AN INTRODUCTORY ESSAY 
 
 ON THE 
 
 ART OF PAINTING ON GLASS, 
 
 BY EMANUEL OTTO FROMBEKG. 
 
 TRANSLATED FROM THE GERMAN, 
 
 BY HENRY JAMES CLARKE. 
 
 B 
 
Digitized by the Internet Archive 
 in 2016 
 
 https://archive.org/details/introductoryessaOOfrom 
 
AN INTRODUCTORA ESSAY. 
 
 Painted windows are allowed to be the richest and most magnificent application of 
 art to the interior decoration of monumental buildings. The brilliancy and live- 
 liness of the colours, of which glass is susceptible on account of its transparency, 
 will always secure to this kind of painting a distinguished rank among the arts. 
 The dazzling combination of colours, which fills the observer with astonishment, on 
 account of their brilliancy, as well as on account of their variety, gives a peculiar 
 character to painted windows, which prevents them from falling into oblivion, even 
 should they be neglected for a time. If we go back to the elementary condition of 
 the art, the symmetrical arrangement of pieces of glass of various forms and colours, 
 combined with more or less skill, they are by no means entitled to engage our atten- 
 tion in a higher degree than the lustre of gold, and the most lively colours of the 
 richest decoration. Yet with what magical charm must they not attract our observa- 
 tion and excite our admiration, when painting invests form with these beautiful 
 colours, and breathes life and soul into them ? 
 
 Painting on glass seems to have made a fresh start within the last few years. 
 The favour with which the productions of this art have been universally received, 
 promises it soon a new and brilliant career. But how has it happened that this 
 species of painting, whose magical effects have been so justly appreciated, has been 
 neglected for so long a time, after having for several centuries exercised the genius 
 of artists, and been cultivated by them to the exclusion of almost every other ? 
 
 Painting on glass has, in fact, experienced a remarkable fate. In the periods of 
 barbarism, when war and devastation had smothered the taste for the arts, it came 
 into existence, and was never more ffourishing than in those centuries of ignorance. 
 At the period of the regeneration of science and the arts, when good taste, and the 
 
 n 2 
 
4 
 
 INTRODUCTORY ESSAY ON THE ART OF PAINTING ON GLASS. 
 
 love of what is beautiful and true to nature had begun to spread through Europe, 
 its splendour seemed on the wane, and in process of time it became almost entirely 
 extinct. 
 
 What, then, are the causes of so remarkable a decay ? In the twelfth century, 
 this art, which had been for a long time still in its infancy, seemed encouraged by 
 the piety of the monks, (among whom alone the wrecks of the sciences and of the 
 secret arts were yet to be found,) to make a vigorous attempt to release itself from 
 the state of oppression into which it had fallen. But while the spirit was active and 
 ready to soar, the means were wanting, and much time was spent in the choice of 
 the proper mode of carrying it into practice. Many kinds of painting would have 
 to be tried ; and, at a time when taste had not yet been refined by long practice, 
 and especially by the study of classical models, the preference would naturally be 
 given to that kind of painting which was most capable of seducing the eye by the 
 brilliancy of its colours. The combination of colours was the sole charm that paint- 
 ing could lay claim to ; the merit of a beautiful outline, on the contrary, one which 
 exhibited grace, purity, and correctness of form, was utterly neglected. 
 
 Hence the splendour of painted glass, and the almost universal admiration paid 
 to it by those who felt themselves compelled to do so by the guardian genius of 
 the art. 
 
 But in the succeeding centuries taste was cultivated. Art had less of the ma- 
 terial, and found other facilities and other means of producing effect. She strove 
 after effects of a much higher kind ; and as genius endures with impatience the 
 bridle of a difficult execution, the obstacles which the painting on glass presents to 
 the expansion of thought, would considerably diminish the favour that it had enjoyed 
 in consequence of the liveliness of its colours. Oil-painting was soon called into 
 existence by Jean de Bruges. This new form of the art, the imitation of nature, 
 gained the victory over the one which had preceded it, and painting on glass was 
 driven from its throne. 
 
 The consequent decline of the art was not, however, sudden and precipitate. 
 The revolution which in the sixteenth century took place in the arts, was also not 
 without its influence upon the progress of painting on glass. Its most beautiful 
 works were produced at that time. The most celebrated men did not disdain to 
 support it by their talent ; and never at any time was it more deserving of honour. 
 It had, however, attained the summit of its greatness, and was soon to become a 
 spectacle of the most complete decay. 
 
 Many causes undoubtedly conspired against its further prosperity. To these, 
 among others, belong the religious disturbances and the wars which followed the 
 
INTRODUCTORY ESSAY ON THE ART OF PAINTING ON GLASS. 
 
 .5 
 
 reign of Francis I., and the calamities that were brought on by subsequent discords. 
 But, above all, we must take into consideration the very strong prepossession in 
 favour of oil-painting, awakened by the brilliant successes of its productions ; and, 
 moreover, the favour with which the art of engraving on copper, as well as all those 
 arts which have drawing for their basis, were received. These arts shared among 
 themselves the consideration that had been formerly given exclusively to painting on 
 glass. Finally, we must bear in mind the singular patronage bestowed on oil-paint- 
 ing by those in power. 
 
 The various phases of the art of glass-painting clearly ascertain the mighty influ- 
 ences to which it must have yielded. The study of them oflPers to the inquirer 
 matter for the most serious consideration. In the twelfth and thirteenth centuries, 
 in the shadow of barbarism, if I may be allowed the expression, we see it making 
 considerable progress. In the fourteenth and fifteenth centuries it bears unlimited 
 sway over the arts. In the sixteenth century it becomes a rival to oil-painting, 
 and, after an obstinate struggle, sinks into oblivion. All the old painted windows 
 have something characteristic of the period to which they belong. The modifica- 
 tions which successively appeared in them, offer to the archaeologist points of the 
 deepest interest for observation and comparison, while they are at the same time the 
 seals of their respective eras. These distinctive marks exist not merely in the 
 painting, but also in the general conception of the entire work. We have only to 
 cast our eyes upon a window of the twelfth and thirteenth centuries, and we shall 
 discover, in a truly remarkable manner, the whole spirit of the Gothic monuments 
 of that period. This kind of architecture, so rich in its ever alternating details, vet 
 without any confusion, and regular in its monotony, successivelv presents that re- 
 markable feature which we recognise alike in the entire structure and in each of its 
 parts ; and the reason of this lies in the fact, that the observer, before he can com- 
 prehend the numerous details, gradually perceives that they form an essentially har- 
 monious whole. This peculiarity prevails in Gothic church-windows to an extra- 
 ordinary degree. Vv^hen viewed at a certain distance, they present a magnificent 
 decoration of the most lively colours, distributed in a manner worthy of the most 
 skilful workers in mosaic. It is a rich carpet, whose simple but graceful pattern is 
 illuminated in alternate gradations of colours admirably combined. Upon a closer 
 inspection, we obtain a complete view of the forms of the various ornaments, which 
 contribute to the general effect, the naivete of which makes us feel less regret at tlu' 
 imperfection of the execution. 
 
 Gothic painting borders on the mosaic, and we may go so far as to say that to 
 this it owes its origin. Like the mosaic, its art was primarily limited almost ex- 
 
6 
 
 INTRODUCTORY ESSAY ON THE ART OF PAINTING ON GLASS. 
 
 clusively to the symmetrical arrangement of pieces of glass of various colours. The 
 art of drawing played here only a subordinate part ; but, like the latter, it after- 
 wards borrowed its forms from nature. In proportion as the taste for correct draw- 
 ing w'as carried to perfection, the simple arrangement of glass lost its importance, 
 and was finally eclipsed by the art of painting. 
 
 In the sixteenth and seventeenth centuries, correct delineation completely gained 
 the ascendancy in painted windows, and we find in these neither the effects of sym- 
 metry nor of the mosaic. It underwent a change in every particular, to an historical 
 kind of painting, of a much higher and more elaborate style, but which was no 
 longer so rich and so brilliant : the sentiments of the soul gained at the expense of 
 the impressions of the senses. 
 
 In the intervening centuries a transition took place from the one extreme to the 
 other. At first we see the ground diversified with a thousand brilliant colours, on 
 which, however, larger figures, drawn with greater skill, and after a pattern more 
 or less understood, are occasionally to be met with, and occur as exceptions. In 
 process of time, these figures are surrounded with splendid borders or friezes, which 
 are finally obliged to give way to architectural backgrounds, and the imitation 
 of the antique. These are the various forms under which the art of painting on 
 glass was cultivated during a period of more than 600 years. In the eighteenth 
 century it seemed to be completely lost. 
 
 But is it destined to lie neglected, because the reign of oil-painting will endure? 
 Painting on glass cannot, for a moment, contend for the approbation of artists as the 
 rival of the latter. The difficulty which attends the practice of it, and the necessity 
 for the co-operation of chemistry in the productions of this kind of painting, leave 
 its resources ever insufficient to enable it to vie with oil-painting, to which, on that 
 account, it must unquestionably yield the pre-eminence. But if the artist w^ho de- 
 votes himself to glass-painting is content to avail himself only of the legitimate 
 resources of his art, if he does not strive after effect, nor endeavour to pursue the 
 path of oil-painting, wo have not the slightest hesitation in asserting, that painting 
 on glass, considered as a monumental style of painting, constitutes an art, inimitable 
 in itself, capable of being executed with great spirit, and worthy of engaging the 
 most distinguished talents. 
 
 But then the painter on glass must refrain from attempting to imitate oil-paint- 
 ing. On the contrary, he must acquire the conviction, that, although these tw^o arts 
 have unquestionably a point of contact, they, nevertheless, possess sides extremely 
 dissimilar. To these belong, in the first place, the proper modes of practising them 
 respectively ; lastly, the different conditions under which their effects are produced. 
 
INTRODUCTORY ESSAY ON THE ART OF PAINTING ON GLASS. 
 
 7 
 
 Thus, for example, painting on glass, on account of the distance at which the picture 
 is placed from the spectator, requires to he treated in a perfectly distinct manner. 
 It excludes detail, which, on an opaque surface, is susceptible of gi’eat elfect, but 
 which, through the transparency of the glass, is lost, even should not a defect in the 
 burning have done injustice to the talent of the painter. But if, after all, the 
 artist be bent upon giving to his performance all the harmony of an oil-painting, he 
 must sacrifice the transparency, and the liveliness of the colours, which constitute 
 the most beautiful feature of this kind of painting. Besides, the presence of the 
 leading and the iron bars, which unite the various portions of a painted window, and 
 which it is in vain to attempt to conceal entirely in the shadows of the picture, must 
 ever prove the stumbling-block on which the claim of the artist to imitate oil-paint- 
 ing is sure to founder. 
 
 There is a fact, which observation itself has demonstrated to an inexperienced 
 artist, and which must lead us to deliberate upon the method of proceeding in 
 practising the art of painting on glass. It is this, viz., that in the colouring of 
 a very elaborate cartoon, the half-tints, which have been diversified in gradations 
 of colours delicately and harmoniously blended together, always run together into 
 one colour, producing the same effect in every part, as soon as they are viewed at a 
 distance. It is not our intention to account for this remarkable phenomenon, but 
 we content ourselves with merely calling the attention of the glass-painter to the 
 fact, in order that he may join with us in drawing the following conclusion from it. 
 
 A painted window, of very elaborate execution, which is designed to adorn a 
 building dedicated to the worship of God, and consequently must be viewed at a 
 certain distance, not only loses the fineness of the details, but is also obscured by 
 the blending of the half-tints, and therefore becomes heavy, dry, and hard. 
 
 The art of painting on glass, for the purposes of decoration, is founded solely and 
 entirely upon the observation of the above-mentioned fact. This species of painting, 
 in fact, owes its origin to the necessity which the artist is under of conforming his 
 work to the conditions imposed upon him by the distance at which the spectator 
 must view the painting. What would be said of an artist who thought of treating 
 decorative painting exactly as he would miniature painting? If we insist strongly 
 upon this truth, it is for the purpose of applying it to painting on glass, which is 
 indisputably a decorative kind of painting, and must be cultivated in this acceptation, 
 except, perhaps, in the case of small cabinet windows, similar to those which are 
 known under the name of Swiss-painted glass. If these rare exceptions be not taken 
 into account, the painted glass in church-windows is at such a distance from the 
 spectator, that it would be more prejudicial than useless to attempt perfection and 
 
8 
 
 INTRODUCTORY ESSAY ON THE ART OF PAINTING ON GLASS. 
 
 elaborateness of detail, as it is practised in the case of an oil-painting. A pure and 
 correct style of drawing, united to a simple and vigorous copying, are the qualities 
 which the painter on glass must, before all things, endeavour to attain. 
 
 Unfortunately the assumption of superiority which has impelled mankind in all 
 ages to outdo their predecessors, has also misled those who, in modern times, have 
 attempted to revive the art of painting on glass. It is seldom that we avail ourselves 
 of the experience of the former, and we attribute to their impotency that which is in 
 reality the result of mature consideration, which, however, we are utterly incapable 
 of appreciating. Thus, too, it has been taken for granted, that the last painters of 
 the sixteenth and seventeenth centuries were not in a condition to make further 
 advances in their art. Their performances were criticised, at the same time that 
 they were compared with the contemporaneous productions of oil-painting. The 
 recognition of this principle would, in our opinion, have been more modest, as well 
 as more reasonable ; viz., that the glass-painters of former times preserved their art 
 free from all imitation ; that a long experience taught them to be content with bor- 
 rowing spirited ideas from oil-painting, and not to aim at producing the same effects 
 by means differing so widely from one another, so that in the end they made paint- 
 ing on glass an isolated art, unlike any other in its effects as well as in its means, 
 and one which is subject to peculiar conditions. 
 
 But, on the other hand, it has been said, that the ancients did not understand 
 the art of painting on glass ; and, under this impression, an attempt was made to 
 execute what they had never been able to perform. This kind of emulation is un- 
 doubtedly noble and honourable ; but it is to be regretted that such praiseworthy 
 exertions have been misdirected ; for, instead of continuing the progress begun by 
 the ancients, when it was so easy to do so, artists consume their emulation in im- 
 potent attempts, until a personal experience induces them to resume the labours of 
 the ancients, at the point where the latter have left off. 
 
 We must, however, do justice to him who rescued from oblivion an art that had 
 been so long neglected. For this our thanks are due to the learned superintendent 
 of the royal porcelain manufactory at Sevres, Flerr Brongniart, who has contributed 
 much to its revival. 
 
 W e believe we have now satisfactorily defined what we understand by the art of 
 painting on glass. In our opinion there is still a future for this art, if its votaries do 
 but follow the paths marked out for them. With respect to the kind of composition 
 best adapted to it, we shall content ourselves with merely remarking, that the good 
 taste of the artist alone must preside over his conceptions. As, however, some have 
 given their opinion in favour of the Gothic style exclusively, others in favour of the 
 
INTRODUCTORY ESSAY ON THE ART OF PAINTING ON GLASS. 
 
 9 
 
 style at the period of the revival of the art, according to the several directions which 
 their studies have taken, we cannot forbear expressing our opinion upon this subject. 
 We have no thought of enlisting followers for either party ; but, without the smallest 
 intention of drawing a comparison in this controversy, we may be permitted merely to 
 hint, that the artist should not allow himself to be taken up with these discussions, 
 and that in the conditions of his art alone he has to seek for the spirit that must 
 direct the sueforestions of his imagination. lie should avail himself of all the re- 
 sources aflPorded him by the nature of the things on which he has to exercise his 
 talents. Ought he, for example, to forego the powerful effects which a skilful ar- 
 rangement of colours enables him to produce ? Should he disdain to derive advantage 
 from the lively colouring of the glass, because it is the most goodly dowry of the 
 Gothic style of the art? We think, not ; but we are far from advising him, on the 
 other hand, to sacrifice to such endeavours all the resources of painting which the 
 revival-style is capable of affording him, provided that he uses all these means with 
 moderation ; and, we repeat it, keeps within the conditions of his art. We submit 
 this opinion to the intelligent artist, who does not allow his ardent spirit to be carried 
 away by his ideas ; but we have no hope of convincing those who, in the wanderings 
 of their fancy, as well as in the right path, have become the slaves of their ima- 
 gination. 
 
 A very natural question presents itself to the mind, with regard to the erroneous 
 belief which universally prevails, that the secrets of the art which were known to the 
 ancients are lost. Are we capable, if not of surpassing, at least of resuming and 
 continuing, the labours of the ancients ? When we compare the glass of the old 
 church-windows, of any period whatever, with the glass of our manufactories, we can- 
 not for a moment doubt that our system of manufacturing it produces far more per- 
 fect results, certainly as far as regards its transparency, whiteness, and clearness, and 
 generally with respect to all those qualities which are peculiar to glass. Besides, it 
 is allowed that the methods of working have been considerably improved. And if, 
 on the other hand, we compare fragments of old painted glass with that which we 
 manufacture at the present day, it will appear in the most convincing manner, that 
 our painted glass is not in the slightest degree inferior in point of colour to that of 
 the ancients. There was a time when the manufacture of coloured glass was discon- 
 tinued, because in consequence of the decline of the art of painting on glass this 
 article was of no further use ; but none of the secrets of the colouring were lost. 
 Persons who were little aware of these circumstances, and mistook the effect for the 
 cause, maintained that the reason why the art yielded nothing more, was, that the 
 painters on glass no longer understood how to produce the ruby of the ancients, 
 
 c 
 
10 
 
 INTRODUCTORY ESSAY ON THE ART OF PAINTING ON GLASS. 
 
 But this assertion was very soon shown to be false ; for as soon as ever the determin- 
 ation to restore painted windows manifested itself, the glass-house of Choisy in 
 France, among others, proved hy the most successful results, that the art of manufac- 
 turing coloured glass was in no way lost, but was only asleep. In fact, we possess a 
 multitude of receipts of the ancients, according to which coloured glass was produced 
 in former times. Moreover, in pigments we are much richer than the ancients ; our 
 pigments, too, are much better, more adhesively enamelled, in consequence of the 
 improvements which have been introduced into the system of burning in the colours 
 in modern times. 
 
 From what has been premised, we may conclude that our artists are in no respect 
 in want of the material elements ; on the contrary, they are far better aided by re- 
 sources and means which await their disposal than the ancients were ; and if their 
 works attain no remarkable superiority, the reason of it must be sought for in the 
 fact, that the best means and modes of execution in the arts are unfruitful, when 
 they are not employed with sufficient taste and spirit. 
 
 Glass-painting has, in our time, risen into life again, surrounded by the fairest 
 hopes ; and what we know of the artists who are already practising it, leaves us not 
 the slightest reason to doubt that it will soon be cultivated with a success worthy of 
 the present age. We would gladly contribute in some degree to draw it forth from 
 the state of oblivion in which it has been for a long time buried. For this purpose 
 we shall now communicate a number of practical observations which lie in the sphere 
 of glass-painting. We believe that we cannot contribute more effectually to the dif- 
 fusion of the art, than by clearly laying down the methods employed in its practice. 
 We shall advert to those both of the ancients and of the moderns, and compare them 
 with one another, in order to show the improvements that have taken place in our 
 time. At the present day, when artists as well as amateurs are most zealously en- 
 gaged in glass-painting, we flatter ourselves that this information will not be unin- 
 teresting to many. Little has yet been written about it, and the majority of the 
 publications that have appeared on the subject, treat more of the history than of the 
 practice of the art. 
 
 The art of painting on glass by no means consists in the mere application of the 
 colouring materials to the surface of the glass, by methods similar to those employed 
 in oil-painting. The colours used are of a peculiar kind, and possess the power of 
 vitrifying at a high temperature, and of flxing themselves unchangeably upon the 
 glass. Consequently the glass, after the paint has been applied, must be exposed to 
 a certain heat in a furnace adapted to this purpose. Appropriate means must also 
 be employed in the application of vitriflable colours. 
 
INTEODUCTOEY ESSAY ON THE AET OF PAINTING ON GLASS. 
 
 11 
 
 A painting on glass, — as for example, a church- window, — always consists of a great 
 number of pieces of coloured glass, whose various hues illuminate an ornamental 
 pattern or an historical subject. These pieces of glass are either symmetrical or irre- 
 gular, so as to agree with the sentiment exhibited in the composition itself. After 
 they have been arranged in their proper places, they are encased in lead, and united 
 so as to form one complete piece. These pieces are united by an iron frame-work, 
 called the arming'^. 
 
