viscidity, tenacity, or smell w-hich constitute real white pitch. The picea or epicea, spruce-fir tree, which produces the latter, does not contain the resinous juice dissemi- nated through particular reservoirs, as it is in the spruce fir, nor under the bark, as in the pine. A white resinous and pretty thick substance exudes from the bark, and is collected by the peasants in summer. They melt it, and, having strained it through a cloth, put it into barrels. The real Burgundy pitch is prepared ia this manner. When the resinous juice is collected too late, and has become rather too thick, they lessen its consist- ence by mixing with it, over the fire, a little turpentine and oil of turpentine. This substance is employed 4 44- TREATISE ON VAP.NI3HES. only for those common kinds of varnish applied to ships and boats. BLACK SOLID PITCH. Burgundy pitch melted, and mixed, at the time of its liquefaction, with lamp black, constitutes a black semi-friable substance, susceptible of melting at a com- mon temperature, and which is known under the name of black pitch. Its surface, though smooth, has a dull appearance. I must here observe that it ought to be diftinguished from naval pitch, which has a smooth shining surface: the latt-ris produced from the pme and the spruce fir, altered by the action of heat in the preparation of tar. TAR. LIQUID BLACK PITCH. BRAI GRAS. TARC. The different «processes hitherto applied to turpen- tine, or the resin resulting from the desiccation of it, in order to modify its state and consistence, or to mul- tiply its uses, have not such an influence over its na- ture as to occasion any alteration in it, and much less to produce a partial destruction of it. The degree of heat employed only gives it a specific liquidity, which in no m.anner deranges its composition. Even the di- stillation, which furnishes essence of it, extracts merely the more subtile and volatile part, which under the in- fluence of the air and of the sun would have been lost. But when converted into pitch the case is not the same. The degree of heat requited for this operation, being higher, must destroy the vegetable organization, znà reduce it to charcoal. The resinous substance GERMAN METHOD OF MAKING TAR. 4^ escapes complete destruction only in consequence of the fluidity it acquires, and of the water of vegetation it carries with ]t. PROCESS FOP. MAKING TAR ACCORDING TO THE GERMAN METHOD. Various substances, which in appearance are very different, furnish tar. Several processes are employed for obtaining it ; but in whatever manner extracted, whether from coals, turf, or wood, the results are the same, as far as relates to the oily product, which is the principal object. These processes vary according to the nature of the matters employed. In some parts of Germany, and particularly in the duchy of Deux-Ponts, the mountaineers perform this operation in furnaces of a very simple construction. They consist of a square chimney, the base of which is inclined towards one of its lateral parts, and in the bottom of it is formed an aperture, through which the product is conveyed to an external reservoir. This furnace is filled with pieces of old resinous fir, split, and placed in a vertical position close to each other. When the furnace is full it is kindled at the top, and when completely on fire it is covered with earth, in the same manner as in the process emplo)^d for burning common charcoal. The heat being gradually communicated down- wards, liquefies the resin, v^-hich flows towards the lower part by the help of the resinous sap and the water of vegetation, and carries v/ith it the carbona- ceous parts. It then passes iuto the exterior réservoir. 46 TREATISE ON VAPvNISHES. where it escapes the action of the heat, and is removed thence by the workmen and pat nito casks. ; This, still resinous oil is thicker or thinner, according to the age of the wood employed for the operation. The older the firs, the more they abound with resin. When the operation is finished, the charcoal which has been left Is taken from the furnace. By these means a supply of this aidcle is obtained for the use of the mines, and for other purpos s. It is observed that the sum of the product forms nearly a fourth of the wood employed when it is very resinous. The char- coal forms nearly a third. PROCESS FOR OBTAINING TAR ACCORDING TO TH3 R.USSIAN METHOD. In Russia this operadon is performed on a larger scale, and in a more ceconomical manner. The immense fo- rests with which the vast deserts of that em-oire are covered, and the distance -of towns and villages, v/hich lessens so much the consumption, leave to the pur- chasers of them, when those they have chosen are not in the neighbourhood of a mine, only one object to be accomplished, vvhich is that of making tar. The resinous vrcod is cut into pieces of different lengths, according to the purposes to which it is to be applied. Those destined to form the frame- work or sides of the furnace. A, (Plate /.) are longer. Those from which the tar is to be extracted are cut into shorter pieces of equal length. This length, in gene- ral, is three or four feet*. * See B, Plate IL which represents a section of tlie furnace. '^rr^a^nae^ne/Tfyâ (jtj To front pa (je 46. "7 /'/y/ ^/ y r ////'// / r>/ ////'^ Of ■////' p/ //f/frf.) //f /lf//j/rr yvv yy/^//r///'orkni'an's hands. The high ' ESSENCE OF TURPENTINE. 65 price of those toys will admit of these accidents being repaired with a kind of varnish which is indeed expen- sive, but endowed with all the required qualities, such as splendour, durability, and readiness of evaporation. ESSENCE OF TURPENTINE. Commerce makes us acquainted with a very odorous oil, highly inflammable, more or less coloured, and of a greater or less degree of fluidity, which is distin- guished by the name of essence or oil of turpentine. The acceptation of the term essence is not the same to the chemist and the perfumer. According to the former, this word expresses that part of a mixture or compound which is susceptible of being separated by the application of heat. He gives the name of essence to the sweet volatile part, v/hich he separates by distil- lation from aromatic substances : hence all the essential oil, volatilized in the course of the operation, is distin- guished by the collective name of essential oil or essence. According to the perfumer, as well as to certain artists, the term essence denotes the union of one or more es- sential oils with alcohol (spirit of wine). Thus essence of lemons, bergamot, lavender, rosemary, &c. is alco- hol impregnated with the aroma (odorous principle) and a portion of the essential oil of these fruits, flow- ers, &c. It is not under the latter point of view that we ought to consider essence of turpentine. It is an essential oil extracted from turpentine by distillation. The lightest and the least coloured is that which ought to be em- ployed for varnish. eô TREATISE ON VARNISHES. Though this oil is common, it is subject to that spitît of adulteration which unfortunately is extended to the simplest articles of commerce. It may be mixed with common alcohol or fat oils of little value, such as that of the seeds of the white poppy, knowTi under the name of oil of pinks. In both these cases the essence' is altered, and the use of it would be hurtful in the preparation of varnish. Water united to weak alcohol (brandy) opposes the solution of resins. Fat oil, though less dangerous, would render varnish unctuous, glu- tinous, and difficult to dry. The first kind of adul- teration may be known by pouring a Kttle of the essence into a phial filled with water to the neck; placing your finger on the mouth of the phial, and giving it two or three shakes. If the essence is pure, it divides itself into small, bright, limpid globules, which soon resume their former situation and volume. If it be mixed with alcohol, its extreme division renders the water milky, and the volume of the supernatant oil is not the same. In regard to the adulteration by fat oil, it may be detected also by the following sure method: Impregnate the surface of a bit of paper with this essence, and hold the paper before the fire. Pure essence will evaporate completely without leaving any traces on the paper, on which you may afterwards write. If it be mixed with fat oil, the paper remains transparent, and refuses every impression of writing. When alcohol is at hand there is still a speedier method. Add a few drops of essence to an ounce of alcohol : if the essence be pure, the alcohol becomes, charged with it j if mixed with fat oil, the essence passes ESSENCE OF TURPENTINE, 67 into the alcohol, but the fat oil is precipitated entirely to the bottom. If you wish it, you may easily ascer- tain the proportions which have been observed in the quantity of the two oils. I shall here give to this essence a chemical character, which Watin in his work has refused to it. In the first edition, p. 60, he announces that essence of tur- pentine does not mix with spirit of wine. He here no doubt means, that this mixture cannot be made in those propordons which might be necessary to render it fit for the preparation of varnish. It is certain that alco- hol becomes charged with it in relative proportions, ac- cording to the consistence of the essence. The lighter it is it takes up the less, and vice versa. The best alcohol can take up no more than a third of its weight of common essence, and a seventh or an eighth part of the lightest. The same author considers as a disdnguishing cha- racter of the best essence the difficulty it exhibits in its union with drying oil, which forms a principal part of amber and copal varnish. Very often this union is not complete till five or six minutes after the vessel has been taken from the fire, notwithstanding the state of agitation in which the matters have been kept. This effect depends entirely on the difference in the specific .gravity of the two oils, and particularly on the state of .the consistence or inspissation of the drying oil. The variations which may take place in regard to these two ■ .circumstances produce reladve results. The motion ^xcited in the mixture, by the means of caloric (heat), opposes in part the union of the lighter essential oil of s 2 63 TREATISE ON VARNISHES. furpentiiie: it indeed remains a long time at the surface, and does not begin to incorporate but in consequence of the cir^zular motion which is maintained, and when the action of the greatest heat ceases. ETHEREOUS ESSENCE OF TURPENTINE. RECTIFIE» SPIRIT OF TURPENTINE. If the influence of merited reputation induced the iunateur of an art never to deviate from an opinion pro- nounced by an expert master, the progress of the arts Would be slow, and errors would long enjoy the privi- lege of misleading the inquisitive genius, who examines every thing susceptible of improvement. Setting out from this principle, we might give some importance to the idea of reprobation which Watin attaches to the nature of ethereous or light essence. This author an- nounces that essence can be useftd only for fat var- nishes, in order to facilitate their extension, and that ethereous essence has too little body to be applied to varnishes. If this author, whose work is held in considerable esteem, had distributed his compositions for varnish into classes or genera, according to the different uses to which certain compositions may be applied, he v/ould not have emitted so decisive an opinion. Experience, w^hich produces and improves the arts, has induced m.e to pe.y little attention to that importance which is gene- rally attached to the decision of a master. Experience therefore shall be my guide, because it is by it alone that our Opinions ought to be regulated. It appear^ to me that the appiicatiou of ethereous essence of tur- '^ÎTHEREOUS ESSENCE OF TURPENTINE. 69" pentlne should be confined to the composition of var- nish for valuable paintings. The proprietors of the finest collections are continually recommending the use of it, as it has more body than alcohol. There are two methods of rectifying essence of tur- pentine to render it light and colourless, and to give it a less disagreeable and incommodious smell than com- mon essence. First Method. Pour into a glass retort, capable of containing double the quantity of matter subjected to experiment, three parts of common water and two parts of the essence of turpentine. Place this retort on a sand bath; and hav- ing adapted to it a receiver five or six times as large, cement v/ith paste made of flour and water some bands of paper over the place where the two vessels are joined. If the receiver is not tubulated, make a small hole with a pin in the bands of cemented paper, to leave a free communication between the exterior and the interior of the receiver : then place over the retort a dome of baked earth, and maintain the fire in such a manner as to make the essence and the water boil. The receiver will become filled with abundance of vapours, composed of v/ater and ethereous essence, which will condense the more readily if all the radiating heat of the furnace be intercepted by a plate of copper, or piece of board, placed between the furnace and the receiver. When the mass of oil subjected to experi- ' ment has decreased nearly two thirds, the distillation must be stopped. Then leive the product at rest, t» F 3 *J0 ^TREATISE ON VARNISHES. facilitate the separation of the ethereous oil, which is afterwards separated from the water, on which it floats, by means of a glass funnel, the beak of which is stopped by the finger. This etheFeous oil is often milky, or merely nebu- lous, by the interposition of some aqueous parts, from which it may be separated by a few days* rest. The essence, thus 'prepared, possesses a great degree of mo- bility, and is exceedingly limpid. It is only when it ex- hibits these two characters that it is thought proper for the composition of varnish. The second method cannot be employed but by per- sons very expert in chemical processes, and who therefore are well acquainted with those precautions which may be considered as essentially necessary to the success of a distillation of this kind. It is the process I chiefly fol- low, being performed without any intermediate sub- stance. Second Method. The apparatus employed in the preceding process may be used in the present case. I fill the retort tAvo- thirds with essence; and as the receiver is tubulated, I content myself with applying to the tubulure a small square of paper m.oistened with saliva, to afford a free passage to the incoercible vapours. I graduate the fire in such a manner as to carry on the distillation very slowly, until I have obtained a little more than half the oil contained in the retort, I separate the product from a very small quantity of exceedingly acid and reddish water, which passes at the 1 ESSENTIAL OIL OF LAVENDER. ^l same time as the ethereous essence : by these means the operation is much shortened. The oil of turpentine which remains in the retort is highly coloured, and thicker than the primitive essence. It may be used for extending fat varnish, or for coarse oil painting. The essence, when thus rectified, is lighter than the essence commonly sold in the shops. The former is to the latter as 31 to 32 j and the latter is to distilled water as 32 to 56. Its specific gravity is somewhat greater than that of alcohol ; the latter therefore floats on the lightest es- sence, and essence consequently has more body than alcohol. ESSENTIAL OIL OF LAVENDER. The varnisher has not much occasion to make use of this oil, which is better known to the enamel] er, be- cause it has sufficient consistence to prevent the colours diluted with it from running under the brush. Besides this advantage, which is not to be found in oils that are too fluid, it retains a sort of unctuosity, which prevents the inconvenience of too speedy desic- cation. It is on account of this quality that it is n\ost interesting to the varnisher. It is indeed employed in the composition of mordants, to which it communi- cates a sufficient degree of unctuosity to give the painter time to sketch out the design, which the gilder after- wards fills up. This essential oil is extracted by distillation from a certain quantity of the flowers or tops of lavender. The F 4 72 Treatise on varnishes. calyx of these flowers contains a great deal of this oil, which is volatilized in vapour v^ith the water, at thç temperature of boiHng water, and which is afterwards separated from the water over which it floats. Though this process is followed on a pretty large scale in the southern provinces of France, which seem to be the true country of aromatic plants, we must not believe that the essential oil extracted in them is brought to us in a state of purity. Essence of turpentine, which is far more common, is always mixed with it ; and it is by this addition that the distillers maintain among them- selves a competition which is always to the disadvantage of the consumer. It is needless, therefore, to point out the means of detecting an adulteration universally known, and which it is impossible to prevent. I shall only describe the principal characters, which may en- able purchasers to be on their guard against too exces- sive a degree of sophistication. The addition of the essence of turpentine ought to be considered as too strong, when the fluidity of the oU of lavender approaches too much to that of the essence, and when the odour of the plant is so concealed by the latter as to be scarcely perceptible. Another Idnd of adulteration, as lucrative to the distiller as it is prejudicial to the essence of lavender, destined for the composition of varnish and for paint- ing, is practised by mixing it with fat oil, such as oil of behen or oil of pinks. I have already detailed the means of detecting this adulteration in treating of the essence of turpentine. ESSENTIAL OIL OF SPIK.E. 73 ESSENTIAL OIL OF SPIKE. Oil of spike is the result of the distillation, on a grand scale, of a kind of lavender with larger leaves than that vv^hich grows in our gardens. This plant is very common in the ci-devant Languedoc. In regard to the oil which it furnishes in great abundance, it is impossible to find it pure in the shops. What is sold there emits a stronger or weaker smell of turpentine, in which i-s perceived a slight balsamic odour of the plant from which it takes its name. Painters are so fully convinced of the impurity of this oil, that they no longer use it. The varnisher, w^ho perceives no differ- ence between this oil and essence of turpentine but in the price, does not hesitate to supply its place by the •latter ; and in this he acts wisely. Distillers on a large scale bargain sometimes with "their consciences ; and think they act with great deli- cacy when they make choice of essential oil of spike to enlarge the quantity of their valuable essential oils ; such as those of m^yrrh, neroli, mint, kc. They re- serve the essence of turpentine for oils of less value, çuch as that of spike when it is required of the first quality. A process very common in the South of France is, to distil essence of turpentine from oft a certain quan- tity of that plant which is to give the name to the oil extracted in the course of the operation. By this me- thod, the odour peculiar to the plant manifests itself in a more sensible manner than by simple mixture. To 74- TREATISE ON VARNISHES. be able to discover this adulteration requires consider- able practice. This kind of adulteration, however, is not the only one employed. The addition of alcohol and that of fat oil is not neglected. OIL OF WHITE POPPY SEEDS, COMMONLY CALLED OIL OF PINKS. The white poppy, the same kind which in the east- ern regions, such as Natolia, Syria, Persia, and Egypt, furnishes opium, is very abundant in many of the coun- tries of Europe. The oil extracted from its seeds by contusion and expression, a method applied to almonds, is exceed- ingly sweet and unctuous. On this account it is em- ployed by the Orientals for cleansing and softening the skin. ^ The great use made of it under different forms in the East, in Bohemia, Poland, and Italy, seems to have been founded on the opinion entertained of the somni- ferous virtue of these seeds ; but it has been proved by a series of excellent observations, that they do not par- ticipate in this respect in the properties of the plant which produces them. They afford a sweet oily nou- rishment ; and this may serve to account for the use made of them in certain countries by nurses, who mix .them sometimes in broth, and administer it to their children to cure the colic. The accurate knowledge obtained with respect to these seeds, and the oil they contain, is not older than the beginning of the last centuiy ; and it is only owing OIL OF WHITE "POPPY SEEDS. 75 to the advantages which always result from correct ob* servations and conclusive experiments, that we are in- debted for the non-execution of the penalties established by the old police of France against those who mixed oil of pinks with the oils destined for alimentary con- sumption. Since that period, this oil, confined en- tirely to painting, in consequence of the shackles im- posed on its circulation, has always been sold at a cheaper rate than olive oil, nut oil, &c. However, to set bounds to mercantile avarice in regard to mixtures which might be made of it, government authorized the addition of a French pint of turpentine to each cask of this oil, as being allowed to be used only for painting. This mixture was made at the different offices where the oil was entered. Oil of pinks is not extracted from the seeds of the white poppy alone : those of the black poppy furnish it also, and it is used in Germany for lamps, for cook- ing, in salad, &c. In a word, it supplies the place of olive oil to the lower classes. Oil of pinks is unctuous : like fat oils, it must not be used for painting without proper choice, and it re- quires a preliminary preparation to be rendered drying. As it has the advantage over other oils of being colom*- less, it is preferred for delicate kinds of painting. Though age, in regard to this oil, supersedes the ne- cessity of previous preparation, and gives it a drying quality, I shall here indicate the best process for that purpose. T6 TREATISE ON VARNISHES. Pt'oces.'i for giving a dnjing QiLcilitij to Oil of PiiLhs. Into three pounds of pure water put an ounce of sulphate of zinc (white vitriol), and mix the whole with two pounds of oil of pinks. Expose this mixture in an earthen vessel capable of standing the hre, to â degree of heat sufficient to maintain it in a slight state of ebullition. When one-half or two-thirds of the water has evaporated, pour the whole into a large glass bottle or jar, and leave it at rest till the oil becomes clear. Decant the clearest part by means of a glass funnel, the beak of which is stopped with a piece of cork : when the separation of the oil from the water is completely effected, remove the cork stopper, and supply its place bv the fore finger, which must be applied in such a manner as to suffer the water to escape, and to retain only the oil. Oil of pinks when prepared in this manner be- comes, after some weeks, exceedingly limpid and co- lourless. liemarhs. Many artists reject every preparation of oil in which y/ater has been employed as an intermediate substance. It mav, indeed, be dispensed with when they employ coloured oils, with which they mix substances that communicate to them a foreign colour, and which the jicat applied to them contributes to render still stronger. The case is not the same xÀÛi oil of pinks : it still re* raiîis enough of its unctuous quality to impede desicca'- NUT OIL. 77 tion for sonie time, and it cannot lose this qiuillty but "by age, or by processes which are not very complex. In the process here given the oil becomes cliarged with a little water, by which it acquires a nebulous appear- ance, and retains it for several weeks. This interposed water gradually separates itself from it, and at the same time carries with it a mucilaginous matter, a little altered ; the complete separation of which adds to the extreme purity of the oil. Perfect limpidity is the surest sign of the absence of all its foreign particles. A slight heat accelerates the clarification of oil prepared with water. Watin indicates for linseed oil a process which may be employed for oil of pinks also ; and which might be simplified by omitting the calcined talc. Nothing is necessary but to expose it to the action of the sun, during the fme weather in summer, in a vessel the. bottom of which is covered with white lead, or, what is better, with litharge, inclosed between two pieces of fine muslin. Exposure to the sun for some months is sufficient to free the oil from its greasy pardcles, and to render it perfect» NUT OIL. Nut oil is extracted by contusion and expression from the interior part of the fruit from which it derives its name. It is well knovrn in consequence of the great use made of it as an aliment, and in certain arts. The most common kind, that is to say, the oil extracfed by the application of a small degree of heat to the paste, k reserved for lamps ; biit that extracted vvithout the 78 TREATISE ON VARNISHES. aid of heat forms a wholesome and nutritive seasoning, which retains an exquisite taste of the fruit. The burnt taste which this oil acquires, when too much heat is employed to increase the product, is the cause of the preference given to oil of olives in cookeiy. That destined for the arts is generally the most com- mon. The heat occasioned by the torréfaction it expe- riences, disposes it in a wonderful manner for the sub- sequent operations which render it proper for various uses in painting. It is preferred to linseed oil for every kind of painting exposed to the injuries of the air, and particularly to the influence of the sun. LINSEED OIL. Of all the fat oils, the one which forms the subject of this ardcle requires the greatest degree of heat in the process of its extraction ; and therefore it is always more or less coloured and thick. Flax seed contains a small kernel, which would give an almost colourless oil hke that of pmks, if nothing were required to extract the oil except contusion and expression, as is practised for oil of sweet almonds, and for nut oil of the first quality : but the kernel of flax seed is inclosed in a small hard covering, which is very TTiucilao:inous. The mucilage even is so abundant that it would absorb the greater part of the oil during the expression, had not experience pointed out the neces- sity of destroying it by a pretty strong torréfaction. During this process there arises abundance of aqueous vapours furnished by the mucilage, which becomes diy, and which in part is destroyed. When the whitish va- LINSEED OIL. '*f9 pour is succeeded by a kind of dry and blackish fumes, the torréfaction is complete, and the paste is then sub- jected to the press. It may be readily conceived that the preliminary labour must have an influence on the principles of the oil, and alter its purity. The Dutch follow this branch of the arts on a large scale, and furnish almost the whole of the linseed oil circulated by commerce in France. They conduct the process with more skill than the Germans, who carry the torréfaction of the seed to such a degree as to ren- der the oil almost red. This oil is destined for the purposes of painting, and particularly for the manufacture of floor-cloths ; but to give it that drying quality which these arts require, it is subjected to one of the operations described at the end of this article. The society* employs other kinds of fat oil, such as that extracted from the seeds of the beech tree, oil of olives, of sweet or bitter almonds, of hemp seed, oil of walnuts, &c. but they ail have a character of unctuosity, from which it is difficult to free them. I must, however, except oil of beech seed, so abundant in the department of Aisne, and those of the ci-devant Burgundy and Franche- Comté, which is sold there for common nut oil : and in these countries the, painters have never made any complaint against it. Besides, ^he high price of these oils, and particuiariy of olive , oil aiixi oil of almonds, would add to the reason, here mendoned. Painters and Tarnishers, therefore, adhere * The Society of Arts^ Agriculture, and Commerce at Geneva. so TREATISE ON VARNISHES. to the three kinds of oil here described. Linseed oil being inferior to nut oil for painting, is reserved for coarser works. METHODS EMPLOYED TO GIVE TO FAT OILS A DRYING QUALITY. First Process, Take Nut oil or linseed oil 8 pounds*. White lead slightly calcined, - - 1 Yellow acetite of lead (sal Saturn!) I of each also calcined, ----- i i ounce. Sulphate of zinc (white vitriol"), . Vitreous oxide of lead (litharge) ] 2 ounces. A head of garlic or a small onion. When these matters are pulverized, mix them with the garlic and oil over a tire capable of maintaining the oil in a slight state of ebullition : continue it till the oil ceases to throw up scum, till it assumes a reddish co- lour, and till the head of garlic becomes brown. A pelhcle will then be soon formed on the oil ; which in- dicates that the operation is completed. Take the ves- sel from the nre, and the pellicle, being precipitated by rest, v/ill carry with it all the unctuous parts v/hich * The proportions here gnen, ?ud in all tlie other formulae în this v.orkj are according to the old French pound. It is necessary, therefore, to ob-.er\"e that tliis pound is divided mto 16 ounces, çach ounce into S gros, each gros into 3 deniers, and each denier into 24 grains. Some further remarks on tliis subject, with a table. for converting the^e weiglits into corresponding EngUsh denoiui-* nations^ will be given at tiie end of tliis work. — ^Tkans. DRYING OILS- 81 rendered the oil fat. When the oil becomes clear, se* parate it from the deposit, and put it into wide-mouthed bottles, where it will completely clarify itself in time, and improve in quality. Second Process» Take Vitreous oxide of lead (litharge) 1 -i- ounce* Sulphate of zinc (white vitriol) 4 of an ounce, or 3 gros. Linseed or nut oil 1 6 ounces. The operation must be conducted as in the preceding case. The choice of the oil is not a matter of indifference. If it be destined for painting articles exposed to the im- pression of the external air, or for delicate painting, nut oil or oil of pinks will be requisite. Linseed oil is used for coarse painting, and that sheltered from the effects of the rain and of the sun. A Uttle negligence in the management of the fire has often an influence on the colour of the oil, to which a drying quality is communicated : in this case it is not proper for delicate painting. This inconvenience may be avoided by tying up the drying matters in a small bag ; but the dose of the litharge must then be dou- bled. The bag must be suspended by a piece of pack- thread fastened to a stick, which is made to rest on the edge of the vessel in such a manner as to keep the bag at the distance of an inch from the bottom of the ves- Bel. A pellicle will be formed, as in the first operation, but it v.'ill be slower in making its appearance. G ^ TRr.ATISrr on VAÎt^'I5H£3. In this process the oxide of lead, v.hcn it is free, and ^/hén it rests on the bottom of the vessel, is in a great part reduced. Small grains of lead even are often ob- served in it. • '* Third Troce-s. A drying quality may be communicated to oil by treating in a heat capable of maintaining a slight ebul- lition linseed or nut oil, to each pound of which is added three ounces of vitreous oxide of lead (litharge) reduced to fine powder. I have known painters who carried the dose of vi- treous oxide of lead to a fourth part the quantity of oil employed. This case is reserved in particular for' baked oils used in painting, where speedy desiccation and the greatest degree of durability are required. I have often used drying oil, prepared by extending the dose of the vitreous o:dde of lead to a fourth part of the quantity of the oil. The preparation of floor- cloths, and all painting of large figures or ornaments, in w^hich argillaceous colours, such as yellow and red boles, Dutch pink, &c. arc employedj require this kind dî preparation, that the desiccation may not be too slow ; but painting for which metallic oxides are used^ such as preparations of lead, copper, &c. require only the doses before indicated, because these oxides con- tain a great deal of oxygen (the base of pure ah'), and the oil by their contact acquires more of a diying' quality. Nay, I have painted v/ith unprepared nut oil, tak- ing the precaution to- add to the pulverized colour \'i- Î DRYING OILS. 83 treous oxide of lead (litharge in very fine powder*), about 3 or 4 ounces for each pound of oil. The paint- ing, in this case, acquired a body as speedily as if baked oil had been employed. This method is expe- ditious ; but it can be practised only with colours which are not susceptible of being attacked by litharge. Fourth Process» Take Nut oil 2 pounds. Common water 3 pounds. Sulphate of zinc (white vitriol) 2 ounces. Mix these matters, and subject them to a slight ebul- lition till little water remain. Decant the oil, which will pass over with a small quantity of water, and separate tl^e latter by means of a funnel. The oil remains nebulous for some time ; after which it becomes clear, and seems, to be very little coloured. This method is employed by some of the English artists, and I have tried it with success: the oil is rendered somewhat less drying thafi by the other processes, and is attended with this incon- venience, that it remains nebulous for a very long time, even when exposed to the influence of the sun. * To reduce the vitreous oxide of lead (Iltliarge) to a state of great division, v.ithout incurring the risk with which dry pulveri- zation is sometimes attended, I grind the oxide with water ; I Iheu •spread out the divided matter in an iron shovel, and place it over a gentle fire. The moisture is soon evaporated, and the remaining matter requires very little stirring v/heu mixed up. 1 his method may be applied v/ith great success to painting in ^vhich different kinds of ocliTie are employed. Si- /;•■•'■ .l^kÈATÏSE ON VARNISHES, f'-' >C ' ^/' Fifth Process. . .-■Take Nut or linseed oil 6 pounds. Common water 4 pounds. Sulphate of zinc 1 ounce.- One head of garlic. Mix these matters in a large iron or copper pan ; then place them over the lire, and maintain the mix* ture in a state oi ebullition during the whole day : boiling water must from time to time be added, to make tip tor the loss of that dissipated by evaporation. The garlic will then assume a brown appearance. Take the pan from the fire ; and having suffered a deposit to be formed, decant the oil, which will clarify itself in the vessels. By this process the dn'ing oil is rendered somev/hat more coloured : it is reserved for delicate colom"s. This method is one of those which require the utmost attention; and therefore by some it has been condemned. If the water mixed with the ingredients, îmd that added in a state of ebullition during the pro- cess, to supply the loss of that dis:ipated by evapora- tion, be too abundant, and if tovv'ards the end of the operation it be not all made to disappear by a careful evaporation, it will unite itself to tlie drying: oil, and communicate to it the colour and the coDsistence almost &[ creaiu. In this case the oil will ciaiify slowly ; there will even reuKiin an interposed portion, which it wili DRYING OILS.^ /^n •r ^x, 7 be difficult to separate. This incoriii^îeriGè'^se^ justify the censure passed by some artfeçs^n";^^ cess. However, when well conducted, if^^a^rds a very simple method of obtaining oil exceedingly dry- ing, and much less coloured than that subjected to the' direct impression of the fire ; but it requires to be kept for some time. House-painters, &c. are less interested than portrait- or landskip-painters, and those who paint decorations, in the different researches which tend to destroy the brown or reddish tint, which is one of the characters of oils rendered drying by the common processes. For brown or dark colours they employ the oil twenty-four hours after it has been prepared, reserving that which clarifies itself by deposition for the more delicate kinds of painting. This, however, is not sufficient ; be- cause the least tint communicated to fine colours vi- sibly alters their tone. Researches, therefore, have been made to find out for this particular case processes different from those which we have here described, without excepting even the last. Watin indicates one for nut oil, which may be ap- plied to linseed oil, and even to that made from the seeds of the white poppy, in case artists should liave any objection to employ water as an intermediate sub- stance. This process is attended with complete suc- cess, and gives a drying oil free from any foreign colour. I have mentioned it in describing the process for communicatmg a drying quality to the oil of white poppy serd. In every case in which sulphate of zinc (white vitriol) is employed, according to the English G 3 86 TREATISE ON VARNISHES. method, without any mixture, it is proper not to cari:y the- evaporation of the water beyond three-fourths of the whole. In describing the preparation of oil of pinks, it has been seen that water is an intermediate substance pro- per for keeping the temperature necessary in this ope- ration at a fixed point, and which is incapable of alter- ing the principles of the oil by making it undergo a commencement of decomposition. The well-known property it possesses of being reduced to a state of va- pour affords a certain method of avoiding the accumu- lation of caloric (heat). By varying the process, and following a contrary course, it may be rendered the sole cause of the drying quality required to be given to a fat oil. Water in the state of snow will exhibit the two conditions essentially necessary to produce this effect : extreme division of parts and multiplication of contact between the rnoleculse of the oil and the oxy- gen gas contained in the snow. It is on this principle that the following process is founded : Sixth Process. When the long continued cold of winter gives to snow a pretty dry consistence, take any quantity at pleasure of linseed oil, nut oil, or oil of pinks, and mix it with snow, kneading the mixture in a bason with a wooden spatula, or in a mortar with a pestle. Form it into a solid mass, and place it in an earthen, a glass, or a porcelain vessel with a large aperture, and cover the aperture with a cloth to prevent the introduction of foreign bodies. Expose the vessel in a place acce^ '4 DP.YING OILS. ST sible to the cold, but sheltered from the influence of the solar rays. On the return of a milder temperature the snow will dissolve into water, which will separate itself from the oil. If the oil has not been exceedingly clean and pure, the water is found to be charged with, its impruriues. If the severe temperature continues two months, as is the case during some winters, the oil will acquire in a higher degree its drying quality. A part of the oil retains then a little water, and it forms a pellicle, which in colour and consistence resembles that composition known under the name of painters* cream or butter*. The oil is decanted from off the water, or it is re- •inoved with a spoon and put into a bottle. Rest, by separating the interposed particles of water, is sufficient to clarify it. This separation may even be accelerated .by exposing the oil to the heat of a balneum mariae. " Taiutevs who leav'e long intervals between their periods of iabour are accustomed to cover the parts they have painted widi .a preparation v/hich preserves the freshness of tlie colours, and which they can remove wlmy they resume their work. This pre- paration, which is as follows, is called painters' cream; Take Very clear nut oil 3 oimces. JVIaslic in tears, pulverized, 5 ounce. Sal Saturui in powder (acetite of lead) ^ of an ounce. Dissolve the mastic in oil over a gentle fire, and pour the mix- ture into a marble mortar over the pounded salt of lead j stir it widi a wooden pestle, and add water in small quantities till the mutter assume the appearance and consistence of cream, and refuse to admit more v/ater. I liave found means to introduce /I ounces inio ihiii cwniposition by whipping it with a bunch of «mall twigs. G 4 S8 TREATISE ON VARNISHES. The oil by this simple mixture acquires a drpng property, and appears as little coloured as it was before it was subjected to this process. The circumstance, therefore, of the division of the molecular of the oil, which multiplies, and facilitates its contact with the oxygen gas contained in the snow, concurs in an effecr tual manner to produce the required result — that is to say, the disappearance of that unctuous and fat state which is one of the principal distinguishing characters of fat and essential oils. Modification of the same Process, If an oil already rendered drying, by one of the 'preceding operations, be employed in this process with as few reacting ingredients and as httle heat as possi- ble, the oil becomes drying in an eminent degree. It is then very thick, and a part of it is so confounded with the water that the result is a glutinous and almost resinous matter, which adheres so much to the inter- posed liquid that it obstinately retains that form, what- ever process may be employed to break the union of the water and the oil. But in treating oil of hemp seed in this manner, I observed, in the course'^||kp second operation, the separation of two very distinct oils ; one of v/hich having a greater specific gravity than water fell to the bottom of the vessel, while the other occupied the upper part in such a manner, that the whole of the liquid produced by the melting of the snow formed an intermediate stratum between these two oils, The first, thai: is to say the heaviest, v/as very little \ DRYING OILS. . ' 8D ^ ■ coloiu"ed: it was less so than the second';, and even y than the oil of hemp seed itself was before its" mixture with the snow. The first stratum of oil formed two zones, the upper one of which was clear; the other was opake and of a chamois colour. The latter, which retained water, was exceedingly thick, and as if resini^ fied. The water which served to separate these two kinds of oil was nebulous. In general its present state depends on the greater or less purity of the oil employed, and on that of the snow. These two varieties of oil arc highly drying ; and when kept for a summer, I have found great difficulty to extract them from the bottles in which they were preserved. The heaviest oil, and that found the least coloured, may be used for the preparauon of paste made with white lead or Cremnitz white, employed to repair bro- ken enamel *. Sevenlh Process. These attempts lead to another kind of experiment, more direct, which confirms in a complete manner the theory respecting the causes of the state of inspissation, and the drying property which oils acquire by the dif- ferent processes usual among artists. The results be^ fore detailed induced me to try to discover means pro- per for shortening the operation, by exposing oil to the influence of a current of oxygen gas. Though I had observed in my experiments on essence of turpentine exposed for a considerable time to the contact of oxy? * On tliis subject see Part IL êo TREATISE ON VARNISHES. gen gas, often renewed, that this process was not suf- ficient to facilitate a reciprocal combination, since the gas filtered through the stratum of oil and the mass of trater covered by this oil, without adding in a sensible manner either to its state of inspissation or to its specific gravity*, I could not see in this first eflect any thing to prevent similar experiments on fat oils. It was possible that the chemical difference which existed be- twe(m the two kinds of oil might conduce to give new results; and it was also possible that, by direct- ing on the oil a current, of oxygen gas, accompanied with caloric, I should be able to destroy that kind of inactivity Vv^hich the gas exhibited in the experiments just mentioned. ' With this view I exposed nut oil, inclosed in a very narrow long tube, to a current of oxygen gas, disen- gaged from manganese by sulphuric acid. The orifice of the tube was arranged in such a manner as to pre- sent a certain resistance to the too speedy dispersion of the gas which escaped from the mass of oil. The ab- solute weight of the oil before the experiment was three ounces. After the disengagement of the gas, which continued five hours, the oil had experienced no other change than a slight modification in its colour, v/hich was become clearer. Its weight was absolutely the same, and it retained its taste of the fruit. I exposed the same oil, but ^yilhout success, to a f.ew mixture, the gaseous disengagement of which con- fiiiucd eight hours: I then hoped that the mixture* or * Joivrnal de Fhysifi'dCj .aIjxs et Avril I7i)^- DRYING OILS. 91 combination of an acid with oxygen would enable me to add a new process for giving a drying quality to oil more siîeedily, and for obtaining it colourless. Eighth Process, Muriatic acid (marine acid), which of all the mineral acids produces the least change on oils, exhibited, in its affinity for oxygen gas, that mean state of com- bination which seemed likely to answer the purpose I proposed. I therefore directed into a tube filled with ,oil a current of oxygenated muriatic acid gas, employ- ing as much care and attention as possible in the operation. Signs of a combination instantly appeared. The colour of the oil was altered ; and a brown but transparent tint soon succeeded to the beautiful lemon colour which it had retained. Its fluidity and the odour of the fruit gradually disappeared, to give place , to those of baked oil. When examined by a balance, tvv/^enty-four hours after, it weighed 33 grains more. In this state it impressed on the tongue the savour of rancid oil, with a slight taste of acid exceedingly dif» ficult to be perceived. The passage of the oxygenated îicid gas had condnued six hours. The same experiment, repeated on the same oil, -still deprived it of its colour. The rancid odour was more perceptible, but the weight had increased only 12 grains. The three ounces of oil then announced an addition of 45 grains, or of 15 grains per ounce. This oil being exposed to the sun for fi\e days, I 'nixed one part of it with tiiree parts of water. The mixture, assisted by motion^ formed a very tliick cmuU. 92 TREATISE ON VARNISHES. sion, which by rest separated into two parts. Thç supernat2Lnt oil always remained white like an emuU sion. Exposure to the sun, and afterwards in a bal» neum marise, did not effect a separation of the inter- posed water. This is a property peculiar to dr)ing oils. Time alone overcomes all difficulties. The water, when drawn off, scarcely produced any change in blue vegetable tincture. Concentrated liquor of carbonate of potash (alkali of potash) produced with it no effervescence. It was now of importance to make a trial of this drying oil on delicate colours, such as the aluminous rose-coloured lakes extracted from Brasil wood. This colour, mixed up \Aith this oil and spread over a piece of walnut-tree wood, was five days in dr) 'ng ; on white wood it required only two days. The union of white lead with the lake, in order to form a dark flesh colour, required for walnut-tree wood only tvv^o days, and for white wood twenty-four hours. The colours retained their full brilliancy. These trials might have appeared sufficient to give conlidence in regard to the employment of this process, in which a very intimate union is observed between the eil and that principle which renders it drying in a very little time by the help of the acid, which serves as a midium. It is not expen.âve, and oil prepared in this manner will abi:okiLely be colourless unless when that of pinks or of v/hite poppy seeds is used. I employed, jn each of these experiments, tliree ounces of pure pulve- rized mr.gnesia, and 2-|- ounces of common sulphuric •acid, diluted with an ounce of waier. I adapted ta- DRYING OILS^. 93 the retort a small intermediate receiver, placed between it and the bent tube, which was conveyed to the bot- tom of the cylinder containing the oil. By these means the acid emanations, which escaped from the retort, did not reach to the oil. This operation may be very well performed in a sand bath. The continuance of three ounces of nut oil, ex- tracted without heat, upon four ounces of water satu- rated in a great part with oxygenated muriatic acid, did not produce so speedy an effect. Two months f lapsed before the oil had acquired the odour and con- sistence peculiar to drying oils. It was exceedingly- limpid, and its bright lemon colour had become orange. I shall conclude this article with some general ob- servations on the process which communicates to fat oils those qualities by which drying oils are charac- terized, and on the principles of the theory respecting Ihem. General Observai iom. Eveiy oil is susceptible, without preparation, of com- posing a colour by its mixture with a colouring body» -and even of constitutincc a durable varnish with*the «ame colour. In this particular case, the time necessajy for the desiccation of such a mixture will always be proportioned to the nature of the oil employed. The fattest and the most unctuous will also be the slowest in drying: there are some which will even require several years before they attain to the necessary con- sistence and solidity. Art has found means to overcome this difficulty by 94 TREATISE ON VARNISHES. certain mixtures, which modify the principles of the oils, and render them proper for a speedy renovation of the strata. It is probable that the mixture of certain oils with metallic oxides, such as litharge, ceruse, verditer, &c., the drying effect of which is very speedy, may have served as a guide to the first person who made researches in regard to colours. Every discovery produced by accident remains a long time in the hands of the author; but new trials soon multiply the results, and increase the resources of the art. Jealousy, in matters relating to the arts, views every thing with an observing eye. It creates particular compositions ; and hence that variety of formulae which art, in extending itself, either confirms or rejects. Roudnc taught, in general, that to free an oil from Its greasy particles, and to give it a drying quality, no- thing was necessary but to bring it into contact with different substances known to be more or less effec- tual for that purpose, and which, by help of a well regulated fire, free it from an unctuous matter, the presence of which would commmiicate to colours a viscidity which would render the use of them more dis- agneeable, and even impossible, in consequence of its slowness to assume a body. The effect once obtained, the first authors of such processes would proceed no further. Whether the oil by this application of certain foreign bodies received any new principle, or lost one itself, or whether it ex- perienced only a simple modification in its substance, was to them of little importance. Satisfied with the effect, thev gave themselves no trouble about the cause; DRYING OILS. 95 Their only aim was to render the effect certain, at the expense even of the colour of the oil, by adhering to a certain regularity in the execution of the process. This was the strict result of the experiment. At present art goes further, by proceeding from the effect to the cause. This is accomplished by researches which conduct to theory ; and theory simplifies every thing by throwing new light on what is already known, and fixes the great value attached to good descriptions of the arts. If we consult experience in regard to the art of common house-painting, it will be seen that the sub- stances which best answer the ends proposed in the preparation of oils are exactly those which contain the greatest quantity of oxygen (the base of pure air), and which are the most susceptible of abandoning it in favour of the oil with which they are in contact. This is the result of a real elective affinity, determined by the application of caloric, or by a kind of particular processes. This essential condition is perfectly answered by me- tallic oxides. They resign to the oil the oxygen which deprives them of their metallic brilliancy, and v/hich gives them the pulverulent form : this process is a kind of combustion. The oxide deprived of its oxygen as- sumes then its first metallic form. This is what is ob- served in the remaining matter of an oil rendered dry- ing by litharge. The case is the same when ceruse, white lead, massicot, salts of lead, &c. are employed. The direct inliuence of oxygen in the state of gas, and united to the muriatic acid, is accompanied with 96 TREATISE ON VARNISHES. the same effects as I have indicated in the eighth pro- cess : in a word, the metallic salts, the acids of which are highly charged with oxygen, have the same pro- perty, but in a degree inferior to pure oxide*. After all these eifects, which result from the appli- cation of these first substances to oils, it needs excite no astonishment that oil exposed to the sun, and parti- cularly in leaden vessels, according to V/atin's manner, should in the course of time acquire a dicing property. The oxygen gas, which forms part of atmospheric air, soon renders them rancid by the development of an acid principle. This effect, arising from th', combi- nation of the oxygen, would be speedier if the mixture were exposed to a higher temperature than that given to it by the sun : but in this case the principles of the oil in a state of decomposition would communicate to it a colour, which would confine the use of it to com- mon painting. If fat oil then be exposed in a leaden vessel in a place where it has a free communication with the exterior air, or if a glass vessel in which plates of lead are put be employed, the oxidation of the lead will be effected in both these cases by the modifications which the oil experiences, and which are necessary to render it dry- ing. The experiment may even be varied. If glass vessels filled with oil to which a metallic oxide has been added are exposed to the sun, and if the vessels be- closely shut, the result will be exactly the same, but slower. In the latter case, the metallic oxide will ap- * See the word Oxidcj Part II. DRYING OILS. ©7 proach its former state by the loss of a part of the oxy- gen which constituted it an oxide ; and this transition will take place according to the quantity of the oxygen liberated and given up to the oil. It is needless to ob- serve, that a higher temperature than that produced by the sun would give the same results as the first pro- cesses here described. These results are always- the same, but produced sooner or later according to the nature of the substances employed, and the energy of the means which constitute the process. If we consult all the books which treat on house- paindng, &c. and on the matters employed for th'at purpose, we are struck with the variety of the for- mulae, both in regard to the doses of the re-agents and the method of using them. Some authors recommend the concurrence of water : but this is rejected by others, in consequence of the property it possesses of not being miscible with oils, and of the difficulties it presents in regard to clarification. The first quality, however, renders it proper for this use, and it has that also of acquiring, over the strongest fire, only a deter- minate degree of heat, because it carries oif in its state of vapour the excess of caloric ; the accumuladon of which in the oil, treated t^'ithout this medium, would not fail to become prejudicial. The process is slower ; but this slowness is compensated by the state of the dr^'ing oil, which is colourless, and even pretty limpid, when the greater part of the water is evaporated to- wards the end by a gentle heat. Some ardsts, imitating the author of Le Parfait Fernisseuî'y inclose their re-agents in a small bag ; and .» H ^8 TREATISE ON VARNISHES. Others, after the ej^ample ofWatin, mix the ingredients with the oil. The fact is, that all these methods suc- ceed, and produce a dicing oil very little colom-ed, if the f/re has been properly managed, and if substances ■which might give to the oil a foreign colotir be kept at a distance from these mixtures. It will, therefore, be? proper to employ only metallic oxides, such as ceruse, •white lead, litharge, and fiowei^s of zinc. Some me- tallic salts participate to a certain degree in the same property. Of this kind are the sulphate of zinc and acetite of lead (white vitriol and salt of lead). * Watin himself, who seems to have overlooked the true theory of this operation, does not appear sufficiently nice in the choice of the matters he employs for free- ing oils from their greasy particles. He indicates as an essential substance ombre earth, which in general con- tains' a bituminous matter, that communicates to oil a foreign colour. In like manner he prescribes the use of a kind of stone, pretty rare, called Muscovy talc, •with the influence of which on oil we are as yet lit- tle acquainted, and the place of which is supplied in France by a species of sulphate of lime, very common at Paris and in the neighbourhood of that city. It is known to the vulgar under the n^me of wiroir d'ane^ In the preceding formulae I have varied the doses as well' as the nature of the re-agents. In this respect, however, there is a sort of rule established in some measure by a series of practical observations : tliat is, to extend the quantity to one-eighth of the oil em- ployed.' This quantity will be sufficient in the ordinary cases of painting, if the matters used are all of the- DRYING OILS. 99 same energy ; that is to say, if they are all capable of furnishing during the operation the same quantity of acting principle — oxygen. I made a point of abstaining from substances whose influence, in this point of view, did not appear to be fully proved, and from those which would communicate to oil a foreign colour : in a word, the formulas given in this work have all been proved by experiment. The process most common among artists who are desirous of freeing an oil from its greasy principles, consists in communicating to it, before they add the drying ingredients, a degree of heat nearly equal to that which produces ebullition. This method would be attended with inconvenience if the whole matter were abruptly mixed, and especially if the vessel were not of a sufficient size to obviate the effects of the swelling of the oil. Ceruse and acetite of lead (salt of lead), sulphates of lime (selenites), and ombre earths, contain moisture, which expands and distends the oil. This tumefaction is so speedy that there is always some danger of its catching fire. The previous calcination recommended for certain matters, without specifying the reason, as for ceruse and salt of lead, is to be considered here only in a pracdcal point of view, as a mere precaution in the process. When these matters are employed without previous calcination, it will be proper not to add them to the almost boiling oil but in small separate portions. In all cases where preparations of lead are employed for freeing oils from their greasy principles, great care must be taken not to stir the mixture too much with a H 2 100 Treatise on varnishes. > spatula, because the oil then becomes charged with the lead, and, combining with it, retains it under the form of soap. The oil is thus rendered exceedingly thick, and assumes the consistence of jelly. It will be sufficient to leave the mixture to itself over a gentle fire capable of making the liquid enter into a slight degree of ebul- lition. I have known painters of ornaments, and coach painters, who preferred adding sulphate of zinc (white vitriol) to their colours rather than applying it to the Jjreparation of their oil. This method is defective. The salt refuses to incorporate with the oil. It then renders the painting mealy, and even occasions cracks in it. The garlic, often added to preparations of this kind, is eVriplOy^d' merely for the purpose of indicating the iiiôment when the whole aqueous part of a mixture is evaporated : it however possesses of itself a very dry-? ing 'quality.' The gTirlic alone, or the juice of garlic, employed in a proper dose would render oil exceedingly drying. It is even used, in certain cases to form a ground to colours which refuse to adhere to the bodies on -which tliev are applied. ■ Drying oil is employed for several purposes. When colourless it is- much sought after by those who paint pictures. It enters into the composition of varnish, and it serves itself as varnish in oil painting, either em-- jîloyed alone, or diluted with a little essence of turpen- tine. When destined for house painting it will be ad- vantageous to use, for the last coating, that to which I give the name of resinous chijmg oil, and which exhi- bits all the qualities of a varnish. I hav€ often em- - , RESINOUS DRYING OIL. 101 ployed it for painting applied to bodies sheltered from, the rain and the sun, by mixing it with the delicate colours. It is to be recommended also for strong. gc3^ lours, such as yellow, red, green, and in |jartieul.ar ochres. The preparadon of it is as follows: -"' '. RESINOUS DRYING OIL. Take 10 pounds of drying nut oil if the paint is de- stined for external articles, or 1 pounds of drying linseed oil if for internal. Resin 3 pounds. Turpentine 6 ounces. Remarks. . Cause the resin to dissolve in the oil by means of a gentle heat. When dissolved and incorporated with the oil, add the tuipendne : leave the varnish at rest, . by which means it will often deposit portions of resin and other impurities ; and then preserve it in wide- mouthed bottles. It must be used fresh-: when suf- fered to grow old it abandons some of its resin. If this resinous oil assumes too much coïisistence,. dilute ,, it with a little essence, if intended for articles sheltered from the sun, or with oil of pinks. . „ , . ; In.my country, where the principal par4: of the mason ■^#ôrk consists of stones subject to crumble to pieces, k is often found necessary to give* them a coating of oil paint to stop the efi'ects of this decomposition. This painting has a great deal of lustre, and when the last coadng is applied with resinous oil it has the effect of a yarnish: To give^ it more durability the first ought to V . H 3 - 102 TREATISE ON VARNISHES. be applied exceedingly warm, and with plain oil or oil very little charged with the gray colour, which is added to the two following. In general, eveiy first coating with oil applied to a Wall, ceiling, &c. ought to be exceedingly warm, to harden the surface which is to receive the painting. DRYING OIL FOR PRINTERS* INK. Printers' ink is a real black paint, composed of lamp Élack and linseed oil, which has undergone a degree of baking superior to that of the different drying oils already mentioned. A greater or less consistence is given to it, according to the strength of the paper; and this depends on the degree of baking given to the oil, or on the mixture of a greater or less dose of lamp black. The degree of heat applied to the oil is sufficiently great to decompose it in part, and even to make it in- flame. Should this prepared oil retain unctuosity, it would fill the eye of the letter, run upon the paper, and communicate to it a semi-transparency of a yellow colour. This effect is particularly striking in works printed with bad ink. The preparation of this ink is simple : Boil linseed oil for eight hours in a. large iron pot, and add to it bits of toasted bread, for the purpose, no doubt, of ab- sorbing the water contained in the oil. Leave it at rest till next morning, and then expose it eight hours more to the same degree of heat, or until it has acquired the necessary consistence: then add lampblack worked up with a mixture of essence of turpentine and turpentine. DRYING OIL FOR PRINTERS IKK. 103 ITiis operation is to be performed in the open air, to prevent the bad effects of the vapour of the burnt oil, and, in partie alar, to guard against accidents by fire. This process deserves a place here, because it -form.s a part of those employed for giving oils a drving qua- lity, and as the result of it is real oil painting ; but, beiiîsf foreign to the art of the varnisher, it is not i)ecessary to jiiake any further obseiTations on this subject. n 4 [ 104 1 CHAPTER III. General ohservations on varnishes ^ u>ith a dlstrilution of them into Jive genera, determined by their nature and state of consistence. Xke word varnish is a general expression used to de- note every dry or liquid substance, the extension of which over solid bodies gives to the surfaces of them a certain lustre by a combined effect of the reflection and refraction of the rays of light. Confining our view to this single effect, there are many substances which may be confounded with those that appear to us to possess all the essendal qualities necessary for producing this lustre in a permanent manner. Thus water, oil^ and indeed every fluid, spread over the surface of polished wood, soon changes its appearance, and gives it a cer- tain lustre, which must not be confounded with that resuking from the application of a real varnish, because this effect is not permanent. The case is not the same with pure gums, such as that of the cherry tree, plum tree, &c. and in particular gum arabic, when diluted with a certain quantity of water. These substances form real varnish, the effect of which is permanent, and which is sometimes em- ployed with success to preserve from alteradon certain porous bodies, such as eggs ; and to heighten in other bodies the splendour of their natural colours, as is the case in regard to shells. The same end is aecomplish- çd under the hand of the naturalist by albumen (the GENERAL OBSERVATIONS ON VARNISHES. 105 white of ïin egg) diluted with a little brandy. It is the same substance also which gives a lustre to that kind of varnish with which boots and shoes are covered. In the last place, gelatin (animal jelly) diluted with water participates in the same properties. In a word, every liquid, transparent substance which deviates from the sim-plicity of the composition of water ; vv'hich is sus- ceptible of uniform extension over a solid body; which does not suffer itself to be entirely dissipated; and which, in evaporating in part, leaves on the body it covered some traces of its presence, exhibits the phsenomena of a varnish, and approaches more or less to the qua- lities of real varnish. In consequence of these reasons I might have been induced to form varnishes of this kind into a particular class, had I not been prevented by considering that the art of the varnisher can dispense with this supple- ment. I shall yield to the same motive in regard to stony and saline substances, which by means of certain processes and the assistance of heat are converted into a kind of glazing, which has been ingeniously applied to the decoration of the fine kinds of pottery— a branch of industry that maintains so many manufactories of . earthen- ware .and. porcelain. These, however, are reaî varnishes ; and in the arts are knovm Qnly under that technical appellation. The art, then, the processes of Ms^hich I mean here to examine and describe, is confined ■ to the composition and use of the varnishes resulting from a solution, of , resinous or gummo-resirious sub- stances in different spirituous or oily liquids, according i06 TREATISE ON VARNISHES. to the consistence required to be given to the varnishes, and the use to which they are destined. Confined within these limits, the art of the varnisher consists in discovering and applying to practice certain formulae of composition ; and in endeavouring to unite the essential qualities which constitute good varnish ; namely, lustre, transparency, and durability. The last quality is the most difficult to be obtained. From the knowledge acquired respecting the nature, of the substances capable of being employed in the composition of varnish, one might be induced to be-, lieve, that if the application of it to objects of lux- ury be of a modern date, the invention of it may be traced back to that antient peiiod when the art of heal- ing acquired its formulae. The apothecary was ob- liged, in consequence of his profession, to make fre- quent solutions of resinous substanccis in spirituous ve- hicles. These solutions, known under the name of tinctures^ were so many kinds of varnish, wliich to become really so required only to be applied to objects dilïerent from those for which they were intended. It is probable that the period of their application to the purposes of luxury is not much latei than that when, the Jesuit missionaries made known, on their return from China, the beautiful lacquered wares of that coun- try. The chemists, who found in these beautiful spe- cimens objects of comparison, exerted themselves to discover the means of imitating thei^,e compositions by substances with which they were familiar. It may he readily conceivedj fvcm this short view, that every resi-, COMPOSITION. 107 nous or gummo-resinous solution in a proper fluid, suLcepùbie of depositing by evaporation the substance k is charged with, and of making it appear under the form of a transparent lamina, brilliant and more or less solid, constitutes what in the language of the arts is called varnish. FARTS OF WHICH THE ART OF THE VARNISHER IS COMPOSED. The art of the vamisher comprehends three essen- tial parts : 1st, Composition. 2d, Application. Sd, Polishing. FIRST PART. Composition, This part is confined to resinous, inflammable sub- stances, which have a certain analogy to some spirituous liquors, in consequence of which they are disposed to unite with them mechanically, by that kind of afli- nity which the integrant moleculse of resinous bodies, and those of the fluid that serves them as a vehicle, exercise on each other. In consequence of these conditions, established on the analogy and homogeneity of the substances em- ployed, it may be readily conceived that this part must be confined to a certain number of resinous bodies and oily substances, the composition of which ap- proaches very near to, and is often identically the same Ï08 TREATISE ON VARNISHES. as, that of resins. Thus all essential oils, the spon- taneous or forced evaporation of which leaves a resin> ous residuum, exercise on resins, which are only dried essential oils, a kind of affinity, founded oft this homo- geneity of principles, and on this necessary analogy. •■ In all cases, the solution of resins seems ta take place iii tlie inverse ratio of the quantity gf the essential water, or that which enters as a principle into the com- position of the vehicle employed. Sometimes, how- et^er, the solution depends so much on a particular state of composition, that it forms an exc^pt-ion to this kind of rule. A vehicle is often employed, the com- position of which deviates so much from the nature of essential oils, that water seems to be one of its predo- minant principles. This difference, however, does not constitute a character which ought to make it be rejected ; since, on the contrar)'', water is considered as one of the principal agents in the composition of rarnish, when applied to resins, the choice of which has been determined by experiment: of this kind is alcohol (spirit of wine). ' But on the orie hand, if varnishes formed with alco- bol seem to be those mos- endov.'ed with a drying qua- lity, as well as the most brilliant, and the least dis- agreeable to the sensation cf smell ; and if they are the least liable to communicate a foreion colour to the o .grounds on which they are applied; they are, on the other, destitute of that consistence and solidity which are justly considered as the most essential qualities of varnish, the excipient of which is of an oily nature. The: observation of these differences has iiiduced AEPLICATiO>f AND POLISHING. W$ artists to . confine themselves, in the employnvant of yamish, within certain bounds. None of the compo- sitions known are indiscriminately proper for all pur- poses ; because a certain concordance ought to exist between the varnish and the article to the decoration of which it is intended to contribute. The varnisher finds it sometimes convenient to retard the desiccation of his composition, that proper time may be left to the designer to delineate and even, to detail his subjects. . In other cases, he -endeavours to give to the bodies which he covers with his composidons a soHdity capa- ble of oj^posing. a certain resistance to shocks and t(j friction. . These circumstances, which are well known to all persons acquainted with tlie detail's of this art, render it necessary to have compositions of various kinds, which it Y/ill be proper to treat of separately. The method of classing, objects, according to their essential properties, has appeared to us that best suited to the present case. We shall, therefore, apply it to the distribution of varnishes, being persuaded that it will facilitate researches respecting the different kinds of yamish, and the varied cases of their application. i- - SECOND,. AND THIRD PART. AppUcation and polishhig. ■■■ The- two.