 After the brief explanation we have just given of the conditions to which glass- 
 painting is subject, we have to determine its connexion with other arts. In the first 
 place, it is evident that the science of the chemist must be united to the talent of the 
 painter, and that the glazier himself must lend his assistance. We have therefore 
 divided this little work into several sections, in which the various branches of the art 
 will be successively treated of. We have circumstantially discussed the following 
 particulars ; — 
 
 1. The quality of the pigments, their composition, their preparation, and lastly, 
 all the chemical operations which are necessary previous to the painting ; 
 
 2. The means used in laying on the colours ; the various methods employed for 
 this purpose, and every thing which has reference to the proper art of glass- 
 painting ; 
 
 3. The manner in which the vitritiable colours are burnt in ; and fourthly, 
 
 4. That part of the glazier’s art that is concerned in the putting together painted 
 windows in churches. Finally, we have given an account of the various mixtures 
 with which the glass is coloured en masse. 
 
 Glass-painting, as it is practised at the present day, has scarcely any thing in 
 common with that of the ancients, as far as regards the colours. When this art, 
 which had been entirely neglected for a whole century, was rescued from oblivion, 
 the improvements in the manufacture of glass had so materially changed the quality 
 of this substance, that the ancient methods employed in the painting were no longer 
 applicable. Towards the middle of the eighteenth century, glass was still composed 
 almost exclusively of flint and potash or soda. This simple silicate was deficient in 
 fusibility, and preserved an extraordinary tenacity even at the highest temperature ; 
 it was difficult to purify, occasioned an enormous expense in fuel, and was not capable 
 of being worked well. In the year I 76 O, Bose d’ An tic tried a mixture of lime in 
 the form of carbonate of lime, which Kunckel had before proposed. A striking im- 
 provement in glass was thus obtained. When combined with silica, and with soda or 
 potash, it forms a bisilicate, which is much more fusible than the simple silicates. 
 
 3 Germ. Armirung. 
 
 c 2 
 
12 
 
 INTRODUCTORY ESSAY ON THE ART OF PAINTING ON GLASS. 
 
 The proportions of these substances were, however, for a long time badly determined, 
 and it was not till lately that the makers were enabled to impart that fusibility to 
 glass which renders it so easy to work, and so cheap to manufacture. 
 
 It is obvious that the pigments of the ancients, which were prepared for a hard 
 kind of glass, could not have fusibility enough for the glass which is now manufac- 
 tured. Other ingredients had to be sought for. But if the ancient methods of 
 painting were no longer in accordance with the quality of the glass, still less were we 
 acquainted with them. Moreover, the knowledge of enamel colours for metals, as 
 well as for various kinds of earthenware, afforded easily applicable principles, accord- 
 ing to which a series of properly fusible colours could be composed. The vast con- 
 quests of chemistry within the last fifty years, promised besides, to this manufacture, 
 a very certain success. Modern glass-painting is thus almost entirely of late origin ; 
 and, with the exception of the process of burning in, has experienced modifications 
 in every particular in a very remarkable manner. If we believe the testimony of the 
 authors as far back as the period at which Levieil wrote, the glass-painters at that 
 time burnt in their colours in iron boxes, in which the glass was arranged in layers 
 with calcined and pulverized lime strewed between the strata of glass. But towards 
 the year 1758, an English artist made known a new method of burning in, which he 
 employed himself, and which, with some trifiing modifications, has remained in use 
 since that time. We shall describe this method more particularly in its proper place. 
 The superiority of this new method of burning in the colour over the ancient method, 
 and especially over that of Levieil, is incontestable. According to the method of the 
 latter, the melted pigments were placed in contact with powdered lime : a portion of 
 this powder adhered to the colours, and injured the transparency. If this was not 
 always the case, the reason was, that the pigments, on account of their slight fusi- 
 bility, merely adhered to the surface of the glass, and then again its transparency was 
 impaired. The painted windows of the Levieil family furnish a proof of this, and in 
 particular that in the chapel at Versailles, the blues of which are so obscured, that 
 they appear black ; and among others Pierre Levieil himself, in his work, admits the 
 fact. 
 
 What we have said about the process of burning in, as far back as the time of 
 Levieil, is founded upon the testimony of the writers who have left us some very in- 
 teresting notices of the state of glass-painting at that period. To these, among others, 
 belong Kunckel, Haudicquer de Blancourt, Levieil, &c. We have not, however, 
 received their opinion upon this matter without due reflection. For how could it be 
 supposed, that in the sixteenth century, when both glass-painting and enamel-painting 
 were so generally honoured and cultivated, it should never have occurred to any 
 
INTRODUCTORY ESSAY ON THE ART OF PAINTING ON GLASS. 
 
 13 
 
 of the artists, who were frequently skilled in both arts, to subject the process of burn- 
 ing in to those conditions which are indispensable in enamelling, namely, a contrivance 
 for heating the plates of glass, isolated and entirely removed from contact with any 
 other body which can adhere to the colours when in a state of fusion, soil their sur- 
 face, and deprive them of their transparency ? This fact may easily be explained with 
 regard to the former centuries, in which the Gothic style only was cultivated in 
 glass-painting. Because, as this kind of painting is limited to a mere outline upon a 
 ground of glass, coloured en masse, little depended upon the smoothness and bril- 
 liancy of the colours which wei'e applied in the painting ; on the contrary, a complete 
 opacity was indispensable. But in the age of a Pinaigrier, or a Jean Cousin, when 
 the use of pigments for painting almost entirely superseded that of coloured glass, it 
 is hardly to be supposed that the glass-painters were unacquainted with a method of 
 burning in similar to that which is now employed. And this is the less credible, in- 
 asmuch as the works of this period prove that pigments could be prepared of great 
 clearness, free from all impurity, and just as good as the enamel-painters could pro- 
 duce. It may well be supposed that the traditions of the Levied family have not 
 informed us what the process w^as before their time. The progenitor of this family 
 lived somewhere about the end of the seventeenth century. Glass-painting, which was^ 
 gradually declining, was at that time only cultivated by a few artists. The Pinai- 
 griers, and those of their school, had carried all the secrets of their art with them 
 into the grave ; and this was the case at that time with all who practised an art which 
 w'as enveloped in mystery. Even the very writers who furnished the public with in- 
 formation upon the arts, always reserved that which was most useful for themselves. 
 Cassius did so, according to his own confession, and Levied made it a subject of 
 complaint against Kunckel and Taunai. Before Guillaume Levied but one artist, 
 Jacques de Paroi, had written about glass-painting, and from this common source 
 several authors who followed him, as well as the painters who in the most modern 
 times devoted themselves to glass-painting, seem to have drawn. To the former be- 
 long Felibien, Florent le Comte, and Haudicquer de Blancourt ; and to the latter 
 the Levieils and the brothers Recollet. This is proved by their receipts, which they 
 have transmitted to us, which are for the most part like one another, and are many of 
 them completely identical. 
 
 It may be easily supposed that the Levied family w^ere unacquainted with the 
 method of their ancestors, who kept it a secret, when it is certain that Pierre Levieil 
 himself, in spite of his profound erudition, was ignorant of what was anterior to his 
 time, although it had been made known. Fifteen years after the appearance of the 
 English work which we spoke of, and actually at the time when he was writing, he 
 
14 
 
 INTRODUCTORY ESSAY ON THE ART OF PAINTING ON GLASS. 
 
 still continued to adhere to the manifestly antiquated traditions of his family. How- 
 ever it may he in other respects, we have certainly, in the present state of our know- 
 ledge, no reason to envy the ancient glass-painters in regard to their methods of ope- 
 ration. Consequently, we have nothing to hope for from pretended discoveries of the 
 secrets of the ancient artists, which were at times so pompously announced, because, 
 as we have before stated, the improvements which took place in the arts in conse- 
 quence of the progress of science, have placed us in an entirely new situation, which 
 makes the methods of operation that were in vogue at a period far distant from the 
 present time appear utterly useless. 
 
PART I. 
 
 CHAPTER I. 
 
 OF THE QUALITY AND COMPOSITION OF THE PIGMENTS. 
 
 By the pigments necessary for painting on glass are understood vitrified or vitrifiable 
 substances of various colours, which are applied to the surface of the glass, and fixed 
 by being exposed to a temperature which brings them into a state of fusion. 
 
 Several qualities are indispensable to the pigments : — 
 
 1, fusibility at a given temperature ; 
 
 2, the power of adhering firmly to the glass and completely uniting with it ; 
 
 3, a peculiar transparency, or an opacity ; 
 
 4, a glassy appearance after fusion ; 
 
 5, a sufficient hardness to resist entirely the friction of solid bodies j 
 
 6, insolubility in water ; 
 
 7, the being unchanged by the action of the air, moisture, and the gases, 
 
 which are ordinarily diffused through the atmosphere ; lastly, 
 
 8, an expansibility equal to that of the pieces of glass that are to he painted 
 
 with them. 
 
 The fusibility of the pigments must always be greater than that of the glass. 
 As the latter becomes soft at a red heat of some intensity, it is necessary that the 
 pigment should be in a state of fusion and become fixed to the glass, before it reach 
 the temperature at which it would he spoilt by bending, from being at the point 
 of fusion. 
 
 The pigments are almost always more or less transparent, and only a few must 
 be opaque. In contradistinction to the other enamel-paintings, which convey to the 
 eye merely reflected rays of light, a painting on glass receives it colour from trans- 
 mitted rays. We can understand, therefore, that transparency is a quality very 
 frequently necessary to the pigments. It is not always indispensable, that this trans- 
 parency should be perfect and possess the clearness of glass ; on the contrary, 
 it is often an advantage, when the objects which are behind the window cannot 
 
16 
 
 OF THE QUALITY AND COMPOSITION OF THE PIGMENTS. 
 
 be distinguished. A half- transparency is usually sufficient, provided that it admits 
 of a rich and magnificent colouring; but there are cases in which the painting 
 requires perfectly opaque pigments. 
 
 The hardness of the pigments varies according to their composition. They 
 must always possess a degree of hardness sufficient to enable them to resist easilv 
 the friction of hard bodies ; but since the causes which operate mechanically upon 
 painted windows, to the destruction of the pigments that lie on the surface of the 
 glass, are exceedingly rare, the artist need not always exclude those pigments that 
 are even of moderate hardness. 
 
 The resistance of the pigments to the ehemical action of bodies must be such, 
 that they cannot be affected by any of those agents to the influence of which they 
 are ordinarily exposed, e. g. the action of the air, water, sulphuretted hydrogen % and 
 other gases diffused in the atmosphere ; but it matters little whether the pigments 
 are capable of being acted upon by bodies with which they only accidentally come in 
 contact, or not. 
 
 The unchangeableness of the pigments is as conditional as that of the glass, and 
 is usually in proportion to their hardness. 
 
 Expansibility is one of the physical qualities of which the pigments must possess 
 a precise and accurate amount. In the frequent changes of temperature which the 
 painted plates of glass undergo, during and after the burning, the expansibility of 
 the pigment must be in exact proportion to that of the glass. Were it otherwise, 
 the expansion and contraction taking place irregularly in both bodies, would pro- 
 duce movements in the glass in opposite directions, which must occasion numerous 
 fractures. These are in fact the accidents produced by pigments whose expansibility 
 is ill suited to the glass. Pigments of this kind crack and split, and soon peel off 
 the surface of the glass in the form of scales, while the glass itself, which on account 
 of its thickness possesses firmness and a greater power of resistance, remains 
 uninjured. 
 
 The pigments are composed: — 1, of colouring materials ^ which in most cases 
 belong to the class of metallic oxides ; 2, of fluxes ® or vehicles for colour, which are 
 vitreous or vitrifiable compounds, through the medium of which the colouring matter 
 is fixed upon the glass. These fluxes are generally silicic, boracic, or borosilicic 
 salts, in which the acids are combined with the bases in certain proportions, and 
 whose state of neutralization varies according to the several indications of which we 
 shall afterwards have occassion to peak. 
 
 ^ Or, hydrosulphuric acid, — schwefelvvasserstofFsaure. 
 
 FarbestofFen. ^ Fluszmitteln. 
 
OF THE QUALITY AND COMPOSITION OF THE PIGMENTS. 
 
 17 
 
 In order to colour the pigments, the colour which a substance in its uncombined 
 state affords is sometimes employed, sometimes that afforded by its combination with 
 another substance which usually forms a part of the flux. In either case the colour- 
 ing matter is always mixed with the pigments. This observation admits of a very 
 nice distinction between them, so that we have divided them into two classes. 
 
 The first class comprehends those pigments in which the colouring matter is 
 uncombined with the flux, and is in a state of simple mixture, as, e. g., in the case of 
 oil-painting the colour is mixed with the oil. We shall call them pigments coloured 
 hy mixture 
 
 The second class comprehends those whose colouring matter is in combination 
 with the flux, has become a constituent part of it, and forms with it an entire vitrified 
 mass, possessing all the properties of glass itself. We shall call them pigments 
 coloured hy combination^. 
 
 This classification of the pigments has not been invented merely for the purpose 
 of systematical arrangement, but is grounded rather upon practical considerations 
 of the greatest importance. 
 
 The composition of the fluxes is not arbitrary. Independently of the peculiar 
 qualities which they must possess in order to be really unchangeable, it is also ne- 
 cessary, since they are the medium through which the union between the vitreous 
 and the colouring matter is effected, that they should be adapted to the nature of the 
 former, to ensure their adhesion to it for a long period, and that they should also 
 accord with the qualities of the colouring materials which they have to unite with 
 the glass. The necessity there is for the fluxes being accommodated to all the re- 
 quirements of the colouring materials, is the principal reason why a much larger 
 quantity of this vehicle must be employed, as we shall show hereafter. We shall 
 first consider the composition of the fluxes in the several relations they bear to the 
 colouring matter. 
 
 In the pigments of the first class it is necessary that the flux be of such a quality 
 that it will preserve the colouring matter in the isolated state upon which the ob- 
 taining the requisite colour depends, and that it contain nothing that can effect a 
 change in the properties of the colouring matter. In the fused colours ° of the second 
 class, on the contrary, it is indispensable that the flux should exhibit a powerful 
 action upon the colouring matter, by which action the combination from which the 
 colour is to be obtained is effected. We shall now make a few observations, from 
 which we shall deduce the principles of the composition of the fluxes, considered in 
 that point of view in which we exhibited them above. 
 
 a Durch Mischung gefarbte Pigraente. b Durch Verbiiidung gefarbte Pigmeiite. ' Glasmalerfliissen. 
 
 D 
 
18 
 
 OF THE QUALITY AND COMPOSITION OF THE PIGMENTS. 
 
 The fixed acids ^ combine with bases in all proportions ; hut each of these com- 
 binations has a certain point of saturation at which, when in a liquid state, it pos- 
 sesses just as little afl&nity for a greater quantity of base, as for a greater quantity of 
 acid. This neutral state takes place in the most easily fusible combination ^ and 
 the reason is as follows ; — 
 
 If among the combinations of a fixed acid with a base but little or not at all 
 fusible, that be chosen which possesses the greatest fusibility, and an attempt be 
 made to unite wkh it successively fresh quantities of base, it will be observed that 
 the temperature must be raised in proportion to the increased amount of base brought 
 into combination. This, for example, is the case with the silicates of lime “, iron, 
 cobalt, copper, &c. 
 
 If, on the contrary, we wish to add successively to the combination of a fixed in- 
 fusible acid with a base fresh quantities of acid, it is a well-known fact, that the 
 temperature must likewise be raised in proportion to the quantity of acid which has 
 entered into combination. Therefore, it may be asserted, that in the combinations 
 which consist of a fixed acid and a base, beginning at the most fusible combination, 
 an increase of base or acid requires a proportionate increase of temperature, provided 
 that the substance which is to be added is not very easily fusible, and its combination 
 in consequence independent of the temperature. 
 
 The principle which we have just established is certainly subject to modifications, 
 sometimes in favour of the bases, sometimes in favour of the acids, according as they 
 are more or less fusible In the silicates of lead the same degree of temperature is 
 not necessary for the combination of a quantity of base, as is requisite for the com- 
 bination of a larger quantity of acid, because the ready fusibility of the former 
 makes its combination with the silica independent of the temperature. But we have 
 in the borates of iron, cobalt, and copper, an example of the contrary, and here the 
 rule is modified in favour of the bases, because the fusibility of boracic acid ® renders 
 an increase in the temperature unnecessary. 
 
 But exceptions like these are not to be found in the combinations we have just 
 been speaking of, if, in the place of the fusible element, an infusible one be substi- 
 tuted in the mixture. This is the case, for instance, when oxide of iron is added to 
 silicate of lead, or silicic acid to borate of lead. 
 
 From what has been premised, we infer that when we begin at the neutral state, 
 the temperature which is requisite to unite an oxide with a flux, affords a rule for 
 determining the disposition of this flux to become still more saturated. The more 
 
 “ Feuerbestandigcii, ^ Leiclitfliissigsten. Kieselsauren kalk, &c. 
 
 ® Bor sail re. 
 
 Sclimelzbar. 
 
OF THE QUALITY AND COMTOSITION OF THE PIGMENTS. 
 
 19 
 
 it is saturated, the greater difficulty it has in combining with a larger quantity of 
 base, provided that the latter is not easily fusible. The proportions of the base, 
 which have to be brought into combination, depend upon the temperature : the 
 amount of base is determined according to a given temperature, the above-mentioned 
 cases of easy fusibility excepted. If, therefore, we were to add a fresh quantity of 
 base under the same conditions, it would not enter into chemical combination. This 
 circumstance has now been taken advantage of in the composition of the fluxes of the 
 pigments of the first class. 
 
 When the temperature at which the pigments pass into the liquid state is deter- 
 mined, the proper point of saturation for them is at the same time that which is 
 proper for the flux, because we are assured that the colouring matter which has to be 
 combined with it will remain uninjured. 
 
 If, then, we take the melting point of the pigments at a cherry-red heat, experience 
 teaches us that the triple silicic and the double sub-boracic salts of lead, soda, 
 and potash, which are then completely fused, can be saturated no further. If, 
 therefore, we wish to colour a pigment with an oxide which shall only remain 
 with its flux in the state of mechanical mixture, we must add to the latter the triple 
 silicic and the double sub-boracic salts, of which we have just been speaking. 
 
 But if we wish to obtain a colour by means of an oxide which is to enter into 
 chemical combination with the flux, the degree of saturation at which this combination 
 is effected is fixed wdth as little precision as that of the temperature. If in this case 
 it is judicious to employ a less saturated flux, this may only be done within the limits 
 in which the pigment preserves its indispensable physical properties. As the tem- 
 perature lends its aid, the combination of the oxide is always obtained. Hence it 
 follows, that however the composition of the fluxes of the pigments of the first class 
 is subject to certain strict conditions, this is not the case with the pigments of the 
 second class. But even in these, as we shall soon see, directions of great importance 
 must be given. 
 
 In the composition of the fluxes for pigments of the first class we have taken a 
 moderate red heat as the point of saturation, for the following reasons : first, the 
 glass which is painted is capable of bearing only a slight degree of heat, and the 
 standard is its point of fusion, consequently the temperature must not be raised to 
 this limit. Besides the degree of saturation which we have recommended is at the 
 same time that at which the flux accommodates itself best to the expansibility of the 
 glass, without our being thereby obliged to sacrifice the other desirable qualities of 
 the pigments. 
 
 The saturation of the flux, and the temperature which it has to undergo, are 
 
 D 2 
 
so OF THE QUALITY AND COMPOSITION OF THE PIGMENTS. 
 
 however not the only things which must he attended to in the composition of the 
 pigments. There are other secondary conditions, which are likewise of importance, 
 partly to prevent the combination of the oxides with the pigments of the first class, 
 partly to favour their combination with those of the second class. The exact degree 
 of heat is not always easily obtained ; and if it should happen to he exceeded in the 
 pigments of the first class, the flux immediately regains its power over the colouring 
 oxide. The change in this substance is in proportion to the quantity of flux. 
 Hence we have a reason for prescribing as little flux as possible in pigments of this 
 kind. 
 
 An opposite principle directs us to use as much flux as possible in the pigments 
 of the second class. Besides, it is known that a greater saturation of the oxide is 
 still more favourable to its combination. In order that the pigments of the first 
 class may not be exposed to injurious alternations of temperature, the fluxes are not 
 fused together with the oxides before they are required ; while, on the other hand, 
 no use is made of the pigments of the second class until a previous fusion has shown 
 a perfect combination of the colouring matter. 
 
 We have already observed, that the saturation of the triple silicic and double 
 sub-boracic salts “ has been selected, because it fulfils the requirements of the colour- 
 ing matter and of the glass, without endangering the intrinsic qualities of the pig- 
 ment. In fact, we are strictly obliged to confine ourselves to these limits, if we wish 
 to avoid the unpleasant results that have been mentioned above. 
 
 When a salt of silicic acid and a metallic oxide is combined with a silicic salt, 
 having an alkaline base, by the agency of heat, the one is dissolved in the other. 
 Does this result from an act of combination, or from simple mixture ? The learned 
 observations of Dumas upon the fortuitous crystallization of glass have proved, that 
 the difierent kinds of glass are composed of certain definite silicates, and we have 
 reason to believe that they are in a state of combination with one another. But even 
 independently of the quality of these silicates, their various states of saturation produce 
 numerous modifications in the properties of these compositions. The most important 
 fact, however, which has been noticed, is the following; — Mr. Faraday has observed, 
 that if only a slight addition be made to the quantity of oxide of lead which the 
 common flint glass contains, this glass, which before was quite proof against moisture, 
 then acquires the property of a hygrometer in a remarkable degree, and in damp air 
 soon loses its transparency. Several others have ascertained the truth of this fact 
 from their own experiments. Flint glass is a silicic compound, of which the acids 
 contain eight of oxygen to one of base. Whenever glass in general contains a 
 
 ® Des dreifach kieselsaiiren und doppelt basisch-borsauren Salzes. ^ Hygrometrisch wird. 
 
OF THE QUALITY AND COMPOSITION OF THE PIGM^INTS. ‘21 
 
 greater quantity of base, it is much more easily affected by water. This may be 
 said of window-glass, looking-glasses, &c., especially when they have been polished. 
 All these combinations yield an alkaline silicate, which is soluble in boiling water, 
 and an insoluble silicic earth is precipitated. This takes place at the various 
 desfrees of saturation which lie between the octosilicate and the bisilicate. But it 
 
 o 
 
 is a very remarkable fact, and one which has been especially observed with regard 
 to those glasses which contain lead, that if flint glass containing a soluble alkali, be 
 reduced to a bisilicate in such a way as to be combined with a greater quantity of 
 lead, this flint glass when pulverized gives up almost all its alkaline silicate in cold 
 water, and that, too, almost immediately. 
 
 Hence it is, that the combination of a silicic salt of lead with an alkaline silicate, 
 which is very easily decomposed in mass, in proportion as we descend from the 
 octosilicate, possesses no stability at all when we reach the bisilicate ; for then the 
 latter has become soluble in cold water, and is immediately dissolved in it. It is, 
 however, probable that this is not the case with all bisilicic compounds ; for basic 
 silicates are combined with one another in those kinds of glass which contain lead, 
 whilst in bottle glass, for example, silicates of any kind are combined with basic 
 silicates ; and combinations like these have more stability. But our business here 
 is only with the silicates which contain lead ; for the pigments that are usually 
 employed almost always contain lead. The reason of this is, that the silicic salts of 
 lead are extremely useful in modifying the expansibility of the pigments. By in- 
 creasing or diminisbing the quantity of oxide of lead, we almost always succeed in 
 imparting a degree of expansibility to tbe pigments equal to that of the glass. The 
 same result cannot be obtained from an alkaline silicate. This shows us the reason 
 why potash is avoided in the composition of the pigments. Tbe necessary fusibility 
 and expansibility require that the fluxes should be brought into that state of satura- 
 tion in which they have very little stability, and are very liable to decomposition. 
 At a high temperature the potash is decomposed, and evaporates ; when cold, the 
 pigments are easily affected by moisture. This disagreeable circumstance is avoided 
 by substituting for the potash borate of soda. The latter is much more fusible than 
 the silicate of potash, and consequently enables us to obtain a proper fusibility, 
 without lowering too much the degree of saturation. And so less colouring, less 
 liability to change, and greater hardness are simultaneously obtained. 
 
 dhe whole matter may be shortly summed up thus ; 
 
 1. In the pigments coloured by mixture, those silicates only may be used whose 
 acids contain at most three times as much oxygen ^ as the bases. 
 
 Krystall. Sauerstoff. 
 
OF THE QUALITY AND COMPOSITION OF THE PIGMENTS. 
 
 2. In the pigments coloured by combination, a greater quantity of oxygen in the 
 acids can only be of advantage when all other conditions have been complied with. 
 
 3. No pigment containing lead is to he prepared which contains the silicate of 
 an alkali in a state of saturation beyond that of the trisilicate ; that is to say, which 
 contains a smaller portion of acid, or a greater quantity of base. 
 
 4. In every case, the indispensable conditions of fusibility, hardness, and expansi- 
 bility, must be satisfied. 
 
 In the composition of fluxes, silicic and boracic salts of various metals are usually 
 combined, because the salts formed by these combinations possess greater fusibility, 
 and because among the simple silicates and borates, which might perhaps be suffi- 
 ciently fusible, they would not have the requisite whiteness if they were employed 
 alone. For instance, the silicic and boracic salts, which contain a great quantity of 
 base, would possess sufficient fusibility *, but they have a yellow colour, which is more 
 distinct in proportion as they are saturated. It is therefore necessary to combine 
 them with a certain quantity of alkaline silicates or borates, in order to render this 
 colour less conspicuous. 
 
 It would be better if the silicic or boracic salts, which are used in the pigments, 
 were all insoluble, like those of lime, aluminum, lead, &c. But the necessity for 
 obtaining a great degree of fusibility requires the use of alkaline silicates and borates, 
 which within certain limits obtain a sufficient stability from their combination. 
 
 From the principles which have been laid down above, it might seem that two 
 kinds of fluxes are sufficient for the two classes of pigments. This would certainly 
 be the case, if nothing more than the proper colour were attended to in the prepara- 
 tion of the pigments. But these pigments, which are made on purpose to be laid 
 on the glass, must possess the same expansibility as the latter. Now the physical 
 properties of the pigments are modified in a remarkable degree by the various sub- 
 stances employed in colouring, collectively and separately, in different ways. Con- 
 sequently, it is only by changing the nature of the flux that we are capable of 
 imparting the requisite expansibility to the pigments. Hence, also, arises the 
 necessity for the existence of a great variety among the fluxes. When we come to 
 treat of the pigments particularly, we shall also specify the fluxes proper for each. 
 We shall, however, mention a few here, which may be adduced as an illustration of 
 the rules we have laid down. 
 
OF THE QUALITY AND COMPOSITION OF THE PIGMENTS. 
 
 23 
 
 FLUXES FOR PIGMENTS OF THE FIRST CLASS. 
 
 No. I. No. 2. No. a. 
 
 Silica * . . . . . 1 pt. 3 pts. 2 pts. 
 
 Oxide of lead . . . . 3 ,, 8 ,, 6 ,, 
 
 Calcined borax ® . . . . 0 ,, 1 ,, 1 ,, 
 
 Haudicquer de Blancourt, vdio has described the preparation of the flux, No. i, 
 in his Art de la Verrerie, calls it rocaille, and it was formerly used as a glaze for 
 common pottery ware. This flux, however, whose state of saturation is admirably 
 adapted to the preparation of pigments of the first class, cannot be advantageously 
 employed in every case. It frequently happens that a colouring oxide, when mixed 
 with it, contributes to its decomposition since it favours the separation of its elements. 
 The pigment then undergoes a change on exposure to the air, the surface loses its 
 brightness, and crumbles to powder. We are, however, unable to specify the nature 
 of the action of the colouring substance. Perhaps it is only mechanical, and pro- 
 ceeds from the great distribution of parts ®, and from the porosity itself, which a 
 powder in the state of simple mixture imparts to the pigment ; perhaps, too, the 
 oxide of lead has less affinity for the silica than the new substance which tries to 
 supplant the first. 
 
 The rocaille flux is, after all, only employed with advantage in the pigments of 
 the first class when they have previously to be melted. The more intimate mixture 
 of the flux with the colouring matter then imparts a greater density to the pigment, 
 which defends it against the action of the air. We prefer this explanation. When 
 the pigment does not require to be melted first, it is advisable to substitute No. 2 or 
 No. 3 for No. 1 ; for they are only a modification of the latter, and possess greater 
 stability. 
 
 FLUXES FOR PIGMENTS OF THE SECOND CLASS. 
 
 Silica 
 Minium^ . 
 Borax 
 Saltpetre . 
 
 No, 1. No. 2. No, 3. No. 4. 
 
 3 pts. 1 pt. 3 pts. 3 pts. 
 
 8 „ 8 „ 6 „ 6 „ 
 
 3 „ 2 „ 3 „ 2 ,, 
 
 0 „ 0 „ 1 „ 0 „ 
 
 Every pigment might be prepared according to the above directions, if nothing 
 but the good quality of these vitreous compounds were had in view. But those 
 
 Kieselerde. Bleioxycl. ® Gebrannter borax. 
 
 Zersetzung. ® Vertbeilung. ^ Mennige. 
 
24 OF THE QUALITY AND COMPOSITION OF THE PIGMENTS. 
 
 pigments chiefly that are to he produced hy combination, are so changed in regard 
 to their expansibility by certain oxides, e. g, those of copper and manganese, that, in 
 order to destroy the effect of the latter, it is necessary to reduce the fluxes to a state 
 of saturation, which cannot be done by the use of alkaline silicates, for they must be 
 employed in such small quantities, that they may be enveloped, as it were, by the 
 other silicates, and thus protected from the action of the water. 
 
 In this case the fluxes are very much saturated and less fitted to dissolve the 
 oxides. But even then methods may be employed to facilitate their combinations, 
 which we shall describe when we come to speak of the pigments in particular. 
 
 OF THE PREPARATION OF THE PIGMENTS IN GENERAL. 
 
 The preparation of the pigments, which embraces a number of particulars with 
 regard to each, may however be reduced to two general methods of operation, 
 according as they are coloured by mixture or by combination. 
 
 In the first case, as we have already said, a flux in which the base preponderates 
 is chosen, and with this object in view, care is taken at the same time that the 
 colouring oxide shall remain as short a time as possible in contact with the liquefied 
 flux. For this purpose they are only mixed together by means of the runner upon 
 the mill-stone *, and the mixture is not heated until it is ready to he laid upon the 
 glass ; and exactly as much flux is used as is necessary to give body, smoothness, 
 and brilliancy after the burning in to the pigment. 
 
 In the second case — 
 
 1. A pigment must be selected, in which the acids predominate as much as 
 possible ; 
 
 2. It is also necessary to fuse them together in a strong heat, in order to facili- 
 tate the reaction ; 
 
 3. The flux must likewise be present in as large a quantity as possible without 
 injuring the richness of the colouring ; 
 
 4. The oxide must be perfectly free from combination, which might impede its 
 union with the flux. 
 
 These are the most important varieties of the pigments, with regard to their 
 composition and preparation. We subjoin some further considerations concerning 
 the pigments collectively, that is to say, concerning the means of modifying their 
 properties according to circumstances. 
 
 With respect to transparency ^ the pigments coloured hy simple mixture are 
 remarkably dissimilar to those which are coloured by chemical combination. It 
 a Des Laufers auf dern Reibestein. for the description of which see page lOI. *> Durchsichtigkeit. 
 
OF THE QUALITY AND COMPOSITION OF THE PIGMENTS. 
 
 25 
 
 will be readily understood, that an opaque colouring matter ditfused through a glass 
 vessel diminishes the transparency of the latter, so that the enamel “ which is pro- 
 duced by it will be less permeable to light than another which has been coloured by 
 a substance dissolved in a flux. It is also just as evident, that in the former case 
 the opaque colouring matter diminishes the transparency of the flux, in proportion 
 to the quantity in which it is added to it. Thus the transparency of the pigments 
 is increased according as the quantity of colouring matter is diminished. But this 
 can only be done at the cost of the colouring, and in such circumstances, where 
 intensity of colour is not required, it will be better even to impair its stability; for 
 the more flux there is, the greater the action known to take place upon the colouring- 
 metallic oxides. With regard to the pigments of the second class, their transparency 
 can only be diminished by the mixture of substances which impart opacity to them. 
 
 The hardness of the pigments, under circumstances in other respects the same, 
 increases in proportion to the quantity of the silica. This is just the case with 
 regard to their resistance to the action of chemical agents. Consequently the oppo- 
 site eficct is produced as soon as the base is made to predominate. 
 
 We come now to their expansihiliti/. It is of great importance to make this 
 property of the pigments accord with that of the glass : it may, however, be very 
 easily modified in the case of the former. With regard to this we believe we have 
 observed, that in the borate, silicate, and borosilicate of lead, the base usually pro- 
 duces the opposite effect to that of the acid ; but we are unable to state whether the 
 one diminishes or the other increases the expansibility. It is enough for us to 
 know, that if a pigment becomes full of cracks the proper degree of expansibility 
 may easily be imparted to it, either by increasing or diminishing the quantity of 
 oxide of lead. We would recommend here the former method as the proper one in 
 almost all cases. 
 
 FUSION OF THE FLUXES. 
 
 After the requisite quantities of the various substances that are to be used for a 
 flux have been levigated and accurately weighed, nothing more remains than to fuse 
 them. The powder is first well rubbed and mixed in a mortar. After careful mix- 
 ture it is put into a covered crucible”, which is placed in the furnace‘s, fig. 9; a gentle 
 heat is first applied, which is gradually increased, until the whole is brought into an 
 undisturbed state of fusion, and all bubbles have ceased to form. The crucible is 
 then taken out of the furnace, and the contents are poured into a vessel of cold w^ater. 
 
 ^ Sclimelzglas. Rissig. ' Verdeckten Sclimelztiegel. Sclimelzofen. 
 
 E 
 
26 
 
 OF THE QUALITY AND COMPOSITION OF THE PIGMENTS. 
 
 They are then collected and dried upon paper. The action of the cold water splits the 
 mass into small fragments, which can afterwards be more easily levigated. Without 
 this precaution the flux would concrete into a vitreous mass, difficult to pulverize. 
 This is exactly the mode of operation, when we have to combine a flux with a colour- 
 ing metallic oxide for a pigment of the second class, as is the case with all vitrifica- 
 tions of fluxes or pigments. 
 
 If we would have our colours bright and pure, it is of essential importance that 
 the pigments should be prepared from none but the purest substances. It is conse- 
 quently necessary that we should be well acquainted with the properties of the sub- 
 stances to be employed. We therefore think it advisable to make a few preliminary 
 remarks concerning some of them, and to give a full account of them afterwards in 
 their proper places. 
 
 SILICA. 
 
 Silica is procured from flints % and white ones, or those of a beautiful black colour, 
 are selected for this purpose. The yellow flints are less pure, and contain a great 
 quantity of iron. For this purpose they are heated red hot, and then thrown into 
 cold water to quench them. If the action of the cold water fails in cracking them in 
 such a manner as to allow of their being easily crushed with the fingers into coarse 
 sand, the operation is repeated ; they are then reduced to powder and rubbed through 
 a silken sieve. This powder must then be washed, and the supernatant water poured 
 off as long as a fine powder continues to float on the surface, which gives the silica a 
 )ellow colour. This powder appears to consist of impurities, which originate partly 
 from the furnace, partly from the cast-iron mortar which is employed in levigating 
 the flint ; they seem to be united with very fine silica, which could better be spared 
 than retained in company with these foreign bodies. The particles of iron being very 
 fine are carried off by the water in which the powder is washed, and separated before 
 the process of heating the silica, (of which we shall presently speak,) in which those 
 particles of iron would otherwise be further oxidized, and might not be so easily 
 affected by acids. 
 
 After the silica has been washed in the manner above described, it is strongly 
 heated and thrown a second time into cold water. The little grains of which it con- 
 sists undergo a fresh division which facilitates the action of the acids wdth which 
 they come in contact, and also the fusion of the metals. They are now treated with 
 hydrochloric acid, washed and dried. Silica might also be obtained in the same way 
 
 b Zertlieilung. 
 
 ® Aus den sogenannten Feuersteinen. 
 
OF THE QUALITY AND COMPOSITION OP THE PIGMENTS. 
 
 27 
 
 from white granular quartz®, hut even the purest granular quartz contains a greater 
 quantity of iron than flint does, on which account the preference is usually given to 
 the latter. 
 
 BORAX. 
 
 The borax which is used in the preparation of the pigments fused borax^, which 
 must not be confounded with calcined borax’'. The latter contains still a great quan- 
 tity of water. It is indispensably necessary to make use of the fused and perfectly 
 vitrified borax, not only to enable us to calculate the quantities exactly, but also to 
 avoid the swelling which would take place if borax in any other form were employed. 
 
 We shall hereafter enlarge more minutely upon the manner in which this opera- 
 tion is performed. When the borax is in a state of fusion, and appears perfectly 
 clear, it is poured upon a smooth stone. It then presents the appearance of a beau- 
 tiful white and entirely colourless glass. It must now be kept in a bottle well corked. 
 
 MINIUM. 
 
 The orange-coloured minium as it is called, is most usually employed. It is the 
 purest, and can be used without requiring a particular preparation. We shall only 
 observe, however, that the minium must part with 2.23 per cent, of oxygen, in order 
 that it may be reduced to the state of protoxide ®. 
 
 Of the other bodies which are used for fluxes we shall have occasion to speak else- 
 where. Now that we have finished treating of the pigments in particular, we intend 
 to subjoin a few general reflections, which we recommend to the consideration of the 
 reader. 
 
 GENERAL REFLECTIONS CONCERNING THE COLOURING MATERIALS. 
 
 The chief colouring substances of the pigments are metallic oxides. Sometimes 
 they are simply mixed with the whole body of the glass ; at other times they are com- 
 bined with the silica, and probably form double salts with the silicates of the fluxes. 
 The analogy which prevails between the pigments and the other kinds of glass sup- 
 ports this hypothesis. It is known that in these compositions such alkaline silicates 
 as are soluble in water when uncombined become almost insoluble as soon as they are 
 
 ^ Quarzsand. Gesclimolzener Borax. <= Calcinirten Borax. 
 
 Orange-gelbe. 
 
 ® Oxydul. 
 
28 
 
 OF THE QUALITY AND COMPOSITION OF THE PIGMENTS. 
 
 combined with other silicates, e. g., with silicate of lime, silicate of lead, silicate of 
 aluminum^, &c. 
 
 Now the combination of these bodies is the sole means by which their properties 
 can be modified. 
 
 In the pigments coloured by mixture the colouring oxides are not always used se- 
 parately ; sometimes several are employed, after they have been previously combined 
 with one another. But the conditions to which they are mutually subject are always 
 independent of the flux. 
 
 The oxides which are combined in a pigment of this description do not give it the 
 colour which the mixture of their respective colours would produce, but they give it 
 peculiar shades of colour’', which are determined by their state of combination. 
 
 Several oxides are frequently employed also in the pigments of the second class, 
 but are not combined with one another, and the colour which is obtained is only the 
 result of the mixture of the colours which each oxide produces of itself. 
 
 The combination of the oxides with one another is a valuable auxiliary in the pre- 
 paration of the pigments. Sometimes these combinations impart to the oxides a 
 greater power of resisting the action of the flux ; at other times, on the contrary, 
 they facilitate their solution in the latter. It is evident at once that the former are 
 used for the pigments of the first class ; the latter, on the other hand, for those of 
 the second class. In the former case we should combine oxide of iron, for instance, 
 with oxide of zinc, because the former, by virtue of this combination, which pos- 
 sesses great stability, would prove much more powerful in resisting the action of 
 the flux, and thus the real colour of the oxide could be given to the pigment. 
 
 In the second case, on the contrary, we should combine oxide of cobalt with 
 oxide of lead, so that their less stable combination may bring the former of these 
 bodies into a state of fine division favourable to the action of the flux. This di- 
 rection may be complied with in a very simple manner, if, instead of preparing the 
 flux beforehand in order to combine it with the colouring matter by a second fusion, 
 the colouring oxide be heated when mixed with the ingredients of the flux ; for the 
 oxide of lead, which forms one of these ingredients, will dissolve the colouring oxide, 
 and by that means dispose it to combine more easily with the silica. We have 
 therefore no hesitation in prescribing this method universally for the preparation of 
 the pigments of the second class. We know no reason of sufficient importance to 
 oblige us to use fluxes previously vitrified, as is the case with the pigments coloured 
 by mixture. 
 
 “ Der kieselsauren Thonerde. 
 
 Farbenabstufungen. 
 
OF THE QUALITY AND COMPOSITION OF THE PIGMENTS. 29 
 
 The combination of two oxides forms a real salt, in which the one appears in the 
 character of the base, and the other in that of the acid. We shall now give a list 
 of these bodies, in which those that act as base and those that act as acid are classed 
 according to the energy they exhibit ; — 
 
 ACID OXIDES. 
 
 Antimonic acid. 
 
 Antimonious acid. 
 
 Stannic acid 
 
 INDIFFERENT OXIDES. 
 
 Protoxide of tin. 
 
 Oxide of antimony. 
 
 Oxide of chromium. 
 
 Sesquioxide of manganese. 
 
 Oxide of iron. 
 