- other parts which constitute the art of the varnisher relate more directly to the artist than to the amateur. . Tiiey require more experience than study. The applicadon and polishing of varnish rj&. 110 TREATISE ON VARNISHES. quire practice. The precepts, however, which are ap- plied to this part, present no difficulty which may not be surmounted by an intelligent and skilful amateur. It is the mechanical part of the art; and it deserves observations which will be introduced when we come to treat of the use of varnishes, and of colours, and of the means established by art for giving to the whole the necessary beauty and splendour. Recapitulation, Every resinous substance, soluble in alcohol (spirit of wine), forms a varnish fit to be employed if the resin be of such a nature as to have no decided influ- ence on the colour of the liquid. Resinous substances of a soft and viscid consistence, such as turpentine, Canadian balsam, that of Judea, &c. ; dry resins, such as mastic and sandarac ; soft resins, such as galbanum in tears, gum elemi, gum anima, &c. are susceptible of forming varnishes, by dissolving wholly or in part in alcohol. In like manner, all essential oils, as well as expressed oils, when they have been subjected to those preliminary preparations which give them a dry- ing quality, form varnishes, when they keep resins, gummo-resins, or balsams, in a state of solution. The composition of varnish depends then on the property of solubility, in which several substances par- ticipate, but with modifications depending on their particular nature. These substances, however, when thus united, exhibit mixed properties, much superior to those they possess individually, and which concur to produce results that are sought for in the common^ RECAPITULATION. Ill kinds of varnish; that is to say, speedy desiccation, lustre, and solidity. However apparent the different points of relation which seem to exist between the principles that con- stitute resins, it may readily be perceived that their identity is not completely established. They exhibit in their texture and in their physical properties dif- ferences very striking. They cannot, therefore, all present the same phasnomena, when treated separately. The necessity of the mixtures which constitute the common formula has soon been perceived ; and it is on these mixtures that the variety of the compositions, and of their results, is founded. Certain varnishes possess a drying quality in an eminent degree : these are the least durable. Others are glutinous, fat, and long in drying; but these are the strongest when they have attained to the proper degree of desiccation. Some hold an intemiediate rank between these two kinds ; they have therefore a mean quality between those var- nishes the most exposed to accidents, and those which present the greatest resistance to the impressions and friction of hard bodies. A careful obseiTation of these differences could not but induce the authors who have written on the art of varnishing, to distinguish them by the help of a classi- fication, founded on the nature of their composition, and on the uses for which they are destined. I have thought it my duty to follow the same order. It has the advantage of exhibitin'T- each varnish sur- rounded, in some measure, by its particular properties, and of enabling artists to refer known compositions^ 112 TREATISE ON VARNISHES. and such as may afterwards be invented, to one of the genera or species determined by the order and nature of their component parts. This division also indicates the cp.se in which they may be employed, and the mode of using them. DIVISION OF VARNISHES. Two classes of varnish, Qi\'ided into genera and sub- divided into species, may be admitted in this work. The first class comprehends the varnishes used for ob- jects of natural history, the genera of which are bor- rowed from that of the substances employed, and which may belong to the vegetable kingdom, as the solution of a pure gum ; or to the animal kingdom, such as gelatin (the gelatinous part or jelly), extracted from different parts of animals. I have already spoken of those kinds of varnish which are employed under some particular circumstances, and which depend more on art by their effects than by die state of their compo- sidon. The second class, which is the principal object of this w^ork, ought to comprehend, and indeed does so, the varnishes resulting from the solution of one or more resinous substances in a spirituous or oily vehicle. It will be exceedingly convenient to divide it into five genera, each of which has its proper species. These genera and species depend on the essential quality of the varnishes ; on the state of their consistence ; and on their drying quaUty, more or less striking. The first genus comprehends the most drying var- nishes that can be obtained with alcohol (spirit of .wine). "*•»!» i C i.,. / J, .;<* DIVISION OF VARNISHES, ll^' The second genus presents formulas for varnish nearly similar to those of the first ; but they are of a less drying nature, in consequence of the addition of less drying resins. • This second genus gives different species of mutative or changing varnish, which do not require so much solidity as those destined for glazing metallic surfaces. The third genus is reserved for composidons in which the nature of the excipient is changed. Alco- hol here gives place to essential oils, and in particular to essence of turpentine. This class ought to compre- hend changing varnishes, and those distinguished by I the name of mordants. The fourth genus is destined for the employment of pure copal treated with essence of turpentine, and even with ether. These varnishes vie, in point of solidity, with those of the following genus, and ought even to be preferred to them. The fifth genus admits of fat drying oils being em- ployed as the excipient. It contains the fat varnishes ' made with copal, with amber, and with caoutchouci Their colour, which is pretty dark, confines the use of them to grounds of a dark colour. Each composition will be accompanied with parti- cular remarks, relating to the process; to the nature and qualities of the varnish; and to the circumstances most favourable for its application. This new arrange- ment appears to be the more convenient, as it will better enable the artist to make use of the subjoined obser- vations, than if they were united into one body and ' separated from the formulas. I 114 TREATISE ON VARNISHES, FIRST GENUS. drying varnishes made with alcohol (spirit of wine). First species. No. I. 1 akc Pure alcohol 32 ounces. Purified mastic 6 ounces. Gum sandarac 3 ounces. Very clear Venice turpentine 5 ounces. Glass coarsely pounded 4 ounces. Remarks. Reduce the nrdstic and sandarac to fine powder; mix this pox^'der with white glass, from which the finest parts have been separated by means of a hair sieve ; put all the ingredients with alcohol into a short- necked matrass, and adapt to it a stick of white wood, round at the end, and of a length proportioned to the height of the matrass, that it may be put in motion. Expose the matrass in a vessel filled with water, made at first a little warm, and which must afterwards be main- tained in a state of ebullition for one or two hours. The matrass may be made fast to a ring of straw. The first impression of the caloric (heat) tends to unite the resins into a mass : this union is opposed by keeping the matters in a state of rotary motion, which is easily eifected by means of the stick, without stirring the matrass. When the solution seems to be suffi- 1 FIRST GENUS. 115 ciently extended, add the turpentine, which must be kept separately in a phial or a pot, and which must be melted, by immersing it for a moment in a balneum marige. The matrass must be still left in the water for half an hour, at the end of which it is taken off; and the varnish is continually stirred till it is somewhat cool. Next day it is to be drawn off, and filtered through cot- ton. By these means it will become exceedingly limpid. This simple process is sufficient for the composition of all those species of varnishes which will form part of the first four genera, unless it is necessary to operate on a large scale. Many amateurs are satisfied with simple digestion for such varnishes, taking care to stir often the mixture. This method, which may be proper for varnish composed with alcohol, would be too slow for varnishes of the third and fourth genera. In general the digestion is terminated by some hours' exposure to the sun. This second exposure approaches very near to the use of a balneum marise ; and, like it, requires the precaution of renewing the surfaces by sdrring the sediment with a clean rod. The addition of glass in this case may appear extra- ordinary; but experience induces me to recommend the use of it. This substance divides the parts of the mixture which has been made with the dry ingredients, and it retains the same quality when placed over the fire. It therefore obviates with success two inconve- niences, which are exceedingly troublesome to those who compose varnishes. In the first place, by dividing the matters, it facilitates the action of the alcohol; and. in the second its weight, v/hich surpasses that of resins, I 2 V 1 If) /V ,..:Y.RE-^ TISE ON VARNISHES. pre\éjiàts .these iwit's from adhering to the bottom of the'jntat-rassj.-'aiid also the coloration acquired by the varnish -when a sand bath is employed, as is commonly the case. I have obsen'ed that the best alcohol can never be- come charged with more than a third of its weight of the resinous isubstances subjected to its action. The particular examination I have made of several kinds of varnish, the consistence of which was proper, never indicated a greater increase of weight than a fourth part of the primitive absolute weight of the alcohol em- ployed. In this respect I was struck with the large doses V\'hich the best authors employ in several of their formulae. There are some resins, indeed, so difficult ot solution, that they suffer verv Httle of their substance to be attacked ; and therefore the doses of them may be increased when they are mixed with other resins. But these particular cases may be known. There arises, therefore, a loss of resin, which ought to be prevented by corrections which I shall here propose, and which I have always followed. It would be forming a wTong idea respecting the nature of the resins which appear to be properest for solution in alcohol, were we to believe that they dis- solve enuirely in that fluid v/hen employed in high doses. One may be easily convinced, by a series of very simple trials, that these substances are composed of molecuise, the chemical properties of which vary in regard to their degree of solubility. They ought to be considered as composed of parts exceedingly soluble m a low temperature, and even on thqir simple contact 4 riRST GENUSV<. '^x C VJl 7 with alcohol; of other parts some\Vîjnt/les3'',gpli|bIe, - . . ^ . • ' ■ ^» <■* and which require to be assisted by a little ihsd^ and of others on which the impression of the air, of the sun, and even of the heat of infusion, has effected a modification, which is perceived by the resistance they oifer to the action of the spirituous liquid. These three parts, however, constitute in the resin a homo- geneous whole; and nothing but the process of solu- tion, and its results, can make them be observed under their real characters. But whatever may be the quan- tity of the liquid added to the resinous residuum, with a view to obtain a complete solution, the effect will not ansv/er expectation. When too large a dose of matter, therefore, is added to alcohol, the latter seizes on the most soluble parts, and has very httle effect upon those which are less so. The dry parts of the resin escape the action of the liquid if only a moderat,e heat be employed, as is here practised. In this case the varnish has very little colour; but if it seems to gain in pliability, it loses in point of consistence and solidity. It is of great ad- vantage to unite all these three characters at the same time ; and this may be accomplished by limited doses, and by employing a little more time and pains in the process. The process of making varnish may be reduced to simple trials; or, if conducted on a large scale, is sub- ordinate to general precepts, a view of which will be found in the following chapter. The varnishes which constitute the first genus are employed fof the most part to supply the place of 118 TREATISE ON VARNISHES. glazing. They are brilliant, but do not all possess the same degree of solidity. The first species exhibit more pliability than consistence or body. The appHcation of them seems suited to articles belonging to the toilette, such as dressing-boxes, cut-paper works, &c. The next species possess the same brilliancy and lustre ; but they have more solidity, and are exceedingly drying. Second species of varnish of the same genus. No. IL Take Pounded copal of an amber colour, once lique^ fied according to my method, 3 ounces. Gum sandarac 6 ounces. Mastic cleaned 3 ounces. Clear turpentine 2^ ounces. Pounded glass 4 ounces. Pure alcohol 32 ounces. Mix these ingredients, and pursue the same method as that indicated for No. I. Remarks. The opinion generally entertained of the insolubility of copal in alcohol might have inspired me with some doubt in regard to the emplovment of this matter. I might even have dreaded that criticism which has not spared the authors of the Parfait T^^ernisseur and of the Dictionnaire des Arts, &c. ; but I can assert that the mixture I have here indicated will give a varnish much more durable than if no copal had been employeti* ' FIRST GENUS. Il9- The great division of this substance obtained by grind- ing it on porphyry, and by its mixture with other resins, favours the action of the alcohol over it ; and the parts detached from it are sufficient to give to this varnish a character or solidity very remarkable, and which it would not have possessed in the same degree without copal. If you are desirous to facilitate the solution of a greater quantity of copal, you may add to this for- mula three gros of camphor ; but this dose must not be exceeded. The case already mentioned in regard to an over- charge of dry matters, when there are any which resist, in part, the action of the vehicle presented to them, is here exemplified. If the copal were entirely suppressed, the alcohol would still find a sufficient quantity of mat- ters to form the varnish. Uses. This varnish ir> destined for articles subject to fric- tion, such as furniture, chairs, fan-sticks, mouldings, Szc. and even metals, to v/hich it may be applied with success. The sandarac gives'it great durability. First species of var)iis/t of the scone ^^eiuis, desliiied J'ur {/te same articles as No. J I. No. III. Take Gum sandarac 8 ounces. Pounded mastic 2 ounces. Clear turpentine 4 ounces. Pounded glass 4 ounces. Alcohol 32 ounces. i4 120 TREATISE ON VARNISHES, Remarks. The fomiula for this varnish is e??tracted from Watin's work. The dose of the turpentine appears to me to be rather too large ; because it diffuses through the varnish a viscous matter, which renders it long ii\ drying. Besides, it communicates to it a strong smell, which to many persons is exceedingly disagreeable. This formula authorizes an observation which may be applied to many other cases : when a substance, which by its nature and consistence is exceedingly soluble, is subjected to the action of a pound of alcohol, it preci- pitates in part the other dry substances which do not possess the same degree of solubility. A kind of re- sinous crystallization which covers the bottom of the vessel then takes place, if the mixture be left at rest. This consideration alone would induce me to suppress, in this formula, the half of the turpentine, SECOND GENUS OF VARNISHES. ALCOHOLIC VARNISHES LESS DRYING THAN THE FORMER, AND HAVING A WEAKER SMELL. First species for cut-paper jvorks, dressiiig-boxes, and other articles of the like kind, ^c. No. IV. Take Gum sandarac 6 ounces. Gum elemi 4 ounces. Gum anima 1 ounce. Camphor J^ ounce. Pounded glass 4 ounces. Pure alcohol 32 ounces. SECOND GENUS. Î2Î Make the varnish according to the prescription al- ready indicated. The soft resins must be pounded with the dry bodies. The camphor is to be added in pieces. Remarks. These varnishes of the second genus admit modifica- tions in the nature of the substances which concur to- wards their formation. , They are not so dry as those of the first genus. They give pliability, brilliancy, and solidity to the compositions, without injuring their dr)^- jng quality. Second species of the same genus, destined Jor the same purposes. No. V. Take Gallipot or white incense 6 ounces. Gum anima 7 ^ , ^ , . s or each 2 ounces. Gum elemi 3 Pounded glass 4 ounces. Alcohol 32 ounces. Make the varnish with the precautions indicated for No. I. Remarhs. Varnishes composed according to the last two for- mulas may be employed for the same purposes as those which form the first genus. They are much fitter, however, for ceilings and waintscoting, coloured or not coloured : they may even be employed as a cover- ing to parts pair*ted with strong Tyater colours. 122 TREATISE ON VARNISHES, Tliird specks of (he same genus, for irainscnling^ small articles offtniilure, hilustrades, and rail- ing in the inside of a house. No. VI. Take Gum sandarac 6 ounces. Shell lac 2 ounces. Colophonium or resin -^ White glass pounded .of each 4 ounces. Clear turpentine - - J Pure alcohol 32 ounces. Make the varnish according to the directions given for No. L Iiemarks. Watin prescribes eight ounces of sandarac and six ounces of turpentine. This dose- appears to me too strong, as it is not proportioned to that of the alcohol, which in my formula finds more matter than it can take up. 'iliis varnish is sufficiently durable to be applied to articles destined to daily and continual use. Varnishes composed with copal ought, however, in these cases, to be preferred. There is another composition which, v.ithout forming part of the compound varnishes, is employed with success for giving a polish and lustre to furniture made of wood : wax forms the basis of it. Manv cabinet-makers are contented with waxing common furniture, such as tables, cliests of drav/ers, I'^rc. This covering, by means of repeated fiiction, soon acquires a polish and transparency v/hich resemble those oi varmsh. Waxnig seems to possess qualiucs peculiar SF.COND GENUS. l25 to itself; but, like varnish, it is attended with its in- conveniences as well as advantages. Varnish supplies better the part of glazing ; it gives a lustre to the wood which it covers, and heightens the colours of that destined, in particular, for delicate arti- cles. These real and valuable advantages are counter- balanced by its want of consistence : it yields too easily to the shrinking or swelling of the wood, and rises in scales, or splits, on being exposed to the slightest sho(?k. These accidents can be repaired only by new strata of varnish, which render application to the varnisher ne- cessary, and occasion trouble and expense. Waxing stands shocks ; but it does not possess in the same degree as varnish the property of giving lustre to the bodies on which it is applied, and of heightening their tints. The lustre it communicates is dull ; but this inconvenience is compensated by the facility with which any accidents that may have altered its polish can be repaired by rubbing it with a piece of fine cork. There are some circumstances, therefore, under which the application of wax ought to be preferred to that of varnish. This seems to be the case in pardcular with tables of walnut-tree wood exposed to daily use, chairs, mouldings, and for all small articles subject to constant employment. Eut as it is of importance to make the stratum of v.'ax as thin as possible, in order that the veins of the wood may be more apparent, I flatter myself that the follov^'ing process, which I received from one of my countrymen very expert in the art of making the ard. cics alluded to, v.'ill be acceptable to my readers. I2i Treatise on varnishes. Melt over a moderate fire, in a very clean vessel, two ounces of white or yellov/ wax ; and, when liquefied, add four ounces of good essence of terpentine. Stir the whole until it is entirely cool, and the result will be a kind of pommade fit for waxing furniture, and which must be rubbed over them according to the usual method. The essence of turpentine is soon dis- sipated ; but the wax, which by its mixture is reduced to a state of very great division, may be extended with more ease, and in a more uniform manner. The es-_ sence soon penetrates the pores of the wood, calls forth the colour of it, causes the wax to adhere better, and the lustre which thence results is equal to that of var- nish, without having any of its inconveniences. Fourth species of the same genus. Famish slightli/ coloured for violins and other stringed instrumentSy and even for furniture of plum-tree wood, maho^ ^any^ and rose wood. No. VII. Take Gum sandarac 4 ounces. Seed lac 2 ounces. Mastic - - - "> r , _. . . . : or each 1 ounce, Benjamm m tears 3 Pounded glass 4 ounces. Venice turpentine 2 ounces. Pure alcohol 32 ounces. The gum sandarac and lac render this varnish du- rable : it may be coloured with a little saffron or dra-. gon's blood. SECOND GENUS. 125 Fifth species of the same gemis, ichich the turners of St. Claude employ for boires made of box-wood, of the roots of trees, &c. No. VIII. Take Seed lac 5 ounces. Gum sandarac 2 ounces. Gum elemi l-i- ounce. Venice turpentine 2 ounces. Pounded glass 5 ounces. Pure alcohol 24 ounces. Remarks. The artists of St. Claude do not all employ this for- mula, which required to be corrected on account of its too great dryness, which is here lessened by the tur- pendne and gum elemi. This composidon is secured from cracking, which disfigures these boxes after they have been used for some months. Other turners employ the gum lac united to a little elemi, and turpentine digested for som^e months in pure alcohol exposed to the sun. If this method be follov/- ed, it will be proper to substitute for the sandarac the same quandty of gum lac reduced to powder, and not to add the turpentine to the alcohol, which ought to be exceedingly pure, till towards the end of the infusion. Solar infusion requires care and attention. Vessels of a sufficient size to allow the spirituous vapours to , circulate freely ought to be employed, because it is ne- cessary that the vessel should be closely shut, With- iput this precaution the spirits would become weakened. 126 TREATISE ON VARNISHES. and abandon the resin which they laid hold of during the first days of exposure. This perfect obturation will not admit of the vessels being too full. In general, the varnishes applied to articles which may be put into the lathe acquire a great deal of bril- liancy by polishing. A piece of woollen cloth is suffi- cient for the operation. If turpentine predominates too much in these compositions the polish docs not retain its lustre, because the heat of the hands is capable of softening the surface of the varnish, and in tliis state it readily tarnishes. Sixth species of the same genus, for giciu^ a gold tint to articles of brass. No. IX. Take Seed lac 6 ounces. Amber or copal ground on porphyry 2 ounces. Dragon's blood 40 grains. ïixtract of red sandal wood obtained by water 30 grains. Oriental saffron So grains. Pounded glass 4 ounces. Very pure alcohol 40 ounces. Re marks. To apply this varnish to articles or orn.iments of brass, expose them to a gentle heat, and dip them into the varnish. Two or three coadngs may be appHcd in this manner if neccssarv. The varnish is durable, and has a beautiful colour. Ardcles varnished in this man- ner may be cleaned \^'iLh water and a bit of dry rag. SECOND GENUS. J 27 Seventh species of the same genus. Changing var- nish, or varnish destined to change or to modify the colour of those bodies to which it is applied. No. X. Take Gum guttœ 4- of an ounce. Gum sandarac ) , > each 2 ounces. Gum elemi - - j Dragon's blood of the best quality 1 ounce. Seed lac 1 ounce. Terra mérita ^ of an ounce. Oriental saffron 12 grains. Pounded glass S ounces. Pure alcohol 20 ounces. Remarks. The tincture of saffron and of terra mérita is first obtained by infusing them in alcohol for twenty-four hours, or exposing them to the heat of the sun in sum- mer. The tincture must be strained through a piece of clean hnen cloth, and ought to be strongly squeezed. This tincture is poured over the dragon's blood, the gum elemi, the seed lac, and the gum guttaî, ai! pounded and mixed with the glass. The varnish is then made according to the directions already given.' It may be applied with great advantage to philoso- phical instruments : the use of it might be extended also to various cast or moulded articles with which fur- niture is ornamented. If the dragon's blood be of the first quality, it may give too high a colour 5 in this case the dose may be 15S_ TREATISE ON VARNISHES. lessened at pleasure, as well as that of the other coIouî'- ing matters. It is with a similar kind of varnish that the artists of Geneva give a golden orange colour to the small nails employed to ornament watch-cases ; but they keep the process very secret. A beautiful bright colour might be easily communicated to this mixture ; but they pre- fer the orange colour produced by certain composi-. tions, the prepai'ation of which has no relation to that of varnish, and which I have successfully imitated with saline mixtures, in which orpiment is a principal ingre- dient. The nails are heated before they are immersed in the varnish ; and they are then spread out on sheets of dry paper. Eighth species of the same genus. Changing varnish ichich may he employed to give a gold colour to ivatch-casesy watch-keys^ and other articles made of brass. No. XL Take Seed lac 6 ounces. Amber - - t ^ 5>or each 2 ounces. Gum guttse ^ Exti'act of red sandal wood in water 24 grains» Dragon's blood 60 grains. Oriental saffron 36 grains. Pounded glass 4 ounces. Pure alcohol 36 ounces. Remarks, Grind the amber, the gum lac, gum guttas, and dra- gon*s blood on a piece of porphyry : then mix them ÊECOND <ÎE>TÙS. 129 with the pounded glass, and add the alcohol, after forming with it an infusion of the saffron and an extract of the sandal wood. The vamish must then be com- pleted as before. The metal articles destined to be covered by this varnish are heated, and those which will admit of it are immersed in packets. The tint of the varnish may be vaiied by modifying the doses of the colouring substances. The use of alcoholic varnishes will long be preferred to that of the varnishes which form the third and fourth genera ; which, however, are far superior in all cases where it is necessary to add durability to the other qua- lities required. A comparison, which may be easily made in regard to articles subject to constant employ- ment, will one day support theory and experience, and rectify the public opinion |ijjj this subject. The varnishes of these fifet two genera can bear po- lishing as well as the hardest com.positions which consti- tute the three other genera : but as they are more de- licate, they admit modifications in the operation. It is never begun with pumice stone. The most of these varnishes are desdned for covering preliminary preparations whi'chhave a certain degree of lustre. They consist of cemqnt, coloured or not colour- ed, charged with landskips and figures cut out in paper, which produce an effect under the transparent vamish: most of the dressing -boxes, and other small articles of the same kind, are covered with this particular composidon, which, in general, consists of three or four coatings of Spanish white pounded in water, and mixed up with parchment glue. This first coating is smoothed with ISO TREATISE ON VARNISHES. pumice stone, and then polished with a piece of new linen and water. The coating in this state is fit to re- ceive the destined colour, after it has been ground with water and mixed with parchment glue diluted with 'water. The cut figures with which it is to be embel- lished are then applied, and a coating of gum or fish glue is spread over them, to prevent the varnish from penetrating to the preparation, and from spoiling the figures. The operation is finished by applying three or four coatings of varnish, which when dry are po- lished with tripoli and water, by means of a piece of cloth. A lustre is then given to the surface with starch and a bit of doe skin, or very soft cloth. I shall resume this subject when I come to treat of polishing. THIRD GENUS OF VARNISHES. Particular observations. The varnishes which compose the third genus are less exposed to the alterations to which those that form the first two genera are sometimes subject. The nature of the excipient is here different : essence of turpentine is substituted in the place of alcohol ; and this sub- stance exhibits itself under different degrees of concen- tration. Almost all the resinous substances, and even the colouring substances, hitherto employed, are familiar to this third genus, and by their various mixtures with the essence may concur to accomplish the same views, and produce the same results. It must not however be believed, notwithstanding what has been here said, that the properties of alcohol THIRD GENUSi 131 and those of essence, considered as capable to effect so- lutions, essential to the coloration of varnishes, are identical ; they differ in many respects. Alcohol be- comes charged with some particular substances, which are refractory to essence : of this kind are certain co- louring matters, such as indigo, turnsole, red sandal wood, saffron, &c. On these essence of turpentine produces no effect. In like m^anner, also, essence under certain circumstances exerts all the energy of solution on copal, which resists alcohol unless it be di- vided by a soluble body. At any rate, what it would se- parate vv'ithout an intermediate substance would not be sufficient to constitute a varnish. These differences in the chemical properties of these tv/o liquors are not the only ones which might be ad- duced to justify the admission of this third genus. A consideration of no less importance may be added, namely, the superiority of varnishes made with es- sence to those composed with alcohol. The former unite pliableness and smoothness to brilliancy and du- rability : they yield better to the operation of polishing, and are less liable to crack than alcoholic varnishes. All these qualities, which ai'e well knov/n, ought to induce artists to prefer this genus in all cases where the preservation of the articles to which they are ap- plied is an object of importance. This preference is necessary, in particular, for valuable paintings. In alcoholic varnishes the deposit of the resinous matter, divided and in a state of complete ccluticn, is sooner formed, according as the season, or circum- stances arising from an artificial temperature, accelerate; K 2 132 Treatise on varnishes. the evaporation of the dividing fluid. The nature of this fluid is sufficiently known; and it gives no reason to suspect that any of its parts incorporate with the resinous moleculas, the precipitation of which confirms the effect of a varnish : the alcohol then evaporates en tirely. The case is not the same with essence of turpentine, even the most ethereous, nor with other liquids which have all the characters of oils. They are not suscep- tible of «itirc evaporation. These liquids form with resins a union the more intimate, as they add to their division by the interposition of their own substance. The less oils are light or volatile, the greater therefore will be the solidity of the varnishes resulting from their mixture with resins, and vice versa. The state of dry- ness observed in certain resinous bodies, and which is communicated to the varnishes, resulting from their union with alcohol, is then compensated and corrected in the case of their solution in an oily fluid, which en- velops them in a fixed viscous and yet drying substance. Essence of turpentine, and oils of a greater densit)-, which are still better, would alone form varnishes by a continued succession in the application of coatings. Alcohol in this case would disappear without leaving any trace of its presence. The consistence which varnishes acquire from- es- sence is often increased by that arising from the par- ticular nature of the matters which form part of' the changing vaniishes, and particularly of that of the varnishes distinguished by the name of mordants. In giving the formula for varnishes of this third kind, I THIRD GENUS. 133 shall follow the order indicated by the degree of their tenacity, and of their resistance to desiccation. First species of varnish for valuable paintings. No. XII. Take Mastic cleaned and washed 12 ounces. Pure turpentine \^ ounce. Camphor 4- ounce. White glass pounded 5 ounces. Ethereous essence of turpentine 36 ounces. Make tlie varnish according to the method indicated for No. I. of the first genus. The camphor is employed in pieces, and the turpentine is added when the solu- tion of the resin is completed. But if the varnish is to be applied to old paintings, or paintings which have been already varnished, the turpentine may be sup- ■ pressed, as this ingredient is here recommended only in cases of a first application to new paintings, and just freed from white of egg varnish. The ethereous essence recommended for vamish is that distilled slowly, and without any intermediate substance, according to the second process given for its rectification. Remarks. Ijj,, The question proposed by able masters respecting 3 the kind of varnish proper to be employed for paint- Jl ings has never yet been determined. Every artist b*as 1 K 3 134 TREATISE ON VARNISHES. his prejudices, strengthened by example or uçage, and he inaiRCalns them by specious arguments. The value, however, which ought to be attached to the works of great masters, requires stabiKty of opinion in regard to the choice of varnish which tends to embellish and preserve works of genius. The varnish destined for this use ought to be colour- less, if possible, that it may communicate no foreign tint to the tones of the painting; it ought to unite phabiHty and smoothness to the most perfect transpa- rency, in order to r jurish the colours and the canvas. It must not, however, have too much glazing, as the reflection of the light is injurious to the effect. Alcohol renders varnishes too dry for paintings, as they split and crack. Varnishes composed with essen-' tial oils, which have too much body, give too great thickness to the coating, so that they cover, or impede the effect of the colours. But in choosing varnishes of this sort one of the most requisite qualities is, that the composition should be veiy simple, and of such a nature as not to resist the means employed, when it is necessary to substitute a new coating in the room of old varnish. These considerations have induced some artists to pay particular attention to this object; but they all make a mystery of the means they employ to obtdn the desired effect. The real end may be accomplished by giving to the varnish, destined for painting, pliability and soft- ness, wdthout b' ing too solicitous in regard to what may add to its consistence or its solidity. The lattei* THIRD GENUS. 135 quality is particularly requisite in varnishes which are to be applied to articles much exposed to friction, such as boxes, furniture, &c. The following formula I have employed for thirty years ; and the varnish resulting from it has been ap- plied with success to paintings in the most valuable collections *. * As every thing that relates to the preser\'ation or repairing of paintings is of great importance to artists and amateurs^ the follow- ing observations on this svibject will perhaps not be unacceptable to the reader : The variety of varnishes^ often destructive, which are applied to paintings, occasions some complication in the means employed to remove them in order to substitute others in their place. A new painting has often no other covering than white of egg. This varnish is of the simplest kind : it consists only of two or three ounces of weak alcohol (brandy), in which a gros or one eighth of an ounce of sugar, and the white of an egg, has been dissolved. The white of egg, with the sugar reduced to the state of powder, is beat up with the alcohol, and the varnish is then applied with a very soft sponge to the picture, placed in a horizontal position. This varnish, if a few drops of the juice of garlic be mixed with it, or if the vessel in which the white of egg is beat up be only rubbed with it, will preserve the painting from being dirtied hv flies. When it is necessary to remove this coating, tlie process em- ployed is as simple as that for the preparation of the varnish. A. sponge moistened with warm water is drawn over the surface of the picture with a slight degree of pressure. A kind ot froth is then formed, -which must be washed off with watery and this operation is repeated till no more froth appear. This method is sufficient to remove not only white of egg varnish, but also that made with gum arable, fish glue, or any other matter soluble in water. There is no reason to be under anv apprehension for the K 4 ISO TREATISE QN VARNISHES, Second species of varnish of the same gemis, for grinding colours^ No. XIII. Take New gallipot or white incense 4< ounces, Mastic 2 ounces. Venice turpentine 6 ounces. Pounded glass 4 ounces. Essence of turpentine 32 ounces, colours ; because the -v^'ater has no action on the oil with which the colours have been mixed. Great masters rarely varnish their pictures after they are finished: they protect their tints by a coating of white of egg, and do not varnish tliem till a j-ear after, when tlie colours are completely dry. The metliod here described for removing this coating requires care and attention. The pictui:e is left to àry, and the varnish is ap-» plied A\ith precautions which are well known to all real artists. More ditïiculty occurs in regard to old paintings. Besides var- nishes ou which alcohol and oil produce no effect, they are ofteij spoilt by foreign bodies, the nature of v/hich is unknown, and which resist tlie action of soap. Essence of turpentine Indeed may remove many stains j but it is attended witli the inconvenience of attacking the colovus and softening the oil which gives them body. Olive oil, and also butter, may be substituted in its stead with ad- vantage. These two fat unctuous bodies do not attack the coloursj, or at least produce on them a ver}- slow eriect. Resin, which forms the basis of the old varnishes, gives some hold to an alkaline solution composed of one ounce of potash and eight ounces of water. This is a metliod very much used, but it requires great care. If the alkali removes old resins, and if it con- verts them into a kind of soap, it exercises a similar action on tlie fielours, or rather on the drying oil which binds the coloui-s of ths THIRD GENUS. 137 When the varnish is made with the precautions already indicated, add prepared nut or linseed oil two ounces, Remarhs. The matters ground with this varnish, which is nearly similar to that of Holland, dry more slowly ; they are then mixed up with the following varnish, if it be for a common painting, or with particular var- nishes destined for colours and for grounds. In treat- ing of the diiï^arent kinds of colours, I shall mention painting. lyong habit and tlie eye of a painter, therefore, are re- quired to judge of the inconvenience of this method. Very pure alcohol is a powerful agents not only in removing oily stains, but also tJiose resinous substances which constitute varnishes 5 and it is not attended with the inconvenience of alter- ing ,tli3 colours mixed with prepared oil. It will exercise no action on them^ unless the colours have been mixed with oil of la- vender or oil of turpentine. It will be proper, therefore, to ascer- tain the nature of ilie oil which has been employed, by making a trial in one of the corners of the picture. In general it is proper to begin the cleaning of pictures by first drawing a sponge, dipped in warm water, over the surface of them : if the motion given to the sponge does not produce frotli, the varnish is of a resinous nature. This washing is often suffi- cient to call forth the colours, and restore their original lustre. But if the painting is covered with varnish rendered yellow by time, opake, and v,'hich absorbs tlie colours, place it in a hori- zontal direction ; and having poured pure alcohol over it, keep it moistened in this manner for some minutes without employing friction. If cold water be then applied to the surface, it will re* move the alcohol, and tlie portion of resin which has been dissoh'ed or softened. But care must be taken not to use friction, for fear of attacking the ground. When the surf ice is dry^, the operation is renewed until the varnish is entirely removed. 138 TREATISE ON VARNISHES. the species of varnish which ought to be employed in grinding them and in mixing them up. Watin substitutes in the room of the Dutch varnish, which is commonly employed for grinding colours, a composition which appears to me to be too much charged with ingredients. Essence can scarcely dissolve the half of them. The rest forms a residuum which is mere loss*. Sometimes^ however, tJie painting is covered with a varnish composed of fat oil and insoluble resin, such as copal. In this case the attempt must be abandoned, because the purest alcohol as well as leys will produce no effect. Even essential oils, which Hiight seem proper on such occasions, would only whiten the sur- face of the varnish and intercept tlie light, to tlie prejudice of the colours. However, if the picture be of great value, and seems worth the expense^ ether may be substituted v/ith success in the room of the substances before mentioned. The property I discovered in this liquor of dissolving copal is an evidence in its favour, as being fit for the pui"pose in question. To this property it unites another no less essenli.nl, namely, that of not attacking the drying oil by which the colours are bound. This method is expensive, if the proper kind of ether be employed ; but the loss occasioned by its evaporation may in some measure be prevented, if a cloth dipped in ether be applied to the canvas, and pressed closely down witli a metallic plate or piece of glass. When a picture is dirtied with smoke and dust, a sponge dipped in ox gall drawn over it v.ill restore its original splendour. If ir l]as not been varnished, it will revive the brightness of the colours , provided it be gently nibbed j andin this manner it may be pre- pared for receiving varnish. Flies also dirty paintings, and render it necessary to wash them frequently. This operation is troublesome, and attended witli danger. Some assert that the odour of laurel oil, which tliough * See his i\rt of making Varniihj edit, of 1/72. THIRD GENUS. 189 TJdrd species of the same genus. Fizrnish proper to be employed in mixing up colours Jor grounds. No. XIV. Take Gallipot or white incense 12 ounces. White glass pounded 5 ounces. Venice turpentine 2 ounces. Essence of turpentine 32 ounces. Make the varnish after the white incense has been pounded with the glass. very pleasant, is disagreeable to those insects, and drives them from apartments in which it is kept. As it is of a solid consistence, it ma/ be easily empkyed. Some of it put into tin-plate boxes might be placed on tlie cornices of rooms containing pictures worthy of being preserved from their approach. Varnishes made with essence keep much longer in a mass than those made \^'ith alcohol. They even improve by not being imme- diately applied. My method is to expose them in a place weVL liohted, but sheltered from the direct rays of the sun. In the space of some months they become thick, and acquire an oily consist- ence, vv'hich renders the application of them much more advan- tageous. - If the varnish I have here mentioned be applied to a picmre when ne-vly prepared, the essence speedily makes its way to the colours of *he painting, if it has not been before varnished, and the app ication of it is less œconomical than if it were a year old. It will be proper, in particular, not to apply tlie coatings too soon after each other, especially if the picture has been newly painted, I have known amateurs who applied three coatings of varnish in , tlie course of two or three hours. In this case, the first coating serves as a vehicle to the second, which loses itself in part in tlie first : by these means an uneven surface is formed, and the appli- cation of a third is rendered necessary. But if an inteival of two or tlu'ce d:'.ys be left after the application of tlie first coaling, tlie 140 TREATISE ON VARNISHES» Remarks, Some authors recommend mastic or sandarac m the room of gallipot ; but the varnish is neither more beau- tiful nor more durable. "When the colour is ground with the varnish No. XIII. , and mixed up with the latter, which if too thick is thinned with a little essence, and which is applied immediately, and without any sizing, to boxes and other articles, the coatings acquire suffi- cient strength to resist t^e blows of a mallet. But if the varnish be applied to a sized colour, it must be covered with a varnish of the first or second genus. Fourth species of the same genus» Changing var» rush of a less drying quality than the species No. JT» and applicable to metal. No. XV. Take Seed lac 4 ounces. Sandarac or mastic 4 ounces. Drap-on's blood -^ ounce. Terra m.erita 1 ~ , _, > of each SQ grams» Gum guttœ J Pounded glass 5 ounces. Clear turpentine 2 ounces. ' Essence of turpentine 32 ounces. resinous part of the varnish, which has acquired consistence, in- coi^rates with the colours of the picture, and is capable of en- during the impression of a second coating, which will be sufficient to give the painting brilliancy, and to defend it from the attacks of moisture and of time. THIRD GENUS. 141- Extract by infusion the tincture of the colouring sub- stances ; and then add the resinous bodies according to the prescription given for No. I. Remarks. Varnishes of this kind are called changing ; because when applied to metals, such as copper, brass, or ham- mered tin, or to wooden boxes and other furniture, they communicate to them a more agreeable colour. Besides, by their contact Avith the common metals they acquire a lustre which approaches tliat of the precious metals, and to which, in consequence of peculiar in- trinsic qualities or certain laws of convention, a much greater value is attached. It is by means of these changing varnishes that artists are able to communicate to thin leaves of silver and copper those shining coloui^s observed on foils. This product of industry becomes a source of prosperity to the manufacturers of buttons and v/orks formed with foil, which in the hands of the jeweller contributes with so much success to produce that reflection of the rays of light which doubles the lustre and sparkling quality of precious stones. It is to varnish of this kind that we are indebted for the manufactory of gilt leather, which, taldng refuge in England, has given place to that of papier mâché, whJch is employed for the decoration of palaces, theatres, he. In the last place, it is by the effect of a foreign tint obtained from the colouring part of saffron, that the scales of silver disseminated in confection d'hyocinthe reflect a beautiful gold colour. 142 ^TREATISE ON VARNISHES. The colours transmitted by different colouring Sub- stances require tones suited to the objects for which they are destined. The artist has it in his power to vary them at pleasure. The addition of anatto to the mix- ture of dragon's blood, saffi^on, &c. or some changes in the doses of the more colouring bodies, will easily lead to the modifications intended to be made in co- lours. It is therefore impossible to give limited for- mula. There is one very simple method by which artists may be enabled to obtain all the different tints they require. Infuse separately 4 ounces of gum guttas in 32 ounces of essence of turpentine, and 4 ounces of dragon's blood and an ounce of anatto also in separate doses of essence. These infusions may be easily made in the sun. After fifteen days exposure, pour a certain quan- tity of these liquors into a flask, and by varying the doses you will obtain different shades of colour. These infusions may be employed also for changing alcoholic varnishes ; but in this case tlie use of saffron as well as that of red sandal wood, which does not succeed with essence, will soon give the tone neces- sary for imitating with other tinctures the colour of gold. The fat golden varnish already described ac- quires its colour from a similar mixture of tinctures. This genus of less drying varnishes admits also an- other species, which approach nearly to the nature of fat varni::hes, and which are known under the name" of mordants» THIRD GENUS. 14S Fifth species of the same genus. Varnish distlnguislwd by the name of mordant. No. XVI. Take Mastic 1 ounce. Gum sandarac 1 ounce. Gum guttae 4- ounce. Turpentine -\ ounce. Essence of turpentine 6 ounces. Remarhs. Some of the artists who make use of mordants sub- stitute for the turpentine an ounce of the essence of lavender, which renders this composition still less drying. In general, the composition of mordants admits of modifications, according to the kind of work for which they are destined. The application of them, however, is confined chiefiy to gold. When it is re- quired to fill up a design with gold leaf on any ground whatever, the composition which is to serve as the ' means of union between the metal and the ground ought to be neither too thick nor too fluid ; because both these circumstances are equally injurious to deli- cacy in the strokes : it will be requisite also that the composition should not dry till the artist has completed his design. Besides, many artists never make use of prepared ^mordants. They substitute in their stead an extem- pore mixture, which they correct at pleasure. 144» TREATISE ON VARNISHES. Some prepare their mordant v/ith Jew*s pitch and drying oil diluted with essence of turpenihie. They employ it for gilding pale goid, or for bronzing. Other ardsts imitate the Chinese, and mix with their mordants colours proper for assisting the tone which they are desirous of giving to the gold, such as yellow, red, &c. Others employ merely the fat varnish of the fifth genus, No. XXL, to which they add a little red oxide of lead (minium). Others make use of thick glue, in which they dissolve a little honey. This is what they call hatture. When they are desirous of heightening the colour of thé gold they employ this glue, to which the gold leaf adheres exceedingly well. Every artist makes a mystery of his composition. I present mine because its qualities appear to me to be | i fit for every kind of application, and in particular for ■ ' ;that to metals. Expose boiled oil to a strong heat in a pan : when a i \ black smoke is disengaged from it, set it on fire, and extinguish it a few moments after by putting on the i cover of the pan. Then pour the matter, still warm, •into a heated bottle, and add to it a little essence of turpentine. This mordant dries very speedily ; it has body, and adheres to, and strongly retains, gold leaf when applied, to wood, metals, and other substances. These examples are sufficient to show the-nature of the j varnishes which compose the third genus. The' follow- 1 4 • \ FOURTH GENUS. 14:3. ing genus will make the reader acquainted -ivith; others " which have still more solidity. Under the head No. XXV. will be found another mordant, still fatter,- with which bro\vn colours may be mixed. FOURTH GENUS. COPAL VARNISHES MADE WITH ETHER AND ESSENCE OF turpj:ntine. Preliminari/ obsenatio)is. The distinction which may be established between those composidons of varnish which constitute the three preceding genera, is facihtated by various consi- deradons. The dry nature of the resins which form the basis of them, and their friability, evidently an- nounce that solidity is not one of their inherent qualities. The merit, indeed, of the most of these composidons seems to be confined to their drying quality and to their brilliancy. The two following genera will unite to these first characters consistence and solidity. Copal, which serves as a basis to this fourth genus, seems to trace out an intermediate line between all the genera of varnish. The particular nature of this sub- stance, which unites solidity to transparency, and the property I have found it to possess of entering readily into solution, in a mean temperature, or a temperature approaching that of boiling water, are so many cha- racters which destine it to collect in varnish all the qualities which are sought for in this kind of com- position. J. \. -■y 146 TREATISE ON VARNISHES. A process which furnishes the arts with a colourless Tarnish, possessed of a very drying quaUty; a sweet odour during the time of its evaporation, and in parti- cular a great degree of solidity ; a varnish which, when extended over metallic surfaces, forms a stratum of greater hardness than that found in the vitreous crust which serves as a covering to enamel, since it opposes greater resistance to shocks and to the friction of hard bodies, ought justly to be classed among those discoveries which are most interesting to certain useful arts. Two substances only concur towards its compo- sition : copal and rectified ether. Had I discovered it sooner, I should not have under- taken my researches respecting the solution of copal in essence of turpentine; though the result of them may serve to extend our resources in regard to a great num- ber of different objects. This fourth genus of varnishes comprelicnds formulai which will give so many kinds of composition ; but they will not all possess the drying qualities in the same degree. This circumstance, which traces out the order of their description, indicates at th.e same time that they anay be employed for different objects. The least diy- ing will be proper for metallic articles ; because their desiccation may be accelerated by means of a stove. The theoretical observations I have already kud before the reader, in the preliminaiy remaries in regard to varnishes of the third genus, are perfectly applicable to . those which form the fourth genus, since ihcy exhibit all the qualities of the best varnish. iFOURTH GENUSi 147 Pir.st species. Coped varnish ichli ciher. No. XVII. Take Ambery copal -^ ounce. Ether 2 ounces. Reduce the copal to very fine powder, and intro- duce it by small portions into the flask which contains the ether ; close the flask with a glass or a cork stop- per, and having shaken the mixture for half an hour, leave it at rest till the next morning. In shaking the flask, if the sides become covered with small undula- tions, and if the liquor be not exceedingly clear, the solution is incomplete. In this case add a little ether, and leave the mixture at rest. The varnish is of a light lemon colour. Rernarksi It appears to mè astonishing, that this property which ether possesses of becoming charged with copal should have escaped Macquer, who subjected caoutchouc to a variety of experiments for the same purpose. It is probable, that the knowledge he had obtained of the little eflect which ether produces on amber, prevented him from trying it on copal, the properties of \\'hich it was then usual to confound with those of amber. The affinity v/hich ether has for copal is so great, that when the powder is poured into the flask, some particles of it, seized by the vapour as it escapes from the flask, soon form small stalactites, extending from the extremity of the Card which supports the powder L 2 Î45 TREATISE ON VARNISHES. to a considerable distance uilhin the mouth of the flask. The attraction of fine iron filings, put in mo- tion by the presence of an artificial magnet, will give to persons acquainted with magnetic effects a perfect idea of this phsenomenon. When copal is presented to ether in small portions, as I have indicated, the pov^der which fails to the bot- tom assumes the form of a small mass, the volume of which decreases in a very sensible manner: under these circumst-Linces it exhibits the same pha^nomena as a bit of sugar' ill cold water, except the bubbles of air dis- engaged from the sugar, and which are not produced from copal. Copal vvithout colour, or very little coloured, passes more slowly and in less quantity into ether. Copal \ cry much of an ambery nature was that which ap- peared to me to succeed best. According to the observations which I made, the largest quantity of copal united to ether may be a fourth, and the least a fifth. The use of copal varnish made with ether seems, by the expense attending it, to be confined to repairing those accidents v/liich fre- quently happen to the enamel of toys, as it will supply the place of glass to the coloured varnishes employed for mending fractures, or to restoring the smooth surface of paintings v/hich have been cracked and shattered. The great volatility of ether, and in particular its liigh price, do not allow the application of this varnish to be recommended but for the purposes here indicated. i have seen it applied to wood with complete success, and the glazing it produced united lustre to solidity. FOURTH GENUS. 149 In consequence of the too speedy evaporation of the liquid it often boils under the brush. 1 found, means, however, to retard its evaporation by spreading over the wood a slight stratum of essential oil of rosemary, or lavender, or even of turpentine, which I afterwards removednvith a piece of linen rag : what remained was sufficient to retard the evapgration of the ether. Second species. Copal varnish with essence of turpentine. No. XVIII. Take Copal of an amber colour and in powder 1' ounce. Essence of turpentine 8 ounces. The specific gravity of the essence ought to be seven gros, and from 50 to 52 grains in a flask containing an ounce of distilled water ; Fahrenheit's thermometer being at 59*'. Expose the essence to a balneum mariœ, in a wide- mouthed matrass with a short neck : as soon as the water of the bath begins to boil, throw into the essence a large pinch of copal powder, and keep the matrass in a state of circular motion. When the powder 'is incorporated with the essence add new doses of it ; and continue in this manner till you observe that there is formed an insoluble deposit. Then take the matrass from the bath, and leave it at rest for some days. Drav/ oil the clear varnish, and hlier it through cotton. It» IJO TREAllSi: ON VARXI6Hi;i<. Remarhf!. At the moment when the first portion of the copal is thrown into the essence, if the powder precipitate itself mider the form of himps, it is needless to proceed any further. This effect arises from two causes : either the essence does not possess the proper degree of con- centration, or it has not been sufficiently dephleg- mated (deprived of water). Exposure to the sun, em- ploying the same matrass, to which a cork stopper ought to be added, will give it the qualities requisite for the solution of the copal. This eflèct will be an^ nounced by the disappearance of the portion of copal already put into it. The excipient which I propose to apply to copal, without any intermediate substance, is by most artists considered as entirely destitute of cnerg)'. Some che- mists have given a contrary opinion, and I profess myself to be one of that number. I shall collect under one point of vicvr, and consequently in a particular chapter, the experiments I m.ade to decide this quesr tion, which relates to the solubility or insolubility of copal in essence. The results appear to me more in- teresting, as they are not confined to this single fact, They conducted me indeed to a series of observations tvhich are foreio-n to the subiect of this work. To obtain thus varnish colourless, it v.ill be proper to rectify the essence of the shops, which is often highly coloured, and to give it the necessary density by ex- posure to the sun in bottles closed with cork stoppers^, leaving an interval of some inches between the stopper FOURTH GENUS. 151 and the surface of the liquid. A few months are thus sufficient to communicate to it the required quahties. Besides, the essence of the shops is rarely possessed of that state of consistence, without having at the- same time a strong amber colour. The varnish resulting from the solution of copal in essence, brought to such a state as to produce the maximum of solution, is exceedingly durable and bril- liant. It resists the shock of hard bodies much better than the enamel of toys, which often becomes scratched and whitened by the impression of repeated friction; it is susceptible also of a fine polish. It is applied with the greatest success to philosophical instruments, and the paintings with which vessels and other utensils of metal are decorated. Third species. Copal varnish, made witli essencç by ■means oj' an intermediate substance. No. XIX. Take Copal in powder I ounce. Essential oil of lavender 2 ounces. Essence of turpentine G ounces. Put the essential oil of lavender into a matrass of a proper size, placed on a sand bath heated by an Ar- gand's lamp, or over a moderate coal lire. Add to the oil while very warm, and at several times, the ^ copal powder, and stir the mixture with a stick of white wood rounded at the end. When the copal has en- tirely disrsppeared, add at three different dmes the es- L 4 152 TREATISE ON VARNISHES. sence almost in a state of ebullition, and keep conti- nually stirring the mixture. When the solution is completed, the result will be a varnish of a gold colour, exceedingly durable and brilliant, but less drying than the preceding. Re))ia/'iis. This method ma}' have some advantage over the pre- ceding, in case essence of a proper specific quality, and such as I have recommended, can be procured. Essence, whatever be the state of its specific gravity, is capable in this particular case to dissolve copal, and so also is alcohol. This may be easily proved by a very simple experiment, which requires no great apparatus. Put essential oil of lavender into a table spoon, and heat it by placing it over a chaffing-dish. When it is almost in a state of ebullition add a pinch of copal in powder. Facilitate the mixture by means of a straw ; and when the copal has disappeared, add a new dose till the oil refuses to receive any more. Pour the solution into a phial containing boiling alcohol, and stir the mixture, keeping it always at the same degree of tem- perature. The alcohol will soon seize upon both these substances. The alcohol employed in this experiment must be pure; for the smallest quantity of water, foreign to its composition, would precipitate the copal, which would then unite into a mass. The success of this experiment often depends on a dexterity, v.'hich may easily be acquired by persons ac- customed to such operations. IÏ' you are desirous of completing the experiment without changing the vessel; that is to say, if you em^^ FOURTH GENUS. 153 ploy a meta'llic vessel capable of containing the alcohol added to the oily solution of copal, a part only of the boiling alcohol must be poured in, stirring the mixture with the stick, llie copal, which forms itself into a bail, soon enters into the vehicle. This circumstance allows the remainder of the alcohol to be added, without the least fear of any precipitation. It may be readily perceived that this varnish belongs to the second genus, which comprehends the less drying spirit varnishes. I introduce it here, merely to serve as a new proof of the existence of processes capable of ef- fecting a complete solution of copal in the different liquids commonly employed in the composition of var- nishes. If stronger doses were employed in this process, the varnish-alembic, which I shall describe in the fol- lowing chapter, would be exceedingly proper, Foiirfh .species. Copal varnish by an intermediate substance, according to a meiliod given in the Journal de Physique, No. XX. Take Copal 4 ounces. Clear turpentine 1 ounce. Put the copal, coarsely pulverized, into a vamish pot, and give it the form of a pyramid, wliich must be covered widi turpentine. Shut the vessel closely, and,, placing it over a gentle lire, increase the heat gradually that it may not attack the copal. ^ As soon as the mat-, ter i;; well liquefied, pour it upon a plate of copper. 154 TREATISE ON VARNISHES. and when it has resumed its consistence reduce it to powder. Put half an ounce of this powder into a matrass with four ounces of the essence of turpentine, and stir the mixture till the solid matter is entirely dissolved. Remarks. This varnish is coloured, and has no advantage over that of No. XVIÎI. T:ie turpentine, which by the action of the heat has undergone a commencement of decom- position, even before the copal has entered into a state of liquefaction, contributes greatly to give it this colour. In this respect it is not better than No. XIX. It is even inferior to it. Fifth species. Copal varnish by the medium of cam- phor and essential oil of lavender, destined for articles ivhich require durabilitjj, pliableness, and transparency-^ such as the varnislied wire gauze iised 171 ships instead of glass. No. XXI. Take Pulverized copal 2 ounces. Essential oil of lavender 6 ounces. Camphor J- of an ounce. Essence of turpentine a sufficient quantity, ac- cording to the consistence required to be given to the varnish. Put into a phial of thin glass, or into a small matrass, the essential oil of lavender and the camphor; div) FOURTH GENUS. 155 place the mixture on a moderately open fire, to bring the oil and the camphor to a slight state of ebullition. Then add the copal powder in small portions, which must be renewed as they disappear in the liquid. Favour the solution by continually stirring it with a stick of white wood ; and when the copal is incoiporated with the oil, add the essence of turpentine boihng; but care must be taken to pour in at first only a small portion. An inverse method might be followed, by pouring the essential oil camphorated and boihng on the copal, liquefied separately in the matrass ; but this method requires more practice. Besides, it would give to the varnish a darker colour. This varnish is little coloured; and by rest it acquires a transparency which, united to the solidity observed in almost every kind of copal varnish, renders it fit to be applied with great success in many cases, and par- ticularly in the ingenious invention of substituting var- nished metallic gauze in the room of Muscovy talc, a kind of mica in large laminae, used for the cabin windows of ships, as presenting more resistance to the concussion of the air during the firing of the guns. Varnished metallic gauze of this kind is manufactured, I believe, at Rouen, or in the neighbourhood. All tlicse attempts, the principal object of which was to find the means of making copal unite with any liquid, without haying recourse to the influence of too high a temperature, which might alter the principles of its composition, seem to point out the boundaries of the îiti, without destroying the hope of obtaining complete success. The pliableness and tenacity observed in this 155 'j:;re|\ti5l on varnishes. ■ •■.■ -* * singular siibstaiW/, when subjected to a series of pro- C(y^ès,.> give E^a^on to believe that it may rival that v.'fciet^ cortàtiKÎtes the Chinese varnish, provided the solution- of it can be rendered easy, and secure from those akerations which take place during the common operation. It does not appear that the different inter- mediate substances, hitherto employed, have been at- tended with complete success, or at least such success as supersedes the necessity of further researches. Before I proceed to a simpler method, I must here offer some obsen^ations and experiments in regard to the influence of intermediate substances, and particu- larly that of camphor, or the solution of copal in alcohol. Though this object relates chiefly to var- nishes of the first genus, it êeems connected with that of which we here treat, and admits of this transposition. The camphor which I have employed for thirty years, as a medium to facihtate the solution of resin in the composition of varnish destined for valuable paint- ings *, might be applied in my process in doses of from 24 to 30 grains for every ounce of the pil of lavender. It has indeed the singular property of altering the con- sistence of the driest resins, and of rendering them soft. In this union, which appears to be intimate, the cam- phor itself loses the character which distinguishes it from an essential oil, that is to say, dryness. Apothc- caries have every day an opportunity of verifying this fact, when they prescribe a mixture of camphor in plasters the base of which is resinous. It softens them to such a degree, that it is impossible to preserve the ■)«- Se« No. XII. FOURTH GENUS, r " <'" . 157 or 40 grains for each ounce of resin. \ -v . y- ''* ) Mr. Timothy Sheldrake mentions campIïQj;' as à^e- dium for dissolving copal in essence and alcohol. He gives also another process, in which ammonia (volatile alkaline spirit of sal ammoniac), in the proportion of an eighth part of the essence employed, is substituted in the room of camphor *. Experiment I. Of the three processes which he describes I repeated two; those which regard the solution of copal in essence and in alcohol by a mixture of camphor. That with essence did not succeed. The author himself announce that he always failed, except when he obtained the es- sence from Apothecaries'-hall. It appears that this essence had by chance all those essential qualities which we endeavour to give it by time, and still more speedily by the influence of light. Experiment IL The same experiment repeated with pure alcohol was attended with too little success to make the result be considered as a varnish. The alcohol ap- peared milky, and the copal formed at the bottom of the vessel a mass which did not seem to have de- creased in volume. Next morning the interposed part of the copal, which altered the limpidity of the alcohol, was precipitated, and adhered to the sides of the glass. The process I have described for spirituous tincture of amber would give more hopes of success, Vv'ithout any intermediate substance. "* See Bibliothèque Britannique, vol. xiii. 158 TREATISE ON VARN!SHE3. In regard to the moans proposed by the medium of ammonia, the saline nature of that liquid, if the pro- cess succeeds, will not admit of the product being' placed in the class of varnishes destined for delicate painting. It is a kind of saponaceous compound, the use of which is not to be recommended in such cases. Experiment HI. Another process in \^hich the dose of camphor em-» ployed as the means of union is much greater than in the two preceding processes, may be f^^und in tlie Philosophical Transactions, 'i'he author sa)'s, that by maldng it equal to that of the copal, the whole of the latter will dissolve in the alcohol. Thou2:h this quantity of camphor appears to me to be far too great to render the solution of the copal applicable to cases wliich require the use of varnish, I followed the process exactly. I triturated forty grains of camphor with as much amber-coloured copal. I emplo)'ed the same for all my experiments. I put this powder into two ounces of alcohol of tl^e first quality, stirred it strongly for a minute, and then placed it on a fire of verv hot cinders, continuing to stir it. Tlie liouid roon boiled, notwlth- Jitanding the state of agitation in which I kept it, to prevent the resin frorh adhering to the glass. I enter- tained no doubt in regard to the power of the alcohol over the camphor, though the intimate union which it enters into, in this case, prevents a complete solution^ I The case was not the same \^ith the copal ; the solution of which, to judge by the appearance of the liquid, seemed to me very problematical. It was indeed pi'e- cipitated, and produced a small mas&, ^hfch adhered FOURTH GENUS. 