 Oxide of aluminum. 
 
 Oxide of zinc. 
 
 BASIC OXIDES. 
 
 Protoxide of iron. 
 
 Protoxide of manganese. 
 
 Protoxide of lead. 
 
 Oxide of silver. 
 
 Oxide of bismuth. 
 
 Protoxide of cobalt. 
 
 Oxide of copper. 
 
 We shall now give a few examples of the above-mentioned compositions, as they 
 are frequently employed : — 
 
 Antimonite of lead ..." Yellow. 
 
 cobalt . . . Dark green. 
 
 copper . . , Pistachio green. 
 
 Perantimonite of iron . . . Bees’-wax yellow. 
 
 ^ — zinc . . . Yellow. 
 
 Zincate of iron’’ . . . . Yellow ochre colour. 
 
 It is evident that a great number of combinations similar to those we have men- 
 tioned might be formed. A variety of mixed gradations of colour are obtained from 
 
 Zinnsaure. 
 
 Zinksaures Eisen. 
 
30 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 these compounds, which in painting are called broken tints and which are of great 
 service to the artist. Among these compounds are ; — 
 
 Ferrate of manganese’’, 
 
 chrome, 
 
 cohalt, 
 
 — copper, 
 
 Manganate of cobalt, 
 
 copper, 
 
 chrome, 
 
 Cuprate of silver®, &c. 
 
 We shall treat of the preparation of these colouring substances hereafter. 
 
 CHAPTER II. 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 RED FOR THE FLESH-TINTS. 
 
 This pigment is coloured with oxide of iron, as it is obtained by calcining the 
 green vitrioP of commerce ; but must first he purified, principally in order to rid it of 
 the sulphate of copper®, which it almost always contains, and which, when the pigment 
 is used, turns the red black. 
 
 PURIFICATION OF THE VITRIOL. 
 
 Dissolve the vitriol in twice its weight of cold water, and throw into the solution 
 iron turnings, iron filings, or iron cuttings of any kind. The sulphate of copper udll 
 he decomposed, and the copper precipitated Hn the metallic state in the form of a red- 
 dish powder. The solution should be stirred from time to time, and after the precipi- 
 tation is completely at an end the liquor poured otf and filtered. 
 
 3 Gebrocliene Tone. ^ Das eisensaiire Mangan. " Das kupfersaure Silber. 
 
 Eisenvitriol. ® Schwefelsaiirem Kupfer. ^ Nieclergescblagen. 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 31 
 
 To know whether all the copper has been precipitated, dip into the solution a 
 bright blade of iron, and see whether it is covered with a surface of red copper. 
 
 The filtered solution of sulphate of iron must be put into an iron or leaden vessel, 
 which is placed in a common oven, in order that it may become so concentrated by 
 boiling as to have lost 5-8ths of the water which has been taken into solution. Its 
 specific gravity will then be 40“ of Beaume’s areometer, and the solution will begin to 
 grow turbid ; it is then left to crystallize in a wooden vessel covered with wax ; 
 twelve hours afterwards the mother liquor ^ is poured off, and the crystals are col- 
 lected, strained, and dried. 
 
 DRYING OF THE SALT. 
 
 In order to dry the salt, and to perform the subsequent operation, two pounds of 
 salt at the most should be treated at a time, for the sake of greater facility in mani- 
 pulation. 
 
 Two pounds of the purified crystals are accordingly put into an iron vessel, which 
 is placed in a furnace, and a moderate fire is applied, in order to melt them in their 
 water of crystallization. When this has taken place the liquid mass begins to boil, 
 and soon assumes the consistency of thin paste and the colour of clay® softened by 
 moisture. After it has become concentrated the temperature is lowered, that the 
 melted mass may not boil over. In proportion as the water evaporates and the con- 
 tents of the vessel are drying they are continually stirred, and during this process the 
 bottom of the vessel especially must be scraped with an iron ladle having a long 
 handle, until the salt is at length converted into a more or less coarse powder. It 
 is now allowed to cool, after which it is pounded in an iron mortar, and finally rubbed 
 through a silken sieve. In this state it is fit for the preparation of the red pigment. 
 
 PREPARATION OF THE RED PIGMENT. 
 
 For this operation a very thick cast-iron vessel is required, and it is not a matter 
 of indifference whether merely a common iron vessel of moderate thickness be em- 
 ployed for this purpose or not ; for there would be a danger of its being perforated 
 with holes and destroyed before the conclusion of the operation ; cast iron is more 
 durable than wrought iron when applied to this use. 
 
 Fliissigen Breies. Aufgeweicliteii Tlioiies. 
 
 ^ Mutterlange. 
 
32 
 
 OF THE PIGMENTS IN PARTICULAE. 
 
 An earthen cylindrical furnace must likewise be employed, with a bottom of the 
 same substance, and open at the top. A hole is bored at the bottom, to receive the 
 muzzle of a small smith’s bellows. The dimensions of this furnace must be six inches 
 in diameter, and the same in height. In default of such a furnace, a common one might 
 be used, but the temperature can he regulated much better in the one we have just 
 described j for as soon as the operator ceases to blow, the fuel, receiving no air from any 
 quarter, begins to go out. The vessel must be of the same width as the furnace. 
 
 These proportions for the furnace and the iron vessel must he adapted to 
 the quantity of the salt that can be used at once, in order to perform the operation 
 with due precaution. 
 
 The sulphate of iron, prepared according to the above directions, is heated until it 
 assumes a dark red colour. Meanwhile it is continually stirred with an iron scraping 
 instrument until the operation is finished, in order that fresh surfaces may be conti- 
 nually exposed and the whole may be uniformly heated. The powder at first becomes 
 yellow, then brown, and at last assumes a greenish brown appearance, which after cool- 
 ing changes to red. An acid and pungent gas is now disengaged. The operation is 
 continued until the powder is reduced to about two-thirds of its volume. It is now 
 from the fire and allowed to cool. 
 
 After a little practice, we may know by the colour of the substance when the ope- 
 ration must be brought to a . conclusion. Should the operator, however, want ex- 
 perience, let him take portions of the substance at diflerent periods of the operation, 
 and he will thus be sure of obtaining the requisite tint^. In every case the operation 
 must be concluded before the gas has ceased to be given off ; for if it were prolonged 
 to this point, it would be all to no purpose, and the result could only then he used 
 as a dark brown or iron violet colour. 
 
 The red which has been obtained is put into a vessel, and boiling water poured 
 upon it to dissolve the sulphate of iron that has not yet been decomposed. It is fre- 
 quently stirred, allowed to subside, and the supernatant water is poured off. The red 
 pigment is then cleansed from a few impurities remaining in it by being stirred in a 
 vessel of fresh water, which is quickly poured off as soon as these impurities have 
 subsided. If this operation be repeated as often as is necessary, the impurities will 
 be completely removed. They are generally of a greenish grey colour. The powder 
 of oxide of iron is now washed in a filter with cold water until the latter exudes from 
 the filter perfectly tasteless. The result, when dried, is now ready to be mixed with 
 the flux. 
 
 Niiance. 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 33 
 
 THEORY. 
 
 What takes place in this operation ? In the first place a portion of the acid of the 
 salt is decomposed into sulphurous acid^ which is given olF, and oxygen, which converts 
 the rest of the salt into persulphate of iron”, which is mixed with the oxide of iron 
 that has been liberated. This sulphate is now decomposed again ; sulphuric acid 
 is disengaged, and oxide of iron, mixed with undecomposed persulphate, remains. 
 
 It is well known, that the red oxide of iron changes its colour in proportion as 
 the temperature to which it is exposed is increased. At first it possesses a yellowish 
 red colour, which afterwards passes into a darker red, and finally into violet. If, 
 therefore, it is required to produce a delicate red for the flesh- tints by calcining sul- 
 phate of iron, the latter must be acted upon by a heat suflicient to decompose it, but 
 still not so great as to deepen the red which has already formed. Hence is evident 
 the importance of always keeping it at a dull red heat, and of stirring it incessantly, so 
 that the parts which lie at the bottom may not be too much heated. With respect 
 to this circumstance we subjoin the following practical remark, viz., that in order to 
 keep the powder at a dull red heat, while it is stirred, the bottom of the vessel must 
 be at a cherry red heat. 
 
 The operation must be concluded before the sulphate is all decomposed, (and this 
 is of the greatest importance,) so that the red which is formed may be mixed with a 
 certain quantity of this salt. When the latter has been dissolved by the water in 
 which it is washed, the oxide that remains is in a state of finer division, and possesses 
 a lively red colour. 
 
 If the operation be continued too long, it seems to be prejudicial to the beauty of 
 the red, even if the temperature be not very high. We may infer from this, that the 
 oxide condenses not only in consequence of the high temperature to which it has been 
 exposed, but also on account of the length of time during which it has been heated. 
 And this is the reason why only a small quantity of the salt should be operated upon 
 at a time. 
 
 Red of a beautiful tone from iron may he obtained with much greater certainty 
 by a method which is based upon the theory we have just explained. A mixture of 
 sulphate of iron and sulphate of potash is calcined, as in the foregoing operation, 
 these salts having been previously combined in the state of solution, and then eva- 
 porated and dried by heat. The mixture may be heated merely in a crucible, pro- 
 vided that care is taken to increase the temperature slowly up to the dull red heat, 
 and to keep it so until the operation is finished. But this latter method is less cer- 
 Schwefelige Saure. Scliwefelsaiires Eisenoxyd. 
 
 F 
 
34 
 
 OF THE PIGMENTS IN PARTICULAE. 
 
 tain. In every case the undecoraposed sulphate of iron, as well as the sulphate of 
 potash, is separated by repeated washings with hot water. 
 
 There is still another method which furnishes a red of great richness of colour, 
 particularly for the flesh-tints. It consists in grinding sienna “ in a solution of sul- 
 phate of potash, drying it by heat in an iron vesseP or even in a crucible merely, and 
 calcining it the proper length of time at an incipient red heat, in order to develope the 
 colour of the oxide of iron. The product is then washed with boiling water, to se- 
 parate the sulphate of potash. 
 
 A similar result is obtained by calcining a mixture of equal parts of green vitriol 
 and alum, previously united in solution, and proceeding in other respects according 
 to the method we have just described for obtaining the red from sulphate of iron and 
 sulphate of potash. 
 
 The preparation of the red from iron requires much more delicate manipulation 
 than would he supposed. Whatever method be employed, the calcining must be per- 
 formed with the greatest care, and we v/ould particularly caution the reader against 
 imagining that the details we have given are superfluous. It is difficult to determine 
 which method of preparation deserves the preference, because, on a comparison of the 
 various methods, we cannot always be sure of being subject to the same conditions, 
 and we often lay to the charge of the method that which ought properly to be attri- 
 buted to the manipulation. If we were to recommend one method more than another 
 it would be the second, that which we have most frequently employed. 
 
 It now remains for us to explain why sulphate of potash is used in the preparation 
 of the red obtained from iron. This salt is unchangeable at a red heat, and at this 
 temperature has no chemical action upon the component parts of the sulphate of iron. 
 Its action here is entirely mechanical. It supports, as it were, the complete decom- 
 position of the sulphate of iron. But, although it remains undecomposed itself, its 
 presence is by no means a matter of indifference. When the sulphate of iron is dried 
 in contact with the sulphate of potash, it is kept by the latter salt in a state of fine 
 division, analogous to that which it possesses in the state of solution ; for every 
 minute particle of iron is surrounded by numerous minute particles of sulphate of pot- 
 ash, so that, when the oxide of iron is separated, it must preserve the extremely fine 
 division of the salt by which the oxide of iron was produced. It thus escapes that 
 condensation and conglomeration which oxide of iron always undergoes when it is 
 heated by itself. The unchangeableness of sulphate of potash at a red heat is the 
 only reason why this salt has been selected for the operation in question. It is like- 
 wise employed for the same purpose in similar cases, where, as in the present in- 
 ^ Siena-Erde. Schale. 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 35 
 
 stance, the object is to obtain oxides free from water in a state of the most minute 
 division. There are various methods of applying it to this purpose. 
 
 1. Sulphate of potash is calcined at a red heat, together with the metallic sul- 
 phate whose oxide is to be obtained, provided that this sulphate is decomposable. 
 The process is the same as has been described in the case of the red obtained from 
 iron. 
 
 2. If the salt is not decomposable, the oxide in question is precipitated with 
 potash ; the solution is then evaporated to dryness, and the product is submitted to 
 a red heat in a crucible. The sulphate of potash is next removed by boiling 
 water, 
 
 3. If the oxide of another salt, not a sulphate, is to be obtained, we proceed as 
 follows : after the oxide has been precipitated with potash, and the precipitate 
 washed, it is mixed with a saturated solution of sulphate of potash, next eva- 
 porated, and the rest of the process is the same as we have described above. 
 
 M. de Montami treated certain oxides, probably with the same object, with 
 chloride of sodium in a similar manner, but his efforts were misdirected. He tri- 
 turated red oxide of iron and chloride of sodium dry in a mortar together, and 
 calcined the mixture in a bright red heat. In this way he calcined oxides, free from 
 water and already condensed by the action of the tire, with the chloride. The 
 oxides could not penetrate so deeply into the latter combination, which was applied in 
 a solid state, as if it had been in the state of a red-hot liquid ; and besides, they 
 had undergone a very great change from the heat before it was introduced. 
 
 The red pigment is composed of : — 
 
 Red oxide of iron 1 part. 
 
 Flux No. 1, or No. 3, of the 1st class . . 3 parts. 
 
 The flux must be pulverized before it is weighed, because a certain quantity is 
 always lost by pulverizing it in an iron mortar. It is then mixed with the oxide of 
 iron, and the mixture levigated ; at the same time a sufficient quantity of water is 
 added to obtain a liquid paste, which is afterwards dried on plates. 
 
 This pigment must contain as much flux as will give it brilliancy when it is 
 exposed to a cherry-red heat ; a larger quantity of flux must, however, be avoided, 
 because the flux would react upon the colouring oxide, and contribute to the pro- 
 duction of a green silicate of iron which would be prejudicial to the purity of the 
 red. We shall afterwards explain how this pigment is to be prepared for use, and 
 under what conditions it must be heated after it has been laid on the glass. 
 
 F 2 
 
 ^ Chloniatnum. 
 
36 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 If a greater degree of freshness and brilliancy is required in the red pigment 
 which is used for the flesh-tints, a certain quantity of chloride of silver‘d must be added. 
 The yellow tint which this combination produces imparts a greater liveliness to the 
 red colour of the iron. The taste of the artist can alone determine the proportion 
 of the substance to be added. The chloride of silver must previously be fused with 
 the flux. The oxide of iron is added afterwards. 
 
 PURPLE “ PIGMENT. 
 
 The preparation of the purple is a very delicate operation, the success of which is 
 extremely uncertain. The reason of this is, that the method which is employed in 
 the majority of cases for the preparation of a solution of tin furnishes an exceedingly 
 variable compound, although the process is on every occasion the same. The preci- 
 pitate which by this method is apparently obtained under exactly the same condi- 
 tions, frequently varies from a more or less lively purple to a violet more or less 
 dark, and even of a blackish colour ; and even the purple of the most beautiful 
 tone is not always proof against the drying, and is turned black by the separation of 
 the gold. 
 
 The method employed in most cases is as follows : — Take aqua regia® of 8 parts 
 nitric acid‘s and 1 part sal-ammoniac®, diluted with twice its weight of distilled water. 
 Set the apparatus in a cold place, and introduce small pieces of tin one after another 
 in proportion as they are dissolved. The action of the acid must be slow, and 
 without a considerable quantity of heat being evolved. When the liquor has 
 assumed a yellow colour, not very intense, it is fit for use. On the other hand, 
 dissolve pure gold in aqua regia containing 1 part nitric acid to 2 parts hydrochloric 
 acid. The gold has now to be precipitated by means of a solution of tin. 
 
 For this purpose, a few drops of the solution of gold are poured into a glass, and 
 at least a thousand times their volume of water is added. Into this liquid some 
 of the solution of tin is introduced, a drop at a time, until the water is coloured 
 red. 
 
 This liquor is kept in a vessel by itself, and the same process is repeated until at 
 length the requisite quantity of purple is obtained. In a few moments the purple 
 collects in red flakes, which sink to the bottom. As soon as all the purple is preci- 
 pitated the supernatant liquor is poured away. It is then washed several times 
 with distilled water, which is likewise poured away. Next it is filtered, and whilst 
 it is still moist it is triturated with its flux. 
 
 2 Chlorsilber. Purpurrothes, i. e. purple red. ' Konigswasser. ^ Saltpetersaure. ® Salmiak. 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 37 
 
 The success of the operation depends upon the manner in which the salt of tin 
 is prepared. In order that the purple may he of the proper quality, the action of 
 the acid upon the tin must be neither too strong nor too weak ; if it is too weak, too 
 much protochloride^ of tin is obtained, and if it is too strong, nothing but perchloride’’ 
 of tin is produced. It is necessary to know how to keep the acid in exact equili- 
 brium, so as to obtain a mixture of the two salts combined in as nearly as possible 
 the proper proportions. The difficulties which accompany the regulating the effect 
 of the acid in such a way as to obtain every time the same result, although the 
 operation is not performed under the same conditions of temperature, are obvious to 
 every one. Sometimes the protochloride, at other times the perchloride, is in excess ; 
 this explains the different appearances which this composition exhibits when used. 
 
 If the products of the operation are uncertain, variable in their colour, and dis- 
 posed to decomposition during the process of drying, there is every reason to believe 
 that the salt of tin is of a bad quality. The difficulty of imparting the requisite 
 properties to this composition induced M. Reboulleau, among others, to seek for a 
 simple and easy method of procuring with certainty a solution of tin adapted to the 
 preparation of the purple. It is composed in a way that Dumas also considers the 
 best, viz., of 1 atom of protochloride and 1 atom of perchloride of tin. 
 
 The method employed by M. Reboulleau for this purpose is as follows ; — Proto- 
 chloride of tin is first prepared by introducing grains of pure tin into a leaden 
 vessel which can be closed by a lid of the same metal. A small quantity of con- 
 centrated hydrochloric acid is then poured upon the grains. The apparatus is 
 gently warmed in a sand-bath, and small quantities of acid are gradually introduced 
 until the tin is dissolved. The liquor is evaporated to 40° of Beaume s areometer 
 and allowed to crystallize. We have then merely to convert a definite portion of the 
 protochloride of tin into perchloride. The crystallized protochloride is dissolved in 
 a sufficient quantity of water ; the solution is divided into two parts, one of which 
 is set apart, while chlorine gas is infused into the other until the protochloride is 
 completely changed into perchloride, which is removed for fear it should precipitate 
 gold. This solution is added to the one which was set apart, and thus a solution of 
 tin is obtained, in which the two chlorides are present in accurately determined pro- 
 portions. The success which this method insures in the preparation of the purple 
 is so perfectly certain, that it may be safely recommended to glass-painters and other 
 artists. 
 
 The solution of tin serves only for precipitation from chloride of gold which is 
 prepared by dissolving gold in aqua regia, composed of 1 part nitric acid, and 4 parts 
 ^ Zinnchloriir. Zinnchlorid. 
 
38 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 hydrochloric acid, evaporating it until it is dry, in order to drive olf the excess of 
 acid, and adding a quantity of distilled water sufficient to dissolve the salt wh ich has 
 been obtained. 
 
 The preeipitation of the purple is a part of its preparation that requires very 
 delicate manipulation. The manner in which the mixture of the two salts is effected 
 is not a matter of indifference. Two methods may be employed : the solution of 
 gold may be poured into the solution of tin, or vice versa ; but these two methods 
 do not promise equal success. The following remarks will show why one method is 
 to be preferred to the other. 
 
 When the precipitation of the purple is effeeted by the mixture of the salts of 
 tin and gold, one of these three things will take place ; viz., either the salts will be 
 in proper proportions, or the salt of tin v/ill predominate, or the salt of gold will be 
 in excess. 
 
 If the salts are in proper proportions, the purple precipitate follows, accompanied 
 by certain indications with which it is necessary to be acquainted. The liquor 
 assumes an intensely red colour, similar to that of wine. The precipitate does not 
 follow immediately, but the purple remains a longer or shorter time, as the case 
 may be, in the solution, and frequently it is several hours before the separation is 
 complete. AVhen the precipitation takes place too quickly, it is always a proof that 
 the purple is of a bad quality and contains an excess of gold. 
 
 If the salt of gold is in excess, a precipitate is formed which varies from a pale 
 rose colour® to a more or less lively red, and the separation takes place immediately. 
 In this case also the purple is imperfect. 
 
 If, on the contrary, the salt of tin predominates, no formation of purple takes 
 plaee ; the liquor assumes a yellowish or rose-coloured appearance, without affording 
 any preeipitate. 
 
 From what we have just stated, any one would be inclined to think that if the 
 quantities of the tvv'o salts are previously determined, it would be sufficient to pour 
 the solution of the one into that of the other and to stir them together. But this 
 expectation is not easily realized ; and it is thought more advisable to obtain a proper 
 mixture by adding successive drops of the solution as long as it shall be found 
 necessary ; nor even then is it immaterial whether the solution of tin be poured into 
 the solution of gold, or the solution of gold into the solution of tin. 
 
 Is the solution o f tin to he poured into the solution of gold f As the addition is 
 made by drops, the gold remains in excess in the liquid until the whole of the 
 solution of tin has been introduced. Consequently an imperfeet precipitate may be 
 
 ^ Roseiu’oth. 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 39 
 
 formed if the proper quantity of the solution of tin be not introduced with 
 tolerable rapidity 5 and this is very frequently the result. If, on the contrary, too 
 much solution of tin be added, no precipitation takes place, and it becomes neces- 
 sary to reverse the operation, and to add the solution of gold. This method is 
 therefore very uncertain. 
 
 Is the solution of the salt of gold to he jooured, into that of the salt of tin ? So 
 long as the salt of tin is in excess no precipitation takes place ; but if we continue 
 to add gold the purple soon makes its appearance, and we can always stop at the 
 right time, because we are not obliged to hurry ourselves in the least degree. Only 
 an inexpert operator runs the risk of introducing too much solution of gold. In 
 such a case a precipitate of bad quality would be produced, and the experimen 
 would entirely fail. 
 
 It is evident that, of these two methods, that according to which the solution of 
 gold is poured into the solution of tin has the best prospect of success, and is the 
 least liable to accidents. It may be asserted, that it is the only one which affords 
 invariable results. It admits, too, of the treatment of any quantity we please, while 
 the other method is only applicable when the solution has to be treated with a few 
 decagrammes'' at a time. 
 
 But whatever method be pursued, the solution of tin must at all events be 
 diluted with a thousand times its weight of water, in order that the precipitate may 
 be so much the more finely divided and more gelatinous. After the precipitation of 
 the purple powder has subsided, it is put into a filter and washed with distilled 
 water. It is advisable then to dissolve it in ammonia, and keep it in a well- 
 stopped bottle. The capability of being dissolved in ammonia is the test of its good 
 quality. If this property is wanting, we may be certain that it is of no use, for it 
 will not possess durability. 
 
 In order to unite the purple with its flux, the latter is pulverized, moistened 
 with the ammoniacal solution of the purple powder, and the mixture is effected by 
 levigating them together upon a plate of glass. The relative quantities of the 
 purple and the flux depend upon the richness of the colour which is intended to be 
 given to the pigment. One-tenth of the purple in a dry state gives an intense 
 colour. If we know the composition of the purple, the quantity of gold that is used, 
 the quantity of ammonia in which the purple has been dissolved, it is an easy problem 
 to determine the proportions of this solution, which must be added to the flux, in 
 order to have used the equivalent of one-tenth of dry purple. 
 
 ^ The decagramme is equivalent to 154.42 English grains avoirdupois (the gramme being 15.442 grains,) 
 according to the new metrical system of weights and measures. 
 
40 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 The purple colour which is produced in fused pigments by the above mentioned 
 composition, proceeds from metallic gold in a state of exceedingly fine division. 
 The same colour is likewise obtained from pure chloride of gold, sulphuret of gold, 
 and fulminating gold% in similar circumstances, and these combinations play the 
 same part as the purple powder. When the latter is mixed with its flux and strongly 
 heated, the tin is separated from the gold ; but the latter, reduced to the metallic 
 state, remains in a state of the most minute division, because the flux, being melted, 
 is present in a liquid form. But as soon as the gold can collect together in particles 
 of a larger size, there is a transition from red to violet and blue. This phenomenon 
 is produced by several circumstances, which arise from the following causes : — 
 
 The flux for the purple must contain not much lead, but, on the contrary, a 
 great quantity of acid, and must at the same time possess great fusibility. Stannic 
 acid has in fact a great affinity for oxide of lead. When it is combined with gold, in 
 the form of the purple powder, and is brought into contact with a flux containing a 
 large amount of base, and at the same time lead, it leaves the gold in order to com- 
 bine with the lead before the pigment is completely melted. This premature sepa- 
 ration of the tin from the gold facilitates the agglomeration of the particles of the 
 latter, which then assume the violet or blue colour we have been speaking of. 
 
 A large proportion of acid gives more stability to the silicate and borate of lead, 
 so that it is more capable of resisting the action of the stannic acid. 
 
 The colour of the purple is, on the other hand, destroyed when the flux with 
 which it is mixed wants fusibility. The temperature necessary to fuse the mixture 
 produces at the same time the decomposition of the purple before it can be brought 
 into its incipient state of division. 
 
 So also a purple pigment mixed with its flux, if too strongly heated, would un- 
 dergo the same change from a contrary action, because the too great fusibility of the 
 flux is favourable to the condensation of the gold. 
 
 Consequently it is necessary that the purple, at the moment when it is being 
 decomposed, should be held in solution in a dense mass of liquid glass, in which 
 every one of its particles may, as it were, remain isolated, in the same way as an 
 oleaginous body is suspended in a slimy fluid. 
 
 The flux which seems best adapted to the purple is the following : — 
 
 Calcined borax 7 parts. 
 
 Silica 3 „ 
 
 Minium 1 part. 
 
 This flux possesses suflficient fusibility, and at the same time great stability. 
 
 ® Kuallgold. 
 
OF THE PIGMENTS IN PARTICULAR. 44 
 
 Another still more fusible flux"^ : — 
 
 Calcined borax .... 
 
 Silica ..... 
 
 Minium ..... 
 
 These substances are fused together. 
 
 Another still more fusible flux : — 
 
 Calcined borax 
 
 Silica .... 
 
 Minium .... 
 
 These substances are likewise fused together. 
 
 For the purpose of obtaining a still more fusible flux, it is not unusual to increase 
 the quantity of borax very considerably, without employing the other substances in 
 larger quantities. Thus, for example, the following flux is used : — 
 
 Calcined borax . . . . .12 parts. 
 
 Sand ....... 1 part. 
 
 Minium ....... 1 ,, 
 
 A flux like this is, indeed, far more fusible than the foregoing, and more con- 
 veniently used for glass-painting, because only a moderate heat is required for it ; 
 but such a composition is liable to imperfections, and is not only more easily aficcted 
 by moisture, but is also in the habit of coming off in scales. The purple colours 
 generally possess these imperfections. It is owing to the great quantity of acid 
 which they contain that their expansibility does not accord with that of certain 
 kinds of glass. When this kind of painting is looked at with a magnifying glass, 
 after the burning in, several cracks and fissures may be observed ; and after a certain 
 time, especially when the painting has been exposed to moisture and a variable 
 temperature, it scales oflP, so that at last the glass becomes perfectly bare. It is of 
 importance to examine in every case whether the pigments agree well with the glass 
 in regard to expansibility, and it is frequently necessary either to vary the compo- 
 sition of the flux or to choose another kind of glass. 
 
 A carmine tint is given to the purple by adding to it a small quantity of chloride 
 of silver, previously fused with ten times its weight of the flux which is used for 
 the purple. 
 
 ® Here there is evidently some mistake in the original, this and the foregoing flux being perfectly identical. 
 
 . 7 parts. 
 
 . 3 „ 
 
 . 1 part. 
 
 . 7 parts. 
 
 1 part. 
 
 • 1 » 
 
 G 
 
42 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 As the purple from gold is prepared in different manufactories in a great variety 
 of ways, and the preparation is attended with various results, we shall conclude by 
 stating several methods, for which we are indebted to men whose reputation is great 
 in the scientific world. 
 
 According to Bastenaire Daudenart, the purple is prepared in the following 
 manner ; — 
 
 Nitric acid and gold are taken in the proportion of 8 parts, by weight, of the 
 former to 1 of the latter. In order, however, that the operation may be performed 
 with greater certainty, it is better, in case the acid should be more concentrated at 
 one time than at another, and in order that similar results may be always obtained, 
 to introduce gold into a retort until the acid is completely saturated. Especial care 
 must be taken that the solution of gold is in a perfectly neutral state. 
 
 The nitro-muriatic acid'^, for the solution of gold, is composed of 
 
 Nitric acid ...... 4 parts. 
 
 Muriatic acid’’ ...... 1 part. 
 
 The former acid is poured into a retort, which is placed in a heated sand-bath, 
 the muriatic acid is then introduced, and the liquid is at the same time stirred; a 
 few minutes after, the gold is thrown into it, a small piece at a time. Gold riband® 
 should be preferred, which may be bought at the goldbeater’s, or else the gold, if it 
 is at all thick, should be beaten very thin. 
 
 When the acid is observed to be incapable of dissolving any more gold, the 
 retort is taken out of the sand-bath and placed upon a layer of rushes of a concave 
 form, to receive the globular part of the retort. The liquid is left for some hours 
 by itself, after which it assumes a beautiful dark yellow appearance. 
 
 The solution of tin is likewise made with nitro-muriatic acid, but instead of 
 4 parts of nitric acid 6 are used, and the following compound is obtained ; — 
 
 Nitric acid ....... 6 parts. 
 
 Muriatic acid ...... 1 part. 
 
 Distilled water ...... 4 parts. 
 
 The solution of the tin requires infinitely greater care than that of the gold ; it 
 must take place without any effervescence, and very slowly. Tin leaf'’, such as is 
 used for covering mirrors, is selected for this operation. The solution takes place 
 
 ^ This is erroneously called “ Saltpetersaure,” nitric acid, in the original. 
 ^ Salzsaure. ® Des bandformigen Golblechs. Blattzinn. 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 43 
 
 without heat, and only a very small quantity at a time is introduced into the acid 
 which has been diluted with water ; e. g., pieces of tin leaf eighteen millimetres^ 
 square, one after another, for the space of twelve hours, until the acid is completely 
 saturated. 
 
 When hoth the solutions have heen prepared in this way, the one is precipitated 
 with the other ; and this is the moment when it is the most difficult to obtain a 
 beautiful purple. Many persons have been quite discouraged, and have given up 
 even attempting to prepare this colour, because they have undertaken the operation 
 too carelessly, when, in fact, it requires great nicety, or because they have not clearly 
 understood the theory of the phenomena which take place in the mutual decom- 
 position of the two soluble salts. Care must first be taken that both the solutions 
 are very considerably diluted with water, for without this precaution gold is preci- 
 pitated by the tin in a metallic state, which causes such a cohesion of the minute 
 particles of the metal, that the desired results cannot be obtained in the precipitate. 
 To avoid this disagreeable occurrence, which renders the whole operation fruitless, a 
 large glass vessel, three parts full of distilled, or at all events very pure water must 
 be taken, and into this a certain number of drops of the solution of gold must be 
 poured. The number of drops must be in proportion to the size of the vessel. 
 Suppose the vessel is capable of containing one litre^ of water, as much as eighteen 
 drops of the solution of gold may be dropped into it. This done, the liquid is 
 stirred with a piece of the tube of a barometer, and it must then be of a pale yellow 
 colour, but very clear ; eight, ten, or twelve drops of the solution of tin are then 
 dropped into the vessel, and care is taken to stir the mixture well, just while the 
 solution is being dropped. As soon as the liquid is observed to have assumed a 
 colour like that of red wine, no more solution of tin is added, (we should suppose 
 that this would take place at the sixth drop,) because if the process be continued 
 after the beautiful red colour has appeared, only a purple is obtained which 
 approaches too near to violet. 
 
 There must be a large vessel of porcelain, or well-glazed Delf ware", ready to 
 receive all the red liquid which is transferred from the glass vessel into which the 
 solution of tin was dropped. Accordingly, when the liquid in the latter vessel is 
 well saturated with the purple colour, it is introduced into the large vessel of Delf 
 ware, and a fresh quantity of water is poured into the glass vessel, and then eighteen 
 drops of the solution of gold. Whilst the solution of tin is being dropped the liquid 
 
 ^ The metre is 39.37079 English inches; the millimetre^ being the 1000th part of the metre^ is therefore 
 equivalent to .03937079 inches. 
 
 ^ The litre, or cubic decimetre, is .22009687 of an imperial gallon. ' Fayance. 
 
 G 2 
 
44 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 is stirred with a glass rod ; the drops of the solution of tin must never amount to 
 more than tvro-thirds of those of the solution of gold, especially if the purple is to be 
 of a beautiful rose colour. 
 
 When as much gold and tin as is considered necessary has been precipitated, all 
 the water which has been coloured red is poured together, and then left undisturbed. 
 In the course of twenty-four hours a reddish-brown precipitate settles at the bottom 
 of the Delf ware vessel. To hasten this subsiding, one or two pinches of kitchen salt 
 may be thrown into the red liquor. Some writers have also recommended the ad- 
 dition of a certain quantity of fresh urine ; but some solution of phosphorus may be 
 more advantageously substituted for the latter. In other respects, it is far better 
 that the subsiding at the bottom of the vessel should take place slowly and of itself, 
 and in that case the supernatant liquor must be perfectly clear. This is poured off, 
 and the remainder edulcorated several times with plenty of water : the precipitate is 
 collected upon a piece of white paper, and dried in the shade. In the course of a 
 few days it is easily removed from the paper, whereupon it is put away in a wude- 
 mouthed bottle with a greased stopper, and kept from the light. 
 
 The formation of the purple proceeds : — 1, from the elective affinity of gold and 
 tin ; 2, from the high state of oxidation of the tin ; and 3, from the circumstance 
 that the solutions are diluted with a great quantity of water, to weaken the affinity of 
 the acid for the oxides as bases ; for so long as the metals (gold and tin) are inti- 
 mately combined with the acids in which they are dissolved, there is no chance of 
 obtaining a purple of a beautiful colour. 
 
 Moreover, all the precipitates which are obtained by means of gold and tin differ 
 from one another in a variety of circumstances. The quantity of water poured into 
 the first vessel, namely, mto that into which the solution of tin is dropped to mix with 
 the solution of gold j the number of drops of the solution of tin in proportion to the 
 number of those of the solution of gold ; the purity of the water in which the preci- 
 pitation is effected : all these circumstances might produce a great variety of tints. 
 However, in general the purple is the more disposed to assume a violet colour when 
 the precipitate contains a greater quantity of tin in proportion to the gold ; on the 
 other hand, the purple is more beautiful or more rose-coloured, the more solution of 
 gold the precipitate contains. It is therefore quite at the option of the experimenter 
 to prepare a more or less beautiful purple, if he only act upon this intimation with 
 proper care. Proust and Oberkampf “ have analyzed several red and violet-purple 
 precipitates ; they found in a beautiful rose-purple, — 
 
 ® Annales de Chimie, T. Ixxx. et Ixxxvii. — (^Note of the Author.) 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 45 
 
 20.58 oxide of tin, and 
 79.42 gold, 
 
 and in a violet purple precipitate, 
 
 60.18 oxide of tin, and 
 39-82 gold. 
 
 According to Berzelius, the purple contained — 
 
 28.35 oxide of gold, 
 
 65.00 oxide of tin, 
 
 7.65 water. 
 
 According to Buisson, the purple precipitate contains — 
 
 28.50 gold, 
 
 65.00 oxide of tin, 
 
 5.20 chlorine. 
 
 Cassola, Professor of Chemistry at Naples, gives the following receipt for the 
 preparation of the purple. 
 
 Hydrochlorate of gold is prepared in the usual way : at the same time, tin filings 
 are digested in vinegar for two or three days, and the solution is filtered. The so- 
 lution of gold is then diluted with four or five times its weight of water, and the 
 solution of protacetate of tin is generally poured into it until the red precipitate has 
 formed ; it is then washed and bottled up. 
 
 Cassola asserts that he obtained the same results by using a solution of protoni- 
 trate of tin, procured from tin filings, dissolved in concentrated nitric acid which 
 had been diluted with fifteen parts of water. According to what he says, this solution 
 of protonitrate of tin must not be used until it has been for two days in contact with 
 the tin. Both solutions — that of the tin and that of the gold — must be mixed cold, 
 in which case a purple precipitate, without a tinge of black, is immediately produced. 
 Cassola, however, prefers the process with acetate of tin. He also employed proto- 
 sulphate of tin, diluted largely with water, for the precipitation from the solution of 
 gold, and obtained the same favourable results. The same phenomenon, however, 
 with regard to the colour of the precipitate, takes place in precipitating with sulphate 
 of tin, if it is used in excess, as if muriate of tin is employed in too great a quantity. 
 
 A beautiful purple may also be obtained by the following method : — 1 part thin 
 gold leaf is dissolved in aqua regia, the solution is poured into a glass, and diluted 
 with 15 parts rain water; a solution of parts clean tin filings in muriatic acid, 
 which has been allowed to cool, is added, and at the same time the mixture is con- 
 tinually stirred. After it has remained a quarter of an hour undisturbed, ^ part 
 
46 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 clean urine is poured into it, and the whole is well stirred. About two hours after- 
 wards the liquor is poured away from the purple, which has now subsided, and the 
 latter is completely edulcorated. 
 
 According to Stegers, a very beautiful purple is prepared in the following 
 manner; — 
 
 Fine gold is dissolved in aqua regia. If the gold has been alloyed with silver, 
 the solution is poured away from the precipitated chloride of silver ; the latter is 
 washed with distilled water and added to the solution, which, without being filtered, 
 is evaporated with a moderate heat until a thick incrustation of crystals is formed, 
 and only a little of the red solution hubbies up from under the incrusted surface 
 when the vessel is inclined on its side. The whole is now left to cool, whereby it 
 gradually solidifies throughout, and is dissolved without delay in ten times its weight 
 of water ; to avoid the attraction of moisture, the solution is filtered, and a small 
 quantity of metallic gold is left behind. In order to wash out the filter, a portion is 
 reserved out of the water, which has been accurately weighed, and this is afterwards 
 added to the solution. The crystallized salt of tin of commerce is quite good enough 
 for the purpose ; if it is moist, it should be dried between printing-paper. One part 
 of this salt is dissolved in four parts of distilled water; the solution is filtered and 
 used immediately, because in time it becomes turbid, owing to its attracting oxygen 
 from the air, and submuriate of tin is deposited in the form of a white powder. Next, 
 1 part of gum arabic is dissolved in 3 parts of hot distilled water, and the so- 
 lution is filtered through gray blotting-paper, because printing-paper, on account of 
 its greater closeness, impedes the passage of the glutinous fluid. When the three 
 liquids have been prepared in the foregoing manner, 20 grains of the solution of gum 
 are mixed with 3 ounces of distilled water, and, after careful stirring, 14 grains of 
 the solution of tin are introduced. The vessel in which the latter was weighed out 
 is rinsed with a little water, the whole is then mixed with 23 grains of the solution of 
 gold, and the vessel which contained it is likewise rinsed, not with water, but with 
 the mixture itself. The colour which arises from the above-mentioned proportions 
 of these ingredients is a fiery reddish-brown ; it is only in the fire, when this pre- 
 paration is used for glass-painting, that it developes a purple unequalled in beauty. 
 The colour may be slightly affected by the action of the acid which has been disen- 
 gaged by the formation of the purple in the liquid ; hut this is obviated by diluting 
 the solution with twice its weight of water, dissolving 10 grains of bicarbonate of 
 potash in it, and mixing with it, according to the above direction, some of the solution 
 of tin containing gum. 
 
 To separate the purple, whose precipitation is at present retarded by the gum. 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 47 
 
 alcohol is added to the mixture until it grows very turhid ; for this purpose about 
 twice its weight of 7-5 per cent, spirit is required, that is to say if hicarhonate of 
 potash has heen used, otherwise three times is necessary. In the course of an hour, 
 if the solution has heen occasionally stirred during this time, the purple is precipitated 
 in reddish-hrown flakes, and the surpernatant liquor remains clear, with only a slight 
 tinge of colour. This is decanted, and the precipitate is then washed with some more 
 spirits of wine ; it is strained through a filter of printing-paper, gradually deprived 
 of its moisture hy being squeezed with the latter through blotting-paper, removed to 
 a rubbing saucer, and then ground with weak 50 per cent, spirits of wine to a thin 
 paste, which is boiled for three minutes in a vessel proper for the purpose, and then 
 poured into a cylindrical glass. As soon as it has subsided in this vessel, the liquor 
 is poured away, and is replaced by twice as much water. This operation is repeated, 
 hy which means the gum is removed, all except a slight residue, which can do no 
 harm. Should the purple subside very slowly from the last liquor, and form a dense, 
 almost transparent, red stratum over the sediment, a fact which proves a disposition 
 to be dissolved, the water must be poured away, and a small portion of strong alcohol 
 must again he added to the remainder, in order that the purple may coagulate rather 
 more densely, and the last addition of liquid may be filtered. In either case, the pre- 
 cipitate from which the liquor has been strained is pressed, as before, with the filter, 
 between blotting-paper, and while moist is scraped off with a blunt knife and dried 
 in a porcelain saucer, whereby it diminishes considerably in bulk and becomes of a 
 perfectly dingy colour. 
 