159 to the glass. On decanting the liquid, which had a milky appearance, I was able to separate the copal, which, though it retained a soft consistence, adhered very little to the metallic spatula. This matter, when dried in a gentle heat, weighed still twenty-three grains, and appeared to me as dry as common copal. The decanted liquor retained for some days its ne- bulous appearance, notwithstanding the first separation of the resinous parts interposed. The vessel at length was incrusted with a thin coating of copal ; but I neg- lected to ascertain the quantity. Though this camphorated liquor could not be con- sidered as a varnish, I thought it my duty to make a trial of it on a piece of card, which had already re- ceived two coatings of fish glue. Three successive strata of camphorated liquor gave no satisfactory re- sult : in a word, it was not a varnish. Experiment IV, - Being convinced by preceding researches respect- ing the differences observed in experiments of this kind, when different specimens of copal are em- ployed, I endeavoured to clear up my doubts by changing the copal. I therefore repeated the experi- ment with specimens almost colourless, and of the greatest purity. I observed a difference at the very .moment of mixture. The resin was perfectly diluted; and its state of division between the moleculae of the liquid was such, that the rotary motion I maintained gave to the whole a clouded appearance. The kind of threads which circulated in the mass did not fall down ; but, notwithstanding this phœnomenon, which I always considered as very favourable to solution, ^d the mo- 1^ TREATISE ON VARNISHES. tion I communicated to the Tcssel and tlvit occasioned by ebullition, the resin united itscif under the form of fibres, which settled at the bottom of the vessel. The precipitated copal when properly dried weighed ten grains. The liquid retained opacity, and some days after there was formed a sediment around the vessel, as in the preceding experiment. Still, however, it did not form varnish, though it contained more copal than that of the third experiment. But it presents us with a new fact, which may be turned to advantage. E?< périment V. What I had done rendered it nccessarv for me to try the union of camphor with the brown copal, mak- ing use of an oily excipient, which hiLherto had ap- peared to me the properest for succeeding with this variety of copal. I therefore mixed twenty-four grains of copal with as much camphor, and formed it into a paste, which I treated with an ounce of the commoji essence of turpentine. I produced from it a small mass, which, after exposure to the sun for twenty d:i}'3, still retained pliableness, and an elasticity which miglit be compared to that of caoutchouc. In this state it \veighed twenty-four grains. This result, which I veri- fied on several other occasions, furnishes perhaps a key to one of the processes employed by some of the miners in Ducal Prussia, to give différent colours to amber, and to render it elastic. The intimate union which takes place between the parts of the camplior, the copal, and a small quantity of oil, is, no doubt, alone capable to explain this state of consistence. In a word, this union appears to me to be of such a nature as to v/eaken in these tv/o substances those properUes by FOURTH GENUS. 161 -which they are best characterized : the extreme vola- tiLty of the camphor, and the consistence of the copal. Six months after, this small mass, left in a window and exposed to the sim ft)r some hours eveiy day, still re- tained a pretty solid nucleus, of a bi illiant and vitreous fracture, but sufficiently soft to admit the introduction into it of a needle» This nucltus was incrusted in a spongy, friable matter of a grayish colour. The crust formed about a third of the whole mass. Experiment PL The same dose of camphor and of colourless copal, treated with the same quantity of essence, disappeared almost entirely a few moments after its mixture. In this case the liquor exhibited all the characters of var- nish. A small portion, however, was precipitated, which when collected and dried weighed S^- grains. Experiment f^II. One point still remained to be verified in regard to the success of the last experiment : Had not the essence I employed acquired, by the effect of chance, that disposition or particular state which is communicated to it by the solar light ? In a word, might it not be compared to that which is rendered proper, without any medium, for the solution of copal*? To resolve this question, I subjected to an ounce of the same essence twenty-four grains of the last-men- tioned copal without colour. Agitation of the liquid gave signs favourable to the required solution ; and ' after the action of heat had removed the mcleculse of water interposed between those of the essence, there * See Chap. V. Part I, M 162 Treatise on varnishes. remained no more than four grains and a half of copal united into one mass in one part of the phial. In the course of these different trials we observe anomalies which depend, in a particular manner, on. the nature of the copal, and the state of the oily liquid. Copal which has much of an ambery colour, and even the brown, which for fat varnishes, or those of the fifth genus, is preferred to that destitute of colour, loses in our third and fifth expenments its pre-eminence over the latter, when the object is a solution in alcohol or essence of turpentine, with or without any interme- diate substance. As the first two experiments were made some time before the one in question, I did not think of making a series of comparative trials, employ- ing all the variedes of tint observed in the copal of the shops. I introduce them here m.erely that I may add, if possible, to the confidence which artists ought to place in the experiments I present to them, and to sug- gest new subjects of research to those who may be in- clined to pursue them. From all these facts it is probable, that the difference observed in the result of the attempts made by different authors has arisen rather from the nature of the copal employed than from the method they employed. I must, however, confess that practice is necessaiy for such researches, and that the same materials which give successful results in experienced hands, give only very uncertain results in others. I am, therefore, far from bringing forward my own experiments, as argu- ments sufficient to render useless all those of my pre- decessors. I FOURTH GENUS. 163 itefiecting, however, on the different resources of mercantile fraud, and the facility they afford for de- ceiving persons of considerable experience, there is rea- son to think, that certain solutions of copal, rendered easy, in part or in v/hole, by the proposed medium, may have nothing of copal but the name. This opi- nion might appear too severe, and ever misplaced, had we not recent instances that sandarac, copal in sm^ali fragments, and amber, have reciprocally served to cover each Other for sal? ; and had we not seen, in particular, gum anima new, and consequently in Very transparent fragments, pass for copal, notwith- standing its greater friability, and the sweet odour it emits by friction* I shall abstain from any obser- vations on the high doses of camphor prescribed for these different solutionSi It may enter with copal into such a state of combination as to lose by it a part of its volatility. This state of union appeared to me very important, and well deserving of new researches. I must here remark, that the addidon of camphor in the sixth experiment was useless, as the solution of that variety of copal evidently depended on the state of the essence, as is seen in the seventh mixture. Like many artists, I tried copal according to methods of my ov/n : but not being satisfied with the researches, the results of which I have here communicated, I en- deavoured to overcome all the difficulties which occur in the composition of copal varnish, whether it be re- quired colourless, by employing essence subjected to preliminary preparation, or whether, sacrificing this advantage, which is doubtless very great, to the qua- M 2 164- TREATISE ON VARNISHES. lities found in drying oils, the methods reserved for varnishes of the fifth genus be followed. I ought to consider myself very fortunate if I should be able to substitute a method which holds a mean place, and which is sufficiently sure to deserve being recom- mended. The first object of those who compose varnish is to preserve the particular properties of the substances which form it. The great solubility of most resins in their appropriate liquors, determined the choice of some particular ones for the varnishes of the first, se- cond and third genera ; and it supersedes the necessity of complex researches. We have indeed seen, that the simple contact of resins with certain oils, or with alcohol, assisted by motion, or the temperature of from 50 to 60 degrees of Reaumur (from 144*' to 167° of Fahrenheit), or even that of the sun, is always followed by a success greater or less according to the nature of the resin employed. The series of my processes in regard to copal, and those employed for amber, exhibit however difficulties which I never before experienced. These substances require other means ; and notwithstanding the differ- ence observed between them, with respect to their so- luble property, they seem to be nearly on the same footing, and to deviate in a considerable degree from all the resins yet known, when considered as connected with the composition of varnish. Stopped by the difficulties with which the solution of these bodies is attended when the usual processes are applied, the artist found himself obliged to attack, in FOURTH GENUS. 165 some measure, the extreme cohesion of the aggregate moleculae of which their mass is composed, and to alter a little the state of composition, by applying to them a degree of heat much superior to that which is proper for simple infusion. This method corresponded very well, in part, to his views ; but the dark colour which the varnish assumes is an inconvem'ence which confines the use of it to certain grounds and to certain colours. Hitherto art has made no attempt to obtain a more satisfactory result ; it has introduced no change in the usual processes ; in a word, it has proposed no other modification to preserv^e the first liquefied portions of the copal from alterations occasioned in it by the con- tinued impression of caloric (the heat), but the sacri- fice of that part which is only softened. In this respect I consider myself as more fortunate ; since my at- tempts have always been crowned with success ; and nothing is required to obtain it but a modification in the process which I employ for the fifth genus of var- nish. It is, however, necessary to have a particular furnace, of which the following is a description : Description of a furnace destined for the liquefaction of copal and ajnher. Those who have examined in detail the laboratories destined for a course of chemistry, may easily form a clear idea of the construction of this furnace, by recol- lecting that employed for separating sulphuret of anti- mony from its matrix. But to render it fit for the object in question requires some alterations ; by the help of which one may use it without incoiivenience for the M 3 166 TREATISE ON VARNISHES. liquefaction of solid resins, and even for mixing theni with drying oils. This furnace, a section of which is represented fig. 1 . i?late IV, may be entirely constructed of burnt clay, three large apertures being made in the lower chamber, A, which supplies the place of an ash-hole in the common furnaces. The upper part of these apertures is arched ; and the pillars or solid parts between th?m should be as narrow as possible, in order to enable the artist with facility to extract the liquefied matter, and even to mix it with the drying oil, if this kind of var- nish be required. The upper part, B, or fire-place of the furnace, is separated from the lower part. A, by a bottom, or plate, which answers the same purpose as a grate in the com- mon furnaces. This plate has in the middle a circu- lar aperture, the diameter of which corresponds to that of the tube, C, which it is destined to receive, and which extends a considerable way below it. This plate may either form one piece with thé furnace," or may be moveable. In the latter case it is supported by three projections, or by a circular ledge which projects in- wards. In my furnace this partition is composed of an iron plate covered with a coating of potters' clay an inch in thickness. This precaution is indispensably ne- cessary to prevent the hea.t from penetrating to the lower division, A. The sides of the fire-place, B, are pierced with holes an inch in diameter, and distant from each other about three inches. These apertures admit air sufficient to maintain the caloric (heat) at the degree proper for 4 FOURTH GENUS. 167 this kind of operation. The following are the propor- tions of the three parts of this furnace, which served me for my experiments, and in which I liquefied six ounces of copal in the space of ten minutes, ^\ithout altering its colour in a sensible manner. Inches. Total height of the furnace ----- 17-5- Height of the lower chamber. A, including the bottom, which was an inch in thick- ness 11 Height of the upper chamber, B, or of the fire-place 54- Diameter, taken at the upper interior edge of the fire-place, B - 9-1- Diameter of the same, taken at the bottom or partition --- 7 This part decreases in diameter 2-i- inches, tapering towards the lower part of the furnace, A. The tube, C, is conical at the upper extremity and cylindrical towards the bottom : it is 9-i^ inches in length, 4-i- in diameter at the top, and 2^ towards the middle. Both ends of it are open. The tube, C, is placed in the aperture formed in the middle of the partition, in such a manner as to rise 5" or 4 inches into the fire-place. The place where it joins to the partition is luted with clay, to prevent the ashes or small coals from fallintj down. When this arrangement is made, the net, D, (see fig. 2.) made of brass wire worked very open, is placed M 4" 168 TREATISE ON VARNISHES. in the tube. It has the shape of a funnel, the upper edge of which is made fast to a ring of wire of the same diameter as the upper part of the tube, C. The decrease in the diameter of the tube C conduces to the stabihty of this net, and the conical form of the latter prevents it from coming into contact with the lateral parts of the tube, which is a matter of great import- ance to preserve the copal from too great alteration by the heat, The copal is placed on this metallic filter in pieces not larger than a small nut, and the whole is closed up with the iron plate or cover, E, an ii^ch in thickness, taking care to lute the joining with clay, to prevent all communication with the exterior air. A shallow dish or capsule, F, filled wdth water, (fig. 3.) is placed under the bottom of the tube, C, in such a manner that the tube is immersed in the water two or three fines. The fire-place, B, being filled with burning coals so as to rise above the iron cover of the tube, the first im- pression of the heat on the copal is announced by a kind of crackling, the consequence of its diIatatio;i, which makes it split into small pieces. This noise is a sign of beginning liquefaction, which indeed takes pb.ce soon after. A small iron pallet-knife terminating in an elbow is introduced under the tube, and moved in such a manner as to cause the liquefied part of the copal to fall down into the water, and to bring it under the solid form towards the edge of the capsule. When the operation is finisiied, the copal is spread out on dry g m FOURTH GENUS. 2 69 linen cloths, or on unsized paper, to dry ; it is then piled up and exposed to a gentle heat, to deprive it of all its humidity. While the copal is falling down there is separated a very small portion of oil, which remains fluid after the operation. It floats on the water as well as the copal,*' and gives to the latter a greasy appearance. But when the tube is of sufficient length there \\ill be no neces- si*"y for immersing the end of it in the water, or even for receiving the matter in the water ; but, in this case, a kind of smoke will escape, which may be offensive to the artist. The essential point is to graduate the hre in such a manner as not to alter the colour of the copal. When a very thick smoke issues through the lower aperture of the tube; when the latter is very red ; and when the drops which fall into the water rise into bladders and form small explosions, there is reason to conclude that the fire is too violent. I have succeeded in composing varnish with fat oîî, in the same operation, by substiîutiug for the water drying oil in a stare of ebullition, and maintaiiiing it in that slate by means of a mass of very hot iron, which served it as a supporter. The mixture of the liquefied matter is facilitated by means of a spatula, with a linee at the extremity ; and the boiling essence is afterwards added. The inconvenience of placing under the appa- ratus a volatile and highly inflammable oil may be .readily conceived. I shall always insist more on the separate liquefac- tion of copal, than on the possibility of completing the •inixture of it with a drying oil, to form a varnish of the 170 TREATISE ON VARNISHES^ fifth genus. This new mean enables the artist to compose a very dm'able varnish, very little coloured, and superior to copal varnish composed with drying oil, as the composition of the latter requires processes which alter the essential qualities of the substances that form the basis of it. For operations on a larger scale the dimensions of the furnace may be changed ; but in this case it will be proper to establish the fire-place, properly so called, on a kind of iron tripod, as represented at G, fig. 4, in order that the workman may be more at his ease. I must however always insist on the advantage of em- ploying, in the process, doses of only four and six ounces. The valuable advantages which accompany this new method will be perceived when a trial has been made of the varnish composed with essence of tui-pentine, which results from it. Copal thus prepared has pro- perties different from, and more extensive than, those communicated to it by the common method ; and it has not that dark brown colour v.hich it acquires by too high a temperature, and too long exposure to heat. Immersed here in an atmosphere of caloric (heat), it receives the impression only at the surface, which soon yielding to the power of that agent escapes under the liquid state from the continuance of its action ; new surfaces are successively subjected to the same eflect ; and the final result is copal as little altered as possible, and which can have undergone but a very sUght modi- fication in its constituent principles: the force only of the connexion which existed between its parts, and FOURTH GENUS. 171 which opposed so great an obstacle to the solutiotis proposed to be effected, is diminished. In a word, it is possible to compose fat copal varnish almost colour- less, by making use of oil as little coloured as possible; such as that of pinks prepared in leaden vessels, ac- cording to Watin's method. In like manner also this copal, simply modified, may increase the solidity of alcoholic varnish in a more direct manner than when it is employed without any preliminary preparation. A second liquefaction would perhaps give it the property of being soluble in alco- hol in greater quantity ; but there would be reason to apprehend that the alteration in its principles, carried too far, would give it no superiority over those resins which are most soluble in that liquid. I shall conclude what relates to this fourth genus of varnishes with an ac- count of the experiments I made by applying copal thus prepared to the most usual vehicles. Sivth spe&ies. Copal varnish with essence of iiu\ pentine, ivithout any intermediate substance. No. XXII. Take Copal liquefied, according to my method, 3 ounces. Essence of turpentine 20 ounces. Place the matrass containing the oil in a balneum marise, and when the water is warm add the pulverized copal in small doses. Keep stirring the mixture, and add no more copal till the former be incorporated with tan 172 TREATISE ON VARNISHES. *he oil. If the oil, in consequence of its particular disposition, can take up three ounces of it, add a little more ; but stop when the liquid becomes nebulous ; then leave the varnish at rest. If it be too thick, dilute it with a little warm essence, after having heated it in the balneum marise. When cold, filter it through cot- ton, and preserve it in a clean bottle. This varnish has a good consistence, and is as free from colour as the best alcoholic varnish. When ex- tended in one stratum over smooth wood, which has undergone no preparation, it forms a very brilliant glazing, which, in the course of two days in summer, acquires all the solidity that may be required. The same essence employed with copal of two fu- sions, that is to say, copal liquefied a second time, takes up a third more than in the former case. But it produces very little effect on copal not prepared. The facility which attends the preparatien of this Varnish by the new method here indicated, will admit of its being applied to all coloured grounds which re- quire solidity, pure whites alone excepted. Painted boxes, therefore, and all small articles, coloured or not coloured, where it is required to make the veins appear in all the richness of their tones, call for the application of this varnish, which produces the most beautiful effect, and which is more durable than tur- pentine varnishes composed with other resinous sub- stances. FOURTH GENUS. 173 Neiu experiments and observations on copal. Though essence of turpentine, by the state of its composition, be more proper than alcohol for the pre- paration of varnish, when it is required that it should unite durability to splendour, there are many cases in which alcoholic varnishes must be employed ; and the latter require no less attention on the part of the artist. To point out, therefore, the means of adding to their intrinsic qualities already known, another of still greater importance, namely, solidity, is doing a service to the art. Copal treated according to my method is better fitted to answer this end, as its colour is very little altered. I shall here collect some experiments which I made on this subject, with a view of pointing out to those who pursue researches of this kind, what has been accomplished and what still remains to be done. I must here observe that the alcohol I employed was exceedingly pure. Experiment I. Two deniers of copal, liquefied in a matrass with a fourth of its weight of camphor, pulverized and di- gested for ten days in an ounce and a half of alcohol, scarcely communicated to it any colour; and the spe- cific gravity had increased, at the same temperature, only two grains. The mixture being subjected to the heat of a balneum mariae assumed a slight nebulous tint. This addition to the process had increased the specific gravity of the liquid 3-i- grains. The camphor seems to have been the cause of this increase, if we may judge from the colour- Il4f TREATISE ON VARNISHES. of the infusion, which was not more charged than before. Experimeiit IL Thirty-six grains of copal of one fusion*, and which had been exposed to sufficient heat to undergo a flight inflammation, occasioned by a defect in the construction of the tube, and an ounce and a half of alcohol pre-» sented a complete solution in t\vo days. A new dose of the same copal increased the lemon colour of the liquid, "uathout appearing to decrease much in volume after ten days' digestion. At this period the specific gravity of the liquid exhibited an increase of six grains. Its fluidity did not seem to be sensibly affected, and the copal retained a pulverulent form. When treated in a balneum mari^ the copal formed itself into a mass. This circumstance seemed to be prejudicial to the solution, as the specific gravity of the infusion showed an increase only of two grains. It appears evident that the union of the free parts of the copal had favoured the separation of a portion of that which was in the state of solution, as I always took care to wait for the return of the same temperature before I verified the specific gravity of my liquors. * To avoid circumlocution in the aqi. omit of these experiments, I shall give the common name of copal to tliat which has been subjected to no preliniinary preparation before being pulverized ; tîiat of copal of one fusion to copal which has undergone liquefac- tion only once^ according to my method 3 and that of copal of two fusions to copal which has been tv.'ice liquefied according to the taiiie process. FOURTH GENUS. . 175 Experiment HI. Thirty-six grains of copal of one fusion, and which had been received in water at the time of its lique- faction, on examining its specific gravity showed an increase of only two grains and a half after being di- gested ten days in I4- ounce of alcohol. The colour of the liquid had experienced very little change. This digestion treated in a balneum marias aban- doned a part of its tint, and lost some of its specific gravity, which was reduced to 1-^^ grain of increase. Experiment IV\ A mixture made cold of tv/o ounces of copal of one fusion, and an ounce and a half of coarsely pounded glass in twelve ounces of alcohol, remained in the pul- verulent state during the whole time of a long diges- tion, even when assisted by some exposure to the sun*s rays, and stirring the mixture from time to time. The glass in this case contributes to the permanence of that state. Some minutes after mixture the. liquid assumed an ambery tint, which afterwards became darker. After fifteen days' digestion the specific gravity of the alcohol was found to be greater by seven grains., What had taken place in the second and third expe^ riments made me omit, in this case, to employ a bal- neum juariae: I preferred long digestion. Three months' infusion had carried the increase of the specific gravity to thirteen grains per measured ounce of liquid ; but the mixture did not form a varnish. I7& TREATISE ON VARNiSHLS. Experiment V, I mixed two gros of copal of one fusion with the sânie quantit)'' of camphor and six ounces of alcohol. To facilitate the action of the alcohol I pounded in a m.ortar, for a full hour, the camphor and the copal, moistened with some drops of alcohol: the addition then of one-sixth of alcohol extracted from it a liquor of a limpid and ambery tint. The mass, which had become soft, exhibited the consistence and appearance of turpentine which has been knead- ed in waiTn water, and drawn out into the form of a cord between the fingers. A new dose of alcohol ren- dered the liquid milky; but it soon after deposited the divided portion of the copal which gave it that appear- ance. The sediment remained pulverulent. It was under this state that the successive addidon of alco- hol reduced the whole of the small mass of cam- phorated copal. The liquid separated from the divided portion, which disturbed its transparency, had acquired a very dark orange colour : some days after, this colour had become more intense. At this period the specific gi^avity showed an increase of six grains. The use of a balneum marios carried this increase in half an hoiu- to fourteen grains ; but during this opera- tion the copal foiTued itself into a mass, and its con- sistence was soft, and so tenacious that I was able to take it from the vessel with the stick which had served to keep it in modon : this matter had a greenish tint. When exposed for twelve davs to the temperature of scventy-tv/o or sevent}'-seven degrees of Fahrenheit, this small mass still retained its flexibilitv; but its surface FOURTH GENUS. ]77 was white and as it were farinaceous, the efFect of the tranmdatioji of a part of the camphor. Though the spirituous infusion appeared to be char- ged, it did not contain a sufficiency of copal to malte it answer the conditions of a vai'nish. However, when spread out by means of a brush on wood prepared with gum, the first stratum gave indications of varnish, and the third formed a complete varnish. But this varnish, which was exceedingly slow^ in drying, since at the end of six days it still adhered to the fingjrs when placed on it for some time, became tarnished during its desic- cation. This efFect, which is unknown when our tur- pentine copal varnishes are employed, may be ex- plained by the particular union which copal forms with camphor. Experiment 11. One gros of copal powder fused in a matrass with a third of its weight of gum sandarac, put into a mixture of nine gros of alcohol and three gros of sulphuric ether, exhibits nearly the same ph^enomena as the pre- ceding mixtures. It sustains pretty well the division of its parts, and gives to the liquid a lemon colour.; but it disturbs its limpidity. Its specific gravity, ex- amined after eight days' digestion in a window which received the solar rays three hours each day, gave an increase of full eight grains. It appears probable that the cloudiness which the Kquid retains arises from a partial precipitation of the copal attacked by the ether, and precipitated in part by the alcohol, which does not exercise over it the Same energy* N 178 TREATISE ON VARNISHES. The infusion treated in a balneum marias became clearer, without being perfectly limpid. This effect might be ascribed to the evaporation of a part of the ether. The state of the solution experienced scaixely any change from this process, since the total increase observed in the specific gravity of the liquid vv^as only nine grains. The matter still retained its pulverulent form. Experiment VII. The same quantity of copal united to sandarac, thrown into an ounce and a half of alcohol, becomes very much divided, and remains pulverulent. The liquid assumes a beautiful gold colour, without losing any of its limpidity. Eight days' digestion added only two grains more to the weight, which expressed its specific gravity. The balneum marise doubles this addition. In the last process the matter had retained the pulverulent form, for which it was indebted to the sandarac. Experiment VIIL It appeared necessary that I should compare the ef*. feet of a mixture of alcoholized ether on copal, lique- fied according to my method, with that of the mixture which had served for the sixth experiment, in order that I might appreciate better the influence of the san- darac. The same doses were employed for the present experiment. The copal became soft, and formed at the bottom of the vessel a small mass, pretty similar in consistence and colour to turpentine. It however* yields to violent stirring, and extends in the liquids FOURTH GENUS. 179 tinder the form of very thin leaves, which by rest are soon collected into a mass. The liquid assumes a beau- tiful lemon colour, somewhat greenish : but it is less charged than in the two preceding experiments. The ether does not. appear to have here so strildng an influence as on copal mixed by fusion with sanda- rac ; since digestion for eight days, in the same win- dow, added only two grains to the specific gravity of the liquid. The application of a balneum mariae only doubled this addition. This process seems to have no advan- tage over those of the first and second experiments. As the copal seems to give more hold to the alcohol when divided by an intermediate body, or when modi- fied by one liquefaction, there might be reason to hope that a second would add to the extent of the solution, by taldng copal of two fusions received each time in a vessel filled with water. Experiment IX, Two gros of copal of tv/o fusions, one ounce of coarsely pounded glass, and eight ounces of alcohol, treated as the mixture of the fourth experiment, gave to the liquid an orange colour ; and eight days after the addition to the specific gravity was six grains : three weeks after it was nine grains. • The application of a balneum marias formed of it a mass. This solution seemed to exhibit no mxore advan- tages than that of the 4th experiment, \^ith copal of onlv one fusion. N 2 ^ 180 TREATISE ON VARNISHES. Experhtient X. Thirty-six grains of copal of two fusions, mixed with an ounce and a half of alcohol, maintain themselves pretty well under the pulverulent form, during a di- gestion of ten days. The liquid assumes little colour, and its specific gravity is increased only three grains. By the use of a balneum mariîe the liquid becomes turbid when cold ; the copal forms itself into a mass, and the increase of its specific gravity is reduced to two grains. Experiment XL The same quantity of copal of two fusions put into the ethereous mixture of the sixth and eighth experi- ments, unites into one viscid mass ; but still susceptible of division by strong shaking. After twenty-four hours the copal exhibits a firm consistence, and by a hard body may be reduced to coarse powder, even in the liquid, A digestion of ten days communicates to the liquid a beautiful gold colour, and increases its specific gravity six grains. The ethereous mixture has more action on copal of two fusions than on that which has been subjected to one liquefaction ; but this superiority is not so great as to admit of its application for making copal varnish. It is probable that it would have a more decided advantage over every other resin employed for alcoholic varnish, as is indicated by the mixture of copal and sandarac in the sixth experiment. These ethereous mixtures may be more happily applied with resins exceedingly soluble in alcohol, and by these means concur to the improvement of the varnishes of ^he first and second genera. FOURTH GENUS. 181 The balneum niariïE occasioned no great change in the state of the sokition, the specific gravity of which by this second process was increased only l-^ grain, forming by this increase a total of 9^ grains. Experiment XI I. C. Moulot, in the Journal de la Société de Médecine à Paris, gives a process for dissolving copal entirely in alcohol. Nothing is necessary but to project the pulverized copal by pinches into the alcohol saturated with camphor. The opinion which I conceived from -my own researches on this matter induced me to repeat the experiment, and to employ for this operation copal ■without any preparation, and that of one fusion. The solution of the camphor was effected in alcohol exposed for three days to the sun in a vessel closed with a cork stopper. The specific gravity of the alco- hol decanted from off the remaining camphor appeared by my areometer to be thirty grains heavier than that of the alcohol employed. I subjected, at four different times, forty-eight grains of common copal in powder to an ounce and a half of this alcohol saturated with camphor. I each time stirred the mixture to divide the copal, which appeared to nie disposed to unite into a mass. In this state of division the alcohol assumes a milky appearance ; but by rest there is formed a thin sediment, w hich, under the form of fine snow, occupies the half of the liquid. The part of the latter which floats over the deposit shows no al- teration, either in its colour or its limpidity. I conti- ■jivjed to shake the vessel for six days successively, in N 3 182 TREATISE ON VARNISHES. order to facilitate the solution ; but without any appa^ rent success, even under the influence of the sun du- ring some hours every day. The hquor being then filtered, I was able to observe its specific gravity. It was inferior by one grain to that of the alcohol em- ployed. The sediment readily detached itself from the paper by pouring pure alcohol over it ; but it was separated in the form of lurnps, which I was able to unite into one mass by kneading them in alcohol. This operation, which laid hold of a part of the camphor united to the copal, restored^to the latter its former state of dryness. There was, indeed, separated a fine powder, a part of which united itself to the small kneaded mass ; while another remained suspended in the liquid, which as- sumed a milky colour. ^After this washing, the small mass of copal, in regard to consistence and colour, had a great resemblance to the glutinous mxatter separated from farina by washing it in water. In this state it weighed fifty-six grains, which was eight grains more than the weight of the copal employed. But it still contained camphor and alcohol, which concurred to produce that state of pliability which it still retained. By some hours' exposure to the sun it was dried to the centre : it then weighed no more than thirty-seven grains. On adding to this quantity four grains of tlie copal precipitated from the remaining solution, which I had mixed with the alcohol of the washings, and about two grains of the same matter lost on the filter, I found a deficit of 5 grains of copal, which remained in the state of solution, and which could, be precipi' FOURTH GENUS. 185 tated by pouring pure alcohol into the Kqtiid, which contained the solution and the alcohol of the washing. Hence the maximuvi of the solution of copal, by C. Moulot's niethod, may consume at m.ostfrom eight to ten grains of this matter, with the quantity already mentioned of camphorated alcohol. Before the liquor was filtered I spread out some of it on a piece of wood prepared with gum water. The evaporation of the liquid caused to be deposited a slight stratum, white and as it were mealy, which was re^ moved by the least friction. This was camphor iTiixed with a little divided copal, which rendered it somewhat rough to the touch. Experiment XIIL The above processes were repeated with the same doses, and under the same circumstances, on copal of one fusion. On the first projection of the powder the liquid ac- quired an ambery colour ; but the powder fell to the bottom of the vessel, where it assumed a viscid and soft consistence. Two days after, however, the de- crease observed in its volume indicated a more exten- sive solution than in the preceding experiment. The camphorated alcohol had enough of colour, and yet it retained its limpidity. After being infused six hours in the sun, mere dé- cantation was sufficient to separate the liquid from the soft matter exhibited by the copal ; and my areometer indicated an increase of six grains, on comparing its N 4 184« TREATISE ON VARNISHES. present specific gravity with that of the camphorated alcohol. I tried, but Avithout success, to knead the soft matter which covered the bottom of the vessel. I therefore contented myself with washing it, to remove the cani- phor which gave it that consittence. The alcohol em- ployed in washing it cam.e off clear, and after reposing for some seconds, the copal had resumed its former dryness. After its complete desiccation it was found to be reduced to twenty-nine grains, estimating at two grains the loss occasioned by the parts which adhered to the sides of the vessel, and to the small spatula em.ployed to detach it. The nineteen grains, then, which formed the deficit, had passed into the camphorated liquid. Though this circumstance proves that copal, pre- pared according to my method, is superior, by its so- luble property, to unprepared copal, the result is not yet sufficient to constitute a varnish. The application of a stratum of this solution to wood, prepared with gum, was attended with the inconveni- ence already mentioned ; tlie only difference was, that the wood exhibited a light brown tint. I confine myself to this plain account of the process indicated by C. Moulot. My regr£t is, that I had not time to repeat these expeiiments on different varieties of copal, rather vv^ith a view of observing the differences which might occur in its union with cam^phor, than with a hope of composing a varnish by tliis method. The principal object of this new labour was to as* certain the utility of a mixture of copal with othu^ FOURTH GENUS. 18S resins, more soluble than in alcohol, and not to add •new formulae to the first two genera of our varnishes. Though the greater part of the results I have here given ^re unsatisfactory, there are some of them which seem to authorize, and even to require, the addition of copal to certain compositions with alcohol. The well-conducted digestion or maceration of copal prepared by a first liquefaction with pounded glass, as in the fourth experiment, or of copal treated over the fire with a solid resin, such as sandarac, (Exp. VI.) or of mixtures of other resins, the solubility of which in alcohol is confirmed, m^ay still add to the durability of the varnishes of the first and second genera. One micfht even be induced to believe that the tinctures formed in the fourth, sixth, and ninth experiments, applied to one of our copal varnishes with essence weR dried, would unite to the advantage of destroying the disagreeable odour of the essence, that of adding evea to the substance of the copal, if those genera of var- nish which abandon their odour more readily than fat varnishes with essence had need of such a palliative. But no circumstance seems to show that the use of camphor as an intermediate substance is advantageous in the composition of copal vai-nishes with alcohol. The sixth experiment exhibits some results which an- nounce a more extensive solution than by the other processes. However, if we compare these trials with those already mentioned, we shall soon be stopped by uncertainty in regard to the extent of the result, and particularly by the inconvenience arising from the vola- tile nature of the camphor. This inconvenience is not 186 TREATISE ON VARNISHES. an imaginary evil ; it is sufficiently proved by the state of the small flexible masses of the copal, which too slow desiccation renders spongy and pulverulent. In a word, if such a composition had not against it the strong and disagreeable odour it emits, and the slow desiccation of the varnish, one might be stopped by the certainty of seeing the varnish insensibly lose its lustre by the slow volatilization of the camphor ; split, or exhibit a mealy and spongy surface, and abandon all the characters which belong even to the most common varnishes. These experiments discover also another point of utility. They throw light on the course proper to be followed in the preparation of copal varnishes with al- cohol, whether it be employed alone or m.ixed with •similar substances, and on the superiority of simple digestion to infusions exposed to too ardent a sun, or , to a balneum marise. The action of digestion is slow ; but it must produce more effect on a substanee the parts of which remain divided, than rapid infusion of the same substance, which the action of the caloric (heat) reduces to a mass. Besides, the second and third experiments prove, in the most convincing man- ner, that what is obtained by long maceration is often destroyed by strong infusion in a balneum mariœ. I r But other experiments prove also that, if long mar Mi ceration geems to be proper in many cases in the com position of alcoholic varnishes, and particularly oPJi those which have copal for their basis, the case is not the same in regard to copal varnish made with essence M ij of turpentine. Infusion in a balneum rp^irias completes» ^ (,; 4 FOURTH GENUS. JST m two minutes, a solution which could not be effected jn several hours by maceration, and even motion. A, israrnish of the first quality, and of an excellent con-^ sistence, which requires neitheir claiification nor filtra^ tion, and which possesses the property of drying speed- ily, will at length be obtained. If ccpal, previously liquefied according to my method, be used for the composidon of this varnish, no preparation of the es. sence will be necessary. That least proper for becom- ing charged with copal can, in this case, take up 1-^ gros, and even more than two gros of the copal which has undergone two liquefacdons. But in the latter pase the varnish is a little coloured. After the opinion I have given in regard to the em- ployment of camphor, which is supposed to be very useful for compledng the solution of copal in alcohol, I ought to abstain from all further reflections on the method proposed by C. Moulot. In this respect I refer to the results of the twelfth and thirteenth experiments; but I think it indispensably necessary here to call thç reader's attention to the consequences which might be deduced from a comparison of the state of the consist- ence of a soluuon of copal in essence with that of the came solution in alcohol, and from remarldng what veal singularity these two solutions exhibit in their spe- cific gravity. . We have seen, in treating on the method of making in a few minutes turpentine copal varnish, that though this varnish had a very oily consistence, its specific gra- vity was increased only fifteen grains per measured 'S>uncej according to my areometer. V/e have seen. Ï8S TREATISE ON VARNISHES. " nn the other hand, that the highl^'-charged tincture of copal of the fourth and ninth experiments, .and that of the camphorated copal of the fifth experiment, retain the fluidity by which pure alcohol is characterized, though their specific gravity, and particularly that of the latter, approached very near to the specific gravity of var- nish composed with essence. To these two results I shall add two other observations, made on a highly charged tincture of gum anima, the specific gravity of which had increased fourteen grains, according to my areome- ter ; and on a tincture of amber, the increase of which was seventeen grains, v»ithout the state of the fluidity of the alcohol appearing in either of these two cases to be lessened. Such efl'ects can arise only from the state of penetra- tion or intimate union of the moleculse of the substances . in contact ; and consequently must relate to their par- ticular nature. It may, therefore, be readily conceived, that this union is more striking and more perfect be- tween alcohol presented to amber, or to copal, or to gum anima, than between these resins and essence of tui-pentine ; since two ounces in absolute weight of this essence, which we know hold in solution nearly three gros of copal, weigh only fifteen grains, of the seven gTos and twTnty-six grains expressed by the specific gravity ascertained by an areometer, the capacity of which is an ounce of distilled water at the temperature of 59'' lof Fahrenheit. This chemical state of resins, in different liquids which sen^e for the composition of varnishes, is truly singular, and in this particular point of view deserves Ï'OURTH GENUS. 189 to be further examined. But what proves in a very con- vincing manner that essence is better suited than alco- hol to the composition of varnish, is, that one stratum of my turpentine varnish spread over wood, without any preparation, renders the surface exceedingly bril- liant, by depositing on it a very durable glazing ; while three strata of the different tinctures of copal are re- quired to produce upon wood the appearances of varnish. Alcohol, then, does not seem to be suited to dry and solid substances, such as copal and amber, which are besides so different from common resins by their other properdes. All hope, therefore, of composing with it an alcoholic varnish must be renounced, if v/e banish from the composition every intermediate body capable of serving as a bond of union to the divided parts of these two substances, which; the alcohol abandons by the effect of evaporation*. It is known, in general, that alcoholic varnishes are the most delicate, and that they would have still less consistence should those by whom they are made neg- lect to introduce into the composition of them as an essential inp-rcdient a viscid and tenacious substance, such as turpentine, or some other of the same kind, which acquires modifications either naturally or by the effects of art. If this remark is well founded in the case of common varnishes of the first and second ge- * I composed very good varnish with the tincture of copal fur- nished by tlie fourth experiment, by adding mastic and one-eighth of turpentine, according to the quantity of the tincture ; but though this varnish contained enough of copal, it could not be considered as pure copal varnish made with alcohol. J9Ù TREATISE ON VARNISHES. nera, ought it riot to excite doubt also in regard to qualities assigned, without any foundation, to simple spirituous tinctures of copal and of amber, wheii matters such as turpentine, or any other capable of «diminishing the dryness of these two substances, are banished from the composition of them ? But by ad- mitting these necessary correctives we approach thé varnishes of the fourth genus ; and in this case it is more convenient, and even more useful, to make the copal vamiBh -with turpentinCj following the prescrip* tion indicated. In general, varnishes with essence hold a proper medium between those which might be com-* posed with alcohol and copal, and those which admit the use of drying oils, as in our fifth genus of var- nishes. No theory is good unless founded on experience^ From experience, therefore, I think myself authorized to assert, that the successive application of alcohol charged with copal or amber, without a mixture of turpentine Or other resins, cannot exhibit the qualities of à superior varnish. The spirituous liquid abandons 6oon after by evaporation the substance it had appro- priated to itself, and leaves it under an almost pulve- rulent form, which the least friction whitens and causejl to disappear. There is only one case capable of mode* rating this effect, which is indeed certain : it is when colouring parts are mixed with this kind of varnish. I have as yet observed only one fact, which proves that amber varnish composed with alcohol is capable of glazing any surface. I observed it at the mouth of a phial ccntainmg highly charged tincture of amber, em*- FOURTH GENUS. 391 ployed for daily use. The successive accumulation of the resinous part may alone serve to explain this fact. Essence has a great advantage over alcohol in the com- position of varnishes ; as it concurs by its om'U sub- stance to the connection of the resinous pails of which they are constituted. Alcohol, on the other hand, is entirely dissipated. Varnishes vdth essence, therefore, are more pliable, more brilliant, and more durable, than those made with alcohol. I have also observed in these new trials, ailromalies in the common properties of copal, which embarrass those who employ it, and which are calculated to involve in uncertainty every thing we know, and every thing which can be an- nounced as new in regard to this singular substance. I. have already spolcen of them in my experiments which' follow the article on the varnisti No. XXI. The copal soU in the shops exhibits various shades of colour, and the case with it is different from that of all the resins applied to varnisheSj in which the varied tints they may acquire do not seem to affect their che- mical qualities, or to announce new ones contrary to those which are the most apparent. There are some specimens of it which might be confounded with the purest gum arabic, that rs to say, absolutely colourless, îind exceedingly transparent. Other morsels have a v«ry light lemon colour, which in other pieces appears more ambery, with the transparence and splendour of the most beautiful topaz. In the last place, this colour is often darker, and sometimes brown and very dull. The numerous experiments I was obliged to make enabled me to take advantage of these different varieties Ï92 TREATISE ON VARNISHES". of copal, and to observe that the property of solubility- sought for in this substance is not sufficiently stable to be in any measure distinguished by certain exteiior signs. It depends, no doubt, on many circumstances still unknown, and determined by the age of the tree which fuiTiishes it; by its local exposure, by the nature of the soil, and by the influence of its native atmo- sphere : I have, however, had the satisfaction of con- vincing myself that the copal proper, in general, for making varnish is that which one might be tempted to reject on account of its colour, and of a certain dull aspect disgusting to the artist, who in this case attends too much to the extreme purity of the substances em- ployed in the preparation of transparent varnishes. The colour of copal, however, may sometimes be consulted to enable one to judge of its degree of solubility, espe- cially in all cases of a charged composition, such as that of the fifth genus of varnishes. This assertion is supported by a great number of facts : but it does not establish a general rule ; for I have seen copal ex- ceedingly pure, and almost colourless, dissolve as speed- ily in ether as copal of a bright topaz colour. I have in my collection several pieces of this kind : other spe- cimens extend themselves in that liquid under the form of very fine snow, which yields to all the motions com- municated to the vessel, but which resists a more ex- tensive acdon on the part of ether. It was copal of a similar Idnd, but somewhat more coloured, which I employed for these latter experi- ments. This resistance, however, is overcome by the preparation here recommended, that is to say, lique- FIFTH GENUS. 193 faction in the furnace above described ; but when pre- sented to the essence, the ether or alcohol, it must be jn. powder. When I made choice of this copal, I had reason to hope that the results I should obtain from it would be still more extensive, on repeating the same processes with copal better fitted for the composition of varnish. FIFTH GENUS. FAT VARNISHES. Preliminary observations» The varnishes of this genus are the most durable, but they are the slowest in drying. They are destined for objects exposed to friction, or to shocks from hard bodies ; and are employed, in a particular man- ner, for the decoration of carriages. They are applied to v/ood, to iron, to brass, and to copper : they are used also for painting waiters, Argand's lamps, tea- pots, and other utensils of the same Idnd which are in daily use. The matters which enter into the composition of these varnishes are few in number. The artist con- fines his means to the solution of copal and of amber in essential oils, in prepared linseed oil, and in nut oil or oil of poppies. In the first experiments on balloons, caoutchouc or elastic resin was added to these sub- stances. We may place in the last rank that common kind of varnish with which ships and other vessels are daubed over. In this case the processes are not confined to simple o 194 TPvEATISE ON VARNISHES. infuFions. The dry and solid nature of the substances destined to serve as the basis of these varnishes requires other means, and a higher temperature. Though these substances have properties common to them all, they possess others which are peculiar to each of them. It is these differences which induce artists not to confound them, or not to employ them collectively in the com^ position of their varnishes. Copal, indeed, presents less resistance to liquefac- tion, at a given temperature, than amber. It is more susceptible of decomposiuon ; and the varnish result- ing from the mixture of it with any oil is less coloured, and not so dark as that obtained from a mixture of amber with the same oil. If copal were mixed with amber in the same operation, it would in a great measure be destroyed before the latter were in a state of liquefaction. There is a fat varnish then with copal, and another with amber. To these I shall add that of caoutchouc or elastic resin. Though the doses indicated, in my different formula?^ for this fifth genus of varnishes have been proved, the last portions of the copal, and particularly of the amber, must not be melted if the varnish be required as little coloured as possible. The portions of the amber which have escaped liquefaction may be easily sepa- rated by a sieve, or by deposition. Copal presents less resistance, and, when em.ployed in small fragments, is soon liquefied. In other respects I must recommend the method indicated at the end of the description of •.- my furnace ; because the matter, when once liquefied, escapes from the burning atmosphere, the continued 3 FIFTH GENUS. 195" influence of wj^^cb weiiki .have a prejudicial effect on the nature of tte siibstance, and consequently hurt the solidity of .the; Yarnish. First species. Extracted from IVatiii^s ivork. No. XXIII. Take Picked copal 16 ounces. Prepared linseed oil, or oil of pinks, 8 ounces. Essence of turpentine 16 ounces. Liquefy the copal in a matrass over a common fire, and then add the linseed oil, or oil of pinks, in a state of ebullition: when these matters are incorporated take the matrass from the lire, stir the matter till the greatest heat has subsided, and then add the essence çf turpentine warm. Strain the whole, while still warm, through a piece of linen, and put the varnish into a wide-mouthed bottle. Time contributes towards its clarification ; and in this manner it acquires better qualities. In general, there is much advantage in not employ- ing too violent a heat. The varnish by these means succeeds better, and acquires less colour. If it after- wards becomes too thick, add a little warm essence, that the mixture may take place more speedily. It was in this manner that the celebrated Martin com- posed his beautiful white fat varnishes. o2 196 TREATISE ON VARx^ISHES, Second .^ppcics of the same genus, employed in the ■mcuiKj'actorks of Geneva for ivatch-cases, m imita- iion of iortoise-sliell. No. XXIV. Take Copal of an amber colour 6 ounces. Venice turpentine l-?r ounce. Prepared linseed oil 24 ounces. Essence of turpentine 6 ounces. It is customaiy to place the turpentine over the ccpal, reduced to small fragments, in the bottom of an earthen or metal vessel, or in a matrass exposed to such a heat as to liquefy the copal : but it is more advantageous to liquefy the latter alone, to add the oil in a state of ebullition, then the turpentine lique- fied, and, in the last place, the essence. If the var- nish is too thick, some essence may be added. The latter liquor is a regulator for the consistence in the hands of the artist. The doss of oil, in this case, appears to me to be too great : eighteen ounces would be sufficient. This- varnish is durable and transparent; but it dries v/ith difficulty. In general a stove is employed to hasten the desiccation : it is susceptible of a iine polish. IlfTII GENUS, 197 Third .species. Amher varnish. No. XXV. Take Amber, coarsely pounded, 16 otinccs. Venice turpentine, or gum lac, 2 ounces. Prepared linseed oil' 10 ounces. Essence of turpentine 1 .5 or ] 6 ounces. The circumstances of the process are the same as- those prescribed for the preparation of the copal var- nish, No. XXI. ' Remarks. This varnish v/as formerly much used ; but it has given place, in part, to that of copal, which is pre- ferred on account of its being less coloured. Watin introduces more essence and less linseed oil : expe- rience and long practice are the only authority on which I recommend the adoption of the present for- mula. Copal and amber are the two dry substances appli- cable to the composition of varnish, which are the most difficult to be brought to the liquid state. They require the direct application of heat. A varnish might, indeed, be composed, according to the practice of some artists, by treating simulta- neously amber and copal ; bat the difference observed in the phscnomena they exhibit in the fire ought to make this method be rejected. The copal is, in part, decomposed before the amber has completely aban- doned its consistence. Besides, copal varnish without mixture is of an amber colour and very transparent. Q 3 19S TREATISE ON VARNISHES. When mixed with amber the varnish is of a very dark brown colour. Setting out from this fact, the mixture of turpentine IS more proper with linseed oil than with amber; and the oil ought to be boiling when presented to the amber in a complete state of liquefaction. But this precau- tion is still not sufficient, if it be required, as ought to be the case, that the three substances in contact should unite in a speedy and intimate manner. If the whole quantity of oil added to the turpentine were poured in at one time, a portion of the amber would be precipitated. This projecdon ought to be effected at several times, taking care to facilitate the contact by stirring the mix- ture with an iron rod. It will even be proper to bring the mixed matter to a state of ebuUition before it be taken from the fire. Some ardsts do. not wait till the whole of the amber is in a complete state of liquefacdon before they add the oil: they are satisfied with liquefying a paBi^j'and they then separate die fragments of the amber which have not been melted. By this method the varnish is leL.s coloured; but it requires more amber or copal than is prescribed in my formulse. Sonieti mes one is stopped by the fear of not finding vessels rarable of standing the whole operation. A cabt-irou pot will obviate this inconvenience, and ought to be preferred to vessels of earthenware, which either crack or split. When porous they are soon penetrated, by the varnish : besides, they can be employed only once ; the second varnisii made in them would acquire too dark a colour. A cast-iron pot has this advantage FIFTH GENUS. 199 also over pottery, that it can be cleaned, while warm, to remove the portions of the old varnish, which would be coloured by the ûre employed for a new com- position. Before I proceed to the composition of the otlier var- nishes v.'hich belong to this last genus, it may be of use to take a view of the processes I have followed in treating copal in a manner entirely new, and to apply fhem to amber. By adhering closely to the formukvi established by usage and long experience, my principal intention was to enable artists to compare them with the simple method which I have substituted in their stead. I should form an erroneous opinion of artists, and particularly of those who are loth to sacrifice old habits, were I to believe them capable of abandoning, without opposition, the favourable idea they have of the nature of aiiiber, and of the superiority they ascribe to it, but without sufficient reason, over copal. In general, they are much disposed to believe that the character of solidity by which it is distinguished, when considered in its natural state, and which appears to render it superior to copal, is maintained in its mix- ture with drying oijs, and that it becomes the principle of the consistence of the varnishes of which it consti- tutes the principal base. One, however, may be easily convinced, on com- paring the results exhibited by these two singular sub- stances, in the kind of analysis to which they are sub- jected, that the one which, v/hen it appears under its natural characters, seems to have a superiority over ihe other, resigns it to the other vvhen it has been 4 200 .. ,-V^EATISE ON VARNISHES. •E>i^^l^ght to,'^e necessaiy degree of liquefaction, before k. bè nii^Q v^ith oils in the process of making varnish. What is then considered as an essential quality in amber examined in regard to its constituent parts, becomes prejudicial to it when applied to the composition of varnish ; because the greater resistance it opposes to the influence of caloric, at the time even of its liquefaction, alters its principles in a higher degree than is the case in the liquefaction of copal. The latter indeed requires less heat, and passes more readily to the state of lique- faction. The following experiment will give some wei'jht to this assertion : o Preparation of amber occcordliig to my new process already described. Five ounces of amber, of a very dark orange colour, but transparent, and in pieces of the size of a small nut*, treated in my melting furnace, required a half more time than copal before it exhibited the first indi- cations of liquefaction, the fire in both cases being sub- '| jected to the same regulation. A great deal of pretty thick oil, and which always retained that consistence, Vvas disengaged. It envelops in such a manner the parts vvhich acquire solidity by cooling, that it is diffi- cult to separate it by immersion in tepid water, and by means of blotting paper. However, by exposing the * The amber to be liquefied must not be employed in pieces too Jaro^e, or in coarse powder, because it soon forms a raass, and does ; not run so freely. It is indeed very slow, and fornishes more fluid oil than in die present case : tlie varnishes also are more coloured. FIFTH GENUS. \^ ' ^ . ^p% amber to the air for some days, it becoji^çs^^ sÔ^oIk| that the laminse it forms may be broken b^i[weeif't|>e fingers. In this state these laminœ have the transpai'en- cy and colour of the hyacinth. The amber is obtained under this form, when care is taken to bring it to the edge of tlie vessel, filled with Vv^ater, into which it fiOws, by means of a hook, or pallet-knife bent at the extremity. This matter, which is pretty dry in appear- ance, when pounded in a mortar forms itself into a small mass, which readily crumbles to pieces. It is indebted for this flexible quality only to a portion of the free oil, which covers the surface of it under the form of a varnish. When this consistence is compared with that assumed by copal under similar circumstances, one may readily be convinced that the latter, the consistence of which " is drier and even pulverulent, is preferable to amber for the preparation of varnish. I'his opinion will even be maintained in favour of copal of a second fusion, the alteration of which is m.ore observed in the colour it acquires than in its proper substance. This result, which is sufFiciently confirmed, induces me to believe that the process hitherto employed for the composition of fat amber varnish, and in which the amber under- goes a still greater alteration, only adds a thick oil to that presented to it; and that the varnish thence re- sulting can have no superiority over copal varnish, composed a.ccording to my principles; since nothing announces that the consistence, observed in the copal before its mixture, can be v^eakened when it yields to the laws of solution. 1 202 TREATISE ON VARNISHE?. In considering, besides, the state of alteration which amber experiences in the common processes, and the , degree of heat which these processes require, it may still be beheved that the quantity of it which passes into the varnish amounts scarcely to one half- of the whole. One may suppose that a portion reduced to the state of oil readily passes into the oil, and that it disposes towards the same result another portion of amber less altered, and nearer to its state of consistence. The rest is composed of tho portion of the anfber destroyed, and of th:it which resisted liquefaction. It is the carbonaceous part suspended in die mixture which occasions the alteration in the colour of the liquid, and the thick deposit which is formed some time after. The unnatural state of amber in all the forced com- positions^ which constitute this last genus of varnish, is very proper for pointing out the advantages of the formulae given for my fourth genus, and to dissi- pate the least traces of the superiority ascribed, with- out any reason, to amber over copal. By subjecting amber to the processes so happily applied to copal, my intention therefore is rather to gratify the taste of the old artists, who are led away by habit, than to main- tain any doubts on the place which copal and amber ought to occupy in the composition of vaiTiishes, in. regard to the intrinsic qualities they are capable of com- municating to them. Essence furnishes enough of its substance to constitute, and particularly with copal, durable compositions. By giving a preference to the varnishes of tlie fourth genus, the arti;st satisfies, at the FIFTH GENUS. 205 same time, his own knowledge, and the anxiety of those who employ him. By the speedy desiccation of varnishes of this genus he is soon enabled to complete the labour of polishing, which is always tedious when varnishes of the fifth genus are employed. Amber varnish with essence of turpentine. Take Amber, liquefied according to my process, and separated from the oily portions wfiich alter its consistence, 6 or 7 ounces. Common essence of turpentine 24 ounces. Reduce the amber to powder, and if the operation of pounding forms it into a paste, break it with your fingers : then mix it with the essence, and treat the whole in a balneum marine. It will speedily dissolve, and the essence will take up at least a fourth part of its weight of the prepared amber. The varnish which results from it is more coloured than that made with copal and turpentine; but it readily clarifies, even without filtering it through cotton. It may readily be conceived that this varnish forms a part of those of the fourth genus. When one coating of it is applied to white smooth wood, but without any preparation, it forms a very pure and very durable glazing, which speedily dries, but slower than copal varnish. It appears to me to be superior to highly coloured varnishes, which admit the addition of oil in common composidons, and which to be tl\oroughly dried require the use of a stove. 204 TREATISE ON VARNISHZ5. As copal and amber must be liquefied before they are mixed with drying oils, which serve as excipients to fat varnishes, it may be advantageous to follow my process under such circumstances as may seem to favour the preference given to drying oils over essence of tur- pentine. The following formula was attended vvith complote success. Fourth species. Fat amher or copal larnislu No. XXVI. Take Amber or copal of one fusion 4 ounces. Essence of turpentine^ Drying linseed oil ■ If -, roi each 10 ounces. Put the whole into a pretty large matrass, and expose k to the heat of a balneum mariai, or mo^■e it over the surface of an uncovered chaffing-dish, but without fiame, and at the distance from it of two or three inches. When the solution is completed, add sdll a little copal or amber to saturate the liquid ; then pour the whole on a filter prepared with cotton, and leave it to clarify by rest. If the varnish is too thick, add a little vx^arm essence, to prevent the separation of any of the amber. This varnish is coloured, but far less so than those composed by the usual method. When spread over white wood, without any preparation, it forms a solid glazing, and communicates a slight tint to the wood. If you ai"e desirous of charging this varnish with fIFTH GENUS. 205 more copal or prepared amber, the liquid must be composed of two parts of essence for one of oil *. The whole of the processes here given, and which may be applied to the composition of varnishes of the fourth and fifth genera, leave no doubt in regard to the course which will be followed by artists who know how to make use of the advantages they offer, and to compare them with each other. I am persuaded that they will give a decided preference to turpentine var- . nishes treated according to my method, and that in future they will confine fat varnishes to common ob- jects; if they are srill retained, notwithstanding the de- fects with which, it is well known, they are attended. I shall conclude this chapter with an account of three cojiipositions which may be esteemed by some artists , but 1 must recommend the use of amber, prepared ac- cording to the method which I have already described, ■* Amber prepared according to my methoJ suffers itself to be laid hold of by the alcohol, to which it communicates a lemoa colour. What distinguishes it from copal is, that it retains ils pulveiiilent form in the heat used for infusion in a balneum mariae. The tincture resulting from this mixture is attended witlji no greater advantagq to varnishes than those extracted from copal. Ether exercises on it a more striking miction : it readiiy attacks it, and can take up a gros of it. The varnish it produces is coloured^ When deposited on wood dipped in oil, and afterwards well rub- bed with a view to render the dissipation of the ether slower, it left .a solid coating of varnish with a beautiful gold tint : \yljea Spread over wood not immersed ia uil^, it l^ft a coating which re» sembled pale gold. 206 TREATISE ON VARNISHES. Fifth Species of the same genus. Fat vaniish of a gold colour. No. XXVII. Take Amber, prepared according to my method, 8 ounces. Gmn lac 2 ounces. Drying linseed oil 8 ounces. Essence of turpentine 16 ounces. Dissolve separately the gum lac; and then add the amber, prepared and pulverized, with the linseed oil and essence very warm. When the whole has lost a part of its heat, mix in relative proportions tinctures of anatto, of terra mérita, gum guttœ, and dragon's blood, as mentioned page 142. This varnish, when applied to white metals, gives them a gold colour. Sixth species of the same genus. Fat varnish, which may serve as a mordant to gold, and at the same time to dark colours '*. No. XXVIII. Take Boiled linseed oil 16 ounces. Venice turpentine 8 ounces. Naples yellow 5 ounces. Heat the oil with the turpentine, and mix the Naples yellow pulverized. * The varnish No. XVI, of the third genus, that is to «ay, with essence^ is also a mordant. m FIFTH GENUS.- -207 Remarks. Naples yellow is an oxide of lead, the composition of which will be giyen when we come to treat of colour- ing substances*. It is substituted here for resins, on account of its drying quality, and in particular of its colour, which resembles that of gold. Great use is made of this varnish in applying gold leaf. The yellow, however, may be omitted when this species of varnish is to be applied to solid and coloured coverings. In this case an ounce of litharge to each pound of composition may be substituted in its stead, without this mixture doing any injury to the colour \vhich is to constitute the ground (/a teinte dure). There is still another species of varnish, which, like the above, might form a part of those of the thii'd genus, if the matter which serves as the basis of it did not require a drying oil to be employed : it is that of caoutchouc. Sixth species of the same genus. Caoutchouc varnish. No. XXIX. Take Caoutchouc or elastic résina Boiled linseed oil - - /'ofeach 16 ouncesj Essence of turpentine - '' Cut the caoutchouc into thin slips, and put them ante a matrass placed in a very hot sand bath. When the matter is liquefied, add the linseed oil in a state of * See Part II. Cb^p. I, 20^ TREATISE ON VARNISHES. ebullition, and then the essence warm. When ther varnish has lost a great part of its heat, drain it through a piece of linen, and preserve it in a wide-mouthed bottle. This varnish dries very slowly; a fault which is owing to the peculiar nature of the caoutchouc. Remarh'^. The solution of tins singular substance is not con- fined to essential and fat oils. Macquer applied ether to it v\ith success* ; but the processes he indicates do not always answer, and cannot form a part of those which we are desirous to place within the reach of the public in general. In repeating these experiments, I found that the union of caoutchouc and ether did not manifest itself till the volume of that fluid was reduced one half by .the effect of evaporation. It appears therefore that ether exercises a better action on this substance accord- ing as it hsG less tenacity, and as it approaches more to the oily nature. In consequence of this principle, the best rectified ether refuses to form any kind of union with caoutchouc. This, perhaps, is the che- IPÛcal reason proper to be adduced in order to account for the difference between the experiments of Macquer and those of Berniardf. The invention of air balloons led to the idea of ap- plying caoutchouc to the composition of varnish. It t/as necessary to have a varnish which should unite * See Mémoires de 1" Académie des Sciences, 1/63. f See llic article- Caoutchouc. FÎFTîi GENUS. 209 great pliability and consistence. No varnish seemed capable of corresponding to these views except that of caoutchouc ; but the desiccation of it is exceedingly tedious. . The formula which I present is the same as that indicated in the Journal de Physique for April 1781. I only modify the process by omitting the long ebulli- tion of the essence over the caoutchouc. By my method the solution is speedier, and less of the essence is lost. I cannot conclude this chapter without remarldng, that there is even another species of varnish belonging to this last genus, the use of which is very extensive ; and which, no doubt, would occupy the first rank, were it considered in regard to its utility : it is that Vhich results from a mixture of tar, black pitch, rosin, tallow, and sometimes even sulphur, and which is employed for covering the outside of ships, boats, and barges. This varnish preserves them from the influ- ence of the water, retards their desttuction, and pre- vents the velocity of the vessel from being lessened by the additional weio-ht which would be communicated He . . to it nf the water were imbibed by the wood. This varnish then contributes as much to the celerity of th® vessel as to its preservation. C 210 3 CHAPTER IV, ùcnerat olaervai'ions and precepts respecting the prêparatiùrt of varnish on a large scale. Description of an alembic nif It a lalneum mariœ, the use of which prevents ale those ac- cidents that frequently acconrpany the making of varnish. The division I have made of varnishes into five genera, each sub-divided into its species or varieties of composi- tion, rendered it necessary for me to place after each formula the remarks that seemed peculiarly applicable to it. There are others, however, of a more general nature, v.hich seem to belong to the whole art, and which ought to be given by themselves. All the arts have had their state of infancy. The progress of them has been the result of repeated triars, and sometimes of errors ; but, for the most part, they are extended by accident. It is on these frail and un- certain bases that those arts which relate to the most necessary objects have been established. A lorrg repe- tition of the same processes has at length thrown light on their progress ; and in this manner the first el!^nent& of them have been acquired. That of the vamisher could not speedrly attain to its highest degree of perfection. Its origin depended on thai of public wealth, and on the extinction of those wars wliich covered Europe v/ith ruins : it depended on the extension of commerce, which increases the (enjoyments of life, inspires a taste for superfluities, and multiplies our wants. An industrious people, attached OBSERVATIONS AND PRECEPTS. 211 to the aits, and confined to the eastern extremity of Asia, furnished us with the models. The European industry, and particularly that of France, acquired a stimulus ; it invented combinations ; mixtures were muldplied ; and the results, though still imperfect, af- forded sufficient encouragement to ardsts. New at- tempts opened a more successful path ; the principles of the art were discovered, and these were followed by formula and descripdons ; cridcal examinadon deter- mined the choice of them ; and the art was at length established on a solid basis. All resinous or gummo-resinous substances are the only essential bases of varnishes. Every spirituous liquor, resulting from vinous fermentadon, and freed by recdficadon from its superabundance of foreign water, such as pure alcohol (spirit of wine); every es- 'sential oil extracted from plants by disdllation ; and even every fixed or fat oil, obtained from certain fruits by contusion or expression, are the only matters which can be employed as an excipient or vehicle to the resi- nous or gummo-resinous substances destined for var- nishes. Perfect transparency, and even limpidity and lus- tre, are, in the last result, the essential' qualities in the composidon of varnish. There are others, however, equally important, such as those of drying speedily, and giving solidity to the resinous stratum which serves as a glazing to the bodies it covers. A composition of this kind must at the same time be colourless, in order that it may not weaken or disfigure the dnts of the co- lours, which it ought on the contrary to call forth h\ p 2 212 TREATISE OKI VARNISHES. their full brightness, by preserving them from the in- fluence of the air and of moisture. From this correct view it may readily be conceived, that it is not sufficient that a substance should be of a resinous nature, pure and without any mixture of fo- reign bodies, and that it should be entirely soluble in the liquid intended for the composition of varnish : ta be entitled to a place among those destined for this pur- pose by use and experience, it must also have very little colour. There are many substances, indeed, which are re- jected on account of their sofdsh consistence, such as sagapenum, galbanum, &c. as v/ell as of their colour, which would spoil that of the compositions. This would be the case with the resins called bdellium, guiacum, ivy gum, gum ammoniac, and olibanum, though the last two dissolve entirely in alcohol. Some of these J substances did not escape the notice of those who hrst made experiments in regard to varnishes ; but they soon discovered the inconveniences with which they were attended. The choice, therefore, is very much limited ; and it miglit still be confined within narrower boimds, with • out doing much injury to the art. Gum sandarac, em- ployed formerly by the Arabs for this purpose, v/as the only matter which seemed likely to ansvv^er the pro- posed end. It is easily prepared, and possesses lustre; but it is attended with the disadvantage of a little dry- ness, which however may be corrected. On account of the preference given to it over other resinous pro- OBSERVATIONS AND PRECEPTS. 213 -ducts, and the eftects it produces, it has been jdistin- guished by the name of veriiioc. Turpentine, and all the modifications of it by the effect of evaporation ; mastic, which has more solidity than sandarac ; gum anima, and gum elemi, gum lac, and copal, compose nearly the catalogue of the matters which are employed for the composition of drying var- nishes, or those made with alcohol. The extreme ' dryness of some of them is corrected by uniting them with others which are less dry, and which still re- tain a portion of essential balsamic oil, such as gum elemi, gum anima, camphor, and turpentine. The same effect is produced also by substituting instead of alcohol a less dry fluid, such as essence of tur- pentine. Industiy, however, which readily takes advantage of every thing that can answer its purpose, and which ex- .cites the desire of the consumer by the variety of the ■objects it presents to him, has found means to subject the art to modifications, by extending the processes in some peculiar circumstances which seem to favour it. A great step was, no doubt, made by giying to the compositions of varnish lustre, transparency, a drying property, and freeing them from al-l colour; but when the grand models exhibited by the Chinese trade were exposed to view, this was not sufficient. The use of 'the European varnishes, in consequence of the nature -of the principles of their composition, was limited to dressing-boxes, and other small articles which served for the decoration of apartments. But the spirit of imitation, which in France more than in any pther P 3 214 TREATISE ON VARNISHES, country excites genius and leads to di^oyeries ; the innate taste for novelty, so prevalent among that na- tion ; that continued fickleness, vi^hich often condemns to oblivion master-pieces about to be succeeded by others ; and that perpetual fluctuation of fashions and inventions, soon became the most active causes which contributed towards the improvement of the arts of luxury. To the same causes we are indebted for the origin of the art of making boxes and toys of papier mâché cor vered with varnish ; that of gilt leather, w^hich the na- tional fickleness seems to have banished to England ; that of coach-making, which laid painting of every kind under contribution. All these arts called in tp their assistance that of the varnisher, and gave to it a very great extent. Hence the discovery of coloured, changing varnishes ; of very durable varnishes, in the composition of which the artist has been able to over^ come the resistance opposed by copal and amber to their usual solvents : hence also the use of resinous colouring substances; such as terra mérita, gum gutt?e, dragon's blood, saffron, sandal wood, anatto and others. Experience has set bounds to the number of the lir quids proper for serving as vehicles in the composition of varnish. The nature of alcohol was suited to light, drying, and colourless compositions, when artists were desirous to correct the strong odour which accompa- nies most varnishes. In examining the essential oils, artists must have first distinguished those wliich on account of their lightness ^ OBSERVATIONS AND PRECEPTS. 215 seemed to exhibit intennediate qualities between alcohol and oils of the greatest consistence : hence the use of essence of turpentine, oil of spike, and oil of lavender. Essence of turpentine gives to varnish more body than alcohol : it might indeed be substituted in all cases for alcohol, if the strong odour it emits were not, to some persons, a cause for rejecting it. For varnishes, however, destined to be applied to ceilings, wainscot* ing, and furniture, it is far superior ; because it renders them equally brilliant, and gives them more durability. During the summer, in particular, this odour is soon destroyed ; and if the artist takes care to employ an alcohol varnish for the last stratum or glazing, there will be no odour at all. The use of essential oil of lavender is more applicable to delicate oil painting than to the art of the varnisher. Though naturally drier, next to essence, than essential oils, it is still too fat and unctuous for varnishes. It may, however, be introduced in small doses in the composition of varnishes made with alcohol and es- sence of turpentine, when it is necessary to lessen their drying quality, or when metallic colom^s are used in '■ the state of pure oxides. The other essential oils known in commerce are ei- ther too dear, or too fat, or too much coloured, to form part of the liquors destined for the solution of resins. The number of the fat or fixed oils useful to the art is as much limited as that of the essential or volatile pils. Oil of white poppy seed, called improperly oil I of pinks, nut oil, and linseed oil, are the only ones found by experience to be fit for the composidon of fat JP 4 216 TREATISE ON VARNISHES. varnishes, when they have undergone preliminary pre- parations vhich deprive them of their unctuous quality, and render them drjûng. Olive oil would answer the purpose of the artist better than nut oil or linseed oil, which are always coloured, if nature, which presents it without much colour, had not communicated to it an unctuous matter, which can be removed only by de- stroying a part of the oil itself. The case is the same with oil of turnips and oil of hemp seed ; and the pro- cesses to which the seeds of the beech tree are subjected before the oil is expressed from them, give it a red co- lour, which renders it unfit for varnish. To judge, then, from the results alone, varnishes, such as they are exhibited by our five genera, are no- thing but solutions of pure resins, or resinous gums, in an appropriate spirituous or oily liquid. Acid liquors, therefore, and alkaline liquors, though the latter have the property of combining with oils and with resins, and of reducing them to the saponaceous state, are in no case endowed with the essential qualities requisite for the composition of varnishes. The eSect of chemical dissolution ought to be distin- guished from that of simple solution. The views of the chemist are very different from those of the composer of varnish. The former employs every mean to facilitate the separation of the principles of bodies, that he may examine their ultimate and peculiar nature, and reduce them ' to their greatest state of simplicity, for the pur- pose of afterv/ards assigning to them that place which they ought to occupy in the order of created substances. The varnisher, on the other hand, endeavours to pre- OBSERVATIONS AND PRECEPTS. 217 serve the integrity of the substance on which he ope- rates. His means are simple ; they act only superfi- cially, by analogy of composition : in a word, they effect merely solutions, the ultimate result of which is confined to extension of the integrant resinous parti- cles. By uniting all the advantages of a mechanical division, as extensive as the object requires, the resi- nous substances subjected to the action of the agents ■w^hich the varnisher employs, lose none of the princi- pal characters which render them proper for the com- position of varnish ; namely, transparency, durability, inflammability, and lustre. If saline, acid, and alkaline liquors, considered as solvents, are incapable of answering the views of the varnisher ; water, a simple substance, without odour and almost without savour, is no less contrary to them. It is the nature of resins to resist its action. Water also has the property of seizing on the alcohol which holds a resin in solution, and of precipitating the latter under the form of a white powder. These effects, which are the more certain as they depend on the particular na- ture of resins, as well as on invariable chemical proper- ties, require the most scrupulous attention on the part of the artist, in regard to the choice of the alcohol he intends to employ in his compositions. The bcst brandy, and even alcohol superior to brandy, if inferior to the •degree of purity indicated in page 60, are unfit for •maldng varnish. The foreign v/ater which these hquors contain forms an obstacle to the solution of resins ; and it precipitates the resinous portion which the spirituous part has been able to dissolve by tlie aid of caloric 218 TREATISE ON VARNISHES. (heat). The solution is at any rate turbid, and very little susceptible sf claniîcation. Even if we should suppose that the spirituous part is still powerful enough, considering the quantity, to effect a sufficient though incomplete solution of the rerin, the varnish resulting from it would be liable to become mealy, and to crack. Tliis infallible result may serve, no doubt, to ex- plain the seventy with which Wadn exclaims against the wasliing of certain resins in water, — a process re- commended by the author of the Parfait Vernkseiir, But however specious the reasons with which he en» deavours to justify his opinion may be, it is no less certain that some resins require to be washed before they can be employed in the composition of varnish. Masdc, sandarac, and even copal itself, which is di- vided into small portions, &c. require previous wash» ing, which is attended witi: no kind of inconvenience. The case would be the same with amber, were not this precaution rendered useless by the proce3S to which it is subjected. These resins are immersed in water after the fine pov/der has been separated from them by a hair sieve. The fragments and resinous tears are then rubbed be? tween the hands to detach the dust, the lighter parts, and the fragments of bark. These separated parts float on the surface ; and, in consequence of their lightness, afford the means of removing them with facility. The washed resin is then spread out on a piece of dry linen cloth, or a hair sieve, which is covered with a sheet of paper ; and the whole is exposed to a current of iiir to dissipate the moisture, Resins washed in this manner. OBSERVATIONS AND PRECEPTS, 219 and well dried, are much fitter for the composition of varnishes than those which have not been subjected to the same operation. . A few more precautions are still necessary in com- posing delicate varnishes, such as those destined fo? valuable paintings and other objects of luxury. It will be proper to separate the pure resinous tears from those "which are stained, and which even are accompanied with portions of the bark of the tree that produced them. On the neccssitij of a reduci'ion in ilic formuuc. Watin seems to be the first author who was fully sen- sible of the necessity of reducing the formulae to a small number of substances. But, notwithstanding the ad- vantage attending this step towards improvement, many things of importance still remain to be done. By pro- secuting, for example, a series of experiments on ths different resinous substances with alcohol of a known (degree of purity, one might form a table of solution, which would be exceedingly useful to the operations of the variiisher ; because by knov/ing the kind of resin about to be treated, and the degree of the purity of his alcohol, he could immediately determine the doses of the substances proper for the intended composition. There are, indeed, some resins more soluble in al- cohol than others. This labour, which would save expense, and perhaps time, is worthy of further re- searches. The most experienced artists will long be reduced to tlje necessity of judging by simple approximation, and 220 TREATISE ON VARNISHES. according to the old formulae, of the relative quantities of the resinous substances destined for the preparation of varnishes ; and, for fear of sacrificing utihty to ceco- nomy, they will continue to employ more matter than the object requires. Of the choice of the matters. The goodness of varnish depends not only on the choice of the soluble matters, but also on the state of the liquors which are to become charged with them. That oily consistence, which is the first character of a » varnish, before it be emploved, deoends on the na- ture and purity of the liquid, and on the extent of its power over the resinous substance. A varnish may be of an inferior quality, though the vehicle is charged with > as much resin as it can take up. The excellence of alco- ■ hoi cannot be determined merely by the sight ; and for this reason I have enlarged on the means best calculated to serve- as a guide to the artist and am.ateur on tiiis point, which is of the utmost importance. A knowledge of the nature of essential volatile and fixed oils is much less difficult to be acquired. A skil- ful eye can easily distinguish the external characters which belong to each of them. Their smell, colour, and a certain degree of connection between the mole- culœ, which communicate to them the oily consistence, are unequivocal signs to determine the artist's choice. To these may be added, in cases of uncertainty, the indications we have given in treating of each of them ^separately. .Such are the guides in which the artist ought to OBSERVATIONS AND PRECEPTS. 221 place confidence in regard to the composition of var- nish : by these alone he can hope to obtain success. But whatever efforts may be made to produce a max- ijiium of solution in the mixture of the matters, he can attain only to a point of saturation proportioned to the nature of the resins, and to the present state df the liquors employed. When people are nice in the choice which they have to make, the principal object is ac- complished. Of the respective doses of the dry and liquid suhiance,f employed in the composition of varnish. The art, however, is still imperfect, if the practical part be confined merely to the choice of the substances. Too great a number of them, as well as too great doses, embarrass the artist in the account which he ought to give to himself of the expected results. Every art founded on a collection of formula; attains to suc- cess only by a very slow progress. To simplify the formulas, great knowledge and long experience are ne- cessary. One m.ust be able to rise above difficultés, and even criticism, in circumstances when the formula; compel him to follow habit, or when habit gives weight to formulae. * - By simplifying the compositions, and reducing them to a small number of substances, it was easier to follow the effects, and to discover the causes of them : re- searches then became less painful and less expensive. A great deal has been done in this respect, and for the most part in a wrong direction ; but as long as artists were the only guides and regulators, the success was 222 TREATISE ON VÀRNI5KES* - very doubtful. If the celebrated aitist whom I have often quoted was able, by his judicious obseiTations, to make people sensible of the utility and even the necessity of reformation, and of reducing the formulae to a small number of substances, he did not place the art beyond the need of further ad\ice : more was necessary to be done, by reducing the number of matters, and redu* eino; also the doses* It is well ascertained, that the best alcohol cannot become charged with more than a third of its weight of the resinous substance, even when the most soluble is chosen. A temperature capable of bringing it to a state of ebullition may give more extent to the solu- tion ; but cooling soon restores the equilibrium of sa- turation. The varnish soon becomes turbid, and the resinous matter which rem?iins in excess at that point of saturation is precipitated, and, under the form of a crystallization, lines the interior sides of the vessel. Some of the fbrmulse given in the best works still prescribe, in dry matters, a weight equal to tv/o-thirds of that of the excipient. The doses indicated in th& diftei'ent genera of my varnishes are more than sufficient for the prescribed quantides of liquid ; since there still remains a considerable part whichr^scapes its action. In all cases, the process is less enibarrassing, and m.ore secure from those accidents which are the consequence of a mixture too much charged, and which forms 3 mass ; and is certainly less expensive. OBSERVATIONS AND PRECEPTS. 22S Of the effects of mechcinical division on rcsi}is ivJdck oppose the greatest resistance to solution. We are acquainted with some resins, , such as gum sandarac, copal, &c. which seem to resist more than others the action of the dissolving liquors. Copal, in particular, exhibits this character, when the artist en- deavours to dissolve it in alcohol or essence of turpen- tine. This difficulty, however, may be overcome, with greater or less ease, by diminishing the doses of these substances. Simple mechanical division, carried as far as possible, and the mixture of a substance which rea- dily suffers iiself to be attacked, such as mastic and white incense, facilitate solution in a degree which could not be expected, if the two substances were treated separately, and in the usual manner. Experi- ence alone can determine in regard to this point. We have already seen that camphor produces a great effect as an intermediate substance, but the doses must not be carried to excess. Of the use of pounded glass. When one is obliged to operate on a certain mass of matters, the form of the vessel employed is a m.atter of some importance. It is often different from what it ought to be. Its capacity is not always suited to the quantity it is destined to contain. In this case, the first impression of the calonc (heat) tends to agglomerate into one or more masses the whole resinous part àe^ stined to form the varnish, and by these means thwarts 224 Treatise on varnishes. the intention of the artist, who employs his utmost care to favour and maintain that state of division v/hich is so well calculated to promote speedy solution. When one is contented with simple stirring, which may op- pose the union of the resinous parts, and even when broad-bottomed vessels are employed, this object can- not be accomplished. But the consequences of this inconvenience may be greatly diminished by employing a determinate quantity of pounded white glass Vv'hich has been sifted through a hair sieve. It is mixed with the pulverized matter before it is united cold with the alcohol and the essence ; and the division of the parts may still be assisted by stirring it \^ ith a rod of vvhite wood, rounded at the extremity. By this simple me- chanism the matter is kept in that state of divison ne- cessary for the promptitude and perfection of the solu- tion ; and the tumefaction of the liquid, a circumstance -,; much to be dreaded in the process of making varnishes, T is prevented. Besides, the weight of the glass, wliich is greater than that of resins, makes it fall to the bot- tom of the vessel, where it presents an obstacle to the ' adhesion of the softened matters. The use of a balneum miaricC is preferable to that of' a sand bath in operations of this kind, because the ^ temperature of the former has a certain fixed point of elevation, v» hich it is impossible not to exceed with a sand bath ; and in this case there will be great danger of communicating to the varnish a foreign colour, ari- 'sing from the alteration which the resins experience from too great heat. After the operation, mere or lest ÔBSËRVAtlOKS AND PRECEPTS. 225 tàf the resinous substance remains mixed \\'ith the glass. This residuum is reserved for the composition of com* mon varnishes, which may be treated over an open firç. Of clarification. When the water of the balneum marise has been kept in a state of ebullition for a full hour and a half, if the matter of the composition amounts to no more than forty-eight or fifty ounces, there is reason to be- lieve that the solution of the resins is complete. The circular motion with the stick must, however, be still maintained for half an hour after the vessel has been removed from the balneum maris. The whole is then left at rest, to give the undissolved matter time to be precipitated. Next day the clear liquor is decanted^ and then put into proper vessels. Some artists strain, the varnish, still V\^arm, through a piece of linen cloth, and then leave it at rest for a few days to clarify. In both cases, when it is supposed that the excipient is completely saturated with resin, it must be left for some days at rest. The effect of a high temperature is to dispose the vehicle to become charged with a greater quantity of the substances than it can retain when cold. I'his portion in excess is then precipitate-d, either in whole or in part, according to the season = When tlie precipitation is pretty extensive^ small lum.ps of resin are formed around the Vvj^-sel. This abandoned resin often affects a very distinct order of crystallization. Somefimes the precipitation is not so sensible: the var- nish remains a long time turbid, in consequence of the separation of a portion of resin, which continues in, a Q 226 TREATISE ON VARNISHES. State of suspension. When this happens to be the case, there are two methods of giving to varnish all that Hm- pidity which it is deprived of by the portion of sus- pended resin: add to it a warm excipient; this addition dilutes the varnish a little : or it may be filtered through cotton. OfJUtration througli cotton. This operation is simple. Arrange several funnels in as many appropriate receivers (çec Plate V.Jig. 4.), and place in the pipe of each funnel a small ball of carded cotton, about an inch in thickness; press this ball towards the point of the cone, to squeeze the cot- ton together, and place over it a small plate of lead pierced with several holes. Fill the funnels with var- nish, and lay over the vessel a glass cover, or a few sheets of paper. The varnish which passes through the cotton is at first not very limpid; but when the cotton has imbibed a sufficient quantity the liquor passes very clear. The first portion of filtered varnish is then poured again into the funnels; and the filtra- tion being continued, the result will be a very bright varnish, which is put into clean bottles. This filtra- tion, which is soon performed, is indispensably neces- sary for every kind of varnish destined to be applied to delicate articles, such .is cut-paper works, valuable furniture, paintings^ phlloso^; hical ins-;umen*:s, he. Care must be taken to keep the funnels full, and particularly not to leave the cotton uncovered; tise it would be- come incrusteJ with a stratum of dry varnish, which iTvight impede any further filtration. OBSERVATIONS AND PRECEPTS. 22? When the whole is filtered, it will be proper to wash all the vessels with alcohol or warm essence of turpen- tine, according to the nature of the excipient. The product of the washing is kept in reserve till a new -quantity of varnish is made. On the preparation of varnishes in open vessels, and the precautions they require. The varnishes, of which we have here given the dif- ferent formulas, are reserved only for articles of a cer- tain value, and require particular care in the prepara- tion. Those who prepare varnishes make other com- positions which they destine, in general, for wain- scoting, ceilings, common furniture, &c. Some pre- pare them in open vessels, and in the open air, in con- sequence of the accidents which sometimes take place when alembics are employed. It is indeed much easier to save from inflammation a matter which is seen to rise, than one inclosed in metallic vessels, where its tumefaction is not observed. This labour on the first view appears to be easy. It however requires practice and perseverance to obtain the required result without any accident, and to quiet the well-grounded fears which those in the neighbour- hood may conceive of the danger likely to arise from this process. It will be proper to perform this opera- tion in the day-time, and in the middle of a spacious court or garden. The vessel ought to be furnished with high edges, that the ton-ent of vapours which escapes may not communicate with the undulating flame which often extends beyond the fire-place. Gare Q 2 228 TREATISE ON VARNISHES, also must be taken to dispose the vessel in the furnace in such a manner as to cover the fire entirely, and to prevent any portions of the varnish which may be thrown up by a false movement of the spatula fromfall- ing into it. The precautions to be observed, however, are not confined to the manipulations usual on such occasions. When the solution is completed, it is customary to de- posit the varnish in an apartment or workshop to cool, and also to give it time to clarify. This apartment then becomes filled with vaporific emanations, to which fire may be communicated by an inflamed body. These vapours are the more dangerous as they extend them.- selves to a great distance, even beyond the apartment, so that the contact of a hghted taper m.ay occasion an explosion which will carry the flame to the reservoir of the evaporating substance. I have witnessed, along with a great number of auditors, a similar efi'ect, w hich is often accompanied with very alarming circumstances. Great care then must be taken not to enter with a candle into an apartment which may contain such an inexhaustible source of vapours, so highly inflam- mable. If the method of making varnish in open vessels seems to hold forth some advantages, it is not free from inconveniences. The artist, indeed, may carr)'^ on his operation in more security. He can easily prevent the iumefaction of the matter, and consequently ihose acci-. dents which result from it. By means of continued mo- tion he ma}' easily afford means of escape to the vapours^ in a state of expansion; and may rcnevv- the surfaces of OBSERVATIONS AND PRECEPTS. 229 the resin which touch the bottom of the vessel, and wliich, by being altered, might colour the varnish. This is the favourable side of the method j but I shall exhibit also the reverse. This process occasions a very great loss of alcohol or of essence, in consequence of the vapours which rise from the mass. These vapours are furnished only by the more subtile part, or th-it fittest for the solution of resins, and which contributes most to the excellence of the varnish, to its pliableness and lustre. The physical effect which the constant vapour of the essence may produce on the nerves of the artist exposed to it, if he is of a weak constitution, is not a matter of indiffe- rence; since it sometimes occasions a slate of asphyxia. However great may be the precautions taken in pro- cesses of this kind, if they have not always been suffi- cient to prevent serious accidents, this is sufficient to justify the fears of individuals who reside in the neigh- bourhood of the varnisher, and to excite the vigilance of the police to confine to the outskirts of cities all establishments of this kind. Geneva never reflects without terror on the fires which have taken place on different occasions, and on the misfortunes which have thence resulted to individuals. I consider it therefore as my duty, since I am treating on varnishes, to en- deavour to find in the form of the vessels and appa- ratus means proper for obliterating the painful remem- brance of these public calamities, or at least of render- ing them less frequent. Q 3 230 TREATISE ON VARNISHES. Descriptioii of an alembic proper Jor the preparation ofvarnish. The common form of an alembic will not admit us to hope that the solution of resins can be rendered complete, and that those accidents which arise from agglomeration of the resins, and particularly from an accumulation of the vapour which in that agglomera- tion finds a resistance which it endeavours to overcome, can at the same time be prevented. The matters then become tumefied, raise up the capital, spread with an explosion to the fire, often even to the artist, and in this manner occasion conflagrations. The smallest ac- cident which results from the use of a common alembic is the coloration of the varnish, in consequence of an alteration which the resins experience, by adhering to the bottom of the vessel. These effects v.'ould not take place if the form and construction of the alembic af- forded the artist the means of maintaining a circular motion, which would cîiange the points of contact of the inclosed matters; and if, instead of fire being ap- plied to these matters in an immediate manner, it were applied mediately, as is the case when a balneum mariae is employed. These two conditions appear to me to be answered by the construction of the apparatus here described (jsee Plate V.Ji^. 1.). It is an alembic and a balneum marias with a re- frigerator. It consists, 1st, of a common alembic; 2d, a balneum marias ; 3d, a capital ; 4th, another separate piece which performs the office of a refrige- OBSERVATIONS AND PRECEPTS. -J^yl "ïator, and which is adapted to the alembic at the mo- ment of the operation. The alembic «, fig. 1 , is of copper, and made in the usual form ; the aperture h terminates in a tube, de- stined to receive the pipe of a funnel, for the purpose of affording an escape to the incoercible vapours which arise from the water in a state of ebullition. This piece then serves as a receptacle for the water of the bal- neum mariae. To this alembic is adapted the balneum maiise c, made either of tin or of copper; it has the same form as that of the common alembics, and serves to contain the substances which are to compose the varnish. The bottom of it is horizontal, perfectly jflat, and about an •inch less in diameter than the mouth. The upper part of this piece is strengthened by a circular band, which serves to cover the joining where the capital is fitted to 'the alembic. To save expense, this circular band may • be made of lead. The diameter of the capital d, at the base, is propor- tioned to that of the balneum mariae, in such a manner "as to join with the circular band. This piece terminates in a dome, which at the summit has a pipe or aper- ture e, half an inch in diameter. A metallic bar f, fig. 2, soldered at the two extremities, and pierced with a hole corresponding in a vertical direction with the aperture e, and having the same diameter, passes? through the middle of the lower end of the capital. These two apertures are destined to maintain, in an exact vertical position, a small rod of iron ^, connected ■ on the outside with the handle A, which is of wood, Q 4 232 TREATISE ON VARNISHES. and moveable. The lower part of this rod, which is continued to the bottom of the balneum maricC, is furnished with an iron cross /, cut into teeth, while its two extremities are raised up, as seen at k : the lower part represents an inverted x« See Jig. 2 a)id 3. In the upper part of the capital d, is formed a second aperture /, which terminates also in a tube, capable of containing a cork stopper. This aperture facilitates the re-introduction of the parts of the liquid obtained by distillation. A conducting tube 7??, the diameter of which is twice as large as that of the beak of common alembics, tak- ing into account their capacity, proceeds from one of the sides of the alembic. It is by this canal, which is made of a sufficient length, and which is of an equal diameter throughout, that the refrigerator n is con- nected with the alembic. The refrigerator h is constructed in such a manner as to afford a free passage to those matters which might become tumefied, or to condense the vapours which escape from the interior part of the vessel. Both these ends may be accomplished by means of a plain wooden box, well joined together, pf an oblong %ure, through which a tube o, made of copper, tin, or tin-plate, passes in an oblique direction. This tube, throughout its whole length, is of the same diameter as that Vv^hich proceeds from the capital, and is only a continuation of it. When ysed^ the box or trough is filled with cold water. The extremity of this tube terminates in a bent part, py of the .san>e djarneter as the rest, Under this pajt OBSERVATIONS AND PRECEPTS. 233 is placed the vessel q, destined to receive the product of the condensed vapours, and, in case of need, th,e matters which may be raised in the interior part of the apparatus, by the effect of caloric (the he^it), or in consequence of the consistence which the liquid acquires in this kind of operation, or by the negligence of the artist to stir it during the process. This alembic is placed on a portable furnace of burnt clay r, or on a fixed furnace constructed of bricks or other materials: it oucht not to be too hip-h, lest the artist should be incommoded in managing the handle h. It has the same form as other furnaces, and is only modified in the manner of placing the chimneys or vent holes, which ought to be disposed in such a m.anner as to be sheltered from the contact of the in- flammable matters, that may fall on the edge of the furnace. This end may be obtained by making the c^Dcrtures of these chimneys issue through the sides of the furnace, at the distance of two or three inches from the upper edge, and forming over each of them a small projection. The same purpose will be answered by placing on a common furnace a ring, the edge of which, s, extends about an inch beyond the exterior - diameter of the furnace. This ring supports the alem- bic. It may be made of burnt clay, or a kind of soft Stone which is very common jn the neighbourhood of Geneva. Remarks. Distillation is a process so common that any one may conduct it. I might, therefore, pass it over in silence j but when applied to the present object it re- 234 . TREATISE ON VARNISHF.S. ■ , « quires, on fhe part of the artist, more attention and more care than in ordinary cases. Nothing must be neglected, if one is desirous of avoiding all reproach in case any disagreeable event should take place. The following then is the conduct I should observée in the preparation of varnish, according to the method here proposed : — When the matters are put into the balneum mariai, cover that part with its capital, and cause the agitator to touch the bottom of it. Lute the two parts exactly, at the place where they are united, with bands of paper and flour paste. Then make a few turns with the handle before heat is applied, to divide the matter ; keep the tube b of the alembic open; and shut closely the tube /. Adapt the refrigerator to the alembic, and cement a few slips of paper over the place where the two vessels are joined ; introduce into the alembic such a quantity of water that the body of the balneum marise may be half immersed in it, and then kindle the fire. It is of some importance to move the agitator, at the moment when the fire is kindled. If this precaution be neglected, the resinous matter forms itself into a rnass, and in that state opposes more resistance to the action of the vehicle. Continue the rotary motion during the whole process, but without too much pre- cipitation. The solution to be complete requires only an hour or an hour and a half, reckoning from the moment when the water begins th boil. If the level of the water employed be fixed at half the interior height of the balneuui maria', or a little Il.T. 234. .^ {"y/^ To fiontpane 234. .^.../.. /n> ■ /Ay /> /r/ff./ 'f rf/'c '/' ''/ f e( '/ /fy(->/' ■ OBSERVATIONS AND PRECEPTS. 235 higher, the inconveniences attending too great a quan- tity of that liquid will be avoided. By the force of ebullitioxi part of it is thrown up through the tube, and often incommodes the artist ; but there is still a greater inconvenience. When the balneum mariae is thus completely surrounded with a boihng liquid, the vapour of which has not the means of free escape, the alcohol, which becomes so much more charged with caloric as it acquires greater density, in the ratio of its union with the resinous part, tumefies, and escapes as it boils up through the apertures which it meets with ; and if it should unfortunately experience the least obstacle to its forced emission, it would burst the vessel, and inundate the artist with matters, which being soon inflamed by their vapours coming into con- tact with those that fall into the fire, would expose him to the danger of losing his life amidst the most excruciating pain, as has frequently been the case. If the kind of alembic here described were destined for various other uses, hke those in chemical laborato- ries, there might be reason to apprehend the effects of some negligence in regard to the care that ought to be taken to keep the tube h open, when the distillation is carried on with a balneum marise ; and to close it with a stopper when distilling with an open fire, that is to say, without a balneum mariœ. For the present pur- pose there is never need of employing this alembic oa an open fire : consequently the artist is not undeT the necessity of shutting the tube, and by these means he avoids those accidents already mentioned. In the con^ 2S6 TREATISE ON \'ARNISHES. tTdry case, the vapours of the boiling wat^r being accu- mulated, and finding no way of escape, would soon burst the apparatus, or would exercise a still greater action on the matters in the bath than if the alembic were filled with boiling water. In proportion as the calonc (heat) acts on the sub- stances inclosed in the balrjeum marias, it unites itself to portions of the vehicle, which it reduces to vapours. A part of these vapours are condensed in the inside of the capital, and fail back on the mai:ter. Another part, escaping from the interior of the apparatus, is con- densed in the lateral tube, which traverses the refrige- rator, and proceeds in a liquid form into the receiver. This product is composed of the most volatile and the most subtile part of the liquid employed for the solution. This loss, if extended, diminishes in a considerable degree the energy of the alcohol not volatilized : in a word, the quality of the varnish would suffer by it, if the product of the distillation, when a certain quantity is collected, were not restored to the mass. The aper- ture / is then opened, and a funnel of tin plate is adapted to it, through v^rhich the liquor that has escaped in the form of vapours is restored to the varnish. The cork stopper is again put in its place ; and the circular motion of the agitator is continued. I think it need» le$s to recommend the utmost care that no portion of the liquid introduced may be suffered to fall into the furnace : artists must be v/ell aware of the conse- ijuenccG. Several compositions require the use of turpentine ; OBSERVATIONS AND PRECEPTS. 237 but it must not be put into the bath at the same time as the resins ; because, being more disposed by its liquid nature than dry^ resins to combine Avith the alcohol, it would occupy the whole of the latter, which would not exercise on the other substances the energy requisite. The mixture of it, therefore, must be deferred till towards the end. It may be easily added, by melting it over a «low fire, and introducing it in the same manner as the product of the distillation. A portion of the disdlled al- cohol is reserved for washins; the vessel which contained o the turpentine, and the funnel which has been em- ployed. When it is judged that the solution of the resinous matters is finished, the whole of the fire is removed from the furnace, and the circular motion of the agi- tator is continued for half an hour, leaving some inter- vals of rest. When the apparatus has in some mea- sure cooled, a sponge dipped in water is drawn over the pieces of paper v/hich cover the joints ; and they are then removed as well as the capital, which has been separated from the refrigerator. The varnish I being then decanted into proper vessels, it may be strained through a piece of dr\ linen, or filtered through cotton. This operation ought to be performed in the day time, lest the inflammable vapours which may escape should be set on lire by ihe candles. The artist, who undertakes this labour with the precautions I have pointed out, v/iil always be secure from those accidents which, in this process, are attended with so dreadful effects. 2SS TREATISE ON VARNISHES. It ought always to be remembered that alcoholic var- nishes never should be prepared in larger quantities than may be required for immediate use ; because they do not long retain those qualities which render them valu- able. When too long kept, they become yellow and greasy. In this respect they are very different from oil varnishes, which improve by time. C 239 ] CHAPTER V. Olservations 07i the uifluevce wliich the solar light has to ren- der essence of turpcfitine proper for the solution of copal, so as to compose a durable and colourless varnish^. Eve ry art which consists only in the employment of a certain number of bodies has, no doubt, fixed bounda- ries, and becomes more susceptible of modifications in its processes than of hnportant discoveries. This may be applied in the utmost strictness to the art of the var- Disher. It consists only in the solution of certain re- sinous substances in spirituous and oily liquors, which however require some particular preparations. It was not till within these few years that this art was reduced to certain principles capable of serving the artist as a sure guide in conducting his operations. In this respect it has undergone ^ sort of revolution, for which it is indebted only to that part of practical che- mistry which has been brought to a level with the com- prehension of artists. The necessity of gratifying the. general taste in evei*y thing that regarded the decora- tion and elegance of apartments, furniture, &c. was the, first cause which tended to produce it ; and simple compositions were substituted in the room of those re- fcipes with which works that treated on the secrets of jthe arts abounded. Each solution has its particular * This forms the substance of a paper presented in 1788 to the isociety formed at Geneva for the encouragement of the arts, agri- buiture, and commerce. 240 TREATISE ON VAïtNISHEâ. laws, depending on the nature of the bodies, and of the liquors which seem to be suited to them. By reducing this art, therefore, to a regular method, the extension of it has been rendered more certain, or at least more pro- bable ; and each discovery, supposing that any can be made, will find a place marked out for it in the series of formulae, the distinguishing characters of which lead to a methodical division, rendered necessary by the- present state of our knowledge* It was under this point of view that Watin published, in 1772, his Art of making and applying Varnishes. Of the matters employed for the composition of var- nishes, copal and amber are reser\'ed for those which - require fat oils as their vehicle. At any rate, these two substances have hitherto been considered as insoluble m alcohol and in essence of turpentine*. The hard- ness, purity, and transparence of copal have rendered this kind of resin an object of many researches. Vari-' ÔUS methods have been tried to dissolve it, but without apparent success* The use of turpentine in the room of alcohol gave only uncertain results. Some chemists assert that they have made varnish in this manner ; others say it is impossible. Artists who practise the art of varnishing declare in favour of the latter opi- nion. This state of uncertainly, instead of making me ab- stain from i*esearches on lliis subject, has, on the con- trarv, rendered it more interesting to me, and more worthy of examination. The advantage which might J result from the discovery of some process capable of communicating to varnish the intrinsic qualities of this Kl'I'JiCTS or LIGHT Ols^ ESSENCE OF TURPENTINE. 241 -dry matter, held for.th a stimulus which it was difficult to resist. I therefore undertook a series of experi- ments on it, which form the subject of this chapter. An artist, no doubt, would not have carried it to the same extent ; but it was necessary for me to exhibit it under another point of view than a mere formula, since the iletail of the results necessarily leads to physical re- searches absolutely foreign to the art of the varnisher. I announced in the ardcle which treats of copal : 1 st, that this substance is partly soluble in alcohol ; 2d, that it may be endrely dissolved in it by means of an inter- mediate substance ; 3d, that ether generally effects a solution of it, and in pretty large doses, according to the state of the ether, and the particulai* nature of the copal ; 4th, that essence has the same property, but with certain limitations, which seem to depend on a particular state of density. - The solution of copal in alcohol was not sufficiently complete to affiDrd any hopes of a satisfactory result. That which takes place by means of an intermediate substance was attended with an inconvenience, which • there was reason to think might be obviated in the so- ludon that seemed possible by essence. The latter vehicle exhibited in its physical properties characters -nearly «imilar to those of alcohol. Like that fluid it is exceedinglv limpid, liquid, and colourless. It possesses -a mean density between that of alcohol and the density ■ of essential oils : in this even it seemed to have with - copal an analogy more striking, and which might lead - to effects of solution that could not be expected from -alcohol. 1 confided, therefore, with the more reason R '242 TREATISE ON VARNISHED. in the strength of this analogy, as the particular nature of the essence permitted me to increase or to lessen at pleasure its common density. It was on these bases that I founded my researches. The first did not afford me complete satisfaction. I re- newed my experiments ; but the results still seemed to be very imperfect. I sometimes found that the esssence which had exercised a partial action on the copal pro- duced no effect at a more elevated temperature. In other circumstances, the same liquid which refused to unite with copal laid hold of it with eagerness after an interval of some weeks. At other times, mixtures of copal and essence kept in a state of infusion for twenty- four hours v/ithout exhibiting any apparent solution, required only a maceration of some m.onths to display all the characters of a complete solution of this kind, and at length of a beautiful varnish. I observed also, that of a certain number of matrasses which contained mixtures of copal and of essence, in doses perfectly equal, and which experienced no otlier difference but that arising from their posidon in different parts of the labr>ratory, several, some months after, exhi- bited all the signs of a complete solution, \^'hile others «howed no indicadons of it. I saw some also in Vvhich the copal remained under the form of lumps, covere^ with an amber-coloured liquor. i evidently foresaw, that to clear up so many doubts, and to discover the truth amidst so much contradiction, a great many ejqperiment.^ would still be necessary. ' I had, || however, reason to think that the solution of the copal \M^ dejenled on a certain stat ." of the constituent principles m^^ ÏFFECTS OF LIGHT ON ESSENCE OF TURPENTINE. 243'' of the essence. I was then sensible of the necessity of mixing it with copal possessed of diiierent degrees of tenuity or density, which might be communicated to it by art ; and I expected I should be able to find that point best suited to the solution of this kind of resin, without communicating colour to the varnish. The following experiments were undertaken in con-' sequence of this new plan of research ; but I must ob- serve that I always made use of the same copal, in the state of powder, and of the same essence of turpentine. 1st. Liquors susceptible of volatilization at a certain temperature always exhibit in their ascent products the more attenuated, as they have required less caloric" (heat), and consequently less time to be volatilized. Such is the case with alcohol, the first product of which is more subtle than the succeeding, • Certain light essential oils are subject to the same law. By applying to the rectification of essential oil of turpentine the method empl-oyed for the rectifica- tion of spirituous liquors, dividing the products into' several portions, I had reason to believe, that those which passed over the last would be less fluid, as well as less ethereous, than the first ; and that the difference observed in their respective densities would follow a gradual progress, according to the different periods of fhe distillation. As it was necessary that this labour should be rendered so easy as to be within the reach of artists, I was obliged to adopt a less complex process. I therefore divided into six equal portions, by means of a tubulated balloon, the product of seventy-two ounces of essence of turpentine, disdlled in a balneuro. k2 i?44 TREATISE ON VARNISHES* marias, according to the method described in Chap. IL Each of these portions was put into a numbered flask^ and the sixth flask was destined to receive the residuum of the distillation. It was necessary that I should first examine the spe- cific gravity of each of these six portions, and compare them in regard to their power over the copal ; but I was prevented by a tedious illness, and other occupa^ tions of a more urgent nature, which left me no time for chemical researches. I, however, took the precau- tion to close the flasks exactly, and to shelter them from the light by shutting them up in a closet, where they remained nine months. 2d. At the end of that period I found four of the flasks covered in the inside with beautiful crystalliza- tioBs, consisting of prisms grouped together in a diver- gent form. No. 1. exhibited small needles, which crossed each other in every direction. They were transparent, and had a silky appearance. A great part of these crystals covered the bottom of the vessel ; some also adhered to the sides, below and above the level of the essence. The most apparent of these crystals were 5-^ lines in length. No. 2. presented two pretty large groups of prisma- ric ciystals, diverging from a common centre. The largest were six lines, or half an inch, in length- No. 3, showed only some rudiments of crystals, scat- tered over the ^ides of the glass above the level of the essence. No. 4., besides small crystals adhering for the mo^ TirECTS OF LIGHT ON ESSEXCE OF TURPENTINE. 245 part to the sides of the glass, above the liquor, con- tained three J^eautiful groups, in part divergent, and < rossing each other different ways : most of these prisms were half an inch in length. No. 5. presented no crystals but at the botto;m of the vessel. They were, however, so numerous that they covered the raised part of the bottom. Maity of these prisms were insulated ; others were disposed in diver- gent radii, in such a manner that one prism ser\^ed as a base to four or five others, which adhered to it only in one very acute point. The largest did not exceed three lines. No. 6., which contained only the reddmim of the distillation, and which had a strong amber colour, ex- hibited no appearance of crystallization. If these crystals really varied in rega'-d to their di- mensions, the case was not the same in regard to their form. In aM of them I observed the quadrangular, flatted prism, with two large and two small faces. They were prismatic lamin?e truncated horizontally. In some ciystals the extremities were continued to a point. Sd. These crystals, when taken from the essence, and exposed on brown paper to dry, have very little solidity. They dissolve in alcohol and in water, the limpidity of which they destroy. There is separated -from them a little oil, which floats on the surface. This effect arises, no doubt, in a great measure from the portion of essence with which they are still en- veloped. The solution of this salt exercises an action on blue vegetable colours^ and makes them become red. It di4 R 3 246 TREATISE ON VARNISHES, not appear to me to exert much energy on a solution of carbonate of potash. The vehicle in which the salt , was dissolved weakened its strength. This solution, when presented to caustic potash, becomes saponaceous, and small threads are formed in it. This concrete, volatile salt almost always appears in an oil exposed to the influence of the light, though . no cr)'stals are produced by cooling, or by its remain- ing in a cold place. In this case, it is more disposed to ■fix itself above the level of the oil than below it. The process which accelerates its formation consists in mak- ing the essence pass over the upper and uncovered • parts of the vessel. Evaporation has a considerable share in the production of the phenomenon. But, if a matrass half filled with essence, and which already exhibits cr)'Stals in the part not occupied by the oil, as well as in the bottom, br exposed to the ardent sun, the former will almost always remain, and often even increase, while those covered by the liquid dissolve into a kind of reddish water, which falls to the bottom of the vessel. This water is exceedingly acid. It effer- vesces with alkalies, renders blue vegetable colours suddenly red, and impresses on the tongue a caustic and burning savour. The salt which produces it ap- pears to be of a benzoic nature : a kind of crystalHzed .acid soap. The concrete, volatile, acid salt of the essence of turpentine, covered by the fluid which produced it, is susceptible then, in this pardcular case, of dissolving jn water, in consequence of the same cause vvhicji f.n-LCTS or LIGHT ON ESSENCE OF TURPENTINE. 247 makes it appear on the free sides of the vessel. A tem- perature somewhat higher than that of the atmosphere would be sumcient to separate the acid from the oil, which ser\ es as a basis to the crystals. I do not know whetlier these effects would be constant. I am, how- ever, inclined to believe they would ; as I consider them to depend on the reaction which the light favours between the acid principle and the oily body. They are those I observed on the six bottles I had exposed to the sun ; and I have since observed them in a great num- ber of similar cases. This phgenomenon of liquefaction, ■ however, was observed in crystals which had been formed in the course of twenty-four hours above the level of the oil, and under the oil ; and which I had kept some time in the cellar, in vessels closely shut : but the crystals which v/ere dry experienced the same fate as those immersed*. ^- The Pharmacopcria of Charas, p. 107 and lOS, speaks of a vo- latile salt of tuqjenline ; but, according to the old language of die- ■ mistry, it exhibits only as it were a substance concealed in oil, essen- tial to its nature, and to which the author ascribes all the effects of essential oil on tlie bladder. " The volatile salt," says he, " which is concealed in the acid part of the ethereous spirit, and in the oils lirst distilled, contributes greatly to the virtues ascribed to them, the principal of which are, that they open the urinar}' con- duits, moderate the heat of tliem, prevent tlie formation of cal- culi, &c. &c." In this passage we see nothing that indicates the existence of an essential salt developed and crystallizable. ï'oultier de la Salle enlarges a good deal on the distillation of ' ethereous oil of turpentine and balsam of turpentine, in the learned .. obsqn'ations with which he has enriched the Translation of the Pharmacopoeia b()7idinens}s. lie admits tliere an acid phlegm, as R 4 248 TREATISE ON VARNISHES. I did not extend any further my researches on the nature of this salt, the acid of which appears to me to approach very near to the nature of the benzoic acid ; but, in the mean tim.e, it may be defined an oily, acid salt, analogous to that extracted from balsams. The volatile salt of amber, perhaps, might be traced back to a similar origin ; and if its chemical properties seem to be different, tliis may be ascribed to the influence of the mineral vapours, which for so many ages have been exercising an action on the resinous matter which con- stitutes amber. These vapours must necessarily have changed its principles, or brought them gradually to that point of modification which removes amber go far from the nature of our common resins, and even from that of copal, which seems to approach it most, as I have since shown; I was perfectly sensible that it would be of great im- portance to canry to a greater extent these researches on an object so nearly connected with the natural his- toi'y of fossil resins. I mjght have attempted a greater number of experiments to discover the peculiar nature in the distHlation of resins and balsams; but he makes no mention of a Volatile, acid essential salt. If tliis concrete salt had been observed, tliat valuable repositoiy of the Stalilean chemistry would have noticed its existence. When essence is distilled with a sand bath, if the retort be revered with a dome of baked clay to facilitate the expulsion of the vapours which circulate above the boiling liquid, this apparatus contribates to the speedy appearance of this concrete salt, because there is less reaction from the fire on the principles of tlie oil 'ï'w'ènty-four hourâ after the distillation of two pounds of esscnco I was able to extract TJ grains of this concrete salt. 3 EFFECTS OF MGHT OH ESSENCE OF TURPENTINE. 249 of that salt, and to trace it in its different combinations with difierent bases; but as this part is absolutely foreign to the arts, I thought proper to confine myself to a plain account of the phccnomena exhibited in the course of some experiments, the only obiect of which was the solution of conal in es:sence of turpentine. 4th. It appeared necessary to examine what might be the specific gravity of each of the numbered divi- sions of the oil, before J. applied them, to the copal. I had only Romberg's hydrometer and common balances at that time in my possession ; and I confess that these instruments would not bear a strict comparison with others since constructed for me by one of our artists, well known to philosophers by his talents and inge-r nuity. They were, however, suiTicient to convince me that the degree of the tenuity of my specimens did not follow a progression corresponding to the period of their appearance in the course of the distillation. No. 4. had a specific gravity less than No. 1., and the latter was some grains heavier than the common essential oil of the shops, which had been employed for the distil- lation. The one last mentioned was to distilled water nearly as seven to eight. I shall enter hereafter into more circum.stantial details respecting the specific gra^ vity of similar producdons. 5th. This variety in the specific gravity of these dif- ferent specimens of the same oil would not have stopped liie, had these specimens been fit for that kind of solu. lion which v.as the principal object of my researches^ but none of them could take up such a quantity of copaî as was sufficient to make a varr.ish. The reacLer may ^50 TREATISE ON VARNISHES. yddge of their degree of energy by the account of tiie following comparative experiments which were all made in small new matrasses. Ten grains of pw-verized copal were mixed with an ounce of each of these separate oils. Each matrass, immei-sed in warm water, was kept for half an hour in a state of circular motion; but under the present circumstances, this process, which in other cases was sufficient to dissolve 72 grains of copal in little more than an ounce of essence, "was not capable of carrying the solution, in each of these oils, to more than ten gi^ains. No. I. approached nearest to the limpid state, which announces a commencement of solution ; the precipitate in it was less abundant. The other small matrasses, distinguished by a number corresponding to that of the flask from which the oil had been taken, showed the copal collected at the bottom in the form of a white glutinous mass, tough and tenacious. This toughness and tenacity, which are not commonly ob- served in the parts of copal treated with a lighter and mare cthereous essence, indicated however that these oils were disposed to operate the required so-, lution, Under this supposition, and in consequence of ob- servations made in former trials, I closed exactly the matrasses, as well as the bottles containing the speci- mens, and left them for a year on one of the shelves in my hiboratoi-y. Their siruation \a"-is such, in regard to the solar light, that they received it only by reflec- tion during four or five months of the year. I waited a lonj]j time, and my expectations wwe not deceived. 4 EFFECTS OF LIGHT ON ESSENCE OF TURPENTINE. 251 6th. At the end of the year I examined the smail matrasses, and the oils corresponding to them. The results exhibited by the former were as follow : No. 1. was limpid, and showed neither residuum nor colour. A drop of water occupied the bottom. I mixed with it ten grains of copal, after having exposed the matrass to a temperature of from 122*^ to l^é'' of Fahrenheit. The copal disappeared in a few moments : forty grains introduced at intervals, in doses of ten grains, disappeared in like manner. The varnish thence resulting had a beautiful consistence, and showed, by its nebulous tint, that the point of saturation had been observed. IMotion alone, without the aid of heat, was sufficient to complete the solution in a qviarter of an hour. Here then, by adding more copal to the first ten grains, I had fifty grains of that ir.atter held in perfect solution in an ounce of essence. No. 2. was of a slight amber colour ; the copal had disappeared, and there were separated from it tvv^o drops of acid, which, by reacting on the principles of the oil, might serve to explain the origin of the tint as- sumed by the essence. This specimen had also become charged with forty grains of 'pulverized . copal, intro- duced at four different times. No. 3. exhibited a tint somevvhat more apparent than the preceding. Two drops of acid water had separated from it; but the liquid was nevertheless transparent. It had become charged with - the same quantity of copal as the preceding. No. 4. had still more of an ambery colour than InI^os. 2. and .'>.. Jt contLiined also acid v.ater. The 252 TREATISE ON VARNISHES. same quantities of copal 'w-cre attended with the s^iiie success as in the former cases. No. 5. v;as nebulous ; which I ascribed to som^ motion accidentally given to the matrass : the water was then confounded ^vith the oil. It had the same tint as the preceding, and presented the same extent of solution as the former specimens. No. 6. had a reddish colour, and I extracted from it some drops of very acid water. ït appeared to be the least proper for making varnish, as it had beei capable of admitting only thirty-five grains of new copal, instead of forty. All these -specimens of varnish l^ad the required con- sistence. They were exceedingly oily ; extended them- selves freely Vv'hen applied under the influence of the sun ; and, in summer, required only two days to fornj on ivor^' or on wood a solid and brilliant glazing. It may be seen^ in this account of my researches, that these oils, which were incapable of becoming charged with copal during the first trial, experienced in the conrse of time a particular modification, but necessary to establish a kind cf analogy which ought to exist between the principles of the two substances in contact. Was the escient cause of this modification the contact of the essence with a certain quantity of copal ? Ir may* be reeollectetl that each of the small matrîisses, subjected to experiment, contained ten grains ©f pulverized copal. This question, therefore, may be answered by an examination of the oils contained in the corresponding flasks. 7th. At this period 1 had received my instrunientjx EFFECTS OF LIGHT ON ESSENCE OF TURPENTINE. 