 According to Buisson, the purple is prepared with the greatest certainty in 
 the following manner ; — 1 gramme of the purest tin is dissolved in a sufficient quan- 
 tity of muriatic acid. The solution must be neutral. Further, 2 grammes of tin 
 are mixed with aqua regia, composed of 3 parts of nitric acid and 1 part of 
 muriatic acid, so that the solution contains no protochloride of tin. Lastly, 
 7 grammes of fine gold are dissolved in a mixture of 1 part of nitric acid and 
 6 parts of muriatic acid, and this solution must likewise be neutral. The latter 
 is diluted with 5^ Utiles of water, the solution of perchloride of tin is added to it, 
 and that of the protochloride is introduced a drop at a time, until the precipitate 
 that is being formed possesses the requisite colour. This precipitate is edulcorated 
 as quickly as possible. 
 
 It is of importance to know that the perchloride and the protochloride must not 
 be produced separately, but both the chlorides at the same time, to enable us to 
 obtain the purple from chloride of gold ; and that it is further requisite that the 
 three chlorides should he prepared for use perfectly free from acid. 
 
48 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 Herr G. Creuzburg®, a practical chemist, particularly recommends, in the pre- 
 paration of the purple, the use of a solution of tin chemically pure ; he therefore 
 advises that the broken tin ore should he first treated with nitric acid, which dis- 
 solves all other foreign metals and converts the tin into an oxide. After the blue 
 solution which contains the foreign metals, and among others copper, has been 
 poured away from the oxide, which is in the form of a white powder, and the latter 
 has been washed, dissolved in muriatic acid, and inspissated, chloride of tin, chemi- 
 cally pure and free from acid, is obtained. It now only remains to observe, that 
 perchloride of tin, digested with metallic tin, gives protochloride of tin. When the 
 two solutions of tin have been prepared in this manner, the remainder of the opera- 
 tion is performed according to Buisson’s method. After a few slight preliminary 
 experiments have been shown about the maximum of perchloride of tin that the so- 
 lution of gold will bear, in order to give the purple with the protochloride, the requi- 
 site quantity of perchloride is poured all at once into the very dilute solution of gold, 
 which is not thereby rendered turbid, and a slow precipitation is produced by 
 the introduction of the protochloride, very much diluted, until the purple tint 
 appears. 
 
 It was now a still more difficult task to find a suitable flux and other ingredients, 
 in order to obtain a beautiful enamel colour. At last it was discovered that anti- 
 mony and white enamel were the substances which, when mixed with the flux, were 
 capable of lightening the tint of fine purple, so that the rose colour was particularly 
 beautiful. The addition of metallic silver and chloride of silver, by which the purple 
 colour used formerly to be brought out more strongly, was not applicable to this 
 purple, and gave a useless colour, mingled with a horny-looking yellow, even on the 
 addition of a very minute quantity of these substances. 
 
 Porcelain, of different kinds of glazing, gave various tints with one and the same 
 purple. 
 
 Herr Creuzburg observes, that antimony not only brings out the purple tint more 
 finely than any thing else, but also gives considerably more body to the colour, so that 
 it bears more flux, and consequently a given quantity goes further. 
 
 Persons who were experienced in the preparation of a beautiful purple, and with 
 whom he was personally acquainted, assured him that they never used the precipitate 
 of Cassius in the preparation of their finest purple, unless they had obtained it acci- 
 dentally. According to their assertion, the precipitate, which is of a grey colour 
 
 3 Journal fiir praktische Cliemie, herausgegebeii vom Prof. Erdmann und Prof. Schweigger-Seidel. 
 Bd. ix. Heft. 6 . — {Note of the Author.) 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 49 
 
 approaching to violet, should give the most heautiful purple ; the dirtier the co- 
 lour of the precipitate, the more brilliant the purple which it gives when fused. 
 This dirty precipitate should contain more gold, and urine should be employed in 
 its preparation. 
 
 Frick, the privy counsellor of the mines, gives the following process for the 
 preparation of the purple : — Tin is dissolved in very dilute aqua regia, without the 
 application of heat, until the liquid begins to assume slightly the appearance of opal ; 
 the tin is then taken out and weighed, the liquid is diluted with a very great quan- 
 tity of water, and some dilute solution of gold and dilute sulphuric acid, in certain 
 given weights, are simultaneously poured into it whilst the mixture is being stirred. 
 The quantity of the solution of gold to he poured into the solution of tin must be 
 such that the weight of the gold will be to that of the tin as 36 to 10. 
 
 We are indebted to Professor Fuchs, of Munich, for a remarkably simple method 
 of preparing the purple. A solution of permuriate of iron is added to a solution of 
 protochloride of tin until the former loses its colour and assumes a greenish tinge. 
 The mixture is then diluted with water, and some of it is poured into the solution of 
 gold which has been properly diluted. The most beautiful purple is immediately 
 produced, while the protoxide of iron remains in the solution without having any in- 
 jurious effect. The precipitate becomes lighter coloured in drying, and appears as 
 a dirty brown powder, 
 
 Herr C. F. Capaun considers the method of Professor Fuchs the best, judging 
 from his own experience, but recommends the following process in the preparation of 
 the purple powder ; — 
 
 Let a solution of chloride of iron (the liquor f err i muriatici oxydati of the Prus- 
 sian pharmacopoeia) be diluted with 3 parts of water, to which let a solution of 
 protochloride of tin, prepared from 1 part of protochloride of tin dissolved in 6 
 parts of distilled water by means of a few drops of muriatic acid, he added, until the 
 mixture has assumed a greenish colour. Let this mixture be further diluted with 
 6 parts of distilled water and kept ready for use. If both the solutions were to be 
 diluted at once with the whole quantity of ivater, the transition of the brown into the 
 greenish colour would not be so clearly perceived. In the mean time, let pure mu- 
 riatic acid be poured upon so much gold as is required for the operation ; let the 
 whole he heated to boiling, and pure nitric acid be introduced in small quantities at 
 a time, until all the gold is dissolved : an excess of acid, especially nitric acid, should 
 be avoided. To this solution let a portion of distilled water (360 times that of the 
 gold to be used) be added, and some of the solution of iron and tin be poured into the 
 mixture, whilst it is being stirred, as long as precipitation takes place. The precipi- 
 
 H 
 
50 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 tate will be of a beautiful purple, when dry will appear browTier, but will dissolve in 
 ammonia and fused pigments with an intense purple colour. 
 
 Dr. Bolley, however, could not always obtain exactly the same preparation ac- 
 cording to the above method 5 he therefore attempted to procure a solution of the 
 sesquioxide of tin in another way. The combination of chloride of tin and chloride 
 of ammonium, {pinksalt as it is called — a salt consisting of an equal number of atoms 
 of chloride of tin and chloride of ammonium,) seemed very well adapted to this pur- 
 pose. This salt is anhydrous, and not affected by the air, so that when exposed to 
 dry it undergoes no changes which would be likely to induce an unscientific chemist 
 to adopt wrong methods of proceeding. It contains an accurately balanced quantity 
 of chloride of tin not liable to change, and this very circumstance renders it adapted 
 to the preparation of the oxidized matter which lies half-way between the protoxide 
 and the peroxide. 
 
 Dr. Bolley does not recommend the production of this sesquisalt of tin by the use 
 of a prescribed weight of protochloride of tin dissolved in water containing muriatic 
 acid, because any directions for doing this would be uncertain on account of the various 
 quantities of water which the salt of tin contains, and partly on account of the in- 
 creased oxidation of the latter ; experience alone teaches us that perchloride of tin 
 boiled with tin can be converted into the protochloride, and consequently, if the right 
 quantity of tin be used, into the sesquichloride. According to Dr. Bolley’s experi- 
 ment, perchloride of tin combined with sal-ammoniac is the same in this respect as 
 perchloride by itself, lire pink salt contains 70*8 pe^^' cent, perchloride, of which 
 32.3 per cent, is tin : if this amount of tin be increased by one-third, the quantity of 
 chlorine remaining the same, sesquichloride will be produced from the perchloride. 
 Consequently 100 pinksalt requires 10. 7 metallic tin. Dr. Bolley subjected 
 and tin in the proportion we have specified, together with water, to the action of heat 
 until the tin was dissolved ; he then used the solution for the precipitation of the 
 purple. 
 
 We now proceed to give a more detailed account of the experiment. 1.34 
 grammes of gold were dissolved in nitro-muriatic acid, an excess of acid being care- 
 fully avoided, and the solution was diluted with 480 grammes of water, the propor- 
 tion specified by Capaun. To 10 grammes of dry pinksalt he added I.07 of tin 
 filings ; 180 grammes of water were weighed out, and of these about 40 grammes 
 were immediately brought in contact with the tin and pinksalt, and heat was applied 
 until the tin was dissolved. The solution was now mixed with the remaining 140 
 grammes of water, and some of it was gradually introduced into the slightly warmed 
 
 ® Pinksalz. 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 51 
 
 solution of gold until all precipitation ceased ; the precipitate soon subsided, was 
 taken out of the filter, washed and dried at the temperature of 100° C.; it weighed 
 4.92 grammes, and had become dark brown. The strained liquor was yet only of a 
 pale red colour. The precipitate dissolved when digested in strong ammonia. The 
 gold which it contained (calculating from the quantity of gold consumed) amounted 
 to 21. 4 per cent., a result which is most in accordance with Fuchs’ analysis of the 
 purple : he found in it 19 per cent, gold. In either case, every one v/ho is engaged 
 in the preparation of the purple for the purpose of applying it to the arts, will find 
 in what we have stated an infallible means of obtaining the most efficacious propor- 
 tions of the peroxide and the protoxide of tin that have yet been discovered. 
 
 OF THE BLUE. 
 
 The blue pigment receives its colour from oxide of cobalt, and belongs to the 
 class of fused pigments which are coloured by chemical combination. The oxide of 
 cobalt combined with silica and boracic acid acts as base. This pigment is also one 
 of those which require to he fused before they are employed. As the peroxide is the 
 most easily prepared of all the oxides of cobalt, it is usually mixed with the flux, for 
 we know that it passes into protoxide at a high temperature. This change takes 
 place much more rapidly and more effectually when assisted by the action of a fixed 
 acid. The presence of the flux satisfies the latter condition. The peroxide of cobalt 
 is reduced in contact with silica and boracic acid, and readily unites with them in 
 the state of protoxide. The ease with which the reduction and combination take 
 place is naturally in proportion to the abundance of silica or boracic acid in the flux. 
 But if, on the contrary, the flux contains too great a quantity of base, the cohalt upon 
 which the action of the acids is now less powerful, is reduced with difficulty to the 
 state of protoxide, and requires an intense heat to effect a perfect combination. And 
 even then the colour is seldom pure, and a blackish blue tint is usually obtained. 
 Another circumstance, viz,, impurity, contributes to impede the solution of the cohalt 
 in the flux. There are even anterior combinations of cobalt with certain oxides, 
 which, whenever they happen, render it extremely insusceptible of the action of the 
 flux. In this case it very frequently assumes a greenish tint. It is therefore evi- 
 dent, that every thing which contributes to resist the conversion of the peroxide into 
 the protoxide opposes the combination of cohalt with the acids of the flux. The whole 
 resistance lies in this ; for if the protoxide is for a moment produced, it is rapidly 
 absorbed again, as will appear from the following remarks. 
 
 H 2 
 
52 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 Certain necessary conditions of expansion frequently require that the vitrification 
 of the cobalt, contrary to the directions we have given, should be etFected in very sa- 
 turated fluxes. In such a case, its combination is assisted in a remarkable manner by 
 the following process. If a certain quantity of oxide of antimony be added to the per- 
 oxide of cobalt at the moment of its mixture with the flux, by virtue of its great alfi- 
 nity for the oxygen, it rapidly and completely eflects the reduction of the peroxide of 
 cobalt. The antimonious acid which is thereupon produced does not injure the purity 
 of the colour in the slightest degree, and does not perceptibly impair the transparency, 
 provided that too much oxide of antimony is not used. It is extremely probable that 
 the protoxide of tin produces the same effect. 
 
 A mixture of oxide of zinc and peroxide of cobalt produces the same effect in 
 another way. The remarkable endeavour of the oxide of zinc to enter into various 
 combinations with the protoxide of cobalt affects the peroxide in the same way as the 
 silica itself. 
 
 Phosphoric and arsenic acid likewise favour the solution of protoxide of cobalt in 
 the fused pigment, whether they are added in an isolated state, or in combination 
 with the cobalt itself, that is to say, in the state of phosphorates and arseniates. In 
 the former case, they act by increasing the quantity of the acids ; in the latter, be- 
 cause they contain cobalt in the state of protoxide. It is then only necessary to mix 
 them with the flux. 
 
 We have said that the peroxide of cobalt is generally employed in order to obtain 
 silicate of cobalt, which colours the fused pigment blue. The principal reason why 
 this is chosen is, that if protoxide were used it wmuld be converted into peroxide be- 
 fore the combination is effected, because it burns at a red heat. The carbonate would 
 furnish the same result. But a combination of oxide of cobalt with oxide of zinc, 
 which resists the action of heat better, may be employed with advantage. This com- 
 bination is obtained by dissolving 1 part of sulphate of cobalt and 2 parts of sul- 
 phate of zinc in a sufficient quantity of water. Into this liquid a solution of sub- 
 carbonate of potash is poured until no more precipitate is produced. This precipi- 
 tate is placed in the filter, washed and dried, and is then the composition which was 
 required. 
 
 Not only does the oxide of cobalt produce the richest colour of all the oxides, 
 but also a very small quantity only is necessary to impart a very deep colour to the 
 fused pigment. The blue pigment is composed as follows : — Peroxide of cobalt 1 
 part, or zincate of cobalt 3 parts, flux from 6 to 9 parts. 
 
 The flux which is used for the blue pigment is one of the three which we have 
 specified among the fluxes for pigments of the second class. The flux and the oxide 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 53 
 
 are levigated together, the mixture is put into a crucible which is kept at a red heat 
 until the contents are perfectly fused and all ebullition has ceased ; the pigment is 
 then poured into cold water, dried, and levigated. 
 
 The oxide of cobalt is employed in various proportions according to the 
 strength or weakness of the colouring. The taste of the artist is easily satisfied in 
 this respect. 
 
 As far as regards the blue pigments of the ancients, they are the best of all their 
 compositions. The receipts of Felibien and Haudicquer de Blancourt, which we pos- 
 sess, afford a very excellent coloured glass. The blue pigments that Levied and the 
 brothers Recollet used to employ seem to have been drawm from the same source, 
 although the imitation is not very correct. This pigment was composed in the fol- 
 lowing manner : — 
 
 Minium .... 1 part 
 
 Oxide of cobalt . . . . 1 ,, 
 
 Silica ..... 4 parts 
 
 Nitrate of potash . . . 3 ,, 
 
 It is a quadrisilicate, and reminds us of M. Guinant’s composition of flint glass. 
 For f2 atoms of oxide of lead, 2 atoms of protoxide of cobalt are substituted here. 
 
 This enamel, like the majority of the ancient ones, is not capable of being used 
 as a pigment, on account of its slight fusibility. However well it might have been 
 adapted to the window-glass “ of the ancients, it is certainly unfit for the glass of the 
 present day, which is much more fusible. 
 
 The saturating point of this pigment was applied by the ancients to other co- 
 lours, particularly to green, on account of which we have dwelt longer upon it than 
 we should otherwise have done. 
 
 OF THE YELLOW. 
 
 The fused pigments may be coloured yellow by a great number of substances. 
 
 A lively and brilliant colour is obtained by means of metallic silver. The oxide 
 of uranium by itself, when dissolved in a flux, furnishes also a beautiful yellow ; 
 but, in most cases, those oxides which are used as colouring materials are combined 
 with one another by twos, and often in greater numbers. Thus, e. g., we combine — 
 
 Protoxide of lead with antimonic acid ; 
 
 Protoxide of lead with oxide of iron ; 
 
 ® Scheibenglas. 
 
54 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 Oxide of zinc with oxide of iron ; 
 
 Oxide of iron with antimonic acid. 
 
 Other compounds likewise furnish useful yellow pigments. Among these are chlo- 
 ride of silver, chromate of lead, &c. 
 
 Each of these colouring substances produces the colour which belongs to it. 
 
 Silver gives a yellow varying from siskin yellow to purple. 
 
 The oxides of lead and antimony also furnish a siskin yellow, but it is opaque. 
 
 The oxides of zinc and iron give an ochre-coloured yellow. 
 
 Chromate of lead, too, yields a very lively yellow tint, &c. 
 
 Among all these colouring substances, the chloride of silver, zincate of iron, 
 and antimoniate of lead, are considered the best. The three tints which are pro- 
 duced by these colouring materials satisfy all the requirements of glass-painting. 
 
 YELLOW FROM SILVER. 
 
 This colour is obtained without the intervention of a flux. The process consists 
 in covering those parts of the glass that are to be stained with a paste composed of 
 chloride of silver and calcined yellow ochre, both levigated together with water. After 
 the glass has been heated to a red heat in the muffle, the layer of ochre which ad- 
 heres to the surface is removed by means of a spatula, and the glass is found to he 
 stained. The yellow obtained in this way varies from siskin yellow to purplish yel- 
 low. It is not always, however, at the option of the artist to obtain any of these 
 tints whatsoever, for some kinds of glass are stained by this process only bright light 
 yellow, while others are capable of receiving a deep orange colour. The orange 
 colour is frequently only to be obtained by repeating the process once or twice. 
 
 That kind of glass which, when plastered over with clay, is most disposed to lose 
 its glaze\ and which partly or entirely gives up the potash which it contains, seems to 
 receive the best colour. 
 
 Dumas is of opinion that the white kinds of glass, those which contain a great 
 quantity of aluminum, are the best for staining with silver, and they are the very 
 kinds which, according to this chemist, can he the most easily deprived of their glaze. 
 In the act of parting with their glaze, which is eflected by the assistance of a paste®, 
 a formation of certain silicates which crystallize, and a separation of a part of the 
 bases, take place. Those of them which are volatile, e. g. the alkalies, are disengaged, 
 and the fixed oxides, e. g. those of iron and manganese, pass into the state of sesqui- 
 oxide. 
 
 ^ Zeisiggelb. Sich zu entglasen. 
 
 ' Cement. 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 55 
 
 This is the case with regard to the separation of a portion of soda or potash, 
 upon which the colouring of the glass by means of silver depends. When the glass is 
 covered with the paste of clay with which chloride of silver is mixed, and exposed 
 to a red heat, the chloride is volatilized, its vapour saturates the glass, and as soon as 
 it comes in contact with the potash which has been liberated, the silver is reduced 
 to the metallic state ; chloride of soda or chloride of potash is produced and vola- 
 tilizes, while the metallic silver is fixed upon the surface, and often even pene- 
 trates a considerable depth into ihe body of the glass. If the quantity of reduced 
 silver is small, the colour is siskin yellow. If it is more considerable, the yellow be- 
 comes deeper, and passes over into a more or less intense red. 
 
 The latter colour may be obtained in less time, and with greater certainty, by 
 using glass with which a certain quantity of chloride of silver has been mixed at the 
 moment of its manufacture. For this purpose the glass must be well refined, and 
 contain no excess of uncomhined alkali by which the chloride of silver would be 
 reduced too soon. The colouring is then effected in the manner we have already 
 described. 
 
 That it is the reduced metallic silver which produces the colour in the glass has 
 been demonstrated by very decisive experiments. 
 
 If we take glass with which ^Vo-th of its weight of chloride of silver has been 
 mixed, heat it red hot, and in this state cause a stream of hydrogen gas to pass over 
 its surface, the glass immediately receives an intensely red colour, which result is like- 
 wise obtained by covering the glass with pure clay. In the former case, the action of 
 the hydrogen gas upon the chloride of silver is manifestly the principle upon which the 
 colouring of the glass depends. Now the action of this gas consists in reducing the 
 silver to the metallic state ; for if the quantity of chloride of silver be increased, the 
 surface, when acted upon by the hydrogen gas, is covered with a stratum of silver 
 possessing a metallic lustre. 
 