25S and balances, the correctness of which enabled me to ascertain the smallest differences. The specific gravity of the oil in each of the six numbered vessels was ex- amined by a flask capable of containing an ounce of distilled v/ater, Fahrenheit's thermometer being at 59*^. The follov/ing table exhibits the results, in the order of their numbers : Table ca/iii':ii2}ig the speci/ic grav'tty of the rmmbered oils. Specitic gravity com- Reh'.livedecrensein Order of the pared with that of au the ab.solute weight numbers. ounce of distilled w a- of the ounce of di- ter. stilled water. Gros, Grains. Grains. No. 1. , 7 . 60 12 No. 2. . 7 . 37 t35 [No. .'3. . 7 . 5S 14 No. 4. . G . 70.'- 'JO, 1 No. o. . 7 . .57 15 In establishing the scale of these numbers, accord- ing to their greater lightness, I sh^ll place them in this manner: No. 4, 2, 5, 3, 1. No. G. was not compre- hended in this examination, because, being only the residuum of the distillation, it was loo thick and too highly coloured to enter iiUo the composition of varnisji. 8th. When the specific gravity of these oils vas known, it remained to ascertain, v/hether the solution of the copal in the t:i,seiice, contained in each of the small matrasses, w hich was very much exten4ed, ought to be ascribed to a modification effected in the essence itself bs (he contact of the copal, which had incor- porated with il only fiowlyj and whether this copal. t254f TREATISE ON VARNISHES. Ts-hen once united to the essence, would not communi- cate to the latter the property of seizing upon new por- tions of the resin. It was necessary, therefore, to apply to an ounce of oil taken from each of the numbered specimens, the same quantity of pulverized copal, that is to say, fifty grains, using only ten grains at a time, as before. The following were the results : The essence No. 1. could dissolve only forty-eight grains of copal, and the solution was turbid. No sedi- ment was produced by two hours rest ; and the addi- tion of -J ounce of tlie same essence formed a varnish of a good consistence, and very clear. Some clouds only were observed at the bottom of the vessel. No. 2. was treated in the same manner for the solu- tion of the first forty grains of copal ; but the last quantity introduced remained untouched. The var- nish, which floated over this sediment, was turbid ; and half an ounce of essence was required to make a varnish of it similar to the preceding. No. 3. was like No. 1. ; but, after tv;elve hours re- pose, there was separated from it a small portion, which might be estimated at tvvo grains : the addition of a quarter of an ounce of the same essence, however, made it disappear. No. 4. refused to unite with copal : the whole mat- ter was precipitated, a few grains excepted. The oil had experienced no change in its colour or consistence. The copal formed a mass in it. No. 5. gave, with fifty grains of copal, the same re- sult almost as No. 2. ; but no precipitate was formed at t-lie time. The state of the soludon, however, an- EFFECTS C¥ LIGHT ON ESSENCE OF TURPENTINE. 25.5 nounced that it would soon appear. It was less volu- ininous than in No. 2. ; and only three-eighths of an ounce of new essence was necessary to make it dis- appear. If the specific gravity observed in the numbered oils be compared with their difterent degrees of power over the copal, we shall find that this power acts in the in- verse ratio of their tenuity and liglitness. The more distant, then, that essence is from the state of ethereous oil, the more energy it exerts on copal. This simple theory -is sufficiently proved, first by the inactivity of the essence of the shops, which I tried before I subjected it to distillation (l) ; and then by that of the oil num- bered 4., which we have examined (8), 9th. To these examples might be added others taken from different experiir.ents, the details of which are suppressed, to avoid extendiiig this chapter to too great a kngth. The following result, however, deserves to be knov/n : an oil which had no action on ccpal two months after rectification, took up forty grains per ounce eleven months after ; and fifty-two grains at the end of eighteen months. The varnish was not more coloured than alcoholic varnish prepared v/ith the great- est care*. Was this owing to the effects of the light? or was it owing only to time, which, without any intermediate * The specific gravity of this oil, examined by the test contain- ing an ounce of distilled water, the thermometer being at 5'2'\ was : At the first period 6 gros (54 grains. At the second - - 7 gi'o^ GS grains. At the third - - - 1 ounce 7 ^vains. 2,70 TREATISE OK VARKiSHÊ^. substance, disposes the parts of the oil to assume pe- culiar 'chamcters, which add to their specific gravity, aiid which render them more proper to become charged V\ith that resin ? This is a question of so much importance that it de- serves to be carefully examined*. But, before I enter on this subject, I shall present the reader with a few " considjerations on the mutability observed in the proper- ties of essence of turpentine. 10th. What takes place in a varnish in which a se- diment of copal is formed may be considered as a new fact, the real cause of which can at present be only conjectured. Whatever care may be taken to favour the solution of the part precipitated, either by the addi- tion of an oil, or by the use of caloric and motion, it remains entire, or the part made to enter into solution is so small as scarcely to be worth notice. The same phenomenon is exhibited by varnishes wliich are only turbid. It would appear that copal contains two substances, the principles of which, dif- ferently modified, are however susceptible of an inti- mate combinadon, as seen in some bodies distinguish- ed by the name of resinous gio/is or gummy resins. A * Some particular facts had familiai-ized me iti so:ne measure witli the idea that the light had had some influence on the present results. It was therefore necessary to ascertain it in a direct man- ner. I con.-equently made researches on the subject, and I gave a detailed account of the results in a memoir inserted in die Journal de Physique for March J/QS. These results confirm that light alone was the cause of the phrenomenon, and it is greater and speedier when the ox}gen gas of the atmosphere has free access to it. EFFECTS OF LIGHT ON ESSENCE OF TURPENTINE. 257 liquor, then, the pnnciples of the composition of which have a more striking analogy to one of the two compo- nent parts than to the other, will be able to separate them. By this separation the insoluble part would be- come only more refractory to the action of the vehicle, and the quantity of it would even be increased, because it would be deprived of its means of union. Several substances exhibit these phssnomena when brought into chemical contact. Notwithstanding the instances which might be ad- duced to jusdfy this opinion, or to give it every character of probability, it is here offered merely as a conjecture. It may not, however, be improper to call the reader's attention to what takes place in a mixture of copal or , of amber with alcohol, and with ethereous essence of turpentine. These liquors seize on a slight portion of ■ these two kinds of resin ; but their energy is confined in such a manner, that if the vehicle of the first infu- sions be decanted, and its place supplied by a new quantity of liquor, the latter will exercise a still weaker action than the former, and so on in succession ; be- cause the part of these resins which is soluble by this kind of process has been extracted, or because what remains is so envefoped by the insoluble part that it is secure from eveiy attack. This may have some relation in theory with our sedi- ments of copal, the sokirion of which cannot be com- pleted till the vehicle in contact has undergone, in it§ principles, new modifications, which develop in it new I affinities with the resinous substance. It is thus that we may judge of it from -what has been observed in ^58 TREATISE OÎ-; VARNISHES. sections 5, 6, and 8. The same chemical effect may take place also when colourless essence, but of a density which may be compared to that indicated in section 9, is employed. 1 1th. Anotlier phsenomenon, which deserves no less 'to be examined, is the ambery colour which the var- nish assumes when made with essence easily decom- posed, and which readily yields water. The varnish speedily assumes colour, if by means of a few shakes the small drops of water adhering to the dome are pre- cipitated to the bottom of the matrass. This water, which is acid, reacts on the oily principle^ and alters it. Every essence of turpentine does not equally pro- duce tliis effect ; which seems to depend on its nature, and the strength of the acid it contains. Of seven matrasses containing this oil, of different degrees of density, and exposed on sand at a temperature of 200 degrees, there was only one which could serve to sup- port the present observation. The experiments men- tioned in the 6th section prove the truth of it. Whea similar oils are used, it will be proper to substitute a balneum marias for a sand bath, if a colourless varnish^ be required. 12th. The facts observed in mixtures of essence with a small quantity of copal (5) render it ne<:essary tQ offer some observations on that subject. What, then, is the cause of this solution, which I have seen carried further on a small quantity of copal (0), with oils pre- served in small matrasses, than with the same oils with* out mixture (S) ? The former were able to dissolve fifty grains of copal per ounce ^ wIhIc Uàc hitter re» 1 EFFECTS OF LIGHT ON ESSENCE OF TURPENTINE. 25^ quired the addition of a new quantity of essence to take up from forty-eight to fifty grains. It will be recollect- ed also, that this addition of essence was made in the relative and inverse ratio of the density of the oil, which served as a basis to the experiment (8). Two causes may concur to produce the effects ob- served in the matrasses charged with ten grains of copal. The first arises from the density of the essence. This density, acquired by the solution of a portion of the copal, extends to the oily body its quality of re- fracting the sun's rays. It disposes it to collect a greater quantity, to yield to their influence, and to acquire from them modifications capable of developing a cer- tain analogy between the principles of its composition and those which constitute copal. The second cause may arise from the precipitation of their acid, which has followed the solution of tlie first grains of copal. This separation of a part of the water contained in the essence itself does not take place in specimens of the same oil without mixture. It appears that the essence in the . matrasses has under- gone a kind of analysis. By this subtraction of a por- tion of the aqueous principle, essential or foreign to the composition of the oil, but so contrary to its resi<- nous combinations, the essence must have assumed a more oily consistence, and have formed a whole of a greater density. This agrees very well with the anterior observations, which indicate (9) thaï the density of the essence, carried to a certain determinate point, be- eomgs a character essential to the solution of copal. V,. These two conjectures seemed likely to open anew s 2 ' 260 TREATISE ON VAR^TISHES.- field for experiments, and the results of them might become as- iiiterestir.''^ to philosophy as the first object of this chapter appealed to be to that part of the arts to which it relates. The matrasses and bottles which contained the proof oils were closely shut with cork stoppers. The varnish, which had dried around the ■«toppers of the matrasses, so as to form a kind of mas- tic, left no doubt in regard to their perfect obturation. To explain the iiKrease observed in the density of the oil, k was impossible to suppose a loss occasioned by the evaporation of the most ethereous part of the es- sence, since there was no apparent decrease in its vo- lume, the level of which had been marked by small bands of paper pasted on the outside. The same cause which opposed the volatilization of the oil appeared to me still sufficient to present an obstacle to the intro- duction of the oxygen gas of the atmosphere, which is considered as the cause of the inspissation of oils. In this phîenomenon, therefore, I could observe only an effect of light. But in what manner did it act ? Was it by combining with the oil the pure air contained in the empty part of the vessels? or was it by combining itself with the oil, in a manner never before observed or suspected ? Light, such as it appears to our senses, possesses, no doubt, in consequence of its great velocity, the same properties as caloric (fire), which has not yet been found to possess gravity ; but, in combining with the matter, would it not add to the gravity of the latter ? It was necessary to make new experiments on this sub- ject. I did so ; and though the results of them were | S ETFECTS QF LIGHT ON EaSENCE OF TURPENTINE. 261 foreign to tlie arts, they are so connected with the theory of the object which I undertook, that I do not l3iink them susceptible of separation*. 1 3th. The experiments which I projecte-d, with .a i-iew to fix my opinioaiin regard to results so singular., seemed likely to give m^ information at the same time respecting the cause of the ditference observed in the density of the products of the first distillation of the essence, and which may be seen in the table (7). This table gives to No. 1, which contains the tirst product of the di- stillation, and which consequently ought to exhibit the lightest essence, a specific gravity greater than is found in the other numberst. This observation rendered it necessary for me to be more circumrpect in the manner of extracting the products of the disdllation which I intended to m^ike. Besides, I considered it as a point of importance to ascertain the specific gravity of the products twenty-four hours after the operation. I th 4ome of ii'drnt clay, which I took from the retort when the vapours appeared to be too violent. _^ S 5 262 TREATISE ON VARNISHES. the dome, the use of which accelerates the escape of the vapours. These ethereous products were afterwards exposed to the influence of the solar light, their specific gravity- being first ascertained by a test bottle capable of con- taining an ounce of distilled water, the thermometer being at 55 degrees of Fahrenheit. The details are ex- hibited in the follo\^ino- table : o Table of the specific gravity of the products tiveniy- four hours after distillation. Order of the Particular characters of the j Their specitic gf avity as rom.parcdwitli that of distilled water. numbers. products. No. . . 1 Colourless, but nebulous in consequence of a little water interposed between gi-os. grains. tlie parts of thu oil . 6 . . ÔO{r 3 Colourless, I'glitj ai^d very limpid .... 6 . . 66 3 The same . . • . 6 . . 66 4 The same . . 6 . . 6'ô,V 5 The same i . , . 6 . . 66^ 6 The same 6 . .67 7 The same .... Nebulous, w'tli a stick- ing odour of bitumen not four.d in tlie preceding, &: of an ambciy colour. This 6 . . 67 full ; product was accompanied 8 w'xxh. 6 cU'ops of acid water. 6 . . (5-\V wh ich had coloured the part of the oil in contact. The residuum of the di- stillation was thick, and weighed about 3 ounces. N. B. The common oil of tlie shops had a greenish tint before distillation, its speciiic gravity was . . 6 . . CS 1 None of liiese oils at- 1 tacked cop..' I. ETFECTS OF LIGHT ON ESSENCE OF TURPENTINE. 263 14th. April 1st 1787, three days after this examina- tion, I closed exactly with pieces of fine cork the bottles which contained the different portions of oil, numbered in the order in which they had appeared in the course of the distillation. I exposed them in the seat of a win- dow which for six months of the year received the solar rays three or four hours daily, and during the same time a strong^ reflected light. The oil in these bottles was exposed, therefore, to the influence of the direct and reflected solar rays ; but it received them only through a window, which preserved it from all external accident. The paper inscribed with the number of each flask was pasted to it in such a manner that its upper edge corresponded exactly with the level of the essence con- tained in the vessel, and only one-sixth part of each of these vessels was empty. 15th. On the 30th of March 1788, after a year's exposure, I again examined on the spot these separate portions of essence, and put them into a balance, that I might compare their present specific gravity with that Vhich they had indicated the preceding year. Nos. 1, 2, 5, 6, and 7 had experienced no decrease jn their volume ; because they had been completely closed. No. 3 had decreased half a line in a surface c^n inch in diameter ; and No. 4 three quarters of a line. The vessels marked ÎSÎos. 1 and 2 were lined above the level of the essence, v/ith a beautiful vegetation of crystals nearly an inch in length, which crossed each flftlier ip every direcdon. They adhered to the an- s4 264 TREx\TISE ON VARNISHES. terior part of the neck of the flask, opposite to that which received the direct solar rays. I thought there was reason to conclude that these crystallizations might have been formed under the protection afforded to them by a plain square of paper, which preserved the em.pty part of the flasks from the direct action of the light and of caloric. No. 8, which was in part sheltered by the angle formed by the frame of the window, exhibited also very beautiful crystals, which adhered only to that part of the glass the least exposed to the direct rays. This se- cond observation gave weight to my first conjecture. The flasks having been inverted and kept in that position for some hours. Nos. â, 4, and 8 sufi'ered a little oil to ooze from them, in consequence of their being badly stopped. The stoppers were tinged internally of a pale-yellow colour, as they would have been by weak nitric acid. Their texture, however, vv^as very little altered. This colour, which arose from the impression of an acid vapour, was observed only in the part which had been in contact with that vapour, and did not extend to the interior part of the cork. The therm.ometer was exactly at the same point at which it had been the- preceding year, that is to say, at 544- degrees j but the consistence of the oil was no longer the same. The two last numbers exhibited even a slight shade of colour, which they did not possess before the distillation. I shall here present a table of the differences observed in the specific gravity of these afferent portions of the same oil, after the interval of EFFECTS OF LIGHT ON ESSENCE OF TURPENTINE. 265 a year, in order that they may be more easily com- pared ; and I shall add a column pointing out the addi- tional weight which each measured ounce of oil ac- quired by the effect of the solar light. The test bottle was always the same ; that is to say. it contained the vo- lume of an ounce of distilled water at the temperature already mentioned. A comparative tahle of specific graviti/. 'order of Speci fie gra- Specific gr.;- Inc.easc ot' 'the mat- Characters of the oils. vity observ-jvity observ- specific gra- ters. ed in 1787. led ir 1788, vity. No. 1 Limpid and co- gros grains. gros. grains lourless oil . 6 66± 7 37i 43i 2 The same . , 6 66" 7 39i 454- 3 ISIore fluid than the preceding, & colourless . . . 6 66 7 33 39 4 Very fluid and colourless . . . 6 66\ 7 24^ 30 5 Oily, limpid, & colourless . . . 6 66A 7 38| 43i 6 Exceedingly oily, limpid and colour- less .... 6 67 7 50-]; 55i 7 Exceedingly oily ana limpid, colour somewhat ambery . . 6 67 7 4/^ 52^ 8 Oily and limpid. but aziibery . , 6 - 1 7 38 4U N. B. All these oils applied to copal in relatif -e propor- tions, according to their density , effected a sohit ion of it. and formed beautiful varnish, except Nos. 3 and 4 in which the copal was precipitated. It may readily be perceived, that the addition to the specific gravity is here in the direct ratio of that of the density acquired during the exposure of the oil to the 266 TREATISE ON VARNISHES. solar light.. Nos. 6 and 7 serve to confirm the follow- ing physical truth ; namely, that among homogeneous liquors, and oils in particular, of a different specific gra.vity, those which are densest possess also the great- est refractive power ; and, consequently, are the most Gapa.ble of accumulating the luminous rays. This principle being laid dov/n, if a greater accumu- lation of light be admitted in the latter, there is reason to believe that the result ought to be a new combina- tion ; and it is in this combination that we ought to look for the cause of the increase observed in the spe- cific "Tavitv, and in the densitv of our oils. No. 8 would have exhibited the same phenomena as Nos. 6 and 7, had it not experienced from the stopper the same inconvenience as Nos. 3 and 4, which showed a sensible diminution of their volume. I have already said ( 1 4), that by inverting the- bottle it lost its oil, through a fault in the cork. This observation, for which I was indebted to chance, led me to the disco- very of a phasnomenon too striking to escape the at- tention of those who cast their eye over the compara- tive table of the specific gravities : it is seen that the increase of it took place also in the direct ratio of their less evaporation. No. 3, v/hich had lost only half a line of its volume, showed also, in the increase of its density by the influence of the light, nine grains more than No. 4, which exhibited a diminution in its volume of tlirec'-fourths of a Hne'\ The numbers which g^ve * The paper ir-dox of tlie bottle No, 8 %vonlcl, no dniiht:_, have shown a sensible dimin-dtion. Butpreaufnuig on too liglit grounds, piiliaps, that tills poriiou of essence çovdd not be eraplo-yed lor EFFECTS OF LIGHT ON ESSENCE OF TURPENTINE. 2G7 access to the external air are exactly those which iliowed the least specific gravity. ]6th. It is impossible to admit as the cause of this increase the evaporation of the most ethereous and most volatile parts of the oil. There was no sensible de- crease in the vessels 1, 2, 5, 6, and 7j and these nmn- bers showed the greatest increase in the density of the oil which thev contained. A simple comparison of facts will be sufficient to show the falsity of this supposition. If we admit, according to the result, an addition to the real specific gra\ity of No. 7, which contained six ounces of essence, we shall find 325 grains added to the specific gravity of the preceding year. These 325 grains make. IS deniers and S grains, the deduction of which from the whole mass of essence would have made a deficit in its first volume of three lines, as I as- certained by experiment. This increase, then, can be explained only by an addition produced under the influence of the light j but whether this fluid, notwithstanding its extreme rarity and great velocity, undergoes any particular modifica- tions, or causes the oily bodies exposed to its direct in- fluence to undergo them, is what I will not pretend to determine. These experiments have discovered to me one fact, which I believe to be new. The influence of light is observed here in a very sensible manner ; but what is the nature of this influence ? Does it enable Ae oxygen gas contained in the atmospheric air to overcome the obstacle opposed to it by the best cork. varnish^ on ?.ccQ\\xit of its colour, I took out two ounces of it fur -another purpose. The index then was of no use. 268 TRP.ATISE. ON VAÎlîrîSHES. Stoppers, in order tiiat it may combine with the oil ? or does it materially coiLcar itself to produce this phazno- Kienon? These questions desen^e further research. In regard to the supposed combination of the oxygen gas extracted from the atmosplieric air, it wiil P'-jear in this case contrary to the evidence oi the results. Nop. 3, 4, and 8, which really lost part of their sub- stance, in consequence of their being incompi' • 'y chut, and which for the. r:nme reason aflbrded accc .; to the external air, ou^'iit to have presented icSuUs r.^ree- able to this supposed combination. We however know them to be contrary ; since the essence they contain is specifically lighter than that of the other numbers. This observation will hold good also in regard to No. 8, xvhich containing an oil more réfringent than Nos. ] , 2, and 5, ought on that account to acquire a greater density than Nos. 3 imd 4, which were iindçr the same circumstancej. I am inclined to believe that the results observed in Nos. 3, 4, and 8, are not to be ascribed so much to the introduction of the external air as to the dil^cidty ex- J>erienced by the light, in commencing and bringing to perfectign its particular mode of combination in the oily vapour which occupied the empty part of the ves- sels, — a vaporous combination which the elevated tem*- perature of the solar rays, or that of the atmosphere, expelled before their union with the mass of the oil. I, however, ofier this idea as mere conjecture : to ascertain the truth of it would require a great many comparative experiments, made with vessels, some full_, and others half fail j but all hermetically sealed. EFFECTS OF IJGHT ON ESSENCJZ OF TURPENTINE. 2G3' To determine the effects of the oxvgen gus or es- sence of turpentine, I arranged, in the month of August ] 787, an apparatus, the results of which I shall exa- mine at the end of a year. î can, however, assert that I have had sufficient time to observe phgenomena which justify the opinion I have advanced in regard to the combination of light with the vapour, and in the vapour of the essence *. Nothing now remains but to deduce the consequences which arise from this series of researches. .General consequences and conclusion. 17th. The object of these researches, as already seen, was to verify a fact, known no doubt to some chemists, but which artists cont'^st, — namely, the solu- bility of copal in an oil lighter and less coloured than fat oils, — in a word, in essence of turpentine. The result of the experiments here detailed shows that this essence is the fittest liquor for maldng copal varnish ; that an elevated teni^perature is not required to favour the process, since it is below that of boiling water. INIere stirring is even sufficient in summer. If the simplicity of this method be compared with that employed in the operation of uniting copal with fat oils, which cannot unite with it but when it is in a 5tate of liquefaction, by the effeci: of a very high tem- perature, much superior to that of boiling water, it * The experiments detailed in the memoir already mentioned [Journal de Physique, Mars l^QS) leave no doubt in regard to the combination effected in the vapour itself, vben the vessel is ex- posed to the direct influence of the sup. ' 270 TREATISE ON VAP.NL^HE::, will be allowed that the liquor which c-an dispense vith this forced liquefaction, which is even satisfied with a temperature of from 88 to ]00 degrees, aided by simple mechanical motion to effect that union, is the best of all for the intended purpose. But these experiments show also in their results, that essence of turpentine does riot always exhibit the qualities requisite for effecting this union. We have seen (9 and IJ) that ethereous oil had absolutely no action on copal ; that its dissolving property was mani- fested in the ratio of its density (5, 6, and 8); that this density is altof^cther independent of the rectification of the oil by a second distillation, which in general gives only a light^ ethereous oil, if the operation is managed with care ; or an oil, the specific gravit)'' of which does not exactly follow the order of the division of the product (4 and 7); that the light alone, bv the effect of a particular combination, the mode of which can only be presumed, becomes the principle of this density, so essential to the solution of the copal (7, 8, IS, 14, 1,5 and IG), that this essence of turpentine, which at the moment of its rectification has exercised no power over the copal, may by the mere effect of the influence of the light dissolve, after a certain time, the pulverized copal which has been precipitated from it untouched j that the copal even increases its energy, ance the essence can dissolve a larger quantity of it than when it is exposed alone, and v.'ithout any mixture of copal, to the same infitjence of the ligiit (5, 6 and 8). These results prove also, that the more the essence of turpentine is disposed to be deccmpcscd, and to fur- EFFECTS OF LIGHT ON ESSENCE OF TURPENTINE. 271 nish acid water, in the course of the distillation, or during the time of the process for making the varnivsh, the less proper it is for the solution of copal ; becausa this free acid does not fail to react on the oil, and to communicate to the whole mass a tint, which it ought not to possess (1 1) ; in a word, that this oil is suscep- ■ tible of giving a concrete volatile acid salt, contained 'in certain balsamic substances (1, 2, and 1.3). The .' existence of that salt, which places turpentine among the balsams, according to the new defniition of Four- croy, was at this time unknown. Some authors assert that they have been able to dis- '. solve copal in essence of turpentine : this chemical pro- , perty of essence, however, was considered as very pro- l;)lematical. The remembrance of it even seemed to be preserved only in consequence of the merit of the authors who admitted the possibility of it. Two per- sons of great celebrity have entertained opposite opi- nions on this subject. Lehmann, whose name is well known in chemistry, asserts that, copal is soluble iu essence*. Wadn, an ingenious artist, refutes this * *■' Copal^ with oil of turpentine, gives a vaniish whidi in » great measure is similar to amber vaniisiî. The first doses are ms^ part of copal and four parts of the oil of turpentine> which is then added in greater quantity, without detenninJng the weight, ia ' wder to dilute the varnish and render it fluid." See'Rechercht'S Historiques et Chimiques du Copal, Mem. de. V Academic de Berlin^ tome it. See also L'Art défaire l'es Vernis, l5'c. par JFaiin, edit. de 1772, p. 162. This is the first author who menlions the solution of ccprJ ia essence of turpentine. As Watln did not succeed, he expresses doubts which, though not accompanied witiî any explaioation, suf- 272 Treatise on varnighEo. opinion, and maintains that it is not soluble * : both, however, are in the right, since this solution depends on a degree of density which the essence sometimes exhibits, and which it may have accidentally exhibited to Lehmann. 18th. The solubility of copal in oil of turpentine being once established, nothing remained but to make use of the observations scattered throughout this essay, in order to discover the speediest, and at the same time the most proper, method for making varnish with essence. There was reason to think, that by dividing the products of one distillation of this essence into seven or eight parts, it might be possible to discover in these divided parts those which would exhibit the qualities requisite for completing the solution; but it was ob- ficiently show that he had strong reasons for not considering tlie results announced as bearing tlie stamp of rigorous exactness. See his Reflections, p. 10(3, The author of Traité sur la CofiJpositïon des Vernis en général, edit, de Paris 1780, mentions also, on the authority of mere tra- dition, the solubility of copal in essence^ but he says nothing of tlie state of the oil. See page 4 ct seq. * " It appears proved in practice, I mean the practice of sucl> persons as myself, that neither alcohol (spirit of wine) nor es- sence can dissolve copal nor amber." See Art défaire les Ferfiis, i^c. edit, de 1/72, p. 111. The last edition of 1782, which I have just received, couiirms the same opinion in tlie article of Re- flections, p. 279. " Copal dissolves neither in spirit of wiiie nor hi any essence, whether in a mass or in powder, but it dissolves in, fat oils." See the same it'ork, p. 37. " Copal will never dissolve in essence of turpentine." Page 8, in the notes which allude lq the fliults of the Parfait Fernisscur. ^ tFFECTS OF LIGHT ON ESSENCE OF TURPENTINE. 273 served that this process at length gave a contrary re- sult (is) j since it often deprived the essence of the shops of that property which it might liave acquired from time, or from any other circumstances. This distillation, however, is indispensably necessary^ when colourless vaniish is required ; because the essence of the shops is always more or less coloured. Besides, this operation, which may be performed on a large scale in manufactoiies, furnishes a very simple method of obtaining the most ethereous essence, the use of which I have recommended in the composition of var- nish destined for valuable paintings *. If the distillation of essence be undertaken with a view of accomplishing both these objects at the same time, it must be performed by means of a sand bath, taking care to cover the retort with a dome of burnt clay f. From a hundred ounces of this oil ninety are ex- tracted ; the first forty of v/hjch, forming ethereous oil of turpentine, must be reserved for the composition of varnish destined for picturesp The last fifty ounces of essence are applied to the composidon of copal var- jnish. The residuum even is not lost; it serves for grinding and mixing up oil colours. If too thick, it is idiluted with new essence. . From ten to twelve grains of pulverized copal are mixed with an ounce of the essence destined for varnish, ^d the mixture is shaken, immersing the matrass in ^ bath of boiling water.^ If the copal readily dissolves in the essence, new dose's are added; and this is con^ * See the Third Genus, No. XII. p. 133. j- See the description of this process, 2d method, p. 70. T ^74. TREATISE ON VARNISHES. tinued till the essence refuses to take up any more. Ic sometimes happens that this essence gives immediately a very beautiful varnish and of a good consistence ; at other times it refuses every kind of union. In the first . case the varnish is filtered through cotton, after it has been allowed to deposit the untouched portions of the copal: in the second, that is to say, when the copal resists the essence, the matrass is closed \^dth a cork stopper, and exposed to the solar light until the essence has acquired an oily consistence. It will assume this state the more easily, the greater the quantity of copal it holds in solution. The influence of the light gra- dually manifests itself on the essence, and the preci- pitated portion of the copal decreases, and at length dis- ' appears entirely. The consequence is, that the essence ' acquires from this matter, "which ' is mixed with it, a new consistence and character, which dispose it to be- come charged Avith a greater dose of the resin; and in this manner to constitute a real varnish. This has been observed in the sixth section. Essence prepared in this manner ought to be pre- ferred to the other vegetable oils, which ' approach nearest to the same state of density or of specific gra- vity. The varnishes, indeed, which result from the union of it, with resins are less fat and of a more drying quality than those made with oil of lavender, oil of I ' thyme, oil of rosemary, &c. employed directly or with some intermediate substance. They are also exceed- ingly durable when copal forms the basis of them;j and they produce the most beautiful effect on metals and polished wood. Copal varnish made with eM EFFECTS OF LIGHT ON ESSENCE OF TURPENTINE. 275 sence has a slight amber colour, which disappears after it has been applied. The oily character, which contributes to its solidity, disposes it to become much better charged than alcoholic varnishes with those vegetable, resinous and metallic colouring parts with v/hich the variety of colours that enrich transparent enamels can^e imitated. It may be readily conceived, that to preserve the transparency of varnish, and to give it that lustre which completes the illusion, none but colouring matters entirely soluble in essence must be employed. It was proper to detach from these particular obser- vations, and even from this part of the work, every thing relating to the use of colouring substances, and the different purposes to which copal varnish made with essence may be applied: a treatise therefore on this subject will be found in the second part of the work vv'hich follows. T 2 i \ PART THE SECOND. ON THE PREPARATION OF COLOURS, AND THB METHOt)S OF APPLYING THEM. lîî THE DIFFERENT KINDS OF PAINTING, &c. TREATISE ON VARNISHES. PART THE SECOND, CHAPTER L Tlisforical account of the mdiire of the colouring snhstafices 7/sed in pahituigy with a description of the processes em- ■ployecl to extract 'them, and of the methods of preparing or modifying them,. 1. HE account given in the first part of this treatise, of the substances which concur towards the composition of varnish, must tend to regulate the appHcation of them in a more certain manner. I'o this advantao-e o may be added that of rendering artists familiar with the different processes which art employs to extract or to modify productions which nature exhibits to us only under fixed and determinate characters. Our know- ledge of an art ought not to be confined to what re- lates merely to. manipulations, which are more or less varied by long practice : it ought to be extended also to every object subservient to it. The composition of the colouring substances, which forms the subject of this second part, requires more ex- tensive and more varied processes, the theory of v/hich cannot be understood without some preliminary know- ledge. In regard to these substances, we shall follow the same course as that adopted in treating of the mat- T 4 280 TREATISE ON VARNISHES. ters employed in the composition of varnishes. It is, therefore, of importance that our observ-ations on the principles of colom*s, and the effects of their mixtures,, should be preceded by an historical account of the sub- stances charged with colouring parts, arfd by a view of the means which art employs to transfer, under some particular circumstances, the colouring principle of one body into another ; or to communicate to it new qualities, which render it capable of extending the won- derful power of combinations. Nothing seems better calculated to make the artist and the amateur sensible that no 'art is independent, and that all lend to each other reciprocal assistance, which concurs to\vard5 their improvement, and often even to the celebrity of the individuals who have sufficient strength of genius to soar be}^ond' the usual beaten trask» Bougival white. Painters often employ white matters for grounds. Ceruse is distinguished by great durability. It forms an excellent priming, proper for receiving other co- lours ; but there are a great many cases, particularly in painting in distemper, which admit the .use of a more common and less expensive white, such as that of Bougival, Spanish white, white of Troye, &:c. Bougival white takes its name from the place where it is extracted, which is near P/Iarly, at the distance of a few leagues from Paris. It is a sort of very fine marly earth. Normandy, Auvergne, and many other di- stricts, contain beds or strata of a white earthy matter, commonly known under the name of tobacco-pipe clay, 5 BOUGIVAL AND CREMNITZ WHITES. 281 This earth, when very white, is much better for house painting than any other white earth of a calcareous na- ture, such as chalk. The celebrated Wedgewood, who has established a very large manufactory of earthen ware, which in elegance and beauty is equal to the finest porcelain, was exceedingly nice in his choice of this clay, some of which he obtained from Normandy. If similar establishments require that purity should be united to whiteness in the clay employed, the same rigour is not necessary in painting. Body and whiteness are the principal characters required. If Bougival white is not a pure clay, it possesses that whiteness which assigns it a conspicuous place in the . order of colouring bodies. It is sold in the shops under the form of oblong cakes, into which it is cut, after the small stones and sand mixed with it have been separated by washing. Washed chalk is often substituted in its stead ; but connoisseurs have no need of analysis to detect this fraud. "Washed chalk gives less body to painting than clay, and does not unite so well with oil when applied to that kind of painting. According to some experiments which I made with Bougival white, sent to me from Marly, this marl con- tains nearly a third of carbonate of lime (chalk). This ' mixture renders it inferior in oil painting to real Spa- nish white, and to white of Moudon. Cremnitz ivhite. The composition of Cremnitz white, in regard to the nature of its base, seems still to be very uncertain. 282 Treatise on varnishes. Three sub^t-v^-^-^^s, which have nothing in common but the name i; ihem, are sold under diis denomina- tion. i>)rec!: -experiments, which I made on specimens obtained from different colourmen, did not justify the idea entertained by some celebrated painters, that this white is merely an oxide of tin * (calx of tin). In seve- *■ I shall embrace the opportunity afforded by the occurrence of tlie term metallic oxide, to give a short view of the theory v/hich establishes this expression in the room of the word calx, employed formerly to denote certain metallic preparations. According to the principles of the Stahlean chemistry, the name of calx was given to every metallic substance which, in conse- quence of being subjected to the action of fire, excl^anged its con- sistence and metallic brilliancy for a new pulverulent form, co- loured or not coloured, according to the nature of the substance,- and according to the degree of heat experienced. The name calx was given also to the same substances, when reduced to powder by acids, or when precipitated from their solvent by another sub- stance which seized on the solvent. It was in consequence of tliis convention that the general denomination of calces was given to litharge, minium, ceruse, white lead, calcined lead, calcined tin^ and all metallic substances precipitated from acids by the means of alkalies, &c. Direct experiments, conducted with great. sagacity by Lavoisier, and repeated by a great number of chemists, have freed chemistry from the shackles of the old school. Combustion, and the iaflam- mation of substances which are susceptible of these two states, have no longer been cpnsidered as the tertn of destruction : on tlie contraiy,. in the hands of the chemist tiiey have produced all the signs and real characters of new chemical combinations. The evi- dence of these com-binations is so striking, that it will no longer admit the vise of the old theoiy, nor allow us to confound meta- morphoses, which metallic substances undergo by tlie action of heat and t-he concurrence of oxygen, with that whicli cfdcareous earth and stones*.of >tlic same kind experience from accumulated caloric BOUGIVAL AND. CREMNITZ WHITES. 283, ral specimens purchased in . diflerent shops, I found oxide of bismuth (calx or magistery of bismuth) j and (ardent heat) . It is well known tliat the latter substances are re- duced to a real calx (lime) by the loss of a little water ; and of a particular acid which was long distinguished by the name of fixed air, because it gave them their state of consistence ; but which is now called carbonic acid, since the decomposition of it has shown that its base consists of carbon or charcoal. Becker, and Stahl his disciple, as well as the old school, placed metallic substances in ihe class of compounds. They considered them as so many bases united to a particular subtile principle, which produced metallic brill ianc)-^, and which they denoted by the name of phlogiston. The action of fire was exercised only on this principle, which it separated from its base, and the latter tlien assumed tlie earthy and pulverulent form. This principle being adniitted, every metallic calx was merely the result of the mediate or immediate application of fire ; it was the metal destitute of phlogiston, which communicated to it the brilliancy and consist- ence it possessed before tlie operation. This first hypothesis ought to have given birth to another, serv- ing to expl iin how a substance, which lost one of its essential principles by the action of caloric (fire), should nevertheless ac- quire an addition of -\fth to its real weight. But this is not the place tor enlarging on the subject in question, I shall, tlierefore, content myself with obseiTing that this theoiy, irreconcilable in regard to tlie most essential points, has given place to a doctrine which, neglecting hypothesis, establishes its foundation only on facts. It ac'mits that metals belong to tlie cla§s of simple substances j that they are combustible j and that in every case of their exposure to fire, instead of losing, they acquire a new element;, Mdiich from simple converts tliem into compound substances. This aaditlonal principle or element is the base of pvu-e ail- or oxygen, and the union of oxygen with caloric (fire) constimtes oxygen gas, which composes, at the least, tlie fourth part of the atmospheric air. HSif TREATISE ON VARNISHES, in two particular cases oxide of lead (ceruse). It did not appear that any of them contained oxide of tin. Other experiments, undertaken with a view to ascertain the composition of acids, have proved by their results that the same oxygen, the union of which with caloric constitutes oxygen gas, known formerly by the denomination of pure air (vital air), is also the acidifying principle, and consequently the generator of acids. On account of this property tlie new chemists agreed to give it the name of oxygen, of which the word oxide is a derivative. Every metallic substance, therefore, which when exposed to a high tem- perature abandons its consistence, its tenacit)', and its brilliancy, to assume tlie characters of a substance pulverulent by the addition of oxygen, the base of vital air, which has served for the combus- tion, ought to exchange its old name calx for that of oxide. Hence the expression oxide of lead, oxide of tin, oxide of copper, iron, bismuth, &:c. j because in this case these meLils are oxidated by oxvgen, which exists in tliera in tlie pure state, and not in that of gas. The heat being increased, it at length favours the combination of the oxygen contained in the air witli the metal, and reduces it to a metallic oxide : but acids furnish, from tlieir own substance^ tlie oxygen necessary for oxidation J audit is tlie speedier as the acid is more disposed towards the combination. All these particular effects are connected with the general theory of combustion, the principal result of which is the combi- nation of oxygen, the base of pure air, with the combustible body. From these observations the reader will be enabled to compre- hend easily the tlieoiy of the reduction of metallic oxides. Thiy reduction cannot take place but when a combustible body such as charcoal is applied to them, under the influence of a very higb temperatiue. The oxygen contained in the metallic substance, which it converted into an oxide, joins the combustible body, by the effect of elective ailînity, and forms with it carbonic acid (fixed air), which escapes : the m.etal being then abandoned re- appears witli its former properties. CREMNITZ WHITE. 286 Two of these specimens seemed to be mixed -with a' great deal of chalk. The Cremnitz white, ■)0ndi coî]-_ tained this mixture, was in cakes of about tv/o or thrc\^ inches square, and different in thickness ; but ic never exceeded an inch. Cremnitz white, made with bismuth oxidated by means of nitrous acid, or in any other mamier, ought to possess no advantage over that which has lead for its basis. It is more liable to be altered by the impres- sion of the light, and of the vapours which arise from stagnant water, privies, &c. Composition of a white colour, to ivldch I give the name of Cremnitz white. I found means to make a beautiful pearl white, which I call Cremnitz white, with the oxide resulting from the rapid solution of tin in nitric acid (pure aqua- fortis), to which was added a fourth part of the subli- mated oxide of zinc (flowers of zinc), and an eighth of white clay, extracted from Briançon chalk washed in distilled vinegar *. This mixture, when thoroughly When the term metallic oxide, therefore, occurs in the chapter on colouring substances, or elsewiiere^ it is always to be nnder- ptood as substituted for the word calx, which has no relation with fhe present theory of chemistry, * To prepare Briançon white, select the whitest specimens, and Tasp tliem with a piece of the skin of the sea-dog. Put the powder into a jar, with a quart of good vinegar for every pound of the powder : stir the mixture daily for two weeks, and decant the .vinegar without agitating tlie deposit : then pour clean water over the deposit, and, having stirred it, threw the whole upon a filter, t>y which means the water of the first washing will be separated. 286 TREATISE ON VARNISHES. washed, dried, and sifted through a silk sieve, gave a very v/hite powder of a mean gravity; and so secure from all changes effected by the impression of the light 'arid of vapours, that no composition of this kind can be compared to it. It is certainly too expensive for house painting ; but it may be useful for objects which require other processes than those employed in com- mon. It would, no doubt, be attended with great advantage in painting pictures. Were it necessai-y to substitute any other metallic substance, lead ought to be preferred to bismuth. Lead rapidly dissolved in nitrid acid (aquafortis) is preci- pitated in a white oxide, which resists in a ' sufficient degree the impression of the light, but less so than tin. Those who wish to avoid the trouble of purify- ing Briançon chalk may substitute in its stead very pure Morat or Moudon white. Spanish ivhite. Spanish white is a pure clay, which may be washed in vinegar to separate such calcareous parts as are mixed with it. But this process ought to be employed only Continue to pour more water over the sediment on the iilter, till the water which passes is found to be insipid. Then spread out the filter with the sediment on a hair sieve, sheltered from dust, and dry it till it appears under the form of a white powder. ïlie vinegar here separates from this argillaceous matter all the soluble parts, which might alter its vmctuosity3 and particularly the ferru- ginous particles which are often mixed with it. The division of Briançon chalk may be eifected by pounding it jjin water, which must be frequently decauted when it contains only tlie fine parts. SPANISH V/HITE. GYPSUM. 28t 'in particular cases, when it is necessary to have it ex- ceedingly pure. Its afc;illaceous nature contributes to the solidity of the ground, when it is employed in cil painting or for varnish. It acquires body ; but in these cases it must be used very dry, like all other earths. ^ When moist, their union with oil and varnish is imper- fect: they granulate under the brush. Rolls of washed chalk, which possess none of the qualities required in Spanish white, are often sold in the shops under the same denomination. The diiference, however, between real Spanish white and the chalk attempted to be sold in its stead, may ■ be easily ascertained. Nothing is necessary but to pour upon the specimen a few drops of nitric acid (aquafortis), or of strong vinegar. If the Spanish white ' be pure, there will be no effervescence ; if an effer- ' vescence takes place, it is owing to a mixture of chalk. In this case, take some small fragments of the white and immerse them in half à glass of vinegar : if they disappear entirely with effervescence, the whole is cal- careous ; if any part remains, it will be argillaceous. The quantities of each of these earths may then be ' estimated merely by the eye. ' ' Gypsum. Gypsum is a natural combination resulting fi'om the iUnion of the sulphuric acid (oil of vitriol) and lime (the base of calcareous earth). It is a sulphate of lime. When subjected to calcination it is exceedingly ^seful in the arts. In this state it is employed in build- 28S TREATISE ON VARNISHES. ing, and in decorations for apartments. It is used also with constant success in agriculture. Plaster when mixed with water, in order to be cast in moulds, is subject to certain rules. To give it proper consistence the water it has lost by calcination ^ is sufficient, If too large a r 'iintit)^ be addtd it weakens its force, prevents it from .inquiring body, and renders it wl;at is called drowned -olaster. In preparing it to be r.nployed as a white colour in house painting, it ouguc to be drowned with a great deal of water. This sup.-iabundance of liquid keeps all its parts separated, and favours the required division. When divided in this manner it forms a very valuable article for whitewashing apartments, and for painting in distemper. The last operation is very simple. When diluted with a great deal of water, stir the mass with a broom, and suffer the powder to be precipitated. Decant the supernatant water as soon as it is clear; then wash the matter a second time, and dry the sediment after the ïquor has been poured off. This white is exceedingly fine, and inore delicate than that of chalk when the calcined gypsum is pure; that is to say, without any mixture of clay. Plasterers do not hesitate to substitute this whitening in the room of ceruse, which is not superior in beauty,, but which is more durable and dearer. When toqi thick a coating is applied, it rises in scales j which is, not the case when ceruse is employed. MOUDON WHITE. WHITE LEAD. 289 White of Moudon or of Marat. For some years past we have obtained from the Pays-de-Vaud, in Switzerland, an argentine, silky white, of an exceedingly fine grain, to which we give the name of Moudon or Morat white ; because both these towns are in the neighbourhood of the place where it is extracted. It is a real Spanish white, a pure clay, which is employed with success in our manufactories of paper-hangings. Our druggists often sell it as an absorbing earth, under the name of nitrous panacea, and even under that of magnesia ; though it stands the action of acids without giving the least signs of effer- vescence; This earth would afford a great resource to a manufactoiy of ceruse: when united to that oxide it forms, in oil painting, pearl or dark grays, which are durable and possess great lustre. ■White lead. White oxide of lead by vinegar > White lead is an oxide (calx) produced by the means of vinegar. The process employed for the preparation of it is the same as that used in preparing oxide of lead, com- monly known under the name of ceruse. Lead readily suffers itself to be attacked. Common air exercises an action on it, and covers it with a v/hitish dust, which is nothing else than an imperfect oxide of lead. This substance may be observed on large edifices covered tidth lead j but the oxidation when left to nature is too u 290 TREATISE ON VARNISHES. slow to supply the wants of the arts; ancj for this reason a more expeditious process is substituted in its stead. It consists in exposing plates of lead to the fumes of vinegar. The jars are half filled with vinegar, and the plates of lead, either rolled up or flat, are suspended over the surface of the acid. The jars are then covered, and being placed on a sand bath, a heat is maintained Sufficient to cause the vinegar to throw up ftimes, which circulate around the metallic plates. These va- pours, being of an acid nature, exercise an action on the lead, penetrate into it, and convert it into a white sub- stance called white lead. These plates are removed when it is observed, on breaking them, that the whole lead is converted into oxide, and that no more traces of the metal remain. When these plates are dried they become very solid. Various other processes are employed for the same pui*pose, but they all conduct to similar results. Some manufacturers place these jars in warm dung, and leave them there twenty or thirty days without examining the state of the lead. They then take them out, or scrape them, to remove the oxidated part of the metal; after which they expose the remaining part to new fumes of vinegar, and continue this operation until the whole of it is converted into oxide. This opera- tion, however, is applied in a more particular manner to the fabrication of ceruse ; for when it is necessary to prepare that white lead sold in cakes, and not in the : form of conical pieces, the plates are exposed to the j fumes of vinegar till they are entirely oxidated. ' I WHITE LEAD. 291 Other manufacturers dispose their vessels in such a manner as to favour a distillation. They cover their jars with capitals, in the form of an alembic, and apply a sufficient heat to distil the vinegar. The distilled vinegar is then kept in reserve for the preparation of acetite of lead (sal saturni). In this process the vinegar acts with more energy, and the lead is completely oxi- dated and in much less time. When the vinegar distilled in this operation is em- ployed for the purification of acetite of lead (salt of lead or sal saturni), the same quantity of common vinegar is put into the jars, to supply the place of that which passes over in distillation. But if the distilled vinegar is not destined for any other purpose, it is put again into the jars as soon as a certain quantity of it is found in the receivers. White oxide of lead, vvhen purchased in cakes and not in the form of powder, is free from any alteration; but it is not uncommon to find in the int-erior part of these cakes small plates of lead in the metallic state. Painters, who do not grind their own colours, are often discouraged by the gray tint which white lead as- ;l sûmes under the muller. This effect, v/hich is merely accidental, lessens their confidence in it, and renders them uncertain in the choice of their white. If the vfhite oxide of lead still contains particles of lead not oxidated, this metallic part becomes divided by the iftotion of the muller, and renders the colour grav. Artists, therefore, ought first to ascertain whether the ■*hite lead is pure, and to select those cakes which are thinnest. Besides, the porphyiy and the muller ought u 2 2^2* TREATISE ON VARNISHES. to be perfectly clean ; because this oxide, which offëlî contains a little acid moisture, is more disposed than afiy other matter to attract parts resulting from prece- ding operations of grinding. To obtain it of a fine quality, it ought to be ground several times. It is often preserved under water in earthen-ware or glass vessels ; but, for the m.ost part, it is kept in the form of small pieces of a conical shape. If form be considered as a matter of indifference, the white, newly ground, is spread out on strong paper,, in a thin stratum : when dry it is removed in scales, a!id preserved in that state in vessels well closed, to defend it from the contact of every kind of vapour. This oxide is lead penetrated by oxygen, which abounds in the acid of vinegar ; but it does not contain enough of developed acid to be considered as a salt. It is reserved, in general, for delicate painting. This ' substance, which I shall call white oxide of lead, stands better than that obtained by the following preparation. Ceruse. Oxide of had hy vinegar.- When a manufactory is established for the prepara- tion of ceruse, less precaution is employed in the ex- prosure of the plates of lead than in the preparation of white lead in cakes. The plates are also thicker ; be- cause the oxide is scraped oft as it is formed. When a certain quantity of it has been collected, it is laid on a flat stone placed in a horizontal direction, and is ground by means of a muller fixed in a vertical posi- tion, which is made to turn round. The oxide is mixed with a little tobacco-pipe clay, or with Spanish white j ■CERUSE. ^ 293 •and when the mixture is well kneaded under the muller, the whole paste is divided into small conical cake's, •which are dried in a stove, or in the open air, accord- ing to the season or the situation of the manufactory. Each cake is WTapped up in paper, and tied with a piece of packthread. It is under this farm that it is sold in the shops. If any doubts are entertained of such mixture being genuine, a comparison which may easily be made be- tween the very high price of white lead, which requires iio subsequent preparation, and the very inferior price of ceruse, which must undergo a more tedious process immediately after it is removed from the influence of the acid fumes, will be sufficient to show the effect of adulteration. White lead, indeed, costs three times the money that cei'use does. Manufacturers are not always scrupulous in regard to the choice, nor even the quantity, of the earthy sub- stance which they mix with the oxide. Some employ Spanish white, or exceedingly white tobacco-pipe clay, and adhere to certain doses, which they never exceed ; but others employ white of Troy es, or washed chalk, which they add even to excess. These diflerences, re^ suiting from operations on a large scale, which are sub- ject to no inspection for the security of commerce, render it necessary to be careful jn the purchase of ceruse. The heaviest, under a given volume, as well as that which does not effervesce when an acid is poured over it, ought to be preferred. Chalk does not give to paint- ing the same whiteness and the same body as white day. U3 294 TREATISE ON \V\RNISHE3. Besides these adulterations, practised in large manti- làctories, others are practised in the retail shops, w hich however may be detected. A second mixture of chalk is added ; but in this case the ceruse is sold in powder, and not under the form of cakes. This fraud, there- fore, may be avoided by purchasing no ceruse except that WTapped up in the manner in which it comes from the manufactory. The most certain indication of an- other mixture of chalk is the higher price asked for ceruse in calves than for that in powder, notwithstand- ing the additional labour, and the loss occasioned by pulverization. Of these two preparations of lead, ceruse only is enaployed in the application of varnishes used for va- luable furniture and for pictuies ; but painters are ac- quainted with other substances Y.iiicli may be substi- tuted in its stead. The Dutch once engrossed this kind of manufacture entirely ; but .within these few years new manufactories have been established in England, France, and Italy. Some Marseillese have established one at Leghorn since the revolution ; and two or three years previous to the conquest of Tuscany were sufficient to confirm its suc- cess. This oxide, dissolved agam in vinegar, and made to crystallize, gives acetite of lead (salt or sugar of lead). Roiien 7vhite. Rouen white is a kind of marl (clay and carbonate of lime or calcareous earth), which is mixed with water to separate from it the sandy or coarse particles. The 1 ROUEN WHITE. TROYES WHITE. 295 water is decanted, while still chai'ged with the lightest matter, which forms a sediment by rest. When this deposit has acquired the consistence of a paste, it is taken out, and divided into small masses of about a pound weight each. The mixture of chalk (carbonic acid united to lime) with clay renders the latter less fit than if pure for painting in oil, or for varnish. This white, however, ÎS better for that purpose than the white of Troyes* JVhite of Troyes, white chalk. White of Troyes is a carbonate of lime (carbonic acid united to lime), known commonly under the denomi- nation of chalk. It takes its name from the tovm near which it is found, and where it forms beds of consider» able extent. This white is often mixed with portions of sand, silex (common flint), and other impurities, from which it must be freed. This is accomplished by washing, as already described in the article on Rouen white. This white is sold under the form of large square cakes, weighing ten or twelve pounds each, and of rolls and cylinders of from sixteen to twenty ounces. It is cut also into long square sticks, to give it the appearance of tobacco-pipe clay, -none of the qualities of which It possesses. This is a fraud which may be easily de- fected by means of strong vinegar, which, with chalk, produces an effervescence ; but which has no acdon on - tobacco-pipe clay, nor on real Spanish white. The use of chalk for the common white-washing of apartments is generally prevalent j but gypsum is far U.4 296 TREATISE ON VARNISHES. superior. It serves also for different grounds, either coloured or not, which are applied in distemper. It is rendered more durable by being mixed up with size. But if it be employed as priming, destined to receive colouring parts, the washing it is subjected to in the ma- nufactories is not sufficient : it must be made to undergo the same operation a second time, when not sepa- rated from those parts which escape washing on too large a scale. The application of it in the preparation of paper hangings is prejudicial to certain colours, and particularly to Prussian blue. Chalk carefully washed is not attended with the inconvenience of altering and destroying the colours. The first advantage arising from large manufactories is the œconomy which may be introduced into every branch of them ; and particularly in regard to the number of workmen. When a common matter is em- ployed, pulverization by the hand becomes ve^y ex- pensive. A mill or a turning muller will perform, in a few hours, what could not be accomplished by seve- ral workmen in the course of as many days. In the operation here alluded to, the matter is placed on a flat stone, in order to be pulverized by a vertical rauller, which revolves in that position. Washing com- pletes the separation of the parts most attenuated from those which stiil require some more revolutions of the muller, if the matter be received in a close hair sieve. It is treated with a large quantity of water, and the mixture is stirred with a clean broom. A sediment is speedily formed by a little rest. The supernatant water is reddish : when the water has been decanted, the de.- WHITE OF ZINC. 297 posit, for the greater security, is mixed up with a new quantity of the same liquid, and as soon as a sediment is formed it is separated in the same manner. The precipitate acquires the consistence of a paste, which is divided into small portions to facilitate its desiccation. This matter when washed, as here described, exercises no action on compound colours ; and Prussian blue (prussiate of iron), according to the account of an in^ genious manufacturer of paper hangings, experiences no more change from it. Carbonate of lime (chalk), which has not been washed, produces the same effect on prussiate of iron as an alkali or lime would do. This affords a new subject of research in regard to this kind of manufacture. White of Troyes, or chalk, is proper only for paint- ing in distemper. With oil and varnishes it becomes brown ; and with the latter it has the inconvenience of splitting. Besides, it is not fit for priming, like clay mixed with a little ceruse. Colours which admit chalk have no lustre, for want, perhaps, of the second wash- ing ; and they are not durable, even though the chalk may be mixed with a little ceruse, JVhiie of zinc. Sublimated oxide of zinc. Calx of zinc. Fhivers of zinc. The discovery of a white colour, unalterable by the impression of oil, light, and vapour, has long been a desideratum to painters. All the known compositions of this kind were attended with the inconvenience of assuniing, after a certain period, tints different from i^hose which the artist was desirous of fixing. A brown-. 29S TREATISE ON VARNISHES. ish or yellowish appearance destroyed the effect, and left the painter very far short of what he intended. Works of genius ought to survive in their full glory the perishable hand of the artist, by whom they have been successfully executed. It was, therefore, doing a real service to painting, to ensure the hopes of the great masters repecting one of those colours which are chiefly employed by them in their compositions. Guyton de Morveau thought he should be able to discharge this task reserved to chemistry, by substituting sublimated oxide of zinc (flowers of zinc) for the oxides of lead and bismuth (white lead and calx of bismuth), the use of which was attended with discouraging incon- veniences. For this purpose he employed the utmost care in the establishment of a manufactory of the sub- limated oxide of zinc, in order that he might give effectual assistance to the art of painting. JMetallic colouring substances have at all times been considered by painters superior in one point to earthy matters, and to those extracted from the vegetable kmgdom. They unite much better with the oil used in mixing them up, and they produce, under the influ- ence of the light, more extensive effects, as well as mellower and better maintained tones, in consequence, no doubt, of their solidity and particular texture. In this respect the application of the oxide of zinc to the sublime kind of painting, formed an acquisition the more valuable as it completely superseded the necessity Cîf using other oxides ; which, for very good reasons, ought long ago to have been confined to common paint' ing and house-painting. \1'HITE OF ZINC, 299 In arts which require long experience, before it is possible to form a correct judgment in regard to new processes, the desired end can be attained only by de- grees. Some painters find this oxide of ^inc too dry ; and, in consequence of this prejudice, they choose ra« ther to expose themselves to inconveniences which they have always dreaded, but with the limits of which they are acquainted, than undertake trials which they fear still more, because they are ignorant of the bounds of their results. Routine very often multiplies difficultly : at any rate it does not seem calculated to remove, nor even to lessen them. We are inclined to believe that in the present case it is more powerful than reasoa. Time alone can determine what advantages will be de- rived from the use of this oxide. In similar cases com- parative trials overcome all difficulties, and exhibit every thing in its proper light. The trials, therefore, may be varied, by comparing the effects of this oxide with ■those of the two oxides in som.e measure proscribed, and those exhibited by that kind of Cremnitz white the composition of which I have already described. The pro- cess is easy, and may be performed by any one. It may even be varied in regard to the addition of white clay. Sublimated oxide of zinc is obtained by fusing that metal in an earthen tube, which performs the office of a crucible, and which is placed obliquely in a reverbe- rating furnace, or in any other capable of producing a heat sufficient to make it enter into fusion. The metal then soon inflames, and emits thick white fumes, which, if the zinc be pure, are converted into very white woolly /lakes. These flakes, which adhere to the sides SCO TREATISE ON VARNISHES. of the tube, are called sublimated oxide of zinc (flowers of zinc). If the zinc contains iron, the oxide is of an orange- yeliow colour : the metal is purified by throwing into it, while in fusion, some pinches of the flowers of sul- phur. Azure, Enamel blue. Sqffer blue. Saxon blue. Vitreous oxide of cobalt. Painters make use of a vitreous matter, which derives its blue colour from the oxide (calx) of a metallic sub- stance called cobalt. It is manufactured on a large scale in Saxony, where mines of cobalt are abundant. From this circumstance only it has acquired the denomination of Saxon blue. Cobalt is not produced by nature in a state of purity. It presents itself to the miner mixed with earths and stones, united to sulphur or arsenic, and often to both. These, however, are not the only matters from which it ought to be separated ; its ore contains, for the most part, bismuth, nickel, and silver. The working of it is attended with many difficulties, which render it neces- sary to multiply the processes. The first operation is that of roasting. The ore is broken, to separate it from |the stones ; and the fragments abundant in ore are placed apart, in order to be subjected to calcination. Those which contain a great deal of stony matter are carried to the stamping mill. As this pulverization is effected in running water, the water carries with it the stony parts, which are hghter than the ore, while the latter reniains partly in the trough, and partly in the AZURE. SAXON BLUE.- i?Ot first reservoir. The pounded ore is then dried, and afterwards roasted^ Roasting is performed by causing flame to be rever* berated on the matter. The part which supports the ore has the form of a very fiat spheroidal segment, in the middle of which is a cavity shaped like a crucible, to receive the bismuth, which proceeds thither on the fii*st impression of the caloric (tire). During the ox- idation (calcination) of the cobalt, the sulphar and arsenic are volatilized ; the first under the form of sul=» phuric and sulphurous acid gas, and the second under that of oxide of arsenic. The latter, in becoming sub- • limed, covers with white and black flakes the whole interior part of a long gaUery. When the cobalt ore has been roasted to the proper degree, it assumes the colour of wine lees. It is then mixed with four or five parts of silex (common flint) pounded in a mill, after it has been brought to a white heat, and quenched in cold water, that its parts may more easily be divided. This mixture, known under the name of safter, is employed by potters mixed with a portion of an alkaline salt, as a blue colour for their earthen-ware. Azure, enamel blue, Saxon blue, smalt, or vitreous oxide of cohall, is saffer reduced to blue glass by the action of a violent fire. The more the glass is charged with oxide of cobalt, the intenser the blue colour be- comes. This vitrification is facilitated by the addition of a certain quantity of carbonate of potash (alkali of potash), or carbonate of soda (effervescent alkali of soda). S02 TREATISE ON VARNISHES, Smalt, or the vitreous oxide of sailer, reduced to coarse powder, is distinguished by the name of coarse Saxon blue, or enamel blue. Some pretend that it is four times fused and pulverized, after it has been pour- ed in a liquid state into a certain quantity of water. This blue is employed in oil painting, and in some kinds of distemper. This vitreous ozàde of saffer requires great care be- fore it can be applied to delicate kinds of painting. It must be ground for a very long time ; and as the glass is exceedingly hard, this mechanical labour, to many painters, is highly disagreeable. It is destined for dra- pery of a soft blue colour ; but it is attended with the fault of being somewhat dry, and this is owing to the vitreous nature of its composition, which prevents it from adhering to the canvas, and irom forming a body with other colours. Were it not for the tenacity of the oil, which serves it as cement or varnish, it would fall into dust. The great consumption which the Genevese artists make of blue extracted from cobalt, and the difficulty they have often experienced to obtain it of a degree of fusibility suited to the delicacy of enamelled articles, have sometimes obliged them to prepare the oxide themselves from the ore. It was for their use, in par- ticular, that 1 have detailed the processes employed for that purpose. Ultramarine. Ultramarine is extracted from Iripif; lazuli, or azure stone, a kind of hea^y zeolite, which is so hard as to strike fire with steel, to cut glass, and tp be susceptible ULTRAMARINE. $0^ of a fine polish. It is of a bright blue colour, varie- gated with white or yellow veins, enriched vidth small metallic glands, and even veins of a gold colour, which are only sulphurets of iron (martial pyrites). It breaks irregularly. The specimens most esteemed are thos^ charged with the greatest quantity of blue. It is found in Asia, particularly in Persia, and in the kingdom of Golconda. A beautiful kind of it is brought also from Siberia, Prussia, and Spain ; but it is not so hard as that of Asia. The Romans, who set a great value on this stone, rendered it so common m Italy that it has been employed for mosaic painting : in a word, they extended the use of it so much, that tliey introduced it by way of decoration in their buildings \dth the same profusion as common marble. The Jesuits, who earned on a great trade with it, contri- buted not a little to make it subservient to the luxury of the arts. The operation of extracting ultramarine from lapi^ lazuli having been much encouraged by the excessive price given for this truly valuable colour, the abun- dance of it has occasioned a considerable diminution of the stone which produces it. This inconvenience has been followed by another. The present price of ultra> marine is superior to that of gold. It is even probable that it will still increase in proportion to the scarcity of thç stone, which has become greater since the sup- pression of the order of Jesuits, and by the dispersion of it in consequence of the general revolution \i'hich has token place in the political state of the ecclesiastical do- minions» 804f Treatise on varnishes.' Several artists have employed their ingenuity on pro- cesses capable of extracting ultramarine in the greatest purity. Some, however, are contented with separat- ing the uncoloured portions of the stone, reducing the coloured part to an impalpable powder, and then grind- ing it for a long time with oil of pinks. But it is cer- tain that, in consequence of this ineffectual nrethod, the beauty of the colour is injured by parts which are fo- reign to it ; and that it does not produce the whole effect which ought to be expected from pure ultra- marine. The most beautiful ultramarine and the richest in colour has, over the best prepared Prussian blue, the in- valuable advantage of uniting in a natural manner with the fins carnation of beauty. It is superior to Saxon or enamel blue in the richness and mellowness of its tone. It is not sandy like Saxon blue ; it never de- ceives by the effect of time the hope of the artist who has applied it. In this point of view alone it is worth a greater price than has been fixed on it. When considered, therefore, in its full splendour, and with all its attributes, it is rather a production of art than of nature. At any rate, if nature performs the first part, art disengages it from all substances fo- , reign to its composition, and makes it appear with its înost valuable characters. ;/ It maybe readily conceived, that these eminent qua-*, lities must have induced those first acquainted with ths processes proper for increasing the merit and value of it to keep them a profound secret. This was indeed' the case. Ultramarine was prepared long before any account. ULTRAMARINE. 305 of the method of extracting and purifying it was known. 'The first writer who speaks of it is Ansehn de Boot, who describes the preparadon of it in his Treatise on Pre- cious Stones. After him, Kunckel and Neumann, who employed themselves on the same processes, speak of them also, but without entering into minute details. They were satisfied with giving the most essential obser- vations necessary to facilitate the complete extraction of the colouring part. Kunckel separates from the stone the most apparent parts of the ultramarine ; reduces them to the size of â pea, and, having brought them to a red heat in a cru- cible, throws them, in that state, into die strongest distilled vinegar. He then grinds them with the vine- ' gar, and reduces them to an impalpable powder. He next takes a quantity of wax and colophonium, equal to that of the lapis lazuli, that is to say, an ounce or half an ounce of each of these three substances ; melts Ûie wax and the colophonium in a proper vessel, and adds the powder to the melted matter ; then pours the mass inip cold water, and leaves it eight days at rest. He next takes two glass vessels filled with water so hot that the hand can scarcely bear it ; kneads the mass in the water ; and when he concludes that the purest part of the ultramarine has been extracted, he removes the resinous mass into the other vessel, where he finishes the kneading to separate the remainder. The latter por- tion appeared to him to be much inferior, as it was paler than the former. He then leaves it at rest for four day6, to facilitate the precipitation of the ultra- 5d^ T^REATI^E O^ VARNISHES. marine, which he extracts by décantation, and wasfies, no doubt, in pure water. According to the remark of this author, ultramarine of four quaHties may be separated by this process. The first separation gives the finest : as the operatic^s are repeated the beauty of the powder decreases. Kunckel considers immersion in vinegja? as the essen- tial part of the. operation. It facilitates, no doubt, the division and even the solution of the zeolitic and earthy particles soluble in that acid. Neumann*s process is much shorter. He first sepa- rates the blue parts, and reduces them, on a piece of porphyiy, to an impalpable powder, which he besprin- kles v.-ith linseed oil. He then makes a paste with equal parts of yellow wax, pine resin, and colophonium, that is to say, eight ounces of each ; and adds to this paste half an ounce of linseed oil, two ounces of oil of tur- pentine, and as much pure mastic. He then takes four parts of this mixture, and one of lapis lazuli, ground with oil on a piece of porphyry^ mixes the v/hole warm, and suffers it to digest for a month. At the end of that period he kneads the mix- ture thoroughly in warm water, till the blue part sepa- rates from it, and at the end of some days decants thé Hquor. This ultramarine, he says, is exceedingly beîwtiful. These two processes are nearly similar, if we except' the preliminary preparation of Kunckel, which consists rn bringing the lapis lazuli to a red heat, and immer- stjig it in vinegar. Jt may be readily seen, by the ]«.-' ULTRAMARINE. S07 cKcious observations of MargrâfF on the nature of this^ colouring part, that this calcination may be hurtful i6 certain kinds of azitre stone. This preliminary opera- tion, however, is a test which ascertains the purity of the ultramarine. As this matter is valuable, some portions of ultra- marine may be extracted from the paste which has been, kneaded in water. Nothing is necessary but to mix it with four times its weight of linseed oil ; to pour the matter into a glass of a conical figure, and to expose the vessel in the balneum marias of an alembic, the water of which must be kept in a state of ebullition for several hours. The liquidity of the mixture allows the ultramarine to separate itself, and the supernatant oil is decanted. The same immersion of the colouring matter in oil is repeated, to separate the resinous parts which still adhere to it ; and the opei'ation is finished , by boiling it in water to separate the oil. The deposit is ultramarine j but it is inferior to that separated by the first washing. JMelhod of ascertaining ichether ultramarine bs adulterated. As the price of ultramarine, which is already very. high, may become more so on account of the difficul- ties of obtaining lapis lazuli, the sources of which seem to have been nearly exhausted,- it is of great import- ance that painters should be able to detect adultera- jtions, which the spirit of avarice introduces into all j articles of value. Ultramarine is pure if, when brought I to a red heat in a crucible, it stands that trial without X 2 " 308 TREATISE ON VARNISHES. changing its colour. As small quantities only are sub- jected to this test, a comparison may be made, at very little expense, with the part wliich has not been ex- posed to the fire. If adulterated, it becomes blacldsh or paler. This proof, however, may not always be conclusive when ultramarine of the lowest quality is mixed with azure or Saxon blue; but if it be mixed with oil, it is found to have very little body compared with its bright- ness. It is well known that vitreous matters, such as azure, exhibit no more body than sand ground on por- phyry would do : ultramarine treated with oil assumes a brown tint. If the painter is satisfied with enjoying in its full plenitude a present of nature exceedingly valuable to his art, without any desire of knowing the principles of its composition, the case is not the same with the naturalist and the chemist. The more valuable an article appears to be, by the service which it renders to the arts, the more worthy they consider it of re- search. This colouring matter, therefore, did not fail to excite the curiosity of chemists. Some, guided by particular results, ascribed it to copper. Others, by extrrxting a few grains of silver from certain kinds of lapis lazuli, thought themselves authorised to ascribe the colour of it to that metal. Margraff, a celebrated chemist of Berlin, asserted that it was indebted for it to iron in a particular state. The sulphates of iron (majtial pyrites), which oftçn heighten the splendour of this substance, afford some reason for admitting in i I PRUSSIAN BLUE. ^9 It this metal : Klaproth is of the same opinion. Does it exist in it under the form of prussiate of iron (Prus- sian blue) modified by a mixture of earthy principle ? The truth of this conjecture can be ascertained only by direct experiments. C. Guyton read in the National Institute, in the year 1 SOO, some observations on the colouring principle of lapis laxuli, which seem to show that it arises from a particular combination of iron and sulphur. He was led to this conclusion by the result of an experiment made, in a strong heat, with a mixture of charcoal-powder and gypsum, coloured red by iron. Though the artificial ultrama> rine which this chemist extracted from it did not answer the expectation of eminent painters, it is still a dis- covery highly interesting to theory. Perhaps it might be substituted for prussiate of iron, which many pain- ters employ, but without placing much confidence in it. Prussian blue, Prussiate of iron. Prussiate of iron (Prussian blue) is the result of a combination of iron with an acid of a peculiar nature, distinguished by the name of the Prussic acid. The discovery of this blue, like many other things, was the mere effect of chance. Dippel, a chemist of Ber* lin, having thrown into his court-yard several liquors which he considered as of no further use, or in order to free his laboratory from them, observed with surprise that some of the stones were covered with a very bright blue colour. He then recollected that he had before thrown out, in the same place, the remains of a solution of sul^ phaté of iron (martial vitriol, green vitriol) j and as these X 3 SIO TREATISE ON VARNISHES. liquors were of an alkaline nature, and had been re- peatedly employed for the rectification of oil of harts- horn, he thought he had now found the key of a dis- covery which appeared to be of great importance. He therefore directed his researches towards this" object, p,nd, after some successful experiments, found means to compose Prussian blue by a sui^e process. At the commencement of the eighteenth century chemistry v/as merely a science of results. The theories applied to a certain aggregate of these results were often the mere offsprings of the imagination. Macquer, the celebrated author of the Dictionary of Chemistry, seems to have fixed for ever the ideas of chemists in regard to the prussiate of iron, by supposing the alkali completely saturated with a particular matter, which Jie calls the colouring matter of Prussian blue, and •which, from the characters of its union with the alkali, he supposed to be of an acid nature. Animal analysis, which has been so much extended under the reign of the pneumatic chemistry, was at that time covered by an impenetrable veil. The part, at least seen by chemists, was confined merely to de- tached and unconnected fragments. As this colour- ing matter exercised its action only under the cover of combination ; and as it eluded ail direct researches, and every method employed to effect a separation of it; the public opinion was divided respecting it till its nature was ascertained by the ingenious experiments oj Macquer. By uniting prussiate of potash (alkali saturated with | the colouring part, of- Prussian blue) and a solution oi 5 ■ ■ PRUSSÎATE OF IRON, 311 sulphate of iron (martial vitriol), he observed the ef- fects of a double decomposition and a double combi- nation. The Prussic acid (the colouring part of Prus- sian blue) abandoned the alkaline base to join the iron, which it converted into Prussian blue; while the sul- phuric acid, which existed in the sulpliate of iron, joined the alkali, to form sulphate of potash. This particular substance, before distinguished by the name of the colouring part of Prussian blue, is therefore an acid; and in the new Nomenclature Ls called the Prussic acid. Its union with iron forms prussiate of iron (Prussian blue), and its affinity for that metal is so great that the strongest mineral acids cannot separate them. Alkalies and lime take it from iron. These sub- stances become saturated with it ; and in this state of saturation they can regenerate the prussiate of iron, when its favourite metal, combined with an acid, is presented to it. This circumstance is indispensably necessary to effect the double decomposition and double combination observed by Macquer. It was reserved for one of the first chemists of mo- dern times to penetrate further into the mystery in which this singular combination was still involved. Berthollet employed himself in researches on Prussian blue ; and it results from his experiments that the prus^ sic acid is a combination of azote, hydrogen, and car- bon, the proportions of which are not yet known*;, • * According to the new nomenclature, that part" of atmo- spheric air which is neither tit for respiration nor combustioii iç named azote. It forms three-fourths of atmospheric air^, an4 X 4 S12 TREATISE ON VARNISHE5. When prussiate of iron is pure, its volume does not decrease in acids, nor does it acquire a more intense colom'. When it loses part of its volume, and acquires greater strength of colour, this indicates a mixture of alumine (the base of alum), which is often intro- duced into its composition. In this case, to obtain it pure, it must be treated v/ith muriatic acid (marine acid), and washed with clean water: it is then thrown on a filter to separate the water from itj after which it Is dried. This colouring substance participates with many other productions of art in the inconveniences resulting from operations on an extended scale. Its colour is not uni- form and constant. Common prussiate is of a pale blue colour, and sometimes exhibits even a greenish tint. The mixture of alumine (alum earth) will serve ■ i\ exists in it in the state of gas, by its union \\ith caloric. Oxygen gas, kno\\'îi formerly by tlie name of pure air, constitutes about one-fourtli part of atmospheric air, \\ithout including the acciden- tal mixture of other gaseous fluids. The base of the fluid distinguished formerly by the rnme of * înftammable gas is now called Jnidroiyai. When united to caloric . jt becomes Iii/a'rogcn gas. This expression has been substituted lor the former, since tlie discovciy^ of the decomposition of \\ater, of ^. wiiich it is a component part. -" Carbon, according to Berthollet, is common charcoal freed from the hydrogen and oxygen which were united with it. These different elements abound in the animal organization. It needs therefore excite no astonishment, if alkali exposed to heat ^^ ith animal substances sh.ould become saturated with these prin- cii>les, which the fire mcdlties in such a mantier as to form of Zj lliem a new acid, without the concurrence of oxygen, which ^ seems to reserve to itself the privilege of acidification. ARTIFICIAL SAXON BLUE. SIS to explain the first effect; but the shade of green de- pends on the state of the prussiate of potash, which is not completely saturated with prussic acid. In this case the free alkaline part, that is to say, the portion not occupied by the acid, precipitates a relative quan- tity of the sulphate of iron, in the state of yellow oxide, the mixture of which with the true blue of the prussiate gives rise to a compound colour, which is green. Tliis oxide of iron is easily separated by immersing the prus- siate in muriatic acid (marine acid). Prussiate of iron acts a distinguished part in house- painting, and even in other kinds. It is, however, often attended with one inconvenience. When ground -with oil it assumes a yellow tint, which some ^eat masters correct by a little violet Jake. This yellotv^ tint seems to arise from the action of the oil. An- other fault which seems to confine the use of this colour is, that the blue it produces is hard, and does not seem to harmonize with that fine carnation which gives chamis to the physiognomy when artfully inter- sected by beautiful veins. Ultramarine alone answers this purpose when employed by the hand of an artist. uArtiJicial Saxon blue made luith prussiate of iron, Saxon blue may be successfully imitated, by mixing 'with a divided earth prussiate of iron at the moment of fe formation and precipitation. Into a solution of 144 grains of suphate of iron (martial vitriol) pour a solution of prussiate of potash (alkah of potash saturated with prussic acid). At the time of the formation of the prussiate of iron add^ in ,3.14? TREATISE ON VARNISHED, the same vessel, a solution of two ounces of sulpha!^ . ,o{ alumine (alum) ; and pour in, at the same time, the solution of potash, — ^but only in such a quantity as may be supposed necessary to decompose the sulphate of alu- mine; for a dose of alkali superabundant to the decom- position of that salt might alter the prussiate of iron. It will, therefore, be much better to leave a little alum, which may afterwards be carried off by washing. As soon as the alkaline liquor is added, the alumine precipitated becomes exactly mixed with the prussiate of iron, tlic intensity of which it lessens by bringing it to the tone of common Saxon blue. The matter is then thrown on a filter, and after being washed in, clean water is dried. This substance is a kind of blue verditer, the intensity of which may vary, according to the greater or less quantity of the sulphate of alu- mine decomposed. It may be used for painting m distemper. Blue verdiier. Nature presents, in certain parts of copper mineSj^. a blue colouring matter which is known by the name of malachite. For the most part it is found in solid' masses, but sometimes in crystals. By pulverization it acquires nearly the appearance of that powder which . painters call blue verditer. It is a natural oxide of, copper: but, however fertile nature may be in pror ducing it, the great consumption made of blue ver- diter leaves no doubt that this matter, which was forr merly procured from Germany, and which is no\y obtained from England, is a result of art, in ^vhich thp ELUE VERDITER.. 51$ copper is brought to a degree of oxidation not always easy to be imitated. It was long imagined that blue verditer was the pro- duct of a preparation, in which lime, muriate of am- monia (sal ammoniac), and copper, dissolved by a mi- neral acid, were acting and constituent parts. This, at least, was the opinion of Rouelle junior, a man justly celebrated in .chemistry. It was reserved, however, for his learned colleague Pelletier to unite the synthesis and analysis he had given of it, and to discover the circumstances which promote or oppose, during the time of the operation, the de- velopment of the blue colour. An interesting detail of the various processes he employed, to procure to his country the fruits of a new manufacture, may be seen in the Annales de Chimie*. Most of the metallic oxides obtained by precipita- tion contain, besides a portion of oxygen, a consi- derable quantity of carbonic acid, (formerly called fixed air, an union of oxygen and carbon). From th.e results of Pelletier's experiments, it appears to be proved, that the colour of the crystals of mountain blue or malachite, and that of blue verditer, cannot be ascribed to a combination of the oxide of copper, lime, and carbonic acid, but rather to a certain degree of the oxidation of the copper. Tliis theory, if I re- collect, corresponds exactly with that given by Mor- yeau, some years before, to explain the cause of the jîifference of the colour of mountain blue arid green» * Yoi. xiii. p. 47. SIS TREATISE ON VARNISHED, "Every precipitation, therefore, of copper, or every hyper-oxygenated natural oxide of copper, such as mountain green or malachite, will not give blue when treated with lime, but will always remain green. în the process employed to make" blue verditer, the lime, according to the remark of the author, seems to act Oft the oxygen contained in the precipitate, and to diminish the proportions. It is to this particular cir- cumstance that we are indebted for the conversion of the blue colour into a green colour, which is constant m precipitates of copper. The process for the composition of blue verditer seems, on the first view, to be simple ; the success of it, however, is often the fruit of long practice. As too circumstantial details are not suited to a work of this kind, I shall confine myself to the most essential points of the operation. An expert chemist may easily supply the rest. Dissolve the copper, cold, in nitric acid (aquafortis), and produce a precipitation of it by means of quicklime, employed in such doses that it shall all be absorbed by the acid, in order that the precipitate may be pure copper; that is to say, without any mixture. When the liquor has been decanted, the precipitate is washed, and spread out on a piece of linen cloth to drain. If "a portion of this precipitate, w^hich is green, be placed on a grinding stone, and if a little quick-lime, in powder, be added, the green colour will be imme- diately changed into a beautiful blue. The proportion of the lizne added is frcm seven to ten parts in a him- GREEN VERDITER. 317 ilred. As the whoie matter has already acquired the consistence (^jLpaste, desiccation soon takes place. A quintal of blue verditer, prepared in this manner, gives the same proportions as those discovered by Pel- letier in the component principles of the best English blue verditer, which are : Carbonic acid - - - - SO parts. Water -34 Pure lime ----- 7 Oxygen ------ 9-^ Pure copper ----- 50 100 Blue verditer is proper for distemper and for ^'^r- nish ; but it is not fit for oil painting, as the oil renders it very dark. If used, it ought to be brightened with a great deal of white. -Green verditer. , Green verditer does not require the same care in the preparation. It is the general result of the precipitation.' of copper, dissolved in the nitric acid (aquafortis), effected by means of chalk or a white marl. In the latter case, the divided clay, which forms part of it^,,. gives pliability to the verditer, when employed as a co- iour. If too much charged with copper it would not be ht for oil painting, as the oil would produce too 4ark a green. In this case it must be corrected by the addition of a httle ceruse or Spanish white. This colour, however, is much better calculated for distemper j and the painter may supply its place in oil S18 TREATISE ON VARNII^HES. painting with verdegris mixed with two or three part§ to one of ceruse. With^very slight do^ of verditer the lightest shades of sea-green may be represented. Cinnabar. I'ermiUon. Red sulpJiurated oxide of vierciiry: The metallic combinations which constitute the greater part of ores depend on a kind of operations which nature performs in silence ; which she varies, and wliich it was reserved for the modern chemistry to discover. Cinnabar, that natural combination of sul- phur and mercury, affords a specimen of these results. Seven parts of mercury and one of sulphur form that brilliant needly m.as?,- of a beautiful red colour, the brightness of which depends on proper proportions of tlie two component principles, as well as on the greatest- possible division of them. Cinnabar, indeed, assumes a very high colour oPxly under the muller. When di- vided in this mechanical manner, it exchanges the name of cinnabar for that of vermilion. Nature rarely exhibits this substance in large masses . and crystallized. In this respect art is superior, since rt prepares it in large masses, and endowed with all the required qualities. It is manufactured chiefly in' Holland. The sulphur is liquefied in large earthen jars, or in iron pots, and the mercury is mixed in the proper' doses. These two matters become heated to such a' degree, by the mere effect of the combinadon, as to' inflame ; and when this result takes place the cinna- bar is more easily sublimated, because the excess of IS Or: CINNABAR. VERMILION. NAPLES YELLOW. 319 siirphur is destroyed. The matter when cold is pul- Srèrized, and made to sublimate in" flat earthen vessels, which are covered by other vessels of the same sub- stance. These sublimating vessels are arranged in long sand furnaces called galleries, where the sublimation is effected only by a very strong heat. ■ If the first sublimation does not produce cinnabar capable of displaying, when ground, a beautiful colour, the matter is subjected to a second sublimation, the eiFect of which is to destroy the quantity of sulphur greater than that essential to the most perfect combina- tion in regard to the tone of coloiu* required in ver- itlinilion. The splendid colour of the vermilion employed for carriages is owing to this composition. It is employed also for painting other articles ; for colouring sealing wax, and, in general, for all ornaments which require a high strong colour agreeable to the eye : of course, it is proper for painting of every kind. Vermihon has no rival but carmine, which, though it produces a mellower and duller colour, is no less pleasing to the eye. s to' Naples yellow. Iclloiu oxide of lead mioced with 2vhite - oxide of antimony hy nitre. It is not long since the nature of Naples yellow was nown. It was formerly believed to be of volcanic )rigin ; and arsenical qualities were ascribed to it, in onsequence of its yellow colour, which gave it some esemblance to orpiment ; and on account of the green, olour communicated to it by iron and steel. This 320 TREATISE ON VARNISHES, effect, generally known to painters, renders it necessary in grinding this colour to employ porphyry and an ivory spatula. All these uncertainties, however, were at length cleared up by the chemical discovery of this composi- tion, the secret of preparing which v/as in the posses- sion of a Neapolitan far advanced in life. Without dwelling on the circumstance of the age of the person "who possessed this secret, and the extensive use made of this preparation, which is fit for painting of everj kind, without excepting enamel and porcelain painting, great merit is to be allowed to the researches of Fou- geroux, who found means to give to this compositioi| a certain effect. The possessor of the secret mixed calcined lead wit a third of its weight of antimony, pounded and sifted, and exposed the mixture to a potter's furnace. Fo geroux de Bondaroy obtained the result by modifyinj the formula in the following manner* : i Composition. Take twelve ounces of ceruse, two ounces of thd sulphuret of antimony (common antimony), half ounce of calcined sulphate of alumine (calcined alum and an ounce of muriate of ammonia (sal ammoniac)J Pulverize these ingredients, and having mixed th thoroughly, put them into a capsule or dish of crucib^'j^'^ earth, and place over it a covering of the same sul stance. Then expose it at first to a gentle heat, whi must be gradually increased till the capsule is mo * MefliQÎ.res deJ['.Aca4iï»le (Jes-Scie^^ee ilf /^2. I ÏTAPLES YELLOW. 321 rately red. The oxidation arising from this process requires at least three hours' exposure to heat be- fore it is completed. The result of this calcination is Naples yellow, which is ground with water on a por- phyry slab by means of an ivory spatula, as iron would alter the colour. The paste is then dried, and preserved fbr use. It is a yellow oxide of lead and antimony. ^ The author observes, that there is no necessity of adhering so strictly to the doses as to prevent their being varied. If a golden colour be required in the yellow, the proportions of the sulphuret of antimony and mu- riate of ammonia must be increased. In like manner, if you wish it to be more fusible, increase the quanti- ties of sulphuret of antimony and calcined sulphate of alumine. I have remarked that sulphuret of antimony, which contains a little iron, like that of Savoy, and sometimes ' that of Auvergne, and which for this reason assumes (after its oxidation a yellow colour, is the most proper for this kind of composition. I have several times supplied this natural want by stirring with a spatula of soft iron white oxide of antimony by nitre (diaphoretic' anti- mony), when in a state of fusion. A kind of yellow from lead, in cakes half an inch m thickness, the edge of which exhibited a needly crystallization, was formerly brought to us from Eng- land. Painters who made use of il knew that muriate of soda (common salt) entered into this composition;, the process foi' preparing which is a*^ follows : I., 322 -Treatise on varnishes* Montpellier y elloiv. Yellow oxide of lead ly tliC muriatic acid. C. Chaptal, formerly professor of chemistiy at Mont- pellier, naturalized in France this preparation, by esta- blishing a manufactory of it in his native town. The same process furnished matter for making metallic yellow, and separated at the same time the alkali from the soda, which serves as a base to sea salt. At that period the French government encouraged chemists to make re- searches respecting the means of obtaining this alkaline salt, at such a price as might enable it to stand in com- petition ^^ith the potash obtained from foreign coun- tries, and to supply its place in the time of war. The proportions, in case of necessity, may be reduced. Take four quintals of vitreous oxide of lead (litharge), well sifted, which must be divided into four equal por- tions, and put into as many glazed earthen vessels. Dissolve also one quintal of muriate of soda (sea salt) in about four quintals of water. ?| Pour a fourth part of this solution into each of the four earthen vessels, to form a paste of a light consist- ence. Leave the whole at rest for some hours, and when the surface begins to grow white, stir the mass with a strong wooden spatula. "Without this motion it would acquire too great hardness, and a part of the salt would escape decomposition. As the consistence increases, the matter is diluted with a new quantity of the solution ; and if tliis is not sufficient, recourse must be had to simple w-ater to main- tain the same state of consistence. The paste is then MONTPELLIER YELLOW. 323 very white, and in the course of twenty-four hours be- comes uniform and free from lumps. It is then suffer- ed to remain for the same space of time, stirring it at intervals to complete the decomposition of the salt. The paste is then well washed to cairy off the caus- tic soda (soda deprived of carbonic acid) which adheres to it ; and to extract the whole of it, the mass is put into strong linen cloth and subjected to a press. The remaining paste is distributed in flat vessels ; attd these vessels are exposed to heat, in order to effect a proper oxidation (calcination), which converts it into a solid, yellow, brilliant matter, sometimes crystalHzed in transverse strias. This is Montpellier yellow, which may be applied to the same purposes as Naples yellow. In this mixture of vitreous oxide of lead with mu- riate of soda, dissolved in a sufficient quantity of water, the latter salt is decomposed. The muriatic acid aban- dons the alkali of the soda, which served it as a base, and joins the vitreous oxide of lead, which is converted into muriate of lead ; and at length, by the aid of caloric (of fire), into yellow oxide of lead. The soda separated by the washings is caustic, that is to say, pure, and without any mixture of carbonic acid. By leaving it exposed to the air it becomes charged with carbonic acid (formerly fixed air), diffused throughout the atmosphere, and is rendered crystallizable. It is then carbonate of soda (salt of soda). Seventy-five pounds of soda, purer than that of the shops, is ex- tracted from this mixture*. •^ See Jourrifll de Physique, August 1794. 524 T*EATISÇ ON VARÏx'ISîris, Indigo. The East and West lîidiec, as \-'eîI as some coun-î tries of the American continent, such as Brasil, Peru, &c. produce a plant called by the Spaniards anillo, the juice of which, when subjected to spirituous fermenta- tion, gives a fecula of a blue or dark azure colour, imported to us under the form of square flat pieces, not very haîrd, which float on water : they are inflam- mable, and when put into the fire are almost entirely consumed. The best and most esteemed is called Guatimala in- digo, from the name of a town in Spanish America, where it is prepared on a large scale, and with the great- est care. When rubbed on the nail it leaves a trace similar in colour to the antient bronze. This character is always much sought after ; and indigo of this kind is called cupreous indigo. A fecula of a blue or dark violet colour, called also indigo, is brought to us from Brasil. It differs from real indigo by being produced from the leaves of the anUlo, while common indigo is formed from all the ex- ternal parts of the plant. The pulverization of indigo is attended with the same iiiconveniences as that of certain colouring substances of which clay forir-s the basis : but the operation may be very much shortened by putting three or four eight- pound shot into a large copper bason with the quantity of indigo intended to be pulverized. A slight circular motion communicated to the bason, held in the two INDIGO* SUS hands over a tablej Vîàll be sufficient to make the bullets roll over the matter, and to pulverize it much betteç- than if pounded and sifted, as in this case it often forms itself into balls, and does not pass through the sieve. These two kinds of indigo can be applied only to painting in distemper, with or without varnish. They are not proper for oil painting, because the oil renders them black or green, and they lose in drying a part of the vigour of their tone. In general, indigo is not em- ployed pure : jt is always mixed ^^ith v/hite ; if piire, i: would become black. Ceruse, indigo, a^d a particle of black, if the proper proportions be obser/ed, give 3 beautiful pearl gray colour. l!> distemper, indigo i^ employed for paintmg th^e sky, sea, and ^U the distant parts of a landskip. The use of indigo is not confined to painting in dis- temper. When subjected to certain chemical processes, it may be extended to miniature painting. Indigo united to sulphuric acid (oil of vitriol) in the state of ^ solution, diluted with v^ater, gives to woollen and silk the beaudful and solid colour of Saxon blue. This bluç of indjgOj and the yellow of indigo produced by nitric acid (aquafortis), when mixed in certain proportions} give a beautifnl and soHd green, which may be em« ployed in that kind of miniature painting which serves to ornament silk, fans, &c. These three colours, when intended for paper groundsj, must be weakened with water. The mucilage proper :^r the latter kind of painting ought to be exttact,^ noi Y 3 S^è TREATISE ON VARNISHES. of gum arabic, but of gum tragacanth, which has mora body. The works which may be consulted in regard to in- digo are Mémoires de Qiiatremere d* lyonval, crowned in 1777 by the Academy of Sciences at Paris, and the Journal de Physique for July 1777? which giyes an abridgment of them. Of lakes. Lakes, in general, are produced by the decomposi^ tion of sulphate of akmiine (alum), by a substance which seizes on the sulphuric acid, and liberates the alu- mine which served it as a basis. This earth, in pre- cipitating itself, unites to the vegetable or animal co- louring fecula, which passes into the bath. It is this colouring fecula, united to alumine, which constitutes the different carminated lakes and crayons. It appears that the v/ord lac or lahe is of Indian extraction, and that it is employed in that country to express a colour, or a solid colouring part : it has therefore a particular acceptation, which has been somewhat generalized in our language. The preparation of crayons, which has given birth to a particular kind of painting, is not confined to the chemical process above mentioned : there is one sim.pler and less tedious ; it is that which serves as a basis to the preparation of Dutch pinks. It consists in mixing up with the coloured bath an argillaceous matter of the first quality, and subjecting the whole to careful evapo- ration, or in exposing the hquid paste on driers of | fpiti LAKES, 327 plaster covered with a clean cloth, to prevent the crayon from adhering to the drier. This method is more ceconomical than the chemical process ; but it requires a very nice choice in the qua- lity of the white destined for the operation, and in par- ticular the precaution of previous washing, to remove the fine sandy parts with which the finest white clays are mixed. The variety observed in the tone of lakes extends also to their qualities. They are more or less capable of resisting the impression of the air and the light, ac- cording to the nature of the substances from which they are extracted. The lakes most in request are those called carminated lakes, whatever may be the intensity of their colour, because experience has shown that they oppose the strongest resistance to the destructive influence of the light. Their colouring part is extracted from cochineal, the price of which has increased in consequence of its intrinsic qualities in various prepa- rations employed in the arts of painting, dyeing, and calico printing. They are imitated with colouring parts extracted from certain vegetable substances ; but the latter produce only false carminated lakes, as their co- louring part is easily altered by the combined action of the air and the light. These colouring parts, however, are still of some use when reserved for temporary ob- jects, as printed calicoes, paper hangings, &c. ; but they tnust be entirely banished from the pallet of the painter who sets any value on the opinion of posterity. The epithet of carminated, applied to the valuable lakes, is Y 4< S2S Treatise on varnishes. derived from a series of operations on the compositîoîî of carmine, which is prepared from cochineal. ît is not so easy as some have imagined to distinguish whether a hike has really been extracted from cochi- neal, or from some vegetable colouring substance. Means have been found, by certain re-agents and va- | rious mixtures, to give such splendour to inferior lakes that the most skilful painters are often embarrassed in their choice. The dread of employing uncertain colours renders them timid, and often makes them neglect co- lours the duration of which they cannot foresee. Among this number are lakes. The inefficacy of the means said to be proper for determining their choice in this respect, has served only to increase their uncer tainty. If vinegar, we are told, be poured over lakes, the colouring part of which has been derived from Brasil wood or madder, &c. they will instantly turn yellow. We shall soon see how little confidence ought to be placed in processes the results of which require ^ more dme than an artist in full employment can devote to them. I have, therefore, thought that this object is of sufficient importance to deserve particular re- searches : with this view I prepared some real as well as false carminated lakes, that I might subject them to the action of some re-agents, and for this reason I have distinguished each preparation by a number, that they may be more easily indicated in the annexed table,] which exhibits the results of comparative experiments ît will be found at the end of this article. CARMINE. CARMINATED LAKE. S29 Carmine. This kind of fecula, so fertile in gradations of tone by the effect of mixtures, and so grateful to the eye in all its shades ; so useful to the painter, and so agreeable to the delicate beauty, is only the colouring part of a kind of dïûed insect, known under the name of co- chineal. A mixture of 36 grains of chouan seed, 1 8 grains of autour bark, and as much sulphate of alumine (alum), thrown into a decoction of 6 gros of pulverized cochi- neal and 5 pounds of water, gives at the end of froin five to ten days, a red fecula, which when dried weighs from 40 to 48 grams. This fecula is carmine. The remaining decoction, which is still highly coloured, is reseiTed for the preparation of carminated lakes. CARMINATED LAKE. No. L The decoction which floats over the coloured preci- pitate, known by the name of carmine, being still highly coloured, the addition of sulphate of alumine, which is afterwards decomposed by a solution of carbonate of soda (salt of soda), disengages the alumine, and the alumine in precipitating itself carries with it the colouring part of the bath. According to the dose prescribed for the composition two or three ounces of alum may be employed. The greater or less quantity of this sub- stance, the base of which seizes on the colouring fe- cula, determines the greater or less intensity obsei"vei in the colour of the lake resulting from it. When tlie S50 TREATISE ON VARNISHES. process is conducted on a small scale, and by way of trial, the precipitate is received on a filter : it is then washed with warm water ; and when it has acquired the consistence of soft paste, it is formed into small cakes or sticks. It is this substance which constitutes the beau- tiful cai'minated lakes used for crayon painting. In operating on a large scale, the whole of the alka- line liquor judged necessary after a few trials to decom- pose the quantity of alum intended to be employed, may : be divided into three or four separate portions. As many clotf^ filters as there are alkaline portions being then prepared, the first portion of alkaline liquor is ^. poured out, and the coloured precipitate resulting from it is received on one of the filters : the coloured liquor which passes through the filter receives thç second por- tion of alkaline liquor, and the latter produces a se- cond precipitate, which is received on a new filter. I'his operation is then continued till the last portion of alka- line liquor has been employed. The lakes deposited on the filters are washed in warm water; and when they • hâve drained, they are carried along with their cloth to ^ {he plaster driers, or to beds of new bricks. These driers, which are made of wrought plaster, in the form cf thick basons, or these bricks, attract the moisture of the paste, and shorten the process. The first pre- cipitation gives a carminated lake of a very high co- ioui" ; the second is somewhat lighter ; and the rest go en decreasing in the same manner. By thèse -means the artist obtains from the same bath shades of colour varied without end, much mellower, and more delicate " than those resulting from a mechanical mixture of CARMINATF.D LAKE. S3l white clay in different doses, and lake saturated "with 'colour by one operation. If the composer of crayons prefer in these opera- tions to mix the bath of cochineal with white clay. Well washed and of the first quality, he may obtain the same shades by diluting with one measure of the decoction of cochineal different quantities of clay. For example, a pound of decoction saturated with colour, and a quarter of a pound of clay ; the same quantity of decoc- tion, and half a pound of clay ; a pound, and so on. This operation, which is conducted in the same manner as th?t ^OY Dutch pinks, is speedier than that performed by a chemical decomposition with alum and an alkali. The lakes obtained are exceedingly beautiful ; but unless the clay be of the first quality they never have the brightness, softness, and mellowness of the former ; as the valine matters employed form a mordant which is not furnished by the second method. In the latter, the ^vashings, which are indispensably necessary to carry off" the salt resulting from the new combination, are sup- pressed. A beautiful tone of violet, red, and even of purple red, may be communicated to the colouring part of cochineal by adding to the coloured bath a solution of ■tin in nitro-muriatic acid (aquaregia). The effect will be greater, if, instead of this solution, a solution of oxygenated muriate of tin (fuming liquor of Libavius) be employed. The addition of arseniate of potash (neutral arsenical salt) gave me shades which would be sought for in vain with sulphate of alumine (alum). S3a TREATISE ON VARNλHE5» JÎnother method ofpreparhig çarminated lake, ly eX'* ir acting the colouiijig part from scarlet clotL Carminated lake may be composed also, without em- ploying cochineal in a direct manner, by extracting the colouring matter from any substance impregnated with It, such as the shearings of scarlet cloth. Put into a kettle one pound of fine wood-ashes with forty pounds of water, and subject the water to ebulli. tion for a quarter of an hour ; then filter the solution ^irough a piece of linen cloth till the liquor passes through clear. Put the liquor on the fire ; and having brought it to a state of ebullition, add two pounds of the sheaiings^ or shreds of scarlet cloth dyed with cochineal, "which must be boiled till they become white ; then filter the liquor again, and press the shreds, to sqyeeze put all the colouring part. Put the filtered liquor into a clean kettle, and place It over the fire. When it boils, pour in a solution of ten or twelve ounces of alum in two pounds of spring water which has been filtered. Stir the whole with a wooden spatula till the froth that is formed be dissipated ; and having mixed with it two pounds of a strong decoction of Brasil wood, pour it upon a filter. After filtration, wash the sediment with spring water, and remove the cloth filter charged with it to plaster driers, or to a bed of dry bricks. The resulf df this operation will be a beautiful lake ; but it has not the soft velvety appearance of that obtained by the first method. Besides, the colouring part of the Brasil ROUGE. S53 wood which unites to that of the cochineal in the shear- ings or shreds of scarlet cloth, lessens in a relative pro- portion the unalterabiiity of the colouring part of the cochineal. For this reason purified potash ought to be substituted for the wood ashes. In this process the sulphate of alumine (alum) un- dergoes decomposition by the presence of the alkaline liquor or solution of wood ashes, which is a carbc» nate of potash. The alumine, in precipitating itself, seiies on the colouring fecula of the cochineal, which rhe scarlet rags have abandoned to the alkali. After the operation, the driers of plaster, or the bricks, v/hich have extracted the moisture from the precipitate, are e2;:posed to the sun, that they may be f.tted for another operation. This method is more complex than the preceding. Besides, it is not ceconomical for colour-makers who may be at a distance, from cloth-dressers. The shear- ings of cloth are in great request among the manufac- turers of paper-hangings, which renders the price of ihem too high to admit of their being employed in the reparation of carminated lakes. This, therefore, h he only process I never repeated. Rouge. Carmine united to talc, in different proportions, forms rouge employed for the toilette. Talc is distinguished-, ^also by the name of Briancon chalk. It is a substance composed, in a great measure, of clay combined natu- pUy with silex. Carmine, as well as carininat':^d lakes, that is to say^ 33"* TREATISE ON VARNISHES. those the colouring part of which is borrowed from cochineal, are the most esteemed of all the composi- tions of this kind, because their colouring part main- tains itself without degradation. There are even cases where the addition of caustic ammonia, which alters so many colouring matters, is employed to heighten its colour. It is for this purpose that those who colour ^ prints employ it. | FALSE CARMINATED LAKES, IN WHICH THE CO- LOURING PART IS DIFFERENT FROIVI THAT OF COCHINEAL. Carminated fake extracted from madder. No. 11. Notwitlistanding the unfavourable opinion entertained in regard to lakes extracted from vegetable substances, C. Merlnet, an ingenious painter, found in the root of madder a colouring substance to which the addition of sulphate of alumine (alum) gives a veiy warm tone of purple red, exceedingly bright, and of such durability as places this lake far above that obtained from a de- coction of Brasil wood. Such, at least, is the account Ï have seen of it*. « ioc fi ill * Certain saline substances^ which chemists and the inanufacturers of colours employ as re-ageuts and mordants, have a very striking influence on several vegetable colouring matters, which tliey mo- dify in a particular manner that depends on their state of composi- tion. Though experience seems to have limited the number of these re-agents, there is reason to presume that new researches in If gard to the numerous saline combinations known in chemistry. i^k CARMINATED LAKE FROM MADDER. 3S.> ,, The following process, which I employed to make lake of madder, was attended with complete success. Experience will soon show what are the proper doses of the principal substance and of the re-agents. Boil one part of madder in from twelve to fifteen parts or pounds of water, and continue the ebullition till it be reduced to about two pounds. Then strain the decoction through a piece of strong linen cloth, which must be well squeezed ; and add to the decoction four ounces of alum. The tint is then a beautiful bright red, whicti the matter will retain if it be mixed with proper clay. In this case, expose the thick liquid which is thus pro- duced on a linen filter, and subject it to one washing and those especially, the base of which is metallic, would still pro- cure new resoui'ces to the art of colour-making, cotton-printing, dyeing, &c. The animal organization, aiid the motion which constitutes life, give, under certain circumstances, results similar to those obsers'ed in certain vegetable or animal colouring matters subjected to the influence of chemical agents. The colouring part of the cactus opuntia, on which the cochineal is produced, and on which it feeds, receives, according to every probability, from tlie insect all those qualities v/hich raise it so far above all tlie colouring feeulse of the ame tone. The case is certainly tlie same with that of madder, rt'hich escapes the operation of digestion when the root is mixed A'ith the food, and which gives to bones as bright a tint as it pro- luces when treated with alum. There is equal reason to presume hat the solid colouring matter which fills the alreoli of gum lac, Ind which the Indians take great care to separate before they sell Iiat resin, is an extract of the substance used as nouri^ihment by he kind of ant which deposits it on the branches of the jujube. All hese particular colouring matters receive, no doubt, from the ani- Dal humours that solidity of tint which is peculiar to them. 536 •treatise on var^jishes, to remove the alum. The lake, when taken from the driers, will retain this bright primitive colour given by the alum. But if in the process for making this lake decomposi- tion be employed, by mixing v/ith the bath an alkaline liquor, the alum which is decomposed deprives the fcath of its mordant, and the lake obtained after the subsequent washings appears of the colour of the madder bath viithout any addition : it is of a reddish brown. In this second operation seven or eight ounces of alum ought to be employed for each pound of madde». This kind of lake, obtained by decomposition, is exceedingly fine ; but it does not possess that bright red colour so much sought after : it may, however, be communicated to it, if the washed precipitate be mixed ■ before it be dry with alum water. If the aluminated madder bath be sharpened with ace- tîte of lead (sal saturni), or with arseniate of potash (neutral arsenical salt), you will obtain, by the addition of carbonate of soda, a rose-coloured lake of greater or less strength. It is that marked No. 3. in the com-, parative table. Lake from BrasU wood. No. IV. Brasil wood affords, for the preparation of those lakes called carminated lakes, two different and very rich colours, if the process which facilitates the remo- val of its colouring part to the alumine disengaged LAÎCE FROM BRASIL WOOD. ■ 3Ô7 from the alum, or to proper clay, be varied. These two shades are obtained by employing chemical decompo- sition, or by plain mixture without decomposition. The two processes I used are as follow : I boiled four ounces of the raspings of Brasil wood in fifteen pounds of pure water, till the liquor was re- duced to a pound and half or two pounds. The liquor had then a dark red colour, inclining to violet ; but the addition of four or five ounces of alum gave it a bright red, inclining to rose-colour. When the liquor has been strained through a piece of linen cloth, if four ounces of the carbonate of soda (alkali of soda) be added with caution, on account of the effervescence which takes place, the colour, which by this addition is deprived of its mordant, will resume its former tint, and deposit a lake, which when washed and properly dried has an exceedingly rich and mellow violet-red colour. If only one half of the dose of mineral alkali be em- ployed for this precipitation, the tint of the lake be- comes clearer ; because the bath still retains the unde- composed aluminous mordant. In the last place, if the method employed for Î3utch pinks be followed, by mixing the aluminous decoction of Brasil wood with pure clay, such as Spanish white and white of Morat, and if the mixture be deposited on a filter to receive the necessary washing, you will obtain from the driers a lake of a very bright dark ïose-colour. The lake which I prepared in this man- ner, making use of pure clay from Morat, is marked No. 5. in the comparative table. The first lake is harder than the second, because not^ z 33S TP.ËATISE ON VARNISHES* withstanding the washing it retains salts which adhere strongly to the clay ; but the second is too soft. Its colour, heightened by the mixture of alum, seems to have a superiority over the aluininous lake of madder, which brings it near to the lakes made from cochineal ; since, according to experiments of which I shall here, give a short viev/, it opposes nearly the same resistance to the effect of certain re-agents. By the same processes a very beautiful lalte may be extracted from a decoction of logv/ood. In general, lakes of all colours, and of ail the shades of these co- lours, may be extracted from substances whicli give up their colouring part to boiling water ; because it is ;ifterwards communicated by decomposition to the alu- mine precipitated from sulphate of alumine, by means of an alkali ; or the tincture may be mixed with a pure and exceedingly white argillaceous substance, such as real Spanish white, or white of Morat. It is the pro- perty of alumine, and of all clays, to form a kind of combination with the divided oily or resinous substances: with which they are in contact, and to retain them r this property constitutes them stones or earths. Some of them, under the name of fuller's earth, are employed for scouring cloth. When lakes are prepared by the medium of alum, |' which is decomposed by the application of an alkaline liquor, carbonate of soda (salt of soda) is to be pre-^ ferred to carbonate of .potash (alkali of potash), because the new salt, which results from the decomposition of: the sulphate of alumine by means of the former, is- far more soluble tlian that which might be formed by- LAKE FROM BRASIL WOOD, S39 potash. The washing of the lake then succeeds better, and no foreign salt remains to make it hard, and some- times efflorescent. Besides, this labour for the greater exactness would require the us.e of pure carbonate of potash, and it is easier to answer this condition with soda than with potash, though soda is never pure. Lakes enter into the composition of solid colours. They may be employed to colour changing alcoholic varnishes ; but in this particular case it would be sim- pler to extract the tincture from cochineal itself, since nothing is required but the colouring part. I have already mentioned, that it has been commonly believed that real carminated lakes, the colouring part of which is obtained from cochineal, C3n easily be di- stinguished, by means of vegetable acids, from those in which the colouring part is a vegetable product. The latter, as asserted, do not stand the test of immersion in these acids without becoming yellow. The trials which have been made do not seem to correspond to the confidence placed by some in this kind of process, since artists are still afraid to employ lakes in the composition of works which they are desirous should be handed do\Ta to posterity. It is rather the latter consideration, than the fear of a pecuniary sacrifice for an article of inferior value, that ought to excite- a wish that means of avoiding this fraud mJght be disco- vered. Both these motives, however, induced m.e to make researches on this subject, by exposing to the efforts of different re-agents the five kinds of lake, the composition of which has been here so minutely de- t^led, that the processes may be applied to eveiy sub- z2 MO' TREATISE ON VARNlSHÊà^ Stance the colouring part of which is soluble in tv^ater. 'Ï shall here exhibit a comparative table of, the effects resulting from the different processes employed. The experiments were made in large watch glasses exposed to the open air ; and as the impression of the light has a more sensible influence on soma colouring parts than on others, I thought it my duty to subject the mixtures toit. Re-agents act in a different manner on the same sub- stance. Some, to produce their effect, require only a. momentary contact ; while others require more timcy and do not manifes? their influence till they have pro- duced a kind of solution. This circumstance, which I could not properly observe in simple mixtures exposed • to evaporation favoured by the sun, induced me to vary the experiments : I put the same mixtures into bottles closely shut, and kept an account of the results observed at the moment of contact, twenty-four hours after, and at the end of three weeks. They are exhi- bited, such as I observed them, in the annexed table. This short view of these results will, no doubt, be sufficient to establish the essential difterences between the various colouring parts applied to the composition of carminated lakes or crayons ; and to prove the in- sufficiency of the means hitherto considered as the most certain, for distinguishing real carminated lakes from those which are only an imperfect imitation of them. Lemon juice, or any other vegetable acid, and in parti- cular vinegar, to which was ascribed, but without any reason, the property of changing to yellow the bright or purple red given to these counterfeited lakes, and Comparative Table of ti^ Re-agenTs. Caustic ammonia. Acetous acid, or strong distilled vinegar. Diluted sulphuric acid. Muriatic acid. Carbonate of potash. No. 1. ,^ -: Lake from cochineal tii ^14in alum and the alkali orab-,; At the time of viixture. Brightened Not dissolved The same tint Not dissolved Bright red. Dissolved, Dark rose co- lour. Dis- solved. Dark violet colour. Not dissolved. Twenty -four '"«^ ^^^^s hoiLrs after, ojtcr. va. colour, The same, jiroyed. dissolved eddish Purple. 3wn. In dissolved. eddish The same. '^^"- ^" dissolved. Rose. ilnut-tree lour. In dissolved îstroyed. Purplish red.t dissolved Re-agents. Caustic ammonia. Acetous acid, or strong vinegar. Diluted sulphur- Comparative ?"• No. 1. Dry lake. Colour pre.s^i^h some and a little less bright abo\ Dry) and of a rose color. ^^ brown Aluminous crystals of a^ °* thick lour. The lake was cryst; ous acid. Muriatic acid. N. B. Carbonate of potash was nc t emp A kind of transparent s:"" ^^^ ^o- beautiful purple colc'ur. 1 To front page 340: 1 Comparative Table of the results of the mixture of some re-agents with different carminated lakes, observed at different periods in close vessels Re-agents. Caustic ammonia. Acetous acid, or strong distilled vinegar. Diluted sulphuric acid. Muriatic acid. Carbonate of potash. Re-agents. Caustic ammonia. Acetous acid, or strong vinegar. Diluted sulphur- ous acid. Muriatic acid. No. 1. Lake from coch ineal treated with alum and the alkali of soda. Jt the time Twenty-fnur Three weeki of mixture, hours after. after. Brightened. Not dissolve! The same tint. Not dissolved Bright red. Dissolved. Dark rose co- lour. Dis- solved. Dark violet colour. Not dissolved. Purple. Purplish red. Beautiful red. Dissolved. Pale red. In a kind of jelly. Piu'ple red. Red of wine lees. Altered, No. 2. Lake from madder with alum de composed by soda. yit the time Twenty-four Three weeks of mixture, hours after. after. Blood red In B,igh,er red. tdissolved. ^ Chesnut. In partdissolved Dark cinna- mon colour. In part dis- solved. Brick colour inclining to brown. In part dissolved. Dark reddish Brick red co- brown. Inpartj lour, or light dissolved. brown. A little alter- ed. In part dissolved. Dark cinna- mon colour. In part dis- solved. Dark walnut tree colour. In partdissolved Dark walnut tree colour. In partdissolved The same. In partdissolved No. 3. Lake from madder with arseniate of potash and salt of lead. Jt the time Twenty-four Three weeks of mijiture. liours after. after. Brickred.Not dissolved. Brick red. Dissolved in part. Yellowish brown. Not dissolved. Dark orange In part dis- solved. Brick red, as by ammonia. Light yellow Red chefîmU colour. Not dissolved. Altered. Not dissolved Pale red. Dis- solved in a great part. Green colour, &: destroyed. Not dissolved Brown. In partdissolved The same. Dissolved. No. 4. Lake from Brasil wood with alum decomposed by soda. At the time Twenty-four Three weeks of mixture, hours after. after. Violet purple Not dissolved Dark red. Dis- solved in part, Bright scarlet Not dissolved Red inclining topurple. Not dissolved Reddish brown. Not dissolved Coffee brown. In part dis- solved. The; Bright rose colour. Reddish brown. Dark violet red. Darker. In partdissolved, Purple red. In partdissolved Bright rose colour. Dis- solved. Dark brown In part dis- solved. Dark reddish brown. Not dissolved. No. 5. Red from Brasil wood and dlôm mixed with earth of Morat.-,;_ M the time Twenty-foh of mixture, hours after Violet purple Not dissolve Violet inclin- Green colour, to brown, desiroyed. Not dissolved Purple red. Not dissolved Scarlet red, a litUe du Dissolved in part. Red inclii to rose colour Not dissolv Dark violet. Not dissolved, Three weeks after. Poppy colour. Purple. Rose inclin- ing to poppy Common violet. Reddish brovvir. In partdissolved Reddish brown. In partdissolved Walnut-troe colour. In partdissolved Destroyed, Not dissolved Comuaralive results of the mixture of the same re-agents with the same takes e.rposed to the air and the sun, observed at the end of a month. No. 1. Dry lake. Colour preserved below^ and a little less bright above. Dry) and of a rose colour. Aluminous crystals of a pale rose co- lour. Tlie lake wa.s cr) stallizcd. A kind of ti'anspnrent saline jelly ofa beautiful purple coU jur. No. 2. Dry. Brick colour below, and a little pale above. Dry. Of a reddish brown colour. Kind of soup ofa light rust colour. Kind of jelly of a capuchin colour. No. 3. Dry lake of a dark brick red colour, a little pale at tlie surface. Dry. Of a pale brick colour. Dry lake, and of a brown colour. Pulverulent lake of a dark mordoré colour. No. 4. Dry lake, witli a surface like talc : a little pale above; colour preserved below. Dry. Purple red colour. Thick soup of a bright brick red co- lour. Dry lake of a flesh colour. No. Dry lake colour prescr\ed, with some white specks iibove. Dry. Purple colour inclining to brown Dark red, of tlie consistence of thick soup. Kind of thick soup of a dark red co- lour. N. B. Carbonate of potash was nc t emplri\e(l in these first experiments. J LAKE FROM BRASIL WOOD. S4l even the mineral acids which I employed, exhibit cha- racters entirely opposite in these colouring parts, which are foreign to that of cochineal. We every where see that the development of the red colour, under diffe- rent tones of shade, is the certain result of the first contact, except in madder red, which acids speedily destroy. They change this colour to that of rust, more or less dark, according to the time it has been exposed to the acid and to the influence of the light. These results, when compared, seem to confirm the great similarity between the colouring part extracted irom Brasil wood and that of cochineal; since acids contribute to their development in the same tone of co- lour, though \îàth modifications which may readily be observed. Were one contented, therefore, with the first view in this respect, the progress of our re-agents would appear to be pretty uniform ; but it would not be sufficient to establish the necessary distinction be- tween lakes extracted from cochineal and those made with Brasil wood ; since with one re-agent, such as sulphuric acid, they exhibit chemical properties which seem to confound them when the effects of the first contact only are considered. This kind of resemblance, however, is limited : it soon becomes weakened by time and the impression of the light ; and it is then easy to distinguish them by the subsequent results, on leaving an interval of three or four days to facilitate and complete the action of the re-agents. Every one of these substances here mentioned be- comes then, in the hand of an intelligent painter or -amateur, the certain means of enabling him to ascer- Z3 342 Treatise on varnishes. tain the nature of lakes. The effects arising from the application of acids are not sufficiently distinct at the moment of their mixture, though they present shades which do not escape the notice of an expert eye ; but an interval of forty-eight hours will be sufficient to ren- der their difference very sensible to persons in the least accustomed to the effect of such mixtures. "The sul- phuric acid employed in the trials to which I here al- lude, resulted from a mixture of the sulphuric acid of the shops (oil of vitriol) and water, in the proportion of one to four. The muriatic acid was applied in the state in which it is sold. If the results be accurately compared, it will be ob- served that they vary in the mixtures according as they are exposed in open vessels, or in vessels closely shut. In the first case, the evaporation of the liquid may serve to account for the Httle influence of the re-agent. Caustic ammonia on such occasions produces no effect, in consequence of its great volatility. The muriatic acid participates in the same inconvenience. Besides, the mixture of light bodies transported by the air, or detached from the ceiling of the apartment, may mo- dify the results. A view of the two comparative tables Vv'ill be sufficient to give v/eight to the present observ^a-? tion, and to determune in regard to the preference which ought to be given in the employment of these mixtures to vessels v/hich can be closed with cork stoppers. The effects may then be observed with more certainty, and to a greater extent. Some of the re-agents seize on the base of the lake, and dissolve it. This effect may furnish a new subject OXIDES OF LEAD. " S43 -of observation, when it is required to discover the n-d" ture of that base which may be composed of alumine, resulting from the decomposition of the sulphate of alu- mine (alum), or pure clay; or, in the last place, of chalk. This solution, then, is better perceived in ves- sels which oppose the evaporation of the liquid than in those which afford a free access to the exterior air. I have exhibited these particular cases in. the comparisons which constitute the first comparative table by the ex- pressions dissolved, dissolved in part, or not dissolved. In all cases the influence of the light is not to be over- looked. These observations conclude my researches in regard to real or false carminated lakes. They may, perhaps, appear prolix to those who in works of this kind look only for the formulae of compositions ; but it ought al- ways to be remembered that I v/rite for the information of the amateur as well as of the artist. OXIDES OF LEAD. GRAY OXIDE OF LEAD. GRAY CALX OF LEAD, First degree of oxidation. The oxides of lead obtained by the means of caloiic (fire) exhibit themselves in the arts under various cha- racters of difference, which may serve to denote v\ ith considerable accuracy the gradation they experience in the process of oxidation, under the continued action of a pretty high temperature. The same gradation ought to be followed in the order of their descripdon. 