 The same colour is also produced, as we have stated, by the surface being in con- 
 tact with a layer of clay, and we believe that the nature of the process by which it is 
 produced is exactly the same. It does not appear, however, as if the clay effected 
 this by an immediate action, that is to say, by the reduction of the chloride of silver. 
 We attribute this action to one of the phenomena which accompany the depriving the 
 glass of its glaze, namely, to the volatilization of the potash. 
 
 Even up to the present day, the staining the glass yellow has been attributed to the 
 oxide of silver ; but experience incon trove rtibly proves that this effect is produced by 
 
 ^ Wasserstoffrap. 
 
56 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 metallic silver. In this there is a striking analogy between the manner of colour- 
 ing of the latter and that of gold. The yellow or red colour proceeds from the 
 silver in a state of extremely fine division, and the purple from gold in the same 
 condition. 
 
 When the silver is in such a state of division as to be capable of colouring the 
 glass, it only continues so under certain conditions. Accordingly, as soon as ever the 
 vellow is produced, care must be taken not to let the glass pass into the state of fusion, 
 for in the disturbance produced by the motion of the liquid mass the particles of 
 silver assemble in larger groups, from whence arises a new colour in place of the 
 former. The silver in this state of less minute division assumes a very intense blue 
 colour. Hence we arrive at this practical conclusion, viz., that silver is only capable 
 of colouring glass at that moment of its formation at which it has been brought to 
 the proper density, and that for the colouring of fused pigments it can only be used 
 within certain limitations of fusibility at a heat which the glass shall be able to bear. 
 
 We have one or two more words to say upon the preparation of the paste for the 
 yellow. Ferruginous clay is used, commonly known by the name of yellow ochre. 
 This clay must be calcined, otherwise the paste which is laid on the glass would he 
 full of cracks, in consequence of the diminution in hulk which clay undergoes when 
 exposed to a strong heat. Those parts of the glass which correspond to these cracks 
 would then receive no colour. Consequently, the yellow ochre must he raised to at 
 least as high a temperature as the glass in the muffle. 
 
 The relative quantities of chloride of silver and burnt ochre are as follows ; — 
 Chloride of silver . . . .1 part. 
 
 Ochre ...... From 6 to 12 parts. 
 
 A greater proportion of chloride of silver would cause the paste to adhere too 
 strongly to the glass. The chloride of silver and the clay are carefully rubbed upon 
 a glass plate with a sufficient quantity of water to form a paste, which is applied in a 
 thick layer to the surface of the glass by means of a paint-brush. 
 
 This yellow is frequently employed to give brilliancy and liveliness to the red 
 obtained from iron. In this case it is applied to the side opposite to the painting. 
 
 Chloride of silver, by itself, is also capable of staining the fused pigments yellow ; 
 hut then it imparts to them a colour of its own, if it mixes with them without being 
 decomposed. Here metallic silver is not the cause of the colour. The chloride of 
 silver must he fused with its flux in the proportions of from 1 to 2 parts of the former 
 to 10 of the latter. When united with one of the fluxes for pigments of the first class, 
 it is used as a mixture for the flesh-red to give it brilliancy. With the purple it pro- 
 duces a carmine tint, and only a very small quantity requires to he mixed with it. 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 57 
 
 The yellow pigment which chloride of silver furnishes can also be employed in 
 an isolated state. 
 
 ORANGE COLOUR FROM SILVER^ 
 
 This orange colour is only a shade of the yellow from silver which we have been 
 speaking of, and is likewise prepared in the same way, except that for chloride sul- 
 phuret of silver in the same proportions is substituted. Similar phenomena may be 
 observed during the process, and metallic silver is always the element of the colour. 
 Orange-yellow is obtained with much greater certainty from sulphuret of silver, while 
 on the other hand chloride of silver answers much better for a light yellow, although 
 it is not always in our power to produce any given colour. 
 
 RED FROM SILVER b. 
 
 A red colour is also infallibly obtained by using sulphuret of silver. In this case 
 the preparation which was employed for the orange-yellow is slightly modified by 
 adding a few drops of sulphuric acid at the moment when it is being used. If no 
 red be obtained at the first laying on of the pigment it must be laid on a second time. 
 
 The sulphuret gives an intense colour with much greater certainty than the chlo- 
 ride of silver, for at a red heat it decomposes of itself, and can therefore produce its 
 effect without the aid of the unglazing. The latter, however, is not prejudicial to it, 
 and is only to facilitate the saturation of the glass by metallic vapours. The mixture 
 of sulphuric acid has, in our opinion, no other object than this. Some sulphate or 
 other is undoubtedly formed by the agency of this acid, which is decomposed in the 
 red heat by the silica of the clay and occasions the internal motion of the glass, 
 whilst it affects its surface. This is what actually takes place in the unglazingof the 
 glass, which unglazing we are convinced is effected by means of a mixture of sand and 
 sulphate of lime. 
 
 The unglazing which is capable of facilitating the colouring of the glass by silver 
 is not so great a change in the glass as to deprive it of all its transparency, but merely 
 a slight modification by which its properties are uninjured. It is worth observing, 
 however, that a piece of glass stained red in this manner does not possess the purity 
 of colour which belongs to one coloured by copper. When the tone of colour is the 
 same for both, that which was coloured by silver appears the darker. 
 
 Sulphuret of silver is prepared in the following manner : — Pure silver is melted in 
 
 ® Silverorangegelb. b Silberroth. 
 
 I 
 
58 
 
 OF THE PIGMENTS IN PARTICULAE. 
 
 a crucible, half its weight of sulphur is then introduced. The sulphuret of silver 
 which is generally used is prepared hy heating together 2 parts of silver and 1 of sul- 
 phuret of antimony. 
 
 OCHRE YELLOW^. 
 
 The ochre yellow pigment is one of those fused pigments which are coloured by 
 mixture. It receives its colour from the mixture of oxide of zinc and oxide of iron. 
 This fused colour is a zincate of iron in which each atom of the one oxide is com- 
 bined with an atom of the other oxide. This salt is obtained from sulphate of iron 
 and sulphate of zinc precipitated with potash, soda, or their carbonates. 
 
 The persulphate of iron is prepared by dissolving 96 parts of protosulphate of iron 
 in 100 parts of water, and adding half as much sulphuric acid as the salt already con- 
 tains. The solution is heated to boiling, when small portions of nitric acid are intro- 
 duced, until all nitrous acid has ceased to be disengaged. This operation may be 
 explained in the following way ; — 
 
 The protoxide of iron contains. 
 
 1 atom of iron .... 
 
 . 339.21 
 
 1 
 
 „ „ oxygen 
 
 . 100. 
 
 1 
 
 OjCIcI * • « • 4 
 
 . 501.16 
 
 1 
 
 ,, ,, protosulphate of iron 
 
 . 940.37 
 
 The persulphate of iron consists of, 
 
 
 2 atoms of iron . . . , , 
 
 . 678.43 
 
 3 
 
 „ „ oxygen . . . , 
 
 . 300. 
 
 3 
 
 9 9 9 9 clCld. • a • • < 
 
 . 1503.48 
 
 1 
 
 ,, ,, persulphate of iron 
 
 . 2481.91 
 
 It is therefore necessary for the obtaining 1 atom of persulphate of iron to add to 
 2 atoms of protosulphate of iron 1 atom of sulphuric acid, that is to say, half as much 
 as the salt already contains, and 1 atom of oxygen besides, which is supplied by the 
 nitric acid. 
 
 The protosulphate of iron, when crystallized, contains 44 — 45 per cent, water, and 
 the sulphuric acid of commerce contains only 81.68 per cent, pure acid. Conse- 
 quently 18 parts of the sulphuric acid of commerce must be added to 100 of crystal- 
 lized protosulphate of iron. 
 
 In order to form zincate of iron, so that each atom of the one oxide shall be com- 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 59 
 
 bined with an atom of tbe other oxide, a solution of persulphate of iron and another 
 of sulphate of zinc, both having the same weight on the areometer, must be prepared 
 separately, and so much in volume must be taken from each, that the salt of zinc may 
 be to that of iron as 2 to 5 ; or a solution of the salt of zinc, weighing 10° B., and an- 
 other of the salt of iron, weighing 25° B., may be mixed together in equal quantities. 
 The precipitate which is then obtained by means of potash, or its carbonates, will 
 contain in its composition the proper proportion ; for sulphate of zinc consists of, 
 
 1 atom of oxide of zinc 503.32 
 
 1 ,, ,, acid ...... 501.16 
 
 1 ,, ,, sulphate of zinc .... 1004.48 
 
 The quantities of the sulphate of zinc and the sulphate of iron, each of which 
 contains 1 atom of oxide, are in the proportion of 2 to 5. 
 
 When the oxides are precipitated by means of a fixed alkali any excess of the 
 precipitating substance must be avoided, to prevent the oxide of zinc from being dis- 
 solved again. Just so much, however, is added as will produce a complete precipi- 
 tation. The product is filtered, washed and dried. Lastly, it is submitted to a red 
 heat, in order to drive off the water which it contains. If the solutions of zinc and 
 iron, after they have been poured together, are treated with an alkaline carbonate, 
 the precipitate must in this case be heated to drive off the carbonic acid. The cal- 
 cining is intended moreover to give stability to the combination of the two oxides. 
 If it is required to colour a fused pigment by chemical combination or simple mixture, 
 the object must be to obtain the colouring oxide in a state of the finest possible divi- 
 sion. By this means, in the former case the combination takes place more easily, and 
 in the latter the mixture is more intimate. Now calcining is always opposed to the 
 direction we have given, for oxides condense by being calcined. This is also the 
 case with the kind of pigments we have just been speaking of. On this account it 
 answers to use the means which we recommended for obtaining the flesh-red ; for 
 they not only admit of compliance with the conditions which require calcining, but of 
 the production of the colouring matter in a state of the finest division. We will now 
 speak of the mixture of sulphate of potash. 
 
 The precipitate from the two oxides contained in the carbonates of zinc and iron 
 is mixed with a concentrated solution of this salt ; the liquor is evaporated, and the 
 precipitate, when dry, is calcined at a dull red heat. It is then softened with water, 
 placed in a filter which separates the zincate of iron from the solution of sulphate of 
 potash ; this precipitate is carefully washed and then dried. 
 
 I 2 
 
60 
 
 OF THE PIGMENTS IN PARTICULAR, 
 
 This we consider to be the best process for the preparation of zincate of iron. 
 The colouring matter which is obtained must now be united with the flux which 
 serves as a vehicle for it. The best kind of flux for ochre yellow is No. 3, of the first 
 class. They are mixed in the following proportions ; — 
 
 Zincate of iron . . . . . .1 part. 
 
 Flux ........ 4 parts. 
 
 As this fused pigment belongs to that class which is coloured by mixture, it ought 
 not to be melted before it is used ; we have, however, found it useful to frit it, e. to 
 keep it at a dull red heat for some time ; it is then levigated for use. In this way 
 the colour becomes more beautiful and more transparent. This method should be 
 employed principally in that kind of painting which the French glass-painters call 
 peinture par enlevage. 
 
 YELLOW FROM ANTIMONITE OF LEAD. 
 
 The fused pigment which is coloured with antimonite of lead belongs to the fore- 
 going class, inasmuch as it contains the colouring matter in a state of simple mixture. 
 It is prepared by fusing in a crucible 1 part of antimonic acid and 3 parts of mini- 
 um, levigating the product and mixing with it twice its weight of rocaille-flux, and 
 then fusing the mixture again. This pigment has the fault of not being transparent. 
 Therefore, although it is one of those which are coloured by mixture, it is advisable 
 to melt it, in order to impart to it the greatest possible transparency. The quantity 
 of flux must also be very small, for the oxide of lead being attracted by the flux is 
 easily liberated from the antimonious acid, and the latter then gives only a feeble, 
 opaque, white colour to the glass. The rocaille-flux is therefore preferred in this 
 case also, because it is the most saturated and consequently the least disposed to act 
 upon the colouring matter. 
 
 The tint produced by antimonite of lead may be modified by adding some oxide 
 or zincate of iron. 
 
 In order that it may be better understood what takes place in the process by 
 which this colour is prepared, we may mention that at a red heat the antimonates 
 are converted into antimonites. 
 
 YELLOW FROM ANTIMONITE OF IRON. 
 
 The yellow obtained from this compound belongs to the same class as the two pre- 
 ceding. Like them it wants transparency, but it possesses a very rich colour, so that 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 61 
 
 it can be used in many cases for mixed tints, and for the shading of green and brown. 
 It is also of great use when employed alone. 
 
 Antimonite of iron is obtained through double decomposition, that is to say, by 
 precipitating persulphate of iron with antimonate of potash. The product is washed, 
 dried and calcined. Antimonite of iron is likewise prepared by direct mixture of 
 antimonic acid with oxide of iron in the proportion of 4 to 1. This latter method 
 admits of the relative quantities of the two compounds being varied at pleasure. 
 The antimonite of iron, like the foregoing, is used with the rocaille-flux or with some 
 flux of the first class. In the former case the mixture must be brought into a state 
 of fusion, according to the treatment of the rocaille-flux in all other circumstances. 
 In the latter case it is only levigated. Three parts of flux to one of colouring matter 
 are required. 
 
 We think it superfluous to speak of the pigments that can he prepared with the 
 aid of the other yellow colouring materials which have been mentioned ; they are 
 little studied, and moreover are not in general used. It may be briefly stated, how- 
 ever, that in modern times the metal uranium has been used in Germany for the pre- 
 paration of a yellow pigment. The process is as follows ; — 
 
 Uranium ore ^ is broken in pieces and roasted, dissolved in nitric acid, the solution 
 filtered and the lead which is present in it precipitated by the addition of some drops 
 of sulphuric acid. The clear green solution is then evaporated to dryness, and the 
 salt is heated until it is converted into a yellow mass. One part of the substance so 
 obtained is ground with three parts of a flux composed of four parts of minium and one 
 part of powdered silica, fused together and levigated. 
 
 OF THE GREEN. 
 
 The green pigment generally receives its colour from oxide of copper, oxide 
 of chromium and protoxide of iron, either separately, or by the combination of 
 two or more with one another. The ingredients of this pigment are in combination 
 with the flux. It is difficult to make its expansibility the same as that of the 
 glass on which it is laid. The oxide of copper, even in a very slight quantity, alters 
 this property in a great degree, and disposes the pigment to shell ofi* the surface of 
 the glass. The oxide of chromium does not partake of this quality in so remarkable 
 a manner, but it requires a very fusible flux to dissolve it. Now this fusibility can 
 only be obtained by mixing with the flux substances which modify its expansibility in 
 the same way as oxide of copper does, and borate of soda in particular is one of these 
 substances. The colour which protoxide of iron gives by itself is not rich enough, 
 
 ^ Uranerz. 
 
62 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 consequently this protoxide can never be employed alone. In most cases it is used in 
 combination with oxide of copper. 
 
 To colour a fused pigment green, the oxide of copper must be in combination 
 with one or more acids of the flux, that is to say, it must be in the state of borate, 
 silicate, or borosilicate. One of the fluxes which we have specified for the pigments 
 of the second class seems best able to effect its solution, but these fluxes receive a 
 degree of expansibility from the copper, which ill accords with that of the glass. 
 Those fluxes therefore must be avoided which contain an abundance of acid, and 
 those should be preferred which contain a large amount of base, especially of oxide of 
 lead, although they possess less capability of being dissolved. Flint-glass ^ {fondant 
 rocaille') seems best adapted to this purpose, and yet no large proportion of oxide of 
 copper can be mixed with it without producing the unpleasant result just stated. The 
 green pigment is therefore best obtained from the following composition : — ■ 
 
 Minium ....... 12 parts. 
 
 Silica . . . . . . . 4 ,, 
 
 Oxide of copper . . . . . 1 ,, 
 
 Red oxide of iron . . , . . -g 
 
 This pigment may be prepared in two ways : — 
 
 1. The colouring oxides are melted in a crucible with the flux which has been 
 previously prepared and ground together with them. 
 
 2. The oxides are fused together with the substances proper for the composition 
 of the flux, after which the whole is well mixed and ground together. 
 
 It is not immaterial which of the two methods is employed ; we have always pre- 
 ferred the latter. In this method, when the mixture begins to be red-hot, the oxide 
 of lead begins to melt, and dissolves the oxide of copper, while at the same time the 
 latter is acted upon by the silica. This previous union of the two oxides is intended 
 to separate the particles of the copper so as to dispose it to combine with the silica 
 as soon as ever it is acted upon by it. In the former case, on the contrary, the oxide 
 of copper is merely acted upon by the silica of the flux. 
 
 The foregoing receipt for the green pigment affords a colour of no great intensity, 
 and we cannot expect to obtain a richer green by merely increasing the quantity of 
 copper, for this, as we have just shown, could not be done with safety. Accordingly, 
 in order to increase the respective proportions of the colouring oxides without risk, 
 the composition of the flux must be modified at the same time by an addition to the 
 quantity of oxide of lead. 
 
 a Bleiglas, lit. lead-glass. This flint-glass, the composition of which is given under the head No. 1 of the 
 flaxes for pigments of the first class, will he found to contain more oxide of lead than the English flint-glass. 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 DARKER GREEN. 
 
 Silica ....... 1 part. 
 
 Minium . . . . . . 4 — 7 parts. 
 
 Oxide of copper ..... 1 part. 
 
 In these receipts we have no intention of laying clown absolute proportions, for 
 we well know that there are certain kinds of glass which will bear a greater quantity 
 of oxide of copper without the colour shelling olf. But we have endeavoured to im- 
 part such qualities to our pigments as will ensure continual success, and consequently 
 we have perhaps carried our caution to an extreme rather than render the success 
 doubtful. 
 
 Oxide of chromium does not answer so well for the green of the fused pigments 
 as oxide of copper ; for it seldom obtains so pure and bright a colour as the latter. 
 Even if it is combined with very fusible fluxes it generally wants transparency, and 
 yet the quantity of the substances which impart greater fusibility to the flux cannot 
 be safely increased. 
 
 Oxide of chromium is mixed with one of the fluxes for pigments produced by com- 
 bination, in the proportion of 1 part of oxide to 9 parts of flux, the same proportion 
 that we specified for oxide of copper ; and we are of opinion that it is better to heat 
 the oxide of chromium with the elements of the flux, than with the flux itself. 
 
 Notwithstanding what we have said concerning the properties of protoxide of 
 chromium, it should not be neglected in the preparation of the pigments. As glass- 
 painting frequently bears a certain degree of opacity very well, oxide of chromium 
 may be employed with advantage, especially if it is only used for the colouring of a 
 pigment by mixture. The green colour peculiar to it, which it possesses before it is 
 united with a flux, makes it very well suited to this purpose, and the only problem 
 now is to preserve it in a state of sufliciently fine division. 
 
 There are other substances which may be used for green pigments, but they give 
 an opaque colour. Among these are zincate of cobalt, Rinmann’s green, and anti- 
 monite of cobalt. Of course these compounds are not acted upon by the flux, and 
 merely form pigments of the first class. 
 
 With respect to this matter we will describe a method which, in our opinion, 
 seems to promise manifold advantages. When it is required to mix oxide of chro- 
 mium with a fused pigment containing lead, the neutral chromate of lead may be 
 used, which furnishes at the same time oxide of chromium and oxide of lead, or at 
 least a part of the latter. When this salt is submitted to a red heat it parts with 
 
64 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 oxygen and leaves behind a combination of the two oxides in the following propor- 
 tions : — 
 
 1 atom of oxide of lead . . . • 1394.6 
 
 1 ,, ,, chromic acid ..... 650.7 
 
 1 „ 5 , neutral chromate . . . 2045.3 
 
 And this gives after calcining, 
 
 1 atom of oxide of lead ..... 1394.6 
 
 ^ „ „ ,, ,, chromium . . . 502. 
 
 1 ,, „ plumbate of chromium . . . 1896.6 
 
 It is evident that the oxide of chromium, which is thus held in combination with 
 oxide of lead, must be in a state of most minute division, whereby its union with the 
 silicates or borosilicates of the flux is facilitated to a remarkable degree. This pig- 
 ment may be composed in the following way : — 
 
 Silica . . . . 
 
 Minium . . . . 
 
 Calcined borax . 
 
 Calcined chromate of lead . 
 
 2 parts 
 ^2 ” 
 
 These ingredients are melted and poured out. 
 
 The old glass-painters frequently availed themselves of the combined effects of 
 yellow and blue, in order to obtain a green. Thus, for example, they gave to glass 
 which had been coloured blue in the melting pot a yellow stain with the help of sul- 
 phuret of silver and the paste. This method is not in general use at the present day. 
 
 OF THE VIOLET. 
 
 There are two modes of preparing violet pigments. The first consists in employ- 
 ing a colouring substance which is capable of producing a violet of itself ; according 
 to the second, the requisite violet is obtained by mixing a blue with a red pigment. 
 The substances which are capable of bringing out a violet without the assistance of 
 another colour are the purple precipitate of Cassius and oxide of manganese. 
 
 We have already explained, in speaking of the red pigment, under what circum- 
 stances stannate of gold affords a violet colour, and have observed, that the purple of 
 Cassius, whenever it is decomposed before the fused pigment can dissolve its particles. 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 65 
 
 produces a violet aud even a blue, according as the change which takes place in it is 
 more or less complete ; and this happens in the case we are now speaking of. If 1 
 part of the purple of Cassius be mixed with 9 parts of one of the fluxes coloured by 
 combination, without fusion, a violet pigment is obtained. This product is the efiect 
 of two causes which operate simultaneously, that is to say, the want of fusibility in 
 the pigment, and the too great abundance of oxide of lead. Should the violet which 
 is obtained in the manner we have just specified be not brought out with sufficient 
 clearness, it may be still better developed by adding to the fluxes of the first section 
 a little of flux No. 1. 
 
 Oxide of manganese gives an exceedingly deep violet colour, but, as we have 
 elsewhere observed, it imparts to the pigments an extraordinary disposition to crack 
 and shell off. This unfortunate property is easily overcome, however, by adding a 
 large quantity of minium to its composition. 
 
 The composition should be as follows ; — 
 
 Silica ....... 1 part 
 
 Minium ....... 6 — 8 parts 
 
 Peroxide of manganese . . . *2 ps^rt. 
 
 When this oxide of manganese is heated in contact with oxide of lead, it rapidly 
 gives up oxygen, and is converted into sesquioxide. 
 
 This pigment is distinguished from the rest by this remarkable peculiarity, 
 namely, that it can only be employed on condition that it is not painted on with any 
 liquid which, after the burning in, leaves a carbonaceous substance in its mass. 
 This will be more apparent, when we remember that peroxide of manganese is used 
 for whitening glass, on account of its property of extracting the carbon, which would 
 impair its clearness. Here the carbon acts upon the manganese, deprives it of a 
 portion of its oxygen, and converts it into a colourless protoxide, while it is liberated 
 itself in the state of carbonic acid. 
 
 Now this would be the case if the pigment, at the moment of its liquefaction, 
 contained carbon which was produced by the vehicle with which it was laid on the 
 glass before the burning in. We would therefore recommend for this purpose a 
 solution of borate of soda, instead of the gum or sugar water, and the thickened 
 essence of turpentine, which are generally used. 
 
 The violet, which is obtained by a mixture of blue and red, is prepared with 
 common smalt and the purple of Cassius, the proportions varying at the discretion 
 of the artist. 
 
 There is another violet, which is produced by the red oxide of iron, which is 
 
 K 
 
66 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 exposed to a white heat for some time ; but it is almost entirely opaque, and pro- 
 duces on the glass only a kind of opaque and dull violet-grey. The pigment which 
 is thus obtained is, nevertheless, of great use in glass-painting, and is prepared in 
 the following way ; — ■ 
 
 Violet oxide of iron . . .1 part 
 
 Flux ...... 3 parts. 
 
 No. 3 of the pigments of the first class is used for the flux. 
 
 OF THE BROWN. 
 
 The brown is an undefined colour, which may be prepared in a variety of ways, 
 according to the requirements of the art, and the taste of the artist. We will 
 describe the principal browns. 
 
 Zincate of iron, which contains one atom of zinc, and two of iron, gives a 
 yellowish-brown, which is frequently used. It is prepared in the same way as ochre- 
 yellow, except that the quantity of the salt of iron is doubled. For the composition 
 we are now speaking of, the salt of zinc must be to the salt of iron as 2 to 10. The 
 flux proper for this is the same as that which is used for the ochre-yellow, and is 
 also employed in the same proportions. 
 
 Zincate of iron, ochre-yellow, as it is called, when mixed with either red oxide of 
 iron or burnt sienna, gives a reddish-brown, whose shade of colour varies with the 
 proportions. 
 
 The same zincate of iron (ochre-yellow) forms, with burnt umbre, a much 
 darker brown than the preceding, and one which has no affinity to red. 
 
 Oxide of iron alone, when properly prepared, affords a brown of considerable 
 utility. It is prepared in the moist way as follows : — A solution of persulphate of 
 iron is treated with an alkaline or carbonized oxide, (with potash, soda, ammonia, 
 or their carbonates) ; the precipitate which is obtained is either an hydrated oxide 
 or a carbonate. It is placed in a filter, washed and dried, and then subjected to a 
 red heat, in order to drive off the water or the carbonic acid. After this prepara- 
 tion the oxide of iron presents a brown colour, whose shade may be varied by heat- 
 ing it more or less. This oxide of iron bears no resemblance to that which is 
 
 o 
 
 obtained in the dry way, although the calcining develops in it a more or less 
 distinct red tone. 
 
 Burnt umbre, when mixed with a flux, also affords a brown pigment. 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 67 
 
 A mixture of peroxide of manganese and oxide of iron likewise serves as a brown 
 pigment of some utility. In order to prepare all these pigments, it is merely neces- 
 sary to know that each of the colouring substances we have mentioned must be 
 mixed with thrice its weight of flux No. 3 of the pigments of the first class. 
 
 No previous fusion is required. The colouring materials are merely brought 
 into a state of the most intimate mixture by levigation together. The brown pig- 
 ments are all pigments of the first class, and possess great opacity, but by virtue of 
 this property they are exactly adapted to the use to which they are applied. 
 
 OF THE BLACK. 
 
 The completely opaque pigments, whatever their proper colours may be, when 
 laid upon glass, appear hlack in a transmitted light. The reason of it is this, viz., 
 that a substance which allows no transmitted ray to reach the eye must cause a 
 shadow, and consequently produce a black colour. Therefore either a hlack or an 
 opaque colour may be used for the black lines of a drawing upon glass, or the parts 
 that are in shadow. There is, however, a diflerence between the effect produced by 
 a really black colour and that of any other colour not transparent. 
 
 When we look at a large transparent surface, e. g., a church-window, besides the 
 refracted rays transmitted through the glass, the eye receives also a few reflected 
 rays, especially if the external light is not particularly intense. In this way the 
 pigments, which only produce a black colour by virtue of their opacity, are slightly 
 tinged with the colour which properly belongs to them. The black which proceeds 
 from them thus loses its hardness, and falls more agreeably upon the eye. On this 
 account pigments of broken tones, as they are called, are used for the black lines 
 and shadows of a picture, and of these the brown pigments exhibit a great variety. 
 
 A pigment which shall appear black in a reflected as well as in a refracted light, 
 may be prepared in two ways : — 
 
 1. Opaque substances of a black colour may be mixed with a flux, e. g., oxide 
 of iron, peroxide of manganese, peroxide of cobalt, and oxide of copper, in such con- 
 siderable quantities as to prevent their vitrification taking place during the time of 
 the burning in. A black pigment, by mixture, is thus obtained, which is composed, 
 e. g., of— 
 
 Oxide of copper . . . . .1 part 
 
 Peroxide of manganese . . . . 1 ,, 
 
 Peroxide of cobalt . , . . 1 ,, 
 
 K 2 
 
68 
 
 OF THE PIGMENTS IN PARTICULAE. 
 
 Oxide of iron ..... I part 
 Flint-glass ...... 8 — 12 parts. 
 
 2. A black pigment by combination may also be prepared, and, after fusion, a 
 certain quantity of oxide may be united witb it, merely in the state of mixture, in 
 order to render its opacity complete, as well as to impart to it the property of not 
 splitting off in scales. This is therefore a combination of the two kinds of pig- 
 ments. For the preparation of this compound, the following ingredients are melted 
 in a crucible, in the following proportions ; — 
 
 Oxide of iron . . . . . .2 parts 
 
 Oxide of copper . . . . . . 2 ,, 
 
 Peroxide of manganese . . . .1 part 
 
 Flint-glass ....... 5 parts 
 
 Fused borax ...... ^ part. 
 
 As soon as the whole is melted, the contents of the crucible are poured out and 
 levigated with 
 
 Peroxide of manganese . ... 1 part 
 
 Oxide of copper ...... 2 parts 
 
 The theory of the composition of this pigment may be explained in the following 
 way ; — by fusing together oxide of iron, oxide of copper, and oxide of manganese, with 
 the flux of flint-glass and the borax, borosilicates are formed. The two former are 
 green, and the latter violet-red. Now green and violet-red, in proper proportions, 
 give a black. The oxides which are afterwards added, as we have already stated, 
 only render the opacity complete, and give the pigment a proper expansibility. The 
 advantage of this latter circumstance is evident, when the effect of the oxides of 
 copper and manganese upon expansibility is considered. If, on the other hand, it is 
 required to prepare a pigment which shall only appear black in a reflected light, let 
 the following ingredients be mixed together without being fused : — 
 
 Black oxide of iron . . . . .1 part, 
 
 or even 
 
 Red or bright violet oxide of iron . . 1 part 
 
 Flint-glass or flux ..... 2— 3 parts. 
 
 When this colour is used, it appears black by transmitted light, but by reflected 
 light it assumes a reddish tint approaching to violet, less hard and more agreeable 
 than black. 
 
OF THE PIGMENTS IN PARTICULAR, 
 
 69 
 
 OF THE WHITE. 
 
 The white pigment is almost useless in glass-painting. We shall, however, treat 
 of it more fully than we should otherwise have done, in order to complete the series 
 of the pigments of which we have here given a short account. 
 
 The white pigment has been used in modern times for ornamenting panes of 
 glass with a kind of drawing whose whole effect depends upon the combination of 
 the dull and opaque white of the pigment with the transparent glass, without the aid 
 of any other colour. This branch of art, which borders a little upon the one we are 
 treating of, seems, however, to have received no particular cultivation. The white 
 pigment is a vitreous compound of more or less opacity, and this opacity is owing to 
 the presence of zincic or antimonic acid. This pigment is prepared according to 
 the following process ; — an alloy is first made of 20 parts of tin to 80 parts of lead. 
 The metal is melted in an iron ladle or a vessel of a similar kind, and the oxide 
 which covers its surface is removed as fast as it is formed. When the entire mass 
 has been converted into oxide, the calcining is continued a little while longer, while 
 the oxide is stirred incessantly until it assumes a perfectly homogeneous appearance. 
 It is then poured into a vessel full of water and well stirred, in order to effect the 
 separation of the unoxidized grains of the alloy, which are mixed with the mass. 
 These grains collect at the bottom of the vessel. The oxide is now dried and is fit 
 for use. When this substance is mixed with potash, silica, and borax, in the pro- 
 portions which we are about to specify, and then vitrified at a high temperature, a 
 white pigment is obtained. 
 
 The white pigment of commerce that is used in enamel-painting may also be 
 employed for the purposes of glass-painting, although it is rather deficient in fusi- 
 bility. It is usually composed of the following ingredients : — 
 
 Potash 
 
 Oxide of lead 
 Silica 
 
 Stannic acid . 
 Calcined borax 
 
 1 part 
 8 parts 
 . 6 „ 
 
 . 2 „ 
 
 . 2 „ 
 
 This enamel is also prepared by fusing together in a crucible the following 
 ingredients ; — 
 
 Carbonate of potash . , . . .2 parts 
 
 The oxides of tin and lead calcined . . 5 ,, 
 
70 
 
 Silica . 
 Borax . 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 3 parts 
 1 part. 
 
 As soon as the enamel has ceased to bubble, and appears in the state of a clear 
 liquid, it is poured out. It must be melted several times after being levigated, or at 
 least pounded in a mortar. It is thus freed from the excess of potash which it con- 
 tains, and at the same time rendered whiter. 
 
 The enamel of M. Clouet, as a specimen of an enamel coloured by antimonious 
 acid, may be contrasted with the above. It is prepared from 
 
 White glass .... 
 Uncalcined borax 
 Saltpetre ..... 
 Purified antimonium diaphoreticmn 
 
 . 12 parts 
 
 . 4 „ 
 
 1 part 
 . 4 parts. 
 
 This is a quadruple borosilicate of lime, potash, soda, and alumina. 
 
 It is less adapted to painting on glass than the one we have mentioned before, 
 and more disposed to scale off, since it is deficient in oxide of lead. 
 
 We recommend the folio wung enamel, which seems to contain the qualities requi- 
 site for painting on glass. Its composition is as follows ; — 
 
 Silica ........ 3 parts 
 
 Calcine “ . . . . . . • „ 
 
 Calcined borax , . . . . . 2 „ 
 
 The ingredients are melted, and then poured out. 
 
 The old glass-painters frequently used white pigments similar in composition to 
 those which we call pigments of the first class. Levied prepared a white pigment 
 by mixing sulphate of lime (gypsum) with rocaille-flux (flint-glass). Felibien, 
 Haudicquer de Blancourt, and the Abbot of Marsy propose the same substance, but 
 with a different enamel. Flint, pulverised rock-crystaU, and the powder of calcined 
 bones, have also been used for this purpose ; a better result would have been obtained 
 with stannic acid employed in the same way. 
 
 CALCULATION OF THE ATOMIC WEIGHTS OF THE PIGMENTS. 
 
 Now that we have shown that the various kinds of glass are composed of several 
 silicates in definite proportions, probably in combination with one another, the study of 
 
 a By calcine is meant the calcined oxide of an alloy of 20 parts of tin and 80 of lead. — (^Atithor’s note.) 
 Berghrystall. 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 71 
 
 their atomic weights ^ must on this account be the more interesting. Moreover, if we 
 would employ ourselves in making satisfactory inquiries into the art of composing 
 the pigments, this cannot be done with any success unless we are acquainted with 
 the calculation of the atomic weights which are made use of in these compositions. 
 We will therefore communicate an easy method of determining the composition of a 
 pigment, or any other kind of vitreous substance, according to the atomic weights. 
 
 TABLE OF THE ATOMIC WEIGHTS OF THE MAJORITY OF THE SUBSTANCES 
 
 USED FOR PIGMENTS. 
 
 Silicic acid ...... 192.6 
 
 Boracic acid ...... 435.98 
 
 Oxide of aluminum ..... 643.33 
 
 Oxide of calcium ..... 356.03 
 
 Oxide of potassium ..... 587.91 
 
 Nitrate of potash ..... 1264.93 
 
 Oxide of sodium ..... 390.92 
 
 Subcarbonate of soda .... 666.25 
 
 Borate of soda ...... 1262.88 
 
 Oxide of manganese ..... I467. 
 
 Sesquioxide of manganese . . . . 1011.5 
 
 Peroxide of manganese .... 555.7 
 
 Oxide of iron ..... 978. 
 
 Stannic acid ...... 935.29 
 
 Antimonious acid ..... 1006.4 
 
 Oxide of zinc ...... 503.32 
 
 Oxide of cobalt ..... 469. 
 
 Peroxide of cobalt ..... 1038. 
 
 Oxide of chromium ..... 1003. 
 
 Oxide of copper ..... 495.6 
 
 Protoxide of lead ..... 1394.5 
 
 When it is required to determine the number of atoms of each of the bodies 
 which are used for a pigment whose composition is known, each of the expressions of 
 the formula must be multiplied by one and the same number, e. g., 100, 1,000 or 
 10,000, just as it may happen to be necessary, in order to enable us to divide all 
 these expressions by the atomic weight of the substance which they represent. 
 
 ^ Atomengewichte. 
 
72 
 
 OF THE PIGMENTS IN PARTICULAR, 
 
 Let a pigment, for example, be composed of — 
 
 Silica ....... 45 parts 
 
 Potash . . . . . , . 6 ,, 
 
 Oxide of lead . . . . . . 70 ,, 
 
 If only the two first expressions of the formula were considered, it would be suffi- 
 cient to multiply them hy 100 ; for the products would be divisible by the atomic 
 weight of the silica (192.6) and that of the potash (587.9). But it is evident, that 
 they must be multiplied by 1000 in this case on account of the third expression. 
 Accordingly we get — 
 
 Silica .... 45,000 divisible by 192.6 
 
 Potash .... 6,000 „ „ 587.9 
 
 Protoxide of lead . . 76,000 ,, ,, 1394.6 
 
 If the division is performed, the following result is obtained ; — 
 
 Silica ...... 240 atoms or 24 
 
 Potash . . . . . . 10 ,, ,, 1 
 
 Protoxide of lead . . . . 50 ,, ,, 5 
 
 Consequently, if every atom of these bodies contains 100 parts of oxygen, the 
 quantities of this gas will be to one another as the atoms themselves, namely : — 
 
 Silica 2,400 or 24 
 
 Potash ...... 100 ,, 1 
 
 Protoxide of lead .... 500 ,, 5 
 
 The oxygen of the acid is four times as much as that of the bases. A double 
 quater-silicate thus appears. The oxygen of the potash is moreover to that of the 
 oxide of lead as 1 to 5, and consequently we have 1 atom of the quater-silicate of 
 potash and 5 atoms of the quater-silicate of lead. 
 
 To compose an enamel, then, which shall contain 5 atoms of silicate of lead and 1 
 atom of silicate of potash, we must take — 
 
 5 atoms of oxide of lead = 1394 x 5 =6976 
 1 atom of potash = 587 x 1 = 587 
 
 Further, if it be required that these bases should form with the silica quater-sili- 
 cates, we must take as many atoms of silica as are necessary, in order that the latter 
 
OF THE PIGMENTS IN PARTICULAR. 73 
 
 may contain four times as much oxygen as the bases. Now if the oxygen of the bases 
 amounts to 6, we get for the silica 4x6 = 24. 
 
 24 atoms of silica = 192 x 24 = 4608. 
 
 By simplifying the expressions we obtain at length, 
 
 Protoxide of lead . . . . .70 parts. 
 
 Potash . . . . . . . 6 ,, 
 
 Silica . . . . . . . 45 ,, 
 
 In order to obviate the necessity of making calculations, we have drawn up 
 Tables, by the assistance of which the reader may discover at the first glance the 
 quantity of any body which corresponds to a given number of atoms. 
 
 SILICIC ACID. 
 
 Atoms. 
 
 5 . . . 
 
 10 . . . 
 
 15 . . . 
 
 20 . . . 
 
 25 . . . 
 
 30 . . . 
 
 35 . . . 
 
 40 . . . 
 
 45 . . . 
 
 50 . . . 
 
 Parts. 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 OXIDE OF 
 
 Atoms. 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 POTASSIUM. 
 
 Parts. 
 
 . 0.6 
 . 1.2 
 . 1.8 
 . 2.3 
 
 . 2.9 
 . 3,5 
 
 . 4.1 
 
 . 4.7 
 . 5.3 
 
 . 5.9 
 
 Atoms. 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 9 
 
 10 
 
 BORACIC ACID. 
 
 Parts. 
 
 0.4 
 
 0.9 
 
 1.3 
 
 1.7 
 
 2.2 
 
 2.6 
 
 3.0 
 3.5 
 3.9 
 
 4.0 
 
 SUBCARBONATE OF POTASH. 
 
 Atoms of Potash. 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 Parts of the sub- 
 carbonate. 
 
 . 0.9 
 . 1.7 
 . 2.6 
 . 3.4 
 . 4.3 
 . 5.2 
 
 . 6 
 . 6.9 
 . 7-8 
 . 8.6 
 
 L 
 
74 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 
 NITRATE OF 
 Atoms of Potash. 
 
 1 
 
 POTASH. 
 
 Parts of the Nitrate. 
 
 . 1.3 
 
 SUBCARBONATE OF 
 Atoms. 
 
 1 . . . 
 
 SODA. 
 
 Parts. 
 
 . 0.7 
 
 2 
 
 
 . 
 
 2.5 
 
 2 
 
 
 
 
 
 1.3 
 
 3 
 
 
 • 
 
 3.8 
 
 3 
 
 
 
 
 
 2 
 
 4 
 
 
 . 
 
 5 
 
 4 
 
 
 
 
 
 2.7 
 
 5 
 
 
 . 
 
 6.3 
 
 5 
 
 
 
 
 
 3.3 
 
 6 
 
 
 • 
 
 7.6 
 
 6 
 
 
 
 
 
 4 
 
 7 
 
 . 
 
 . 
 
 8.8 
 
 7 
 
 
 
 
 
 4.7 
 
 8 
 
 
 . 
 
 10.1 
 
 8 
 
 
 
 
 
 5.3 
 
 9 
 
 
 • 
 
 11.4 
 
 9 
 
 
 
 
 
 6 
 
 10 
 
 
 • 
 
 12.6 
 
 10 
 
 
 
 
 
 6.7 
 
 Atoms. 
 
 1 
 
 2 
 
 3 
 
 OXIDE OF SODIUM. 
 
 Parts. 
 