344 TREATISE ON VARNISHES, When lead is exposed to heat, it readily enters into fusion. Its surface then becomes covered with a pelli- cle of a gray, and as it were an earthy colour : this is the first step towards oxidation (calcination). If this pellicle be removed, it is immediately succeeded by an- other ; and so on till the whole mass is, at length, re- duced to the form of a gray powder. This is gray oxide of lead. MASSICOT. YELLOW OXIDE OF LEAD. Second degree of oxidation. * After the first operation of the temperature is in- creased, the gray oxide assumes a yellow colour ; ançi when this colour is sufficiently developed it is distin- guished by the name of massicot, or more correctly of yellow oxide of lead. I MINIUM. RED OXIDE OF LEAD. Third degree of oxidation. If a greater division in the parts of the yellow oxide of lead be facilitated, which may be done by stirring the matter, and exposing the surfaces to the renewed contact of a reverberated flame, it assumes a red colour, more or less intense, and constitutes what is called red oxide of lead, or minium. A part of this oxide is al- ready very near to reduction ; and when treated over the fire without any medium, in a very close crucible^ gives a little reduced lead. OXIDES OF LEAD. S^-^ Ï.ITHARGE OF GOLD OR OF" SILVER. VITREOUS OXIDE OF LEAD, Foiu'th degree of oxidation. In the last place, if massicot or minium be exposed to an accumulation of caloric, the oxide becomes in. part vitrified, and forms vitreous oxide of lead, knowji under the name of litharge. All these transitions take place accidentally in the process of cupelling, on a large scale, the principal object of which is to oxidate all the lead, in order to extract the silver it contains. The bellows, the wind of which forces the flame to reverberate on the matter in fusion, becomes the cause of the fusion and oxida- tion, which are the consequences of it. Yellow oxide of lead is soon formed : the current of air, which ac- celerates oxidation, next produces red oxide ; and the latter, being in part volatilized, lines the apertures of the furnace. Vitreous oxide of lead then soon makes its appearance, under the form of scum driven forward by the current of air, which the bellow^s maintain on the matter. This vitreous oxide is collected through an aperture made for extracting it, and through which it is made to run under the form of stalactites. The colour of this oxide varies. When red, it is known in commerce by the name of litharge of gold : when in this state it has suffered least from the fire. Oxide of a greenish-yellow colour is called improperly Jitharge of silver : it is in a state nearer to vitrification than the former. The colour, therefore, of the vitre- SéS Treatise on varnishes. ous oxide depends on the action of the caloric, which may be stronger or weaker in the course of the ope- ration. Gray oxide of lead is not used in painting : it is em- ployed only for varnishing earthen ware and common pottery. Yellow oxide, or massicot, was employed in paint- ing before painters were acquainted with Naples yellow and that of Montpellier, which have been substituted in its stead. The use of red oxide, or minium, is more extensive. It is employed in house-painting, coach-painting, &c, to compose beautiful reds, and to serve as a ground to vermilion, which is applied to the painting of decora^ tions which require durabilit)^ Vitreous oxide of lead (litharge) is of no other use in paii.ting than to free oils from their greasy particles, for the purpose of communicating to them a drying quality. Red litharge, however, ought to be preferred to the greenish-yellow : it is not so hard, and answers better for the purpose to which it is destined. When painters wdsh to obtain a common colour of the ochrcy kind, and have no boiled oil by them, they may paint with linseed oil, not freed from its greasy particles, by mixing with the colour about two or three parts of litharge, ground on a piece of porphyry with water, dried and reduced to fine powder, for sixteen parts of oil. The colour has a great deal of body, and dries as speedily as if di7ing oil had been used. DIFFEÏ^ENT KINDS OF BLACK. 34*7 Jjamp hlach. Fat soot resulting from the decomposU tion of resins and oils bijfire. Lamp black, as already seen in the first part of this» work, is produced from the thick smoke exhaled by fat resinous bodies in a state of combustion. It is grease mixed with undecomposed resin, and is attended with, the inconvenience of becoming red. It is not, there- fore, employed in delicate colours. It is destined for the oil colours applied to railing, balustrades, &c. It might be employed, however, in the more deli- cate kinds of painting, if washed to separate from it the foreign niatters, and then reduced to the state of pure charcoal. The last quality may be communicated to it by exposing it in a close crucible to a heat capable of decomposing entirely the resinous or oily parts, which still remain united to the charred part. In this case it emits a thick smoke, which is suffered to escape through a small aperture in the cover. It might appear, on the first view, that the same biack substance might answer in all cases which require jthe use of this colour, Vv'hether destined for an uniform ground, or intended by its mixture with other colour- ing parts to form various shades. Long experience, Jiowever, has established other principles. It is known that a black substance, which produces an admirable effect in a fine composition, woiild produce an inferior effect in a composition of another kind. Hence the di- stinction established between several black colouring substances which borrow their name from the producing substance j as smoke black, black from beech wood. S^S TREATISE ON VARNISHES» black of peach stones, ivory black, or black froj^ri caiciiied bones. ,^ Particular hind of lamp hlach. I have long «nployed a beautiful black, which may be easily procured. Nothing is necessary, for this purpose, but to suspend over a lamp a funnel of tin- plate, having above it a pipe to convey from the apart- ment the smoke which escapes from the lamp. Large mushrooms of a veiy black carbonaceous matter, and exceedingly light, will be formed at the summit of the cone. This carbonaceous part is carried to such a state of division as cannot be given to any other matter by grinding it on a piece of porphvry. This black goes a great way in every kind of painting. It may be rendered drier by calcination in close vessels. I must here observe that the funnel ought to be lUiited to the pipe, which conveys off the smoke, by means of wire, because solder would be melted by the flanie of the lamp. Beech black. Beech charcoal. Beech, like every other kind of wood, furnishes by combustion a charcoal, which, when well ground on porphyry and mixed with white oxide of lead, gives a blueish gray colour. When applied in dis- temper or in oil painting it will be proper to reduce it to an impalpable powder, free from those small brilliant facets observ^ed in charcoal badly ground. This may be easily accomplished by grinding it with water, and rc-grinding it after the desiccation of th^ j blfFERENT KINDS 01" BLACK. Zi3 {)aste. This black, if the paste, after its extreme di- vision, be besprinkled on a filter with warm water, to carry off the saline parts adhering to it, will be iess . apt to effloresce. Black from, ivine lees. This black results from the calcina:tion of wine îees and tartar ; and is manufactured on a large scale iii some districts of Germany, in the environs of Mentz^ \ and even in Fran(îe. This operation is perforaied in large cylindric vessels, or in pots, having an aperture in the cover to afford a passage to the smoke, and to the acid and alkaline vapours which escape during the process. When no more smoke is observed the ope- ration is finished. The remaining matter, which is merely a mixture of srJts and a carbonaceous part very .much attenuated, is then washed several times in boil^ îng water; and it is reduced to the proper degree of fineness by grinding it on porphyry. If this black be extracted from dry lees, it is coarser than that obtained from tartar ; because the lees con- tain earthy matters which are confounded with the carbonaceous part. This black goes a great way, and has a velvety ap- pearance. It is used chiefly by copper-plate printers. - Black from hurnt peach stones. Peach stones, burnt in a close vessel, produce a charcoal, which, when ground on porphyry, is em-s jployed in painting to give an old gray. TREATISE ON VARNISHESi Black from burnt vine twigs. Vine twigs reduced to charcoal give a blueish blacky which goes a great way. AVhen mixed with white it produces a silver white, w^hich is not produced by ether blacks : it has a pretty near resemblance to the black of peach stones; but to bring this colour to the utmost degree of perfection, it must be carefully ground on porphyry. Ivory I'lacL Bone black. Put into a crucible, sun'ounded by biinutig coals, fragments or turnings of ivory, or of the osteous parts of animals, and cover it closely. The ivory or bones by exposure to the heat will be reduced to charcoal. When no more smoke is seen to pass through thé joining of the cover, leave the crucible over the fire, for half an hour longer, or until it has completely cooled. There will then be found in it a hard carbo- naceous matter, which, when pounded and ground on porphyry with water, is washed on a filter with w2.riTL water, and then dried. Before it is used it must be again subjected to the muller. Black furnished by bones is reddish. That pro» duced by ivory is more beautiful. It is , brighter than black obtained from peach stones. When mixed in a proper dose wdth white oxide of lead, it forms a beauti- ful pearl gray. Ivor}'' black is richer. The Cologh« and Cassel black are formed from ivory, f, ibiFEERENT KINDS OF OCHRE/ S5ï OF OCHRES. Of all the metals, iron is that which opposes the least resistance to the chemical action resulting from its contact with different substances, while exposed to the influence of humidity and of the air. Earths, salts, acids, sulphur, arsenic, and even water, become, under certain circumstances, the origin of modifications which transfer it from the order of simple bodies to that of compound substances. Volcanic fires and caloric, dis- engaged by the effect of subterranean com.binations, of which itself appears to be one of the chief prin- Tciples, act upon it in a manner more or less energetic, and communicate to it relative forms and properties. Brown, yellow, and red ochres evidently exhibit the effects of a sort of combustion, or rather oxida- tion, more or less extensive and more or less accele- rated. Water seems to be the principal promoter of this oxidation; but the latter finds there also the agent of its decomposition. The hydrogen, which is one of its constituent principles, escapes under the form of inflammable gas ; while the oxygen, another principle of water, unites to the metal, and converts into an oxide. This oxide is more or less charged with oxygen, and more or less mixed with argillaceous earth and carbonate of lime (calcareous earth). Brown odhre, * When the oxidation of the iron is not very exten»* sive, the result is a brown ochre. Carbonic acid oftejff forms a Dart of it,- ÉS2 Treatise on varnïshesô Ochre de rue. A degree more in the progress of the natural oxi- dation of iron, that is to say, a quantity of oxygen somewhat greater than in brown ochre, and a mixture cf clay, give ochre of a dark yellow colour. This mass constitutes ochre de rue, which is extracted by washing it in a large quantity of water. Calcined ochre de rue. This ochre de rue subjected to the action of accu- mulated caloric (a very active fire) acquires a yellow colour, more or less developed according to the degree of oxidation acquired by the influence of the process. Natural yellow ochres. In many cases nature frees the artist from the trouble of this artificial oxidation. It prepares ochres on a ïarge scale, and very much varied in their colour. They are produced in the ci-devant Auvergne, and in all countries in the neighbourhood of volcanoes, and form articles of commerce under the names of dark yellow ochre and bright yellow ochre. These ochres are more or less argillaceous ; they are often marly, that is to say, mixed with clay, carbonate of lime (calcareous earth), and coloured by iron. They are ■ separated from the sand and stones they may contaia, by careful washing. Red ochre. When this oxidation is effected in the neighbour- hood of volcanic fires, or by the effect of subterranean DIFFERENT KINDS OF OCKRES. 3S3 Combinations of great extent, or under the influence of chemical processes, as in the operation for making artificial sulphates of iron (martial vitriol), in which a great deal of caloric is developed, the colour assumed by the oxide of iron is more exalted. It is a red more or less bright. This red ochre, or red oxide of iron, mixed in various proportions with clay or marl, if a natural production, will be pure red oxide of iron j and if a production of art will be English red. Natural red ochre is very abundant in volcanic countries, as is the case in Auvergne ; the different departments of which produce very beautiful kinds. Clay forms the greater part of it ; and it is this sub- stance which renders it so soft to the touch. The method of purifying ochres is simple. Though drier than pure clays, they are lighter than sand, and the fragments of stones which may be mixed v/ith them. They dilute readily in water, and during this washing suffer to be precipitated those bodies which are heavier than themselves. The water charged with them is decanted, by making it pass into a trough lower than the vessel in v/hich they were washed; and tvhen the sediment is formed, the clear v/ater is drav/n off. The coloured paste is then taken out, and being dried is divided into small masses. When an ochre is composed of oxide of iron and clay, it resists the action of acids» If an effervescence is produced, the composition is of a marly nature. Car- it, till they become charged with a new quantity of crystals. This operation is continued until the inter- vals between the parts of each stick are entirely filled with cr)'stals, so as to represent a solid pyramid, the weight of which is about three or four pounds. The crystals are of a rhomboidal form; and when new are transparent, and have a beautiful green colour. At the end of some time they effloresce, that is to say, become ^hite, and lose their transparency by the effect- of jiir 2b 3 574 TRÎATISE ON VARNISHES. sensible evaporation. These crystals form acetite of copper^ and are known to artists by the name of distilled verdigris, crystallized verdigris, calcined ver- digris*. Acetite of copper, when new, is of a beautiful trans- parent green colour : when old and pulverulent it ex- hibits a dull green. In the latier state it is more proper for being ground v^dth boiled oil. In general all colours of a saline nature, destined to be ground with oil, must be deprived of their water of crystallization ; and this can be accomplished only by reducing them to powder, and exposing them to the sun, or in a stove, before they are mixed with the oil. Colours prepared with acetite of copper (crystallized verdigris) are much brighter than those composed with verdigris. But the high price of this colour prevents it from being employed in all cases. It is therefore reserved for painting of the noblest kind, and for that * Artists have given to certain matters employed in the arts, denominations which are more calculated to embarrass tlian td encourage amateurs. I myself have often been confounded by tlie word calcined, which is applied to several substances as an epithet. This expression is often employed in regard to orpi-, ments (yellow sulphurated oxide of arsenic). If this substance were treated over an open fire, it would be dissipated 3 and in close vessels it would assume a rose or red colour, and form ruby of arsenic. The case is the same with acetite of copper, which is sometimes called calcined verdigris. Calcination would revive the copper: tlie same denomination has been applied to sulphate of zinc. This is a real abuse of words, which habit preserves among our workmen, and which ought to be banished if we are desirous of rendering the language of tlie arts intelligible. SAP GREEN. 375 •applied by the varnisher to certain delicate articles, such as works of papier mache, metals, &c. Those who paint pictures are accustomed to grind this colour with oil of pinks, and to put it into small bladders, which they prick in order to extract by pressure the quantity they are desirous of using. This colour extends exceedingly well. It possesses trans- parency, and is employed with success for glazing certain argentine parts to represent sheets of water. When applied to metal, the reflection of the Hght produces a very fine effect, which is still heightened by the colour. This colour, when mixed with copal varnish and applied to foil, produces a very rich effect. LiqJtid vd'digrisjor colouring maps, ^c. Put an ounce of pulverized verdigris into the bot- tom of a matrass, with eight or ten ounces of good distilled vinegar. Place the matrass on a warm sand bath, and shake it from time to time, till the liquid has acquired a beautiful dark green colour inclining to blue. Leave the mixture at rest, that it may become clear, and pour it into a clean vessel, which must be closely shut. This preparation is used for colouring maps and prints. The colour may be lowered, if ne- cessary, by adding a little w^ater or distilled vinegar in the shell into which the brush is dipped. Sap green. Sap green is the feculent part of the fruit of the buckthorn. The berries, when black and very ripe, are bruised, and subjected to a press, in order to ex- 2 s 4 S76 TREATISE ON VARNISHES, tract the juice. This juice is mixed with a little sul- phate of alumine (alum), dissolved in a sufficient quan- tity of water, and the whole is evaporated over a slow fire till it is brought to the consistence of honey. The extract is then put into a swine's bladder, and hung up in the chimney to dry. When this extract is to be \ised, dilute it with a little water, to which it will communicate a very beau- tiful green colour. This colour is used only by fan- painters, draftsmen who dra\y plans, and for other works of the same kind. It ought to be chosen compact, heavy, and of a beautiful green colour. C 377 ] CHAPTER II. 'Philosophical account of the origin of colours, applied ta 'mater kd colours, simple and componnd; with a description of the processes which art employs to vary the inanler and richness of the tints resulting from the mixture h, has often equalled in its effects, aft^" application," those of the forinei\ It appears even to h^^ $i>msydba-t tpefter suited to the inexperience of ~a youns; COMPOSITION OF COLOURS. 411 artist. Mixing up with essence, indeed, is not free from ineonveniences, when the pîdnt is applied to white wood. I have seen several of these compositions fall off in scales, in consequence either of the iirst stratum having been applied too thick, or without care, or of simple earths having been substituted for metallic ox- ides. The inconvenience, however, apprehended in the application of colours mixed up with varnish may be obviated by putting only a small quantity of colour into the last coating of varnish, to facilitate the beauti- ful reflection of the light from the coloured ground, or by suppressing it entirely. The varnishes which I have. appHed in this manner all stand the strongest blows, even with a hammer, without scaling off.: they are both brilliant and durable. By confining ourselves to the number of colours here mentioned, it may readily be conceived that we are far from the hmits fixed by the different gradations or degradations of the distinct tones, modified tints, or simple shades, which would result from. the variety that might be admitted in the distribution of the same colouring substances. The artist and amateur will, in this respect, foresee all the resources of the art. An examination of the determinate colours was sufficient to give a view of the means which nature puts into the hands of the colourist and painter to gratify the taste or the caprices of the opulent. . C ^12 3 CHAPTER m, i/f the exie?ti which may le given to the use of the iurpeyitnie €opal varnishes Nos. 18. and 22. by impregnating them . 7iit h various solid colouring parts, transparent afid proper Jor answering the purpose of glazing on metallic laminœ, smooth or ornamented; Jhr Imitating transparent enamel y ùndfor repairing those accidents which frequently happen to enamelled articles. Residing in a manufacturing city, where the arts of enamelling and of painting in enamel have been carried to a degree of perfection hardly to be met with but in Geneva, I have often witnessed the trouble, expense, ©fetacles, success, and uncommon activity which al- ways accompany the first enterprises among a people who, in point of skill and industry, approach nearer than any other to the most industrious nations. The case with painting in enamel is not the same as with that which adds to the value of porcelain. The yariety of the toys to which it is applied, their delicate forms,, and the différence in the metallic alloys, require modifications in the composition of the colours, and in that of the fluxes. These modifications, the necessity çf which vis sufficiently shown by the accidents that happen, both m manufacturing and when out of the hands of the workman, to enamelled articles, cannot be ascertained at the moment ; and there is no certain guide to direct the artist in his researches. No work but that of Montami, which is destitute of method, in-» , 1REPAIRING ENAMEL. ' 413 complete, and actually useless in the present state of the art, was v/orthy of the confidence of the enamel painter in his operations. Unacquainted, therefore, with the theory in regard to the nature of colours ex- tracted from mineral substances, and to their degree of vitrescibility, a.nd being under the necessity of rivaling, with success, discoveries which some adventurers, m consequence of a little more applicadon or industry, or perhaps çf a little more good fortune, were enabled to make, his attempts were always hazardous. An an. thus created, in the course of two years, notwithstand- ing the impediments which must have resulted from the secrecy observed by workmen in the same branch of business, is one of the most singular phsenomena which characterize the industry of Geneva, and the particular genius of the artists of that city. Were the manufactory of Geneva removed to a city of the first class, such as Paris, and placed in some measure under the eye of a powerful government, where all the means of encouragement seem to be con- centrated, and where the secrets of the workshop iniist: bow under the influence of learned sociedes and artists^- the destitute state in wliich the art of the enaraeller of toys is at present, in regard to a general theory appli- cable to all the valuable materials employed, would be soon observed ; and this interesdng part of a new branch of industry would, no doubt, find the same protection as the manufactory of porcelain has done* It needs excite no astonish ment that the art of ena^ melling, such as it is practised among us^ where the artists live insulated, v/ithout any communicalion 414- TIUÎATISE ON VARNISHES» which might be of advantage to them, should, notwith* standing its success, be still deprived of those principles which could alone ensure its progress, and preserve to posterity those discoveries which by the instability of fashion may be lost. Nor can it appear wonderful that the finest master-pieces in enamel-painting, as they are so frequently subject to serious accidents, should be en- tirely deprived of their value, if no means can be found to repair such of these accidents as can be repaired without fire. Toys, when once they have gone from the hands of the artist, are no longer susceptible of being renewed ; but means have been found to repair with cements, which assume the solidity of a "vâtreous body, and which are afterwards painted and covered by a colour- ed varnish, the defects occasioned by small fragTuents being detached from certain opake compositions. In transparent enamel this reparation is more difficult. The tint of the varnish must correspond with that of the vitrified coating ; it must possess the same splendour, and its solidity should be equal to that of the enamel itself. This may be accompHshed by the ethereous copal varnish No* 17., and by tli ose of Nos. 18. and 22. By introducing into the ialter varnishes colours iwhich by their tints imitate those extracted by vitrifi- cation from -metallic substances, all the conditions re- quired in the reparation of the dilierent accidents that happen to enariiel are answered j and at the same time anevv' art is ci'êated, which I have had the happiness to see realised. . Sim^e copal var^ilsli, or that iaade with turpentine, I . -REPAIRING ENAM£L, 415 has an ambery colour, which disappears when it has been applied. The oily substance, by contributing ta : ts solidity, renders it at the same time very proper for becoming charged, much better dian alcoholic T-^ar- nishes, with certain vegetable resinous colounng bodies, by means of which the artist can, in a certain degreej, imitate those colours which produce so beautiful am «ffect in transparent enamels. It may be readily con- ceived, that to preserve to these varnishes this (trans- parency, which gives them a resemblance to enamd,, nothing must be employed but resinous or saline mat- ters, entirely soluble in essence. It was in this manner I prepared the colours applied to the lid of the ivory box I presented to the Society of Geneva as a specimea of the new manufacture in coloured varnislies imitating enamel ; and for which I was indebted to the gratitude of a countrvinan, for whom I had prepared the ym- mstL The varnish which serves as a glazing*, and whic% is susceptible of a fine polish, resists better th^m the vitreous flux of enamels, the friction of keys, boxes, and other articles very often carried in the pockets- The daily use made of this box for twelve years, has destrc^'-ed the metallic ring which served it as an oin^^ ?nent, but without injuring; the varnish, * To glaze, in the language of painting, expresses tlie appHica-" iîon of a stratum of transparent matters on a coloured groimd in siich a manner tliat-the colour of t4iis ground becomes more appac rent, more brilliant, pr ligliter. To glaze, therefore, is to applj'. a •colour %vliich has little body, or a transparent tint ivhicii suiFexs tbe grcuiid" on which it k placed to be seen. 4T& TREATISE ON VARNISHES, Mr. Chaporiier, the artist who found means to make SCT successful an application of copal varnish, according to my process, quitted Geneva, his native country, some time after he had been employed on this nev/ art. His success has induced me to devote this chapter to the coloration of this varnish, Traiisparent green colour. Artists are often embarrassed m regard to the choice ef colouring matters, when they are desirous of com- municating a colour to a liquid without injuring its transparency. Some colouring parts are susceptible of being transmittted to alcohol, or even to \A'ater, but refuse to unite with oily substances. Cupreous prepa- rations, in the saline state, are of this nature ; while cupreous oxides (calces of copper) resist the action of water, and pass into oily liquors. Other colours re- quire mordants of an acid or alkaline nature before they 5ecome disposed to pass into water, and refuse every kind of union with oils. Indigo, litmus, cochineal, saffron, bastard saffron, and red sandal wood, prove the truth of this principle, which experience has in' duced me to admit. This" variety in the chemical properties of colouring substances seems to confine the application of some of them to certain vehicles and to certain circumstances, in order to render them useful in the arts. I have often experienced difficulties when, on the faith of authors Vi-ho have written on this subject, I endeavoured to give to copal varnish made with turpentine all the colours- susceptible of producing a rich effect in painting, with* REPAIRING ENAMEL. 41? out altering the transparency of the coloured Vehicle. It must, however, be allowed that the state of the body- employed in these trials is not always what it might and ought to be, if taken from the order of saline sub- stances. One example will be sufficient to show the truth of this observation. I mixed acetite of copper (crystallized vetdigris) f e^ duced to powder, with copal varnish, to communicate to it a transparent green colour. The union t C 437 2 ,0 ^ Ç.\ CHAPTER IV N^ ^y Precepts respecting tlw application of varnishes, coloured or not coloured, which the artist or amateur ought always to keep in rememhrance. Of the diff^erent kinds of painting. Of varnished linen and silk. The best composition of varnish, and the most exact combinations in the colours, are not sufficient to call them forth with all that splendour which it is possible to give to them. An expert hand is required also for the application of them ; and the amateur who has not been accustomed to the labour must possess a correct tast«. The instruments which painters employ are simple, and few in number. A smocth stone, a muller, a spatula, a flexible knife to bring under the muller the colours scattered over the grinding stone, or to remove them; brushes large and small, and a few pots for mixing up the colours, form the whole apparatus ne- cessary for the amateur in the employment of varnishes and colours. The colours cannot be used in that state in which they are purchased in the shops. They require to be purified, ground, and mixed with the different liquors which art employs to facilitate the extension of them over the articles intended to be painted; and these liquors must be different, according to the nature of the colouring parts, and to the uses for which the articles are destined: they are determined also by the consistence which must be given to the composition/ 2f 3 438 TREATISE ON VARNISHES. It will therefore be necessary to offer a few obser\^ations on this subject : 1st. The hard bodies are pulverizc4, and sifted through ' a hair or silk sieve. This preliminary pre- paration is applied to the different kinds of ochre, chalk, clays, or boles; and to soHd substances, such as white lead, litharge, verdigris, and cinnabar. This operation prepares them for being more completely divided under the muller, and facilitates the separation of bits of straws, fragments of wood, or other foreign bodies, which are often met with in some of the com- mon colouring substances. 2d. When the colours are to be applied to painting in distemper they are ground in water, that the lightest particles may not escape, in consequence of the motion excited by the muller. The ground matter is reduced to the consistence of thin paste ; and when the muller glides over the stone, without making any noise, and when the trace it leaves on the colour is smooth and without grains, it is judged that the operation has brought it to the required state of division. ^ 3d. Certain genera and species of varnish destined for delicate articles, which are frequently expoâed to carriage, as boxes, &c. and certain toys, such as fans, boxes for holding counters, &c. do not admit in their composition any matter capable of communicating to them a strong smell, or which would render the de- siccation of them slow. . In these pardcular cases the varnishes of the iirst and second genera are to be pre- ferred. The colours are then ground with the varnish No. I., to which is added a spoonful or two of oil of PRECEPTS RESPECTING VARNISH. 439 pinks to render it pliant; and the colours are mixed lip with the same varnish. But, as it evaporates very speedily, it requires to be employed immediately. 4th. Under some circumstances a more solid var- nish than those of the first two genera is required for mixing up certain colouring parts ; such, in particular, as those extracted from the mineral kingdom, which have a character of dryness that must be counteracted or modified. The colours, in this case, are ground with drying oil, to which a little fat oil has been added. At other times the colours are mixed up with a var- nish of the third genus, such as that of No. 14. ; or of the fourth genus, as the copal varnish No. 18. "When the dryness of the colour or drying quality is not very great, it may be ground with the varnish No. 13., and mixed up with that of No. 14., which belongs to the fourth genus. 5th. There are other circumstances which require greater solidity in the varnish, and which proscribe every liquor or excipient not capable of concurring to pronrote this essential quality. In this case the colours are ground with drying oil, to which a little fat oil has been added, if the colour contains a considerable quan- tity of metallic oxide. If this oil renders the matter too thick, a little essence is mixed with it j and it 'is then diluted with the resinous di7ing oil, p. 120, or with one of the fat varnishes of the fifth genus. 6th. One of the most essential points to be observed in the preparation of the colour is, as already said, the extreme division of its parts. Grinding in water is speedily performed. This liquid, by its nature, easily 2f 4 440 TREATIGE ON VARNISHES. loosens the aggregate moleculse of earthy substances. The case is not the same when varnish^ essence, or oil is employed. The experienced artist, who attends >' to the gain arising from his labour, will readilv be sen- \ sible of the utility of this precept. Habit will soon teach him, that a colour becomes truly profitable only when it has been reduced to the utmost state of divi- sion. He will not, therefore, consider the time which he employs in the operation. But the amateur, who lias not the advantage of experience, soon becomes tired of the labour, which appears to him fatiguing : he consequently gives way to impatience, or to the ardent desire he has of realizing the effect of the in- tended decoration. It will, therefore, be proper that he should coolly consider the inconveniences which result from precipitation, and frequently call to mind .those precepts, founded on experience, which can alone ensure success. The great division of colours is one of the principal causes of their beauty, and of the mellowness of their tones. . The play of the light is then freer; it is pUrer, and more disengaged from those pardal reflecdons which in a granulated colour compose the coloured reflected ray, the brightness and splendour of which are then much altered. 7th. Three of our senses concur to determine the essential point of this division, namely, the touch, sight, and hearing. One may readily perceive that a colour grinds more easily at the commejicement than at tile end of the operation. The granulated paits roll with greater fieedom under the inuUer than when they PRECEPTS RESPECTING VARNÎSH. 44Ï are more attenuated ; and the muller rises more easily at the begiiining of the opei-ation than when it is nearly finished. The air disseminated in the interstices of the still coarse matter lessens and counteracts the force of adhesion, which the weight of the atmosphere esta- blishes between the muller and the grinding stone. The liand which maintains -the circular motion may, therefore, easily distinguish when the division of the parts has attained to its utmost term. The fineness of the parts may be soon observed by the sight. The tr?xe of the muller shows the matter smoother, and the colour is more and more developed ; but if the eye is sufficient to perceive this physical change, it is soon distinguished also by the ear. At the commencement of the operation of grinding, the rolling and friction of the parts of the matter and of the instrument excite under it a kind of noise, which gradually decreases, and v/hich is scarcely heard towards the end. The absorption of the oily fluid, which becomes greater as the division of the parts is completed, requires the addition of more colour to bring the mi^iture to a proper consistence. Care, however, must be taken not to render it too liquid ; because it would run on tlie stone and retai-d the tenn of di\'ision, in consequence of the addition of a little sohd matter vvhich would become necessary. A pretty liquid consistence is less fatiguing, but the act of divi- sion is somewhat retarded. - On the other hand it is the more rapid as the consistence of the matter is thicker: hence time is gained at the expense of a little more fatigue, Tv/o or three trials v/iil soon indicate. 4 442 tREATISE ON VARNISHES. the true consistence proper to be given to the mattef to render the operation easy and expeditious. 8th. The perfection of this operation, and the spee- diness of its execution, depend on the quantity of the substance subjected, each time, to the action of the muller. Those who might believe that the process would be hastened by employing a great deal would be much mistaken : -there is no fixed rule in regard to this point. It depends on the extent of the stone, the length and strength of the workman's arms, and con- sequently on the greater or less restraint he may ex- perience in keeping the muller in continual motion. When heavy matters, such as those obtained from me- tallic bodies, are ground, eight ounces at once will be sufficient. Gth. When the grinding is finished the matter is re- moved with a flexible knife or spatula, and put into a colour-pot. The same operation is repeated with new doses of matter, till the whole quantity judged to be necessary for the work is ground i^'ith the same care. The colour is then diluted with the varnish or pre- pared oil intended to be employed, giving' it the proper consistence. This is what is called, according to the technical tenri, vii.rhig up the colour. In this respect extremes must be avoided ; a colour when too liquid runs, and does not cover with sufficient exactness the article which has been painted : if too thick it forms lumps, can with difficulty be extended, occasions more expense, disfigures the work, and fatigues the hand which applies it. The colour on being taken from the pet ouglit not to drop from the brush when tiu-ned' PRECEPTS RESPECTING VARN'isH. 443 round two or three times in the hand, raising it obliquely to check the thread which is formed. Should the colour, during the operation of applying it, assume too much consistence, a little more varnish must be added, if it has been mixed up with varnish j and essence of turpentine, if it has been made with the latter or with oil. But if this consistence of the colour arises from that of the varnish, it will be proper to heat the alcohol or essence, before it is added to the mixed up matter, in order to prevent the precipitation of a part of the resin of which the varnish is composed. 10th. All matters destined for priming are ground with water*, or with alcohol (spirit of wine), or with essential oils, such as that of turpentine, or with fat drying oils. Colours ground with alcohol, and which are mixed with varnish, must be employed immediately ; but the great volatility of alcohol, and the rapidity with which it evaporates, render this kind of process inconvenient. On this account the varnish with which the colour is to be mixed up is substituted in its stead ; and each time that a new quantity of colour is put on the stone a spoonful of drying nut oil is added, if the colour can bear the slight change in the tint which results from it ; or with the same quantity of oil of pinks, if the" nature of the ground proscribes the use of every thing, that might communicate a foreign tint. 11th. When colours are ground in essence, the. artist ought to stand where there is a current of air, to * This is the case in regard to distemper-^ t 44>4f TREATISE ON VARNlEjiES» avoid the émanation of the essence, which sometime^ exercises^ an action on the nerves, when one is toQ long exposed to it. In other cases the colours must be ground with dry- ing oils or with varnishes of the fifth genus, the con- i^istence of which requires that they should be mixed with a half or a third oi essence of tui'pentine. This is the practice followed in regar4 to copal aiid amber varnish, and in regard to ail colours destined for fo mordants made with the same varnish are employed : one of them admits a mixture of orpi- ment for certain gold colours ; and the second that of cinnabar. The latter favours the application of gold under its natural colour. The extraction of this varnish requires precautions on the part of those employed in that labour, as they are exposed to noxious exhalations, the least effect of which is to produce a dangerous kind of erysipelas. To secure themselves from these vapours, they cover the naked parts of their bodies with a kind of glue, which prevents them from coming into contact with the exhalation. The second substance, which may be compared to our linseed oil, is called girgili : it is known also under the name of tong-yeon. With this oily matter, added to tlie varnish, they mix up their colours, which they CHINESE VARNISH. 453 extend over the polished wood. When the first strata ars dry, they ornament them with various designs in different colours, which they -decorate with gold or silver. They then finish their works, which exhibit more splendour and solidity than taste, and which the worst of our artists would be ashamed to imitate in regard to the design. They employ two methods in the application of their varnish. The first, which has been described, consists in extending the colour, mixed up with varnish, over the polished wood when perfectly dry. The second requires more care. The furniture or articles to be varnished are covered with a very hard coating, formed of a sort of paste made with hemp, paper, lime, fine sand, and some other matter, which, when pro- perly prepared, is applied to the wood. Over this paste, when very dry, and of which they compose also their figures in relief, they extend the kind of oil destined to receive the colours. This oil forms a very solid ground, on which they trace out different designs. They then spread over it two strata of varnish, and on this varnish they apply the gold, which forms the basis of their decorations. Having finished their subjects, they are glazed with a third stratum of varnish, which is polished with some soft body. Our varnishes lose a little of their lustre when ex- posed to the influence of humidity; and the alteration would be still greater were they subjected to it when they come from the hands of the artist. Those of the Chinese are not affected by moisture; it even appears that a damp atmosphere is of use to them, when in the 2 G 3 454 TREATISE ON VARNISHES. artist's hands, or when newly finished. This effect depends merely on the nature of the substances em- ployed in these different kinds of composition. The viscosity of the hoa-kin-tsi requires a method of application which must be different from ours. In China all operations of art are carried on slowly : among us the contrary is the case; and there is reason to believe that this arises from necessity. In some pro- vinces of China, as at Pekin, where the air is very dry, the varnishers are accustomed to expose their works in their manufactories, which are more subject to humidity than to dryness. Very often this condi- tion even is not sufficient, since, according to the re- port of Father D'Incarville, who has given us excel- lent details on this subject, they spread over certain compositions wet or very damp cloths. Our European varnishes would certainly not admit of this method. It has, however, been established in China by experience; and it will not appear extra- ordinary, if we only attend for a moment to the natural effect of dry air on certain gummy or viscid mixtures. The surface of an exceedingly viscous liquid, when exposed to the influence of dry air, begins to be hard- ened, and the first effect of this new consistence is to check the desiccation of the part of the substance which is not subjected to the same influence : the uniformity of the texture is then interrupted. The permanent viscidity of the interior part of the varnish, and the dryness of its surface, soon occasion a shrinking in the latter, which splits or cracks. This is the effect always observed after a similar disposition. The Chinese then CHINESE VARNISH. 455 are obliged to maintain the surface in such a state of pliableness as may preserve harmony of consistence in the whole stratum, in order that the moisture in the interior part may have time to escape. The application of wet cloths, or establishing manufactories in situa- tions where the air can perform the same office, appears to me to accord perfectly with the opinion which ought to be entertained respecting the particular nature of their varnish. But, when the simplicity of the mechanical means employed by the Chinese is compared with all those processes, the aggregate of which constitutes what is here called the art of varnishing considered in all the parts which connect it with the art of making paper boxes, coach-making, painting and gilding, one will be convinced that the imitators have, in the course of a few years, far surpassed the inventors, who in a series of ages have not been able to deviate from the servile routine, which among them confines the mechanical part of the arts to uniform and invariable processes. 2 1st. The strongest smell, that is to say, the odour which immediately follows the application of varnish, arises from the evaporation of the essence. This ema- nation is charged with other vaporous principles, fur- nished by the different resins that enter into the cpm- Dosition of varnishes, or which belong to the colouring- parts mixed with them. Such, in particular, is the nauseous odour of acetite of copper (verdigris). No- thing but speedy evaporation, favoured by a current of ail", or a condensation of these vapours, can answer the purpose of those who wish to get rid of them. 2 G 4 ééë ■:./■ Treatise on varîtishes. k„.V î"*!, Ï^^a^oration is speedier in summer than in autumn, '"Sélàsons during whicli most work of this kind is per- formed. In summer, opening the doors and windows will produce currents of air, and soon disperse these noxious emanations. In autumn, a good fire made in the chimney will accomplish the same end, but in a slower mamier. The disagreeable and even deleterious odour may be weakened by the mixture of some balsamic sub- stance, the odour of which is more agreeable to the organs of smelling. It may readily be conceived that this mixture will produce only a modification, whicU-^ will not admit of the apartments being sooner occu- pied; but the odour will then exercise a different ac- tion on the organs, and be less incommodious. Musk, to persons accustomed to the smell of it, essence of cinnamon,, of leriion juice, of thyme, of lavender, &c» will effect this modification. New hay will answer the purpose still better, if it be very dry; in this ctate it changes the odour, and at the same time it absorbs, a& a mechanical mean, the vaporous em^anation. I have used for the same purpose a kind of con- denser, which niav be easily obtained: I here mean v.ater, several tubs filled with which ought to be placed in the varnished apartment. The greater the surfaces presented by t^ese tubs, the speedier will be the effect. The water by its coldness condenses the odorous va- pour, which is of an oily nature; and one may some- times observe on the surface of it a pellicle, which exhibits the prismatic colours, and which is formed by the condensed vapour of the essence. The water. PRECEPTS RESPECTING VARNISH. \^ 43^ m this case, performs the same office as a refn^f$,to^;.« in the common process of distillation. I have em-* ployed this method with complete success for apart- ments varnished with verdigris, and varnish made v^ith essence. Some workmen, who call themselves painters, exclaim against the use of this condenser, under the specious pretext that it destroys the splendour of the varnish; but this fear is justified neither by reason nor by theory. When the varnish is dry, which may be knowTi by the hand not adhering when applied to it for a minute, and when nothing remains but the last vapours, which are ahvavs long in escaping, nitrous fumigation, so effectual in purifying foul air, may also be employed. For this pv.rpose pour into a cup half an ounce of con- centrated sulohuric acid foil of vitrioH ; and having; added to it half an ounce of pulverized salt of nitre, mix the whole v;ith the shank of a tobacco-pipe, or with a glass tube. The extension of the fumes may be facilitated by carrying the cup about through the apartment. This preventive, however, may alter the beautiful reflection of the varnish, if it be delicate and not completely dry. 22d. Colours applied under varnish, as well as those destined for oil painting, require great attention to cleanliness on the part of those who employ them. The surfaces to v/hich they are applied should be rub- bed or swept, and even washed if necessary : they must, however, be well dried afterwards. The same care' must be extended to all apartments, painted or varnished. Varnish is much more disposed 45S TREATISE ON VARNISHES. to be altered by dirt than oil painting ; and the mean? employed to bring it back to its first state cannot always be the same, because the dust adheres more strongly to the resinous parts which constitute varnish, than to the surface of prepared oil. A few strokes of a brush, with simple washing, will be sufficient for varnishes which are usually kept clean, if the dust be incrusted, soap and water must be em- ployed by means of a sponge, taking care every time that it has been rubbed over the varnish to rinse it in clean water, and to squeeze it before it be again dip- ped in the soapy water. Some employ an alkaline Icy, to which they give tlie name of second water. It is called weak second water when it contains only a sixteenth or a twentieth of the carbonate of potash (alkali of potash) ; when it contains a tenth, it is strong second ivater. They even leave it an hour or two on the varnish before they rub it oft with a sponge, dipped in common water. This method is attended with some inconvenience. The alkiili exercises a strong action on delicate varnishes, and deprives them of their brilliancy ; and if they con- tain red from vermilion, or blue from prussiate of iron, it alters or detaches them. But if this process be improper for cleaning varnishes, the case is not the same in regard to oil painting, and particularly gray grounds, for which it seems to be exceedingly proper. The quantity of the alkali may even be extended to an eighth of the water employed. Some employ for the same purpose water impreg- nated with sulphuric acid (oil of vitriol), in such a s. METHOD OF CLEANING VART^ISH. 4S0 . manner that the acidity may be equal to that of stronpj vinegar. This water is very detergent ; but it tarnishes the varnish, and the application of it must be followed by a thorough washing with pure water. This acid has the fault of forming sulphate of lime (an earthy saline matter, distinguished by the name of selenite), which incrusts the surface of the varnish, so that no washing can remove it. The friction which this ope- ration requires necessarily alters the varnish. It is much fitter for oil painting, which is more solid and less injured by the effects of washing than delicate resinous painting. But it will be necessary to diy the surface well with soft and very warm cloths. If the muriatic acid (the marine acid) were not dearer than the sulphuric, it would answer much better for this purpose ; because it forms with the dust a deliquescent salt, which washing easily removes, and which, when thus diluted with water, exercises no action on resins, nor on the most delicate colours. But whatever may be the means employed to clean varnish or paintings by washing, they must not be left till they have been completely dried with clean and very warm cloths. Moisture is exceedingly hurtful to them ; for this reason they ought to be protected from the impression of fogs. These vapours, indeed, do not possess any quality different from that of aqueous humidity; but as fogs, in consequence of their perma- nence, insinuate themselves more easily into all the mouldings of wainscoting, they fix there, under the form of an incrustation, all the fine dust conveyed by the air ijito the closest apartments, and even into those 460 f R£ATISE ON VARNISI^ES. which are inhabited; and this incrustation incorporates in such a manner with the varnish that brushing is not able to remove it. If the incrustation, however, has not been suiFered to remain too long, washing with water will be sufficient to detach it. 23d. During the process of applying oil colours, if any of them fall on the clothes, it may be instantly made to disappear by rubbing the cloth strongly with a bit of bread. The same effect may be produced by essence, which can be removed aftenvards by pure alcohol, if the stained part be held before the fire. 24th. If any colour be left which you are desirous of preserving, nothing will be necessary but to cover it with water, and to deposit the vessel in a cool place. The brushes may be kept in the same manner, after care has been taken to free them by essence from the colour adhering to them, and to wipe them. Alcoholic varnishes are exceedingly drying, and they possess great splendour: both these are reasons for giving them the preference. Varnishes made with es- sence are also brilliant; but they are less drying, and they emit a strong odour, which they retain a long time, when not covered by a stratum of alcoholic var- nish. Oil painting is very durable ; it is even suscep- tible of the brilliancy of varnish, if the colours have been mixed up with the resinous drying oil, page 120, Part I., or if it has been covered by a varnish made with essence or with alcohol ; but it is slow in drying. This character, which is a sign of its solidity, is a cause of its being rejected by persons who sacrifice every thing to expedition. The time of its desiccation, how- 4 . PRECEPTS FOR OIL PAINTING, 461 ever, may be very much shortened by adding to it some matter of a very drying quality; but the labour is more tedious, and painting of this kind never has the brightness and lustre of varnish. This may ba sufficient to justify the preference given to varnishing ; but as many persons still retain a favourable opinion of the old method of oil painting, and as it has its par-^ ticular rules, it is necessary that some account of it should be given. Oil painting. Oil painting has a character of solidity which makes it often be preferred to that executed with varnish or in distemper. Besides, there are some circumstances, independent of taste, which imperiously require the use of it ; as when it is necessary to apply a colour to external objects exposed to the influence of the weather. This kind of painting is used also for internal articles. All kinds of oil cannot be indiscriminately used for this kind of painting, even when they form part of those which reasons, founded on experience, have in- dicated as alone proper for this use; such as oil of pinks, nut and linseed oil, rendered drying by parti- cular processes. Painting destined for external objects, exposed to the influence of the rain, solar light, &c.' requires nut oil to the exclusion of every other Idnd, because it nourishes and develops the colour. Linseed oil, in this case, is dissipated, and destroys the colour; so that at the end of a very little time the work must be re- newed. 462 TREATISE ON VARNISHES. • In the case of external painting, the colours must not > be ground or mixed up with nut oil to which essence of turpentine has been added; because the latter whitens the colour under the impression of the sun, in the same manner as pure linseed oil would do. Linseed oil may be recommended in painting de- stined for internal articles, which are sheltered from the inclemency of the weather. This kind of painting has its particular precepts, from which it will be proper never to deviate. 1st. When it is necessary to grind and mix up bright colours, such as whites, grays, &c. nut oil or oil of pinks is used. For dark colours, such as ches- nut, brown, and olive, pure linseed oil is preferable, if the painting be destined for internal objects. 2d. Each stratum is applied cold. It is never em- ployed in a state of ebullition, except when it may be ' necessai^ to prepare a nevv wall, or new and damp plaster, in order to make the paint adhere. Without this precaution, the paint rises, and falls off in scales. The first stratum on soft wood requires also a little • heat, that it may penetrate better. Sd. No colour mixed up with pure oil, or oil to which a little essence has been added, ought ever to form a thread at the end of the brush. 4th. The colour must be stirred in the pot from time to time, before any of it is taken up with the brusli, in order that it may preserve the same con- sistence and the same tone. If the ground, in conse-' quence of metallic colours being used, does not retain :precepts for oil painting. 46S the same tint, it may be brightened by pom-ing in a little of the same oil as that with which the colour has been mixed up. Some painters, who are negligent in regard to the consistence proper to be given to the colour, before it is employed, think they can accomplish the required end by adding essence to the colour from time to time, when they think it too thick. This method, in ordinary painting, is not attended with much inconvenience; but it does not answer the purpose in delicate painting. The addition of cold essence lessens the splendour of the colour ; and this effect arises from the resin of the varnish beginning to be precipitated, if a varnish form the basis of the paint- ing ; and from a commencement of separation in the colouring part united to the oil, if the painting be in oil colours. In the latter case, it will be of great advantage to give the real consistence at first; and if it be found necessary to add a little more of the excipient, it ought to be warm: it requires to be well mixed before it is used. 5th. When the paindng is destined for apartments, the first stratum ought to be ground in oil, and mixed up with essence. 1 st. Because tKe latter carries off the odour of the oil. 2d. Because the colour applied over a stratum mixed up with oil, to which essence has been added, or with pure essence, becomes more brilliant, whereas it would penetrate into a stratum with pure oil. 3d. Because essence thoroughly hardens the co- lours mixed up with it ; but if mixed with oil it makes it penetrate to the colour. When you are desirous, therefore, to varnish an oil colourj^^ the first stratum ought to be mixed up with oil, and the last t^vo with 4G*i TREATISE ON VARNISHES. pure essence, When you do not intend to varnish, the first stratum ought to be mixed with pure oil, and the last two with oil to which essence has been added. Essence unites to the two advantages before mentioned a practical utility : it facilitates the extension of the colour. ()th. If the painting be intended for copper, iron, or any other hard substance, the smoothness of which opposes the adhesion of the colours by making them glide, a little essence must be added to the first strata : the essence will cause the oil to adhere. Besides, metals intended to receive varnish or colours must be polished or scoured, that is to say, roughened a little, in order that the colour may lay hold of them : this rough polishing is performed with pulverized pumice stone or tripoli, Vv hich is rubbed over the article with a piece of rag, on each stratum being applied. The article must then be exposed to the sun to facilitate the extension of it, if the varnisli has a considera- ble degree of consistence ; after which it is carried to a stove to hasten its desiccation. My turpentine copal varnish, and that even caHed fat varnish, dry very speedily. The operation of polishing is not per- formed till several strata are applied and have become dry. When such varnishes are used you may begin the polishing with pumice stone, and afterwards finish it with tripoli. 7th. If the wood contain resinous knots, which is the case in particular in fir, the colour runs in these knots, and does not adhere. If simple oil be employed, oil charged with drj^ing matter, that is to say, litharge, mixed with a littio of the ground colour, is prepared separately, and reserved for these r-j^inous parts. Ii' Precepts iît regard to oil fronting. 4^5 the painting be in oil, and intended to be covered with polished varnish, more litharge must be added: it masks the wood, and hardens the resinous particles which exude from it. One stratum will be sufficient, and will give body to the wood : thé labour may be shortened by rubbing the place with a head of garlic. 8th. Some colours, and in particular those which; have an argillaceous ground, as the Dutch pinks, boles, kc, as well as lamp-black, burnt vine twigs, &;c., are long in drying when employed v?ith oil. It "tt'ill, therefore^ be proper to add drying matter to them, according to the colour: litharge to dark Colours, and sulphate of zinc (white vitriol) to bright colours, mixed -with drying oil : this method is always attended with success. I must here observe that drying matter is unnecessary in all cases, and for all colours which ad- mit into their composition ceruse, white oxide of lead,; mid other metallic oxides. 9th. If the addition of drying matter becomes ne- cessary, it must not be added till the moment when the colour is applied, because k tends to rerder it diicker. 10th. One principle, which ought never to be for- gotten, because it is applicable to ail kinds of painting, aiid riiore particularly to the one in question, is, -that, a nevv' stratum of colour ought never to be applied till the preceding is dry. It will be proper also to brush off the dust, which sometimes covers the last stratum ; and which, if mixed with the new one, would not fail to alter the uniformitv of its tint : this observation is applicable, above all, to bright colours, such as whites 466 TREATISE 01^ VARNISHES. and grays. You niay be sure that a stratum is dr}% when it does not adhere to the hand on being applied to it. 11th. All kinds of pamting require that each stra- tum of colour should be of an uniform thickness throughout ; and as this depends on the consistence, it tvill be proper to maintain it in the same state. Habit and experience will be a better guide, in this respect, than any precepts that might be collected. Too thin a stratum cracks by desiccation ; one too thick be- comes wrinkled, acquires undulations, and interrupts the re££ction of the light. The addition of a little ground colour, or of some of the vehicle, vill correct one of these faults. It v.ill not, however, be attended with any incon- venience if a little mofe liquidity be given' to the fii"st stratum than to the succeeding ; because it is destined rather to adl'iere to the substance which it covers, than to esîevblish the tone of the required colour. But the succeeding ones, and pardcularly the last, ought to have sufficient consistence to prevent the shrinking of the painr; the addition of a little essence will, if it be too thick, bring it to the proper point. Î2th. If a soliditv capable of resisting blows and fjriction be required in the paint, this end will be better obtained by applying the first stratum with a me- tallic oxide, such as Montpellier yellow, ceruse, or vitreous oxide of lead (litharge), reduced to fine pow- der, ground in boiled oil, and mixed up with oil to which a little essence has been added, than by the same colour mixed up wiîh oil. PRECEPTS IN REGARD TO OIL PAINTtN(^-'^: 13th. Artists, during the exercise of a profession, acquire habits, which, among persons who are desirous of placing themselves on a level with them, are con- verted into precepts. The amateur, after the first trial, is merely a eervile imitator of the painter. In the use of the brush he does not at first show much dexterity; but being the judge of his own work, he soon discovers that he wants experience ; and he at length attains, though slowly, to results which, in a skilful hand, soon improve. He feels the necessity of varying the strokes of the brush according to circum- stances. Sometimes he employs long strokes, to ex- tend the colour in an uniform manner ; at other times he daubs it repeatedly over the wainscoting, to incrust the matter in the places sheltered by the mouldings or by sculpture. He avoids inequalities ; he is encouraged by the new aspect which presents itself to his eyes; he perceives, and at length is convinced, that the perfec- tion of the application concurs, in a considerable degree, tovv'ards the richness and tone of the colour, and the beautiful development it acquires from the reflection of the light. Every amateur who is fully sensible of the necessity of obtaining these results may be con- sidered as an artist. I will even say more; he is su- perior to a workman without taste, whatever practice he may have had in work of this kind. The labour soon vanishes when compared with the enjoyment he pro- cures. But this kind of painting is attended with one cir- cumstance, which requires the concurrence of different artists,, as the labour is superior to the efforts of tha 2 H 2 i6S TREATISE ON VARNISKES. amateur, however expert. I allude here to coacfe painting, which requires the union of the limner, the common painter, and the gilder. Besides, the appli^ catioli of varnish, in this case, ought to be followed by an operation which is dispensed with in all cases of A'arnishing or painting applied to common apartments> and to external objects: I mean polishing. This ope- ration, which the amateur has no need to perform^ shows the necessity of admitting into this species of painting a division respecting the different kinds of labour which it requires» Division of oil painting* Oil painting may be divided into two kinds; namely, common oil painting, and painting in oil with polished varnish. The first is simple, the other is more exten- sive ; it forms grounds, which are polished and after- wards covered v^^-ith a varnish, which is also polished. This addition of labour induces artists to admit tjie above-mentioned division, the necessity of which does not appear to me to be well fouiided. As painting in oil constitutes a separate kind, disdnct from painting in varnish and painting in distemper, we can admit ne- other divifîioîi than that which form? it into species^ especially -when the same matters are employed in both cases. All oil painting is susceptible of acquiring gi fine polish, when the thickness of the strata admits the application of those processes which polished painting in varnish requires. It may be both varnished and glazed, to increase the brightness of the colour, and to sail it forth in its full splendour. I have even given ^ Polishing. 46# iTiethod of fulfilling, at one operation, the conditions which establish plain painting in oil, and that in which varnish is employed. This method is that which re- quires the use of the drying resinous oil in page 1 20. This distinction is deduced rather from that made between the objects for which this kind of painting is destined, than from the nature of the materials em- ployed, or from the variety introduced in the com]>o- sition of them. All carriages are painted in oil, then varnished, and afterwards polished. Some kinds of valuable furniture and toys made with artificial enamel require also the last-mentioned operation, which gives them a great deal of splendour, and disposes them to ï'eflect'the light in a more uniform manner* Polishing, The processes used in polishing are different, ac- cording to the nature of the varnish which requires it. Hard varnishes, such as those resulting from the solu- tion of amber and copal in a drying oil, or even in essence, as well as certain oil colours, can hear the contact of hard bodies employed for polishing. It is not, however, attended with complete success but when the ground is charged with a determinate number of strata of a colour which, by painters, is called the priming (^teinte duré) *. This priming gives to the * The priming {tc'vitc dure) is prepared by grinding ceinise very fine in pure oiJ^ and raiy.ing it irp with essence of turpentine. Seven or eight strata of it are applied before it is pohshed. The ceruse empkîyed for this purpose must have been subjected to a certain degree of heat, which destroys its whiteness, and prevent» 2li 3 470 TREATISE ON VARNISHES. whole a certain thickness and a great deal of con- sistence. When the priming has received all the strata it re- quires, and when very dry, pumice stone finely pul- verized, and sifted through a silk sieve, is mixed up with a sufficient quantity of water. Some of this powder is spread over a piece of cloth, rolled up in the form of a ball, and the ball is moved .over the sur- face of the colour, to polish it uniformly : to deter- jnine with precision to what degree this has been ef- fected, the polished part is frequently washed with water. When this operation is finished, two or three strata of the colour which has been chosen are applied, the motion of the brush being softened to avoid striie; and it is then glazed with two strata of transparent and colourless varnish, should this number be thought suf- ficient : but if the varnish itself is to be polished in the same manner as the priming ; in a word, if it be re- quired to imitate that which covers the pannels of car- riages, seven or eight strata must be applied. When the last strata of the varnish form undulations, which cut, derange, or break the reflection of the light, it will be necessary to polish it. This last polish- it from weakening the colonrs applied over it. In this state it is called by painters calcined ceruse: the colour of it inclines a little to yellow. It will be proper not to give too much heat to the ceruse destined ior different strata of priming, because it has too jnuch influence on the coloured grounds -which it ought to sup- port. The strata of priming are applied over a stratum formed of tmcalcined ceruse, ground in linseed oilj and mixed up with equal parts of linseed oil and essence. 3 POLISHING. . 471 ing may be performed with advantage by employing tripoli, reduced to fine powder, mixed up with a little y>il, and placed on a ball of serge, or, what is better, of shamniy leather. The fat part may then be re- moved with a little bran, or v.iih. farina, rubbed over it by means of a clean linen cloth. The polishing is then completed with a bit of serge or cloth, without tripoli. It is in this manner that the varnish which supplies the place of glazing on certain kinds of furniture, and the coloured or uncoloured varnishes apphed to metal- lic bodies or plates of metal, are polished. The latter require only uniform friction with a piece of clotli. It is very seldom that there is any need of beginning with tripoli and oil. The finest polishing is that performed by the lathe. Those vv'ho renew the colours on the pannels and bodies of caiTiages, do not amuse themselves by rub- bing them with a piece of serge and pulverized pumice stone. They wear down the old colour to the wood,, with a fragment of pumice stone and water. Some even employ for this operation a piece of felt and fine sand. This process is alone suited to work of this kind. If you vv'ish to render the colour more drying, add half an ounce of the vitreous oxide of lead (litharge) to each pound of colour. If the colour is bright, a gros of the sulphate of zinc (white vitriol) must be substituted for the litharge. 2 H 4. 473 TRI^ATISE ON VARNISHEB. Ofîcax doth. Oil cloth. It is possible that the term wax cloth, given to some cloth prepared in a certain manner, origiuated from the first trials, in which wax perhaps formed a part of the composition; or it may have arisen from one of those modes of concealment, so often employed by inventors, who endeavour to take advantage of their researches, or of a happy discovery. It is, however, certain that this denomination is absolutely foreign to the articles of this manufacture, in which wax is not used. The art of preparing these cloths is one of those which escaped the ingenious and useful undertaking of the lite Academy of ^Sciences at Paris, entitled De- scription des Arts et Métiers. I am acquainted with no author who mentions it even indirectly. What I shall offer, in this work, will be only a sketch of the art, the processes of which, in regard to the grounds and the application of the coloured designs, are so varied and interesting as to justify and even render valuable a detailed description of them. The manu- facture of these cloths, considered under a political point of viev/, is not unworthy the' attention of the public. 1 shall, however, confine myself to some par- ticular experiments, and to the knowledge I have acr quired in regard to this kind of labour : it will be suf- ficient to prove that the preparation of oiled silks and oil-skin is connected with that of varnishes, and de* cendent on it. This art originated in Holland, in consec^uençe, nq OIL CLOTH. 475 doubt, of the wants of commerce, which consumes such a large quantity of articles proper for packing ^oods. It is probable that the first attempts \ver2 undertaken with a view to this end, which seemed to insure to them a constant and extensive sale. It is probable also that the first processes admitted the use of wax, and that the cloth first manufactured might have a resemblance to those packing-cloths which come from India, and which are covered with a waxy sub- stance. The name of wax cloth, Vv^hich was then proper for them, sui"viving the composition, may have served to ilenote, till the present time, finer compositions, exe- cuted with greater care, and yet less expensive; as wax is of more value than the substances now used in preparing these cloths, which are employed for so many useful purposes. If Holland was the birth-place of this kind of manu« facture on a large scale, it is possible that the first processes may have been known and folio v/ed in neigh* bouring countries. This much, at any rate, is cer- tain, that the extent since given to the manufacture, by admitting a certain finish in the designs, must con- tribute to multiply the enterprises. There are indeed excellent manufactories of this kind in the ci-devant Austrian Netherlands, in Germany, and particularly at Franckfort, where the v/orkshops altogether occupy a very considerable extent. Every manufacturer and every v/orkman has his own compositions and methods, which he applies to the Jdnd of work intrusted to him. The process for com» 474' Tr.EATISE ON VARNISHES. mon vai'pished cloths is veiy simple; bat, as I havç already said, their e are others. which require more in, telligënce on the part of the workman, as the same care is necessary as for painted cloths. In these varr nished cloths the art of the colourist is put to tlie test ; because the hnishing, the happy mixture of the colours, the richness of their variety, the natural appearance of the shades, and the delicacy of the strokes, concur to enhance their value, and conseque;ntly to secure to them a speedy sale. But if the diilerence of the labour has so powerful an influence on this kind of manufacture, it may readily be conceived tha.t the quality of the cloth must contri- bute towards the same end; for it is this quality alone which determines the kind of painting that ought to be employed. Varnished cloths, therefore, of different de- grees of fineness are manufactured. Common ivax cloth or varnished cloth. The manufacture of this kind of cloth is very sim- ple, and may be canied on at very little expense. The cloth and linseed oil are the principal articles required . for the establishment. Common canvas, of an open and coarse texture, is extended on large frames, placed under sheds, the sides of which are open, so as to afford a free passage lo the external air. The manner in which the cloth is fastened to these frames is very simple and convenient ; for when it becomes slackened, during the application of the varnish paste, it cTin be again tightened. It is fexed to each side of the frame by a kind of hooks LIQUID PASTE FOR OIL CLOTH. 475 which catch the edge of the cloth, and by pieces of strong packthread passing through holes at the other extremity of the hooks, which are tied round move- able pegs placed in the lower edge of the frame. The mechanism by which the strings of a violin are stretched or unstretched, will give some idea of the arrangement of the pegs employed for extending the cloth in this apparatus. By these means the cloth can be easily stretched or relaxed, when the oily varnish has exer- cised an action on its texture in the course of the ope- ration. The whole being thus arranged, a liquid paste made with drying oil, which may be varied at plear sure, is applied to the cloth* Liquid paste ivith dri/ing oil. Mix Spanish white or tobacco pipe clay, or any other argillaceous matter, with water, and leave it at rest some hours, which v/ill be sufficient to separate the argillaceous parts and to produce a sediment. Stir the sediment with a broom, to complete the division of the earth; and after it has rested some seconds decant the turbid water into an earthen or wooden ves- sel. By this process the earth will be separated from the sand and other foreign bodies, which are preci- pitated, and which must be thrown away. If the earth has been washed by the same process, on a large scale, it is divided by kneading it. The supernatant water is thrown aside, and the sediment is placed in sieves, on pieces of cloth, where it is suffered to drain : it is then mixed up with oil rendered drying by a large dose of litharge, that is to say, about a fourth of the weight of the oil The consistence of thin paste being 47G TREATISE ON VARKISHE?. given to the mixture, it is spread over the cloth by means of an iron spatula, the length of which is equal to that of the breadth of the cloth. This spatula per- ' forms the part of a knife, and pushes forwards the ex- cess of matter above the quantity sufficient to cover the cloth. Though the earth mixed m this manner stHI contains water, it readily unites with the boiled oil. The watei* passes into the tissue of the cloth, which facilitates its evaporation ; and the cloth at the same time acquires the property of not suffering itself to be too much pe- netrated by the oily vaniish. However hquid the var- nish may be, it does not transude to the inferior sur- face of the ck)th. When the first stratum is dry a second is applied. The inequalities produced by the coarseness of the cloth, or by an unequal extension of the paste, are smoothed down with pumice stone. The pumice stone is reduced to powder, and rubbed over the cloth with a piece of soft serge or cork dipped in water. A whole pumice' stone, one of the faces of which has been ground smooth, may also be employed. The cloth must then be well washed in water to clean it ; and, after being suf- fered to dry, a varnish of gum lac dissolved in linseed oil boiled with turpentine, and which is liquefied with essence of turpentine, if necessaiy, is then applied to it. This preparation produces yellowish varnished cloth. When you are desirous of rendering it black, nothing will be necessaiy but to mix lamp black with the Spa- nish white, or tobacco-pipe clay, which forms the basis of the liquid paste. Various shades of gray may be ob- tained, according to the quantity of the lamp black PRINTED VARNISHED CLOTHS. 477 ■V'hlch. is added. Umber, Cologne earth, and different ochrey argillaceous earllis, the nature of which has been explained in the chapter on colours, may be used to vary the tints, wit hout causing any adddition to the expense. Fme priiite d varnished cloths. The process just described for manufacturing com- mon varnished and polished cloths may serve to give some idea of that employed for making fine cloths of the same kind, decorated with a coloured impression. At first this kind of manufacture was confined to com- mon cloths^ with a smooth ground of diffei^ent colouts. Industry, however, has given it greater extent, by find- ing on the palette of the painter ail those materials ca- pable^of making this new art rival that of printed cloths. The firmness of the texture of the cloth, still increased by that of a pliable covering impermeable to watef, 'opened for this kind of manufacture a very lucrative sale, in consequence of a more careful application of the colours, which could be subjected to all the rules of design. The manufactories of Germany, indeed, have varnished cloths embellished with large and small subjects, figures, and landskips, w^ell executed, and which being destined for covering furniture subjected to daily use, gave certain support to this branch of in- COMMON DISTEMPER. " 497 By this attention, in regard to the choice of the matters which are to serve as the ground, the paintings with which apartments are decor-ted wili always pro- duce their effect, to whatever light they may be ex- posed; the greater the light, the livelier and more b ^au- tiful they appear. They participate with crayon- paij ting in the property of not being subject to those reflecdons of the light which prevent the beauty of a painting from being seen, except under a certain point of view, and in a determinate direction of the luminous rays. This method holds the first rank among the com- mon kinds of distemper; but there are many cases which do not require either the same precision or very long details. There has lately appeared in the Décade Philosophique a new process, described by Cadet-de-Vaux, which this author substitutes for that of painting in distemper. Though I have r,ot tried it, the confidence which 1 place in the exactness of a per- son so well known for his knowledge and zeal in regard to every object of public utility, induces me to introduce into this work the formula of his compo- sition. In regard to those kinds of distemper employed for some particular ardcles in the interior part of houses, I shall content myself with extracting from Watin's work such examples as may be useful in our method of buildine;. 2 iv 49S TREATISE ON VARNISHE3, Example IT, Painting in milk. Take Skimmed milk 4 pounds. Lime, newly slaked, 6 ounces. Oil of pinks, or linseed, or nut oil, 4 ounces. Spanish white 3 pounds. Put the lime into an earthen vessel or into a clean bucket, and having poured over it a sufficient quan- tity of milk, add gradually the oil, stirring the mixture with a wooden spatula; then pour in the remainder of the milk and dilute the Spanish white. Milk skimmed in summer is often found to be curdled; but this is of no consequence for the present purpose. The contact of the lime soon restores its ■jBuidity ; but it must not be sour, because in that case it would form with the lime an earthy salt, susceptible of attracting the humidity of the atmosphere. The lime is slaked by immersing it in water, from ^'hich it is taken that it may be suiiered to effloresce ia ihe air. The choice of the oil is a matter of indifférence : any of the three above mentiv)ned may be employed ; but for a white colour that of pinks ought to be pre- ferred. The mixture of the oil with the lime forms a kind of calcareous soap ; and in this state the oil i» .susceptible of an union \^■ith the whole of the ingre- dients. The Spanish white is pounded and carefully strewed PAINTING IN MILK. 499 over the surface of the liquid. It gradually becomes impregnated with it, and falls to the bottom. This, process is apphcable to every kind of distemper made with chalk or with white argillaceous earths. When the white has fallen to the bottom it is stirred with a stick. This painting may be coloured, like every other in distemper, by means of the different, colouring sub- stances employed in common painting. The above quantity will be sufficient to give a first stratum to a surface of 24 square yards. The author, in his rnemoir, explains the advantages of this kind of painting ; they are such that no doubt can remain, in regard to its superiority, when com- pared with the results of painting in distemper with size. It is stronger, and does not, like the latter, detach itself in scales. The gluten which composes it is not susceptible of decomposition, like the glue or animal gelatin which gives body to common distemper. The latter becomes speedily decomposed, and passes to the acid state by the effect of the humidity which it attracts and retains. As the colouring body is not then bound by any gluten, it assumes the form of dust, which is detached by the least friction. Besides, this preparation is less expensive, and par- ticularly in countries where milk is abundant. Jt is also attended with less trouble, especially as the best glues from the clippings of skin spass so readily to the acid state, and lose their strength, independently of the bad odour which they emit in this state of decompo» sition, and of the dampness which they maintain in the walls, 2k2 500 TREATISE ON VARNISHES. This painting in distemper dries in an hour, and the oil which forms part of it loses its odour in passing to the saponaceous state by its combination with the Hme. . One stratum will be sufficient for places which are already covered with any colour, if the latter does not penetrate through it, and produce spots ; two strata on new wood ; one stratum on staircases and on ceil- ings. The author does not confine this composition to dis- temper alone : he applies it also to painting in oil, which he calls resinous paiiiti/ig hi milk^ and which he employs for external objects. As this composition forms neither common distemper nor oil painting, I thought it improper to separate them. Resinous paintbi g in milk. For painting external objects, add to the preceding composition for painting in milk: Slaked lime. Oil, >of each 2 oanceSo } White Burgundy pitch, J Put the pitch* into the oil which is to be added to the liquid milk and lime, and dissolve it in a gentle heat. In cold weather the milk and lime must be warmed, to prevent too sudden a cooling of the pitch, and to facilitate its division in the milk and lime. It appears to me that time alone can determine whether tliis kind of painting be as durable as oil. 4 paiîn'Ting for fire-places. 501 painting ; for the shrinking, to which certain strata of painting on wood are subject, depends in a great measure on the nature of the wood. At Geneva, the fir wood employed for constructing works exposed to the influence of the air is not equally proper for paint- ing in oil. That of Savoy is porous, splits in the air,, and is more subject than any other kind to be eaten by worms. The stratum of painting applied to it de- taches itself in scaly leaves. The Burgundy fir is more compact and more resinous, and the resin it contains, by forming a ground to the painting, contributes to its solidity and preservation. It is always smooth and firm, and has not the inconvenience of yielding to the influence of dryness and moisture, which is always less observed in wood of this kind than in that which is exceedingly porous. The latter kind of painting may be substituted for badigeon^ which will be described as the fourth example of painting in distemper. Example III. raiiitiiigfor tJieJlre-hlaces and hearths in kitchens, &c. The Genevese method. The Genevese employ a kind of stone, known under the name of molasse, for constructing fire-places and stoves, after the German manner. This stone is brought from Saura, a village of Savoy, at no great distance from Geneva : it hr.s a grayish colour, inclining to blue, which is very agreeable to the eye. This tint is similar to that communicated to common whitewashing with Hme, chalk, or gypsum, the dullness of which 2 K 3 502 TREATISE ON VARNISHES. is corrected by a particle of blue extract of indigo, or by charcoal black. Very fine beds of pretty pure clay, the colour of which is exactly similar to that of the molasse of Sura, has been discovered at Y voire, another village in Savoy: it is employed by the scr/ant maids to scour out or conceal the spots of grease or of charcoal which some- times stain the hearths or chimney-pieces in kitchens. They keep by them some of this clay mixed up with a little water, and apply it with a brush destined for that use after the stains have been rubbed with a frag- tnent of the same stone. This is a kind of plain dis- temper without size. Some whitewashers have lately conceived the ex- cellent idea of employing this clay in their distemper for articles much exposed to be dirtied ; such as kitchens, workshops, &c. They treat it with a solu- tion of glue, as in the first example. The tone of its colour, which is always uniform, presents one ad- vantage not found in artificial mixtures, the true tone of which cannot be known till the stratum is dry. In this case, therefore, the operator proceeds with more certainty, and avoids those repeated trials which are inevitably necessai*y to obtain an uniformity of tint when new mixtures must be made to complete the work. Besides, servant maids, by the daily use of this clay mixed up with water, are enabled to wipe out stains and repair other accidents which may alter the uniformity of a stratum of this distemper. Clay of a bright gray colour is very commofi. It is even so rich in variety of shades, that it may be of 1 PAINTING FOR FLOORS. 503 great use in families who wish to imitate this part of the cleanliness of the Swiss. The advantage they might derive from it would not be confined merely to gratifi- cation of the eye. The first step towards an improve- mient in the convenience of domestic life soon leads to attempts towards other objects; and it is in this manner that people, without any direct design, and even with- out perceiving it, remove from their habitations every thing that might alter the salubrity of them. The bene- ficial effects which result from continued care, in re- gard to every thing that tends to promote cleanliness, are too apparent not to be observed and to be justly appreciated. Diseases which become epidemical in. certain districts in our neighbourhood, and which often occasion great ravage, seldom appear among us with the same malignant characters. Cleanliness, I may even say minute attention to cleanliness, both of furniture and persons, together with sobriety, is the best preserver of health. This observation is not foreign to a subject which treats on the best method of giving elegant simplicity to the interior of houses. Example IF", Distemper for parquets or floors of inlaid work. The use of parquets^ properly so called, or those combinations of oak and walnut-tree which produce so good an effect, is not very common in Swisserland, and those which exist admit only of waxing. The name of parquets is given to boards of fir intersected by pieces of walnut-tree j or disposed in compartDients of 2 K 4 j^d^ ^ ■ TREATISE ON VARNISHES. whrGli tiji; walnut-tree forms the frame or border'* ; but tQ,âfich works no other lustre is comrriunicated than, '^kt which they receive from wax, ar d from beiiîg frequently cleaned. Some jfloors have been exe- cuted of plaster, on which the lemon yellow colour destined for parquets of oak produces a vei"y good dFect. To obtain this colour, boil in Î 6 pounds of water half a pound of yellow berries, and as much terra mérita and bastard saffron; add to the mixture four ounces of sulphate of alumine (alum), or carbonate of potash, which is preferable ; and having strained the whole through a silk sieve, add to the strained liquor four pounds of water charged with a pound of Flan- ders glue. Apply two strata of this colour with a brush, and when dry wax it, and polish tiie surface with a rubber. In this preparation nothing is sought fcr in the bastard saffron but the colouring part soluble in water : thai which is soluble in the alkali passes partly into the bath, if carbonate of soda (potash) has been employed. But as the addition of an acid would be necessary to make the latter appear, its effect in this case is scarcely perceived: it contiibutes, however, to the solidity of the tint. Example V. Red for corridors and halls paved ivlih tiles. A brush dipped in the water which comes from a common ley, or in soapy water, or in water charged •■■^ Some of the floors in France and other countries on the con- tinent are constructed in tliis manner. — T. RED FOR FIALLS PAVED WITH TILE s. /■ •:^dêj\. Avith a twentieth part of the carbonate of potasi {alkali of potash), is in general drawn over the tiies.y- This washing thoroughly clearis thein, carries oiF the g(^asy spots, and disposes all the parts of the pavement^^-tp receive the disiemper. They are then left to dry. On the other hand, dissolve in eight pounds of "water half a pound of Flanders glue, and while the' mixture is still in a state of ebuilidon, add two pounds of red ochre, mixing the whole with great care. Thea apply a stratum of this mixture to the pavement, and suffer it to dry. A second stratum is applied with Prussian red, mixed up with drying linserd oil, and a third with the same red, mixed up with size. When the v/hole is dry rub it with wax. Such is the m? thod generally employed ; and this succession of strata is attended with peculiar advantages. The lirst ley, penetrating into the tiles, forms a ground of adhesion to the second ; and the last receives^ from the second a great deal of solidity, and prevents the slowness of the desiccation of the stratum with oil, which would adhere to the feet or be rubbed oft by the scrubber, were it not entirely dry. The third stratum may be dispensed with, if pulverized litharge be mixed with the colour, which will then become more drying. I have shortened the . operation very, m.uch by i;ed- dening the new tiles with a preparation composed of the serous and colouring parts of ox blood, separated in the slaughter-house froin the fibrous part. This preparation is exceedingly strong. If a single stratum of red bole, mixed up with drying linseed oil, be then applied, it may soon after be waxed and rubbed. This ^06 TREATISE ON VARNISHES. applica&on is solid, and costs less than the fonner. I have gfeen, in a house inhabited for tliirty years, the floor of a hall painted in this manner, where the co- lour still retained its lustre without being ix}. the least diminished. I have communicated a very beautiful red colour also with a bath of alumed madder. A pound of madder coarsely pulverized, four ounces of alum, and tweke pounds of water, are sufficient for this prepa- ration. Two strata of it are applied to new tiles, after larhich it is waxed and rubbed. This application produces a very fine effect j but it K not so durable as the preceding. Example VL Distemper in Badigeon, Badigeon is employed for giving an uniform tint to houses rendered brown by time, and to churches when it is required to render them brighter. Badigeon, in general, has a yellow tint. That which succeeds best îs composed of the saw-dust or powder of the same kiùd of stone and slaked lime, mixed up in a bucket of v/ater holding in solution a pound of the sulphate of alumine (alum). - It is applied with a brush. At Paris, in the nei'ghbourhood of that city, and in other parts of France, where the large edifices are constructed of a soft Idnd of stone, which is yellow, and sometimes white, when it comes from the quaiT)^, but which in time becomes brown, a little ochre de Tse is substituted for the powder of the stone itself, BADIGEON. CHIPOLIN. 50Y and restores to the edifice its oHginal tint. But, at Geneva and Lausanne, and in the neighbouring cities, where buildings are constructed of molasse, a kind of soft freestone, the tint given by ochre de iTie would be different from that intended. We are indebted to one of my fellow-citizens, the late Lagrange, for a method, both simple and effectual, of giving to old edifices Z new appearance, and of reviving their original tint : it is adapted to the nature of the stone. Nothing is necessary but to rub the surface of the edifice with pieces of the same mola'^se, taking care to select the hardest : by this process the stone will acquire its for- mer colour. It was employed at the time of the repa- ration of the church of St. Peter, our cathedral, forty years ago ; and the state of that edifice still attests that none better could have been used. SECOND KIND OF DISTEMPER» Example I, T^arnished distemper, Chipolin, Painting in distemper covered with a varnish callel chipolin* and royal white, which vAW furnish an ex- ample of the third kind of distemper, is the most elegant of this sort ; but the preparation it requires renders it very expensive. It is to chipolin that we * The origin of the word c/tzpoZw is very uncertain. On this subject there are two opinions, which seem to have the same de- gree of probability. Some think it is derived from the resemblancç observed between this kind of painting, when well executed, and cipolin or chipolin marble, in regard to tlie pearly or talc-like bril^ liancy which it acquires and retains when well polished. The first 508 TREATISE ON Vx^-RNISHES. are indebted for those brilliant decorations in varnish applied to candelabra with delicate sculpture, the ar- gentine white of which, set off with pale gold, pro- duces such beautiful effects by reflected light ; but this truly noble Idnd of painting, in consequence of the great labour it requires, is reserved for valuable furniture, and for ornamenting apartments in palaces. The eye dv/ells with pleasure on chipolin which has been executed with ingenuity and taste. The vanity of man ought to smile at the sight of those superb apart- ments where the splendour of the painting, heightened by the pale gold which combines so well in this species of it, attests at the same time the pov/er of the owner and that of the arts, which subjects the sovereign .himself to that tribute which they impose on taste and love of the beautiful. Besides the splendour which this kind of painting ac- quires under the influence of the light, it possesses the property of keeping apartments cool. This effect, which would be produced by marble, must result also from chipolin. Being composed of very fine parts, -\rhich a state of solution brings into perfect contact, and whose adhesion is very much increased by the glu- tcrij which gives them a very great consistence, its tex- ture cannot be very much different from that of marble. ripolin^ perhaps^ v.ns only an imitation of this marble, and exhi- bited those greenish veins with which it is cniriched and ornament- ed. Others suppose that this denomination originated from the use which tlie first painters in this branch made of tlie juice of onions, applied by way of preparation. Were I called upon to de- «Ide this question^ I should declare in favour of the lirst opinion. CHIPOLIN. 50^' I have seen chipoliii employed in the decoration of altars, which was harder than marble with crystal- lized grains. The latter is more susceptible of being- scratched. Though this kind of painting is not frequently em- ployed, I think it necessary to give the reader a sufn- cient idea of it, by a short account of the process, as described by Watin in his PaTfait Ferm'sseur ; but I shall remove the veil of mystery which he throws over the composition of the varnish he would employ, were he to undertake chipolin. The following is the order adopted in the distribution of the labour for argentine white chipolin. In regard to further details, the reader must recur to the work above mentioned : . 1st. Wash the wainscoting with a warm decoction of absynthium, to which a few heads of garlic are added. Mix this decoction with parchment glue, which when cold assumes the form of a jelly. This process opens the pores of the wood, and disposes it to aiibrd the means of adhesion to the following strata. 2d. A stratum of warm glue vt^ith Bougival or Spa- nish white, which will give the w^ork more solidity. White of Pvîorat may be substituted for that of Spain. 3d. Eight or ten strata of the same v/hite, well mixed and exceedingly fine ; taking care to preserve the saine degree of strength and the same thickness in each stratum. But care must be taken at the same time not to choke up the mouldings, and to apply the last stra- tum with glue somewhat thinner than that used in the preceding strata. 4th. Soften the surface with pumice stone, to w^hich SîO TREATISE ON VARNISHES. such a form has been given that it can be introduced into the small cavities of the mouldings and sculpture. Employ small sticks of different shapes to polish the mouldings and the plain surfaces. The process of po- lishing may be shortened by drawing immediately over tlie work a soft brush dipped in water. 5th. Clean the cavities of the mouldings and sculp- ture with small iron instruments prepared for that pur- pose. 6th. After these preparations apply two strata of colour made of white oxide of lead, to which a particle ©f prussiate of iron and black has been added, and mixed up with parchment size, strained through a sieve to separate the portions of size still granulated : these two strata must be softened with the brush. 7th. Apply two other strata of thin glue, beaten up cold, and strained through a sieve, to separate the por- tions of jelly not diluted. They are apphed cold, care- fully softening the work, that there may be no need of passing several times over the same place. 8th. Apply, with the same precautions, two or three strata of the varnish No. 2. of the first genus, or of No. 14. of the third; and keep the place warm, to fa- cilitate evaporation and desiccation before the dust can adhere to it : the work will then be completed. Such \s the process for this preparation, which requires eigh- teen or nineteen strata, and a great deal of care in the execution. It is needless to remind artists of the prin- ciple already laid down, that a mau stratum ■mmt 7iot be applied till the preceding be dry. When the chipo- Jili is destined for pieces of sculpture, it is customary- IMITATION OF CHIPOLIN- ^îl to heighten its splendour by that of gold, which is ap- plied and left unbumished on all the salient parts of the work. This addition increases in a singular manner the richness and magnificence of this Idnd of deco- ration. The author, who gives a more circumstantial detail of this labour, points out a method which was known to painters before the publication of his work, and which they employed with modifications, according ta local circumstances, and to the time and expense which they were willing to sacrifice. This method is much shorter than the former, since it enables artists to imi- tate chipolin by an operation which requires onlj twenty-four hours : it will form the subject of the se- cond example. Example IL Imitation of chipolin, Watin prescribes two strata of size made of Spanish white, mixed up with strong parchment glue, hot, and even in a state of ebullidon*. * The application of size so hot swells the wood and retards the desiccaiion. The wainscoting, indeed, at Paris, and in the neigh- bourhood, is of oak, and tliis wood is less liable to swell than our fir at Geneva. I should apply the first two strata in tiiis caseivith ceruse of the first quality : the tint is solid, and calls forth the co- loured strata equally well. They ought to be applied witli essence. Over tliese two strata I would apply two others of colour mixed up with pretty strong glue, kept liquid, and would polish after the first coloured stratum. These ought to be covered with two strata of varnish of the first class, or the varnish No. 14. of the tliird^ or the colour should be aiixed up with the varnish. Sl^ TREATISE ON VAP.NIStlES. The desiccation is accelerated by nmiiitaining a fire in the apartment which has been varnished, if the sea- son be unflivourable. "When the second stratum is dry, rub it with pumice stone to equalize and smooth the surface, and apply three strata of colour. If an azurey gray white be re- quired, mix with great care on a porphyry slab one ounce of ceruse, one gros of charcoal black, and as much prussiate of iron (Prussian blue). Take a por- tion of this mixtur»e, and grind it slightly on the por- phyry stone with the ceiTise which is to compose the colour, adding the latter in portions, that the ingredi- ents may be better mixed. When this first division is effected, sift the v>diole through a silk sieve to complete the mixture. Then add four ounces of this preparation to a pound of varnish , and mix them with a brush. The varnish proper for this purpose is No. 1 . of the first genus. It will be proper not to mix up more matter at a time, because the varnish evaporates. Extend it in as uni- form a manui^r as possible, and when the stratum^ is dry, rub it v/ith a strong new piece of , linen cloth to polish it. This friction, which at first requires consi- derable care, completes the desiccation of the varnisli, and glazes it. For the second stratum take only one half of the powder, and mix it up in the same quantity of varnish as for the first ; and for the third olily half an ounce of powder. If you are desirous of giving lustre to the v/ork you must add a fourth stratum, not;^ more charged with colour, than the third. Then ru^b l;he surface with a cloth, to give it that splendour which ROYAL WHITE. î:^''" ' 5î3- always results from a perfect uniformity in the extension of the varnish. This is the method which I have always employed in painting in distemper, and I recommend it for colours of every kind applied to wainscoting of white wood, which is too much liable to swell under size of every kind, and which renders the first preparadon scaly. THIRD KIND OF DISTEMPEPv. Blanc de roi. Royal 2chite. This kind of distemper takes its name from the use made of it in decorating the interior of palaces. Royal white is very much employed, and is easily executed, when not intended to be covered with varnish : when fresh it is exceedingly beautiful. It is attended with the fault of becoming soon spoiled in apartments con- stantly inhabited, and particularly in bed-rooms, because, not being defended by varnish, the exhalations and other vapours which emanate from living bodies react on the white oxide of lead, and make it first turn yellow and then black. It is employed chiefly for saloons, where the mouldings and carving have been orna- mented* with gold, the paleness of v/hich is richly set off by the splendour of the colour. It is not customary * TJie author here makes use of the word rechampir, which, in a note, he says is a term of art tliat signifies to contrast one colour with another. He adds, that it must not be confounded witli the term rehausser d'or, which expresses painting of a gold colour on canvas, either in oil or distemper, and which represents piece» «f sculptiyre^ bas reliefs. Sec. 2 L 514 TREATISE ON VARNISHES. to varnish white grounds when accompanied with gild- ing and beautiful ornaments. In painting royal white, it will be proper to form, the ground with a stratum of Spanish white, or white of Morat, mixed up with strong parchment size, and applied in a state of ebullition ; paying attention, how- ever, to the nature of the wood, as already remarked. It requires the same operations as chipolin ; but private individuals generally dispense v/ith this nicety of execu- tion, which would require long time, and occasion very great expense. On this account I shall refer to the processes already detailed, in regard to the execution of azurey grayish white chipolin, which furnished the second example of the second kind of distemper. (Seep. 512). To render it very beautiful, white oxide of lead ought to be preferred to ceruse ; and the insipidity of the white should be heightened with a small quantity of prussiate, of iron or of indigo, in the same dosés nearly as for pearl gray chipolin. Polishing with a cloth produces a very good effect ; but the beautiful reflec- tion of the light depends as much on the m.anner in which the last strata are applied as on the polishing which completes the smoothing of the surface. In our happy country (Swisserland), where the luxury of apartments is confined within certain bounds which individuals never pass, where the citizen consults neat- ness and cleanliness rather than pomp and splendour, people are contented with the simple composition of royal white, heightening its dullness with a little prussiate of iron and black. This kind of painting is reserved, in ROYAL WHITS-. 515 particular, for the upper apartments of country houses. Its solidity renders it superior to that with white of Troyes. But all white oxides of lead are attended witJi the inconvenience of experiencing veiy sensible alter- ations in their colour at the end of a certain number of years, which renders it necessary to repeat the applica*- tion of white in bed-chambers, or to cover them with varnish. The splendour given by this addition, and the easy means it affords of guarding against the perni- cious effects of dust, are real advantages which coun- terbalance the expense. Besides, though this preparation seems attended with no insurmountable diiiiculty, even to the amateur, it requires in the artist who ujidertalces it good taste, care, and practice. Royal v/hite, indeed, is not always pre- pared with that care and attention which render it va- luable. A skilful eye is often shocked to see the out- lines of well executed wainscoting disappear under the unequal and too thick daubing of the strata, in which Vv^hite of Troyes even is often substituted for ceruse. As this deception is frequently practised, people ought to be on their guard against it. The employer, who has a double interest to defend, may put the honesty of the artist to the test by a very simple experiment. Place on charcoal a small quantity of the white matter wjiich represents ceruse ; if it be chalk, it will become brown when you blow the charcoal ; but if it be ceruse, it be- comes yellow, changes to a red colour, and is soon re- duced to lead. This revivification of the lead is speedier when the fire is urged by a blow-pipe. 2l 2 516 TREATISE ON VARNISHES. Such are the resources which society derives from the combination of colours and compositions, the variety of which produced by diversity of tastes develops under the hand of the artist very powerful means, which have the threefold advantage, of adding new branches to national industry, gratifying the wants of indivi- duals, and multiplymg, at their pleasure, the enjoy, ments of life. C 517 ] CHAPTER YI. ùfthc inslruments necessary in the art of varnishing : olserr rations on the use of some of them. It is generally believed, and without much examina- tion, that the art of the painter requires more practice or experience than funds. A palette destined for the distribution of the colours, an easel to maintain the pictures at different heights, a rod to support the hand which directs the pencil, a few casts to serve as a guide in the drapery and different attitudes, bmshes, and a brush-holder, are, it 13 said, the whole apparatus of the painter. A good education, an extensire acquaintance with antient and modern history, as well as mythology, great knowledge of the world, a certain ea^e of circum- stances capable of maintaining independence during the long period of study, and of fcicilitating travel, that he may familiarize himself with the beautiful models of antiquity, to correct his taste, and to fix it on the true beautiful and sublime kind of composition, and to enable him to acquire correct ideas respecting every species of painting and in regard to human nature, and in particular genius, are the requisites nccessaiy to consti- tute a great painter. Genius unites the great painter with the great poet, and conducts them to the same end by different routes. The one captivates our senses by warmth of colouring, judicious arrangement, and cor- 2 L 3 518 TREATISE ON VARNISHES. rcctness of design; the other seizes on the mind, and conducts it by the magic, the delicacy and elevation of his thoughts, and by the harmony of his verses. Venus displays as xnany graces luider the pencil of Apelles as. under that of Homer. The scarcity of great painters proves that great ta- lents arc necessary to arrive at celebrity; a point to which all artists of every kind ought to direct their aim. The house-painter and varnisher participates with the former only in the term which serves to denote his profession. The functions of the latter are different. He pursues an occupation merely mechanical, which, requires only a certain, degree of dexterity, taste, and experience. The former composes a great deal and consumes very little; the latter consumes much and does not compose at all, unless he adds designing to his art, which consists merely in a simple application of colours. In cities of a certain extent the painter and varnisher ÎS a dealer as well as an artist. For the most part he is pro\'ided with varnishes and colours of different .kinds, suiîlcient for all the uùdertakings that may be offered to him, and to satisfy the demands of amateurs. The state of the p2iinter and varnisher, considered in this point of view, requires a certain stock which does not '«idmit of his being confounded with those workmen who confine their talents to a mere application of co- lours, and who purchase them as they are used. The painter who composes his own varnishes, wha INSTRUMENTS USED IN VARNISHINC. 519 manufactures his own colours, and who appHes them, requires for his business a situation in which two essen- tial conditions, extent and dryness, must be united. In consequence of the first condition, the premises must be accompanied with a court or yard for the com- position of the varnishes, in order that he may be pro- tected, as well as his neighbours, from the damage which may be occasioned by negligence or other causes. The second condition relates to the care necessary <-o be employed in preserving the colouring matters, which are easily altered by moisture. Whatever may be the dryness of the matters at the time of their preparation, there are some, and particu- larly substances of an earthy nature, and metallic oxides, which imbibe the moisture of the air, and even with great avidity. This moisture is not hurtful to metallic colours, when destined for distemper; but when in- tended for painting in oil or in varnish, the case is different. It injures the splendour of the colour ; and this effect is more sensible with varnish than with oil. ^ Moisture prevents perfect contact betweeri the co- louring part and the excipient. With the concurrence of the air disseminated among the moleculas of the co- louring part, it produces that immense quantity of air bubbles which covers the surface of a colour when mixed up with oil. If the colour is mixed with varnish, this humidity precipitates a part of the resin w^hich is the basis of it : the colour then granulates, runs into globules under the pencil, and breaks the contact in such a manner that it becomes as it were mealy. It 2l 4 520 TREATISE ON VARNISHES'. cuts or changes the reflections of the light, and seems to tarnish its splendour. But, iis it is not always possible to obtain a situation according to one's wishes, great care and attention must be employed to preserve these compositions from hu- midity. They must, therefore, be kept in boxes of hard wood, such as oak or walnut tree; for white wood is a real hlter to moisture. The same end may be ac- complished by shutting them up in glazed earthen ves- sels with a large aperture. These vessels may be easily shut by cork stoppers covered with parchment. Liquid substances requh-e to be kept in glass or stone ware. Varnishes are kept in large strong glass bottles with a wide mouth, for the convenience of taking theni out ; but as light has a powerful influence on thesff compositions, and renders them thick, I would recom- mend wrapping up the bottles in sheep's skin or moist parchment, folding it. round the neck, and tying it with several turns of packthread. This addition is attended with the double advantage,, of guarding against thé in- fluence of light, and of preventing those accidents which result Ironi blows. Drying oils are less delicate than varnishes made with alcohol or essence. They may be preserved exceed- ingly well in stone-vv'are jars, in large bottles, or in leaden vessels with a wide mouth. Leaden vessels are ;iot liable to those accidents which are most to be appre- hended ; and if this advantage be not sufficient to make them be preferred, tliey possess another well known and consistent with theory, which is, that they add to ÛiQ drying qualit)^ of the varnish. THE LABOP.ATORY. 521 A table, weights, and scales, and a few boards to form shelves, are all the utensils necessary for the work- shop of a painter and varnisher. Of the laboratory ; and instruments necessary for the labour. The expense of fitting up a laboratory to furnish articles for common consumption will be very small. However, if to the making of varnish the preparation of different coloured lakes be added, it will be some- what greater. The instruments indispensably necessary are : 1 St. An alembic, constructed according to the prin- ciples explained in the first part of this work, with a refrigerator and portable furnace. 2d. A few bottles for receivers, that is to say, of a pretty large capacity, with different funnels of glass and of tin plate. 3d. Two or three copper basons of different sizes, according to the extent given to the establishment. 4th. Vessels of earthen ware to receive the varnish, which is strained through a cloth, and to contain the first deposit. 5th. Pieces of board of the same diameter as the earthen vessels, to serve them as covers. They are more convenient, and not liable to be broken like the earthen-ware ones commonly employed. 6th. Large glass jars furnished with funnels, and the latter with covers, for filtering the varnishes of the first, second, and thii'd genera. (See the figure Plate V.} 522 TREATISE ON VARNISHES. 7th. A cast iron pot, polished in the inside and fur* nished with a cover, for making varnish of the fifth genus. 8th. Different spatulas of wood, rounded afthe end, 9th. A shovel and a pair of tongs. 10th. Two or three furnaces, of different diameters, And in particular a small one with a sand bath. 1 1th. A small iron hooped tub with handles to con- tain charcoal. 1 2th. An iron capsule, or small vessel with a short handle to take out the charcoal. 13th. Some glass matrasses of different sizes, for the immediate preparation of alcoholic varnish ; which is effected by immersing the matrass into a bason, the w^ater of which is raised to different degrees of heat up to that of ebullition. 14th. A fixed table, some small tables, and a few jboxes. 1 5th. A flask filled mth spirit of wine to prevent the consequences of burns. If alcohol be applied the moment the accident hap- pens, it prevents the rising of blisters, which retard the cure. If the burn be considerable, the apphcation of fresh oil of eggs, and that in particular of a beautiful ,y.ellow colour, is the best topic to allay the. pain and to promote a cure. Simple cerat, composed of one part of yellow wax and two parts of good olive oil, or of three parts in winter, produces an effect which may be compared to that of oil of eggs, and is less ex- pensive. The i-aboratory. 52Ss • 1 6th. An iron mortar of from twelve to fifteen inches, in diameter, with an iron pestle. A slip of brass for* taldng the matters from the bottom of the mortar, and an iron spatula for detaching the matters which often adhere to it in consequence of the contusion. 17th. Two or three pestles of hard wood, with pretty large heads. 1 8 th. Different sieves of hair and silk. The latterv oueht to be close. o 1 9th. Some small iron bullets for the pulverization^- of bodies which are apt to form tliemselves into a paste Certain substances, such as indigo and the argillaceous oxides of iron, are easily pulverized with bullets. 20th. Troughs of plaster for drying lakes. 21st. A frame two feet in length, and from eigh'^ teen to tv/enty inches in breadth, for receiving the fiU tering cloth, when you are desirous of separating the water from the composition of lakes. The cloth charged "viith the sediment is removed to the plaster dryers, oE' to nev7 bricks, v/hich absorb the greater part of the water contained in the sediment. After each operation» the dryers or bricks must be exposed to the open air to diy them, and to render them proper for their first use. 22d. Wooden boxes, and a few tubs of different sizes, for washing and precipitation on a large scale. 23d. A porphyry slab, fixed on a table or stand, furnished with a drawer, containing mullers or grind* Ifig stones ; spatulas of iron, horn, or steel. The stones employed for the extreme division of th« colours vary in their nature,' Some employ the hardest s524 TREATISE ON VARNISHES. marble ; others brèche rock, and, in short, the hardest that can be found. The Itahans use porphyry, a very hard kind of stone, which was exceedingly common, in the time of the Romans. Some beautiful pieces of it are still found, from two to four feet square ; but when of this size they are very dear. 24th. One or more flexible knives, called palette knives ; spatulas of ivory or bone, and some leaves of horn. 25th. Some vessels of tin plate, for contaim'ng the ground colours. ^6th. Brushes and pencils of different kinds. There are several kinds of brushes. Some are com- posed of badger's hair. They are sometimes made of à flat form, and are then called varnishingi brushes. Others are made of goat's hair, or of the fine bristles of swine, or of the wild boar. They are affixed to sticks of greater or less length, according to the purpose for which they are intended. When these pencils are large they are called brushes, and are employed for the strong parts of the work. Pencils are made also of the hair of the martin, of the very pliable hair of children, and of swan's down. The last are fixed into the barrel of a quill, and are used for delicate kinds of painting. The use of brushes or pencils is not limited to one idnd of painting. In general, they are employed in ^different branches of it. Artists who have much em- ployment assign a brush to each colour : they take •care to wipe them when the work is done, and to pre- ser\'^e them by covering them with water. Amateurs a.re not under the same necessity of applying them to v3 THE LABORATORf. 52.5 particular colours, or of preserving them in this man- ner. One brush often serves thern for different colours, if they take care to wash out the first colour before the brush be dipped in another. This may be easily done, if each brush be washed in the liquor suited to that which has been applied in painting. Water easily se- parates every colour in distemper, and essence of tur- pentine all those which have been mixed up with es- sence and with oil. In the first case the pencil is wiped with a piece of hnen cloth ; in other cases a sponge will answer the purpose, if it be wTapped round the brush and pressed strongly with one hand while the brush is drawn through it with the other. In regard to those destined for varnish, washing in alcohol will restore them to their former state, if the varnish has been made with alcohol. Besides, if the varnish has been suffered to dry between the hairs, a few strokes of a hammer or mallet will pulverize and separate the resin which unites them into a solid mass, and by these means will restore to them the necessary pliability. 27th. A vessel of tin plate with a flat bottom and wide mouth, divided into two parts by a partition. Oil or essence is put into one of the cavities : when you wish to clean your pencil dip it in the oil, and press it between your finger and the edge of the partition, in such a manner that the oil stained by the colour shall drop into the empty cavity.^ Painters, from a principle of cleanliness, employ a small stick, which in this ope- ration answers the same purpose as the fingers. S26 TREATISE ON VAkNISHES. 28th. Two palettes, one of walnut or appîe tree, which has been well ijibbed over with drying oil before it is employed for holding the colours. The oil is rubbed in until it refuse to take up any more. This kind of palette serv'es also for varnishing, if the painter follow both the professions ; another palette of tin plate re- served for painting in distemper, in order that it may be placed on the fire when the size becomes fixed. Such is the furniture of the workshop of the painter smd varnisher, who follows all the branches of his art* The extent which a man of industry never fails to give to his undertakings, when they are crowned with suc- cess, may contribute to vary the form and multiply the ïiumber of the instiHiments which are here considered as necessaiy. Tiiese circumstances will always depend on the occasion he may have to facilitate the execution of processes on a large scale ; but the account here given of the nature sud number of the utensils consi* dered as necessary for a painter, can in no case be thought superfluous. Let a real artist be placed in a workshop thus furnished, and he will iijid himself at 'itoJossincoiiKiucting his business. [ 521 3 REPORT Made to the committee of chemistry of the society at Geneva, for the encouragement of the arts, on this new treatise on the art of preparing varnish^ , and of composing the colovrs mixed up with them. By M. Senebier. The art of making and employing varnishes Is of a very modcr-n date in Europe. If we except China and Japan, where there is reason to believe that this art was practised in v«ry early times, we are acquainted with no nation that used it; and if the antients had any idea of it, it must have been lost together with the works which might have revived it. The antient authors make no mention of it, nor have any images been borrowed from it by their poets. "We are ignorant of the etymology of the word var- nish, Vv'hich soine derive from the Greek word hernice^ supposed to signify amber, and others from vermis ros, the vernal dew, because it seems to give a shining ap- pearance to the leaves. The discovery of varnish might be carried back to the fourteenth century, which was tlie period of ther discovery of paiiiting in oil : but it has no resemblance to varnish ; and if the Chinese and Japanese preceded us in this art, it was rather owing to their having the juice of the varnl%h tree^ so well suited to this opera- tion, than to any researches made on purpose. 4 528 TREATISE ON VARNISHES. The lustre of the Chinese and Japanese works at- tracted the attention of the Europeans, and the de- scriptions given of them by the Jesuit missionaries in- duced artists to m.ake attempts to imitate them. The advantages which this art seemed to promise excited their ardour. A taste for neatness, the necessity of preserving from moisture various articles of value, the splendour, lightness, and low price of different kinds of toys, and the desire of having elegant apartments and carriages, contributed towards the advancement of the art of the vamisher. At length the celebrated Martin, about the middle of the last century, establish- ed the importance of varnish, by the perfection to which he brought it in consequence of his employing amber. But as it was necessary that the improvement of chemistry should have an influence on the progress of the art of varnishing, it is founded on knowledge which that science furnishes ; as the substances employed in varnishes have been better studied, they can be com- bined and applied with greater facility. C. Tingry, therefore, was sensible of the advantage to be obtained by subjecting the art of the varnisher to the test of ex- perience; and the manuscript he has presented to you, and respecting which you have charged me to make a report, is the result of this labour. This art, on the first view, might appear trivial; but it adds to our enjoyments, lessens the ravage occasion- ed by time in various objects of value, is interesting to our commerce and manufactures, and may suggest 529 some theoretic ideas which will not be useless to science. In describing an art it is necessary that aitists should be instructed in regard to every thing that belongs to it ; and that they should be made acquainted with the matters they employ, the method of using them, the instruments which may assist them, the dangers to which they are exposed, the means of guarding against them, and the care they ought to take to preserve in a sound state the substances necessary for their opera- tions. A series of processes minutely detailed might, no doubt, answer their purpose ; but in this case the artist would be a mere automaton, exercising his art in the same manner as the bees make their combs. This would not be enough at the present period, when genius, instead of being satisfied with what it possesses, still aims at improvement. It was, therefore, necessary that the artist should learn to think ; that he should find matter for reflection in a rational description of his art, and in an account of the relation which exists be- tween the processes prescribed and the principles exhi- bited to him. Such are the views of C. Tingry in the present work, divided into two parts : the first of which treats on varnishes so called, and the second of the colours used for painting intended to be covered by these varnishes. The preceding reflections are applicable in particu- lar to this art, which abounds with pretended secrets adopted in workshops. These secrets, if good, retard the progress of the arts, by concealing the means of im- proving them ; and, if bad, they injure the artists wixo 2 M 530 TREATISE ON VARNISHES. employ them. I am almost inclined to wish that these secrets may be always concealed from the whole world. This work first contains an useful account of fifty- seven solid and fluid substances which are generally employed in the composition of varnishes-, and of sixty-nine colouring substances often used along with them. The artist will here find information respecting their origin, their properties, and their uses, as well as respecting the adulteration of them, and the means of detecting it. The author shows also the falsity of some prejudices adopted by artists ; gives neiv processes for the rectification of some essential oils, and for freeing fat oils from their greasy principles. He traces out the different modifications effected in turpentine by various methods ; ajid as the arts are more interesting accord- ing to their general utility, it is satisfactory to observe here the advantage which might be derived from the products of the last mentioned substance in regard to -the service of the navy. The solid matters employed in tbe composition of varnishes ought to be more or less transparent ; as it is necessary that they should form a kind of glazing on the bodies which they cover. They are ail found in the class of resinous and gummo-resinous bodies. The Uquids, for the same reason, ought to be colour- • less, that they may not lessen the transparency of the bodies which they dissolve ; they must be volatile, that ithey may evaporate almost entirely, and free from every thing that might attract the moisture of the air, in Drder that they may more easily preserve the bodie? to senebier's report. which they are appHed : — of this kind are alcohol, ethe- reous oils, and some fat oils, which have been render- ed drying. It results, then, from the qualities essential to the substances proper for making varnishes, that a var- nish is a transparent, dry, brilliant, and permanent sur- face, deposited by the fluid in which the resinous sub- stances have been dissolved on the bodies it is destined to cover, and which speedily evaporates. This defini- tion may serve to distinguish real varnishes from those which water seems to form on the bodies on which it falls, because they disappear with it in the same manner as the varnishes composed of water charged with gum or gelatin, and because they have Httle brilliancy and attract moisture. As the varnishes made with spirituous and oily fluids, however, have no resemblance, C. Tingry has formed them into diflferent genera, and these genera indicate by their nature the use to which they ought to be applied. By means of this division he has reduced a mass of recipes and secrets to a small number of general cases, which simplifies the art, and enables the artist to reflect on his operations, and to accommmodate them to the object he has in view. The first genus is formed by the alcoholic varnishes: these are the most drying, and constitute five species, The;se varnishes have more splendour than solidity ; they are applied to pasteboard and to wood. The second genus contains alcoholic varnishes less dicing than the preceding. They are indebted for this ^property and greater solidity to the nature of the resins 2m 2 5S2 TREATISE ON VARNISHES. employed : they are, however, applied to the sam* purposes as the former. C. Tingry observes, in his remarks on these two genera, that spirit of wine never becomes charged with a greater quantity of resin than one-third of its weight. This observation is important ; because all formulae prescribe a much greater quan- tity, the overplus of which is mere loss. The third genus comprehends those varnishes which change the colour of the bodies to which they are ap- plied, and those also called mordants. They are more pliable, mellower, and more solid than the former, yet equally durable. In these varnishes essence is substi- tuted for spirit of wine. They are employed for giind- ing colours and forming grounds. They are applied to wood and metals, to which they give great lustre. These varnishes are used for giving to buttons the most brilli- ant colours, for making gilt leather, and for colouring articles made oï papier machè. The varnishes applied to fine paintings are also placed in this genus. Expé- rience has proved, at Geneva, the excellence ^f that made by C. Tingry. When he speaks of it, he describes, with great minuteness, a method of reviving pictures, Jby cleaning them before they are varnished. The fourth genus is composed of varnishes made with copal of an ambery colour, combined with ether or with essence of turpentine reduced to a certain state. This genus and the following are distinguished from all the rest by their solidity. A very drying varnish, without colour, free from any bad smell, and which, when applied to metals, forms a glazing as hard and as transparent as enamel is 4 senebier's report. 533 the kind, no doubt, which best answers the intended purpose ; and this C. Tingry has discovered, by uniting copal to ether of a certain degree of concentration. It has a great resemblance to that made with essence ; but though the preparation of it is easy and sure, and though it supereedes the necessity of varnishes of this Jdnd made with essence, the author shows how to make the latter with or without an intermediate substance. As the latter have furnished some curious obseiTations, I think it my duty to say a few words respecting them. C. Tingry, in the year 1788, presented to our So- ciety observations on the solution of copal in essence of turpentine. He there explained the cause why eveiy kind of essence is not proper for this operation : he also shov/ed, that the more essence differs from the the state of ethereous oil the more energy it has to dissolve copal ; that its dissolving property, in regard to copal, is in the ratio of its density ; that essence of tur- pentine, newly distilled, exercises no action on copal, but that it assumes tiiis property after it has been exposed some time to the light ; and that essence of turpentine dissolves copal at a heat below that of boiling water. Pie observed that essence is not proper for this solu- tion, when it deposits an acidulous water ; and that it gives spontaneously a concrete volatile acid salt, nearly similar to that formed in certain essential oils which have been long kept, and which, in my opinion, ap- proaches near to camphor. C. Tingry, after long researches on copal, furnishes nev/ resources to artists to enable them to make this var- nish and that of amber in a more certain manner^ to 2m 3 5.'34 TREATISE ON VARNISHES» give them, their ^full splendour, and to avoid certain processes by which they might be deceived. This copal varnish, in consequence of its hardness, may be substituted for transparent enamel : it has withstood on a box, for a great number of years, the continual friction of the pocket, though the same fric- tion has destroyed the metallic ring which surrounded it. The author, therefore, has opened a new branch of industry for the manufacturing of foil and of vari- ous kinds of toys much used, in which transparent en- amels, far more expensive and more hazardous in the execution, are employed. In a word, this varnish will supply enamellers with the easy and sure means of re- pairing those accidents which happen not only to trans- sparent, but also to opake, enamel, as experience has shown in our manufactories. The last kind of varnish comprehends fat varnishes. They are exceedingly solid, and dry veiT slowly. They are made with essential oils, or some fat oils, or with both these kinds of oil united and combined with amber or copal. These varnishes are distinguished by their transparency, their lustre, and their solidity. They may be applied, with ad^■antage, to carriages, and utensils "exposed to daily friction, such as stools, waiters, &c. In treating this subject, C. Tingry shows how to distinguish diying oils from others, and furnishes new means for obtaining them with facility, by pointing out a process for oxygenating them, when necessary. The varnishes made at present are much superior to .ihose of China, which are confmed to three colours, red, yellow, and black \ which require long tedious 1 SENEBIER S REPORT. 535 processes, prejudicial to the health of artists, and which are never proper for delicate articles. This an- lient nation may boast of expert and patient hands; but the Europeans have been guided by genius. C. Tingry gives general precepts for making var- nishes on a large scale. He collects every thing that ought to be expected from a learned chemist and expe- rienced artist : he details the most successful manipula- lations, describes the most convenient form of the ves- sels, and prescribes the most appropriate methods for the filtration and clarification of the liquors. He makes known also a new alembic, which has the double ad- vantage of facilitating the mixture of the matters during the operation, and of preventing the dangers, so com- mon and so alarming, which arise from the fire in pro- cesses of this kind. The second part of this v/ork treats on the application of colours. The same order is here followed as in the former; and a description is first given of the colouring matters employed in varnishes. To proceed with certainty in the composition of co- lours, it was necessary to have some principle to serve as a guide. This principle the author found in the fundamental colours, which exhibit the different refrin- gibility of the rays of light by the prism : and as- each colouring substance does not always give individually the required colour or shade, he establishes this colour and shade according to the effects produced by a mix- ture of the different rays refracted. The author then describes the common processes for the composition of colours, and fixes the cases in which SS6 TREATISE ON VARNISHES. they can and ought to be employed, by showing the method of combining them with varnish. He here stops to consider the different kinds of lakes employed in painting ; that is to say, the colouring fec«las combined with alumine or calcareous earth. These productions, in consequence of their import- ance, deserved great attention : but it was still neces- sary to find out some more certain means than any before employed of ascertaining the fixity of the colour of lakes; and these the author has here given. But as a knowledge of the manipulations employed in the preparation of colours is not sufficient, the author describes also the workshop of the vamisher as well as his operations. He insists, in particular, on the ex- treme division of the colouring matters used for colour- ing varnishes, and determines the cases in which the diiferent varnishes ought to be employed : he prefers the application of varnish charged with its colour to transparent varnish extended over a coloured ground ; because on applying a colour in distemper to wood, it is injured by being moistened with the size, which forces the coloured coating to detach itself in scales ;, but he supposes that wood intended to be varnished is very dry. The author, however, does not confine himself to details of tliis kind: he shows in what m.an- ner the expense may be lessened, without hurting the beauty of the work ; and thus renders equal service to •the artist and to his employer. The author gives also a description of painting in oil, which he treats with the same care ; determining the cases in which it ought to be preferred, and pointing senebier's report. 537 out, according to circumstances, the oils and colours that ought to be employed, with the method of pre* paring and applying them. As waxed cloth and waxed silk are, strictly speak- ing, varnished cloth and varnished silk, since no wax is used in the preparation of them, the author makes them the object of his researches, and with the more reason as this part of the arts had been entirely neg- lected by men of science, though it may become a capital object of commerce. He describes the method of manufacturing these cloths, which vary according to the use for which they are destined. He next de- scribes the method of maldng the celebrated English court plaster, which is applied to cuts, and of detect- ing the spurious kind. This part is followed by numerous details in regard to painting in distemper. As it is founded on the pre- paration of glue or size, the author makes known the different kinds ; establishes the cases in which this kind of painting may be employed, and describes the different grounds necessary to be made, according to the colours intended to be applied to them : he describes with mi- nuteness the different processes for each method. The work concludes with precepts to colourmen and artists in regard to the preservation of the substances employed in varnishes. The author appears to me to have treated in this work the art of the varnisher and that of the house- painter, &c., in a useful and complete manner. I am therefore of opinion that it merits the approbation of 538 TREATISE ON VARNISHES. the committee of chemistry. I even request that the committee will prevail on the Society for the encou- ragement of the arts and of commere to thank C. Tin- gry for the labour he has undertaken, and to beg that he will suffer the public to enjoy the fruit of his re- searches, as it must improve the practice of an art, one part of which is universally employed, while the rest may produce new branches of industry, or facili-» tate and render more productive those already known. ENGLISH AND FRENCH WEIGHTS. The translator thinks it necessary to inform the reader, that the quantities of the ingredients in the dif- ferent formulae given in this work for the composition of varnishes, &:c<, are expressed according to the old French denominations. As they could not be converted into correspondent English denominations without frac- tional parts, which would have been still more ti'ou- blesome, and might have occasioned mistakes, he thought it better to leave them in their original state, and to subjoin a table of the French pound, with rules for reducing the French to English troy weight ; but if weights be made according to the old French stand- ard this reduction will not be necessary. In many cases, also, where the ingredients consist of ounces, no difficulty will occur. The reader, therefore, is requested to observe that the old Paris pound, poid de marc, of Charlemagne contains 9216 Paris grains, which are equal to 7561 Enghsh troy grains. It is divided as follows : 1 pound - - - - 16 ounces. 1 ounce - - - - 8 gros or drams. I gros . - - - 72 grains. Sometimes the gros is divided into 3 deniers, and the denier into 24 grains. The English troy pound, of 1 2 ounces, contains 5760 English troy grains, and is equal to 702 1 Paris grains* 540 ENGLISH AND FRENCH %-EIGHTS. The English avoirdupois pound, of 16 ounces, con- tains 7000 English troy grains, and is equal to 8538 Paris grains. To reduce Paris grjuns to English troy grains, divide by 1-2189. To reduce Paris ounces to English troy, divide by 1 -01 57 34, or the conversion may be made by means of the following table : The Paris pound = "7361' The ounce = 472-5625 The gros = 59-070S The grain = -8204 If Paris pounds, therefore, are given to be reduced to English troy grains, multiply by 7561 ; if French ounces are given, multiply by 472-5625 : the product will be English grains, and so of the other denomi- nations. ERRATA. Page 83, line 14, for lakcd oils read boiled oils. 119, line 8 from the bottom, for Fint species read Third sprries. 156, line 13, for or read o)i. 207, line 8 from the bottom, for Sixth species read Seveûth specie^' 4^ ■02% en THE END. ^. Taylor f Pri-itcr, Bldd- Hone Court f I'Ucl'stteit, %. mi Ti^" f^* SI»--..*. w ii^'>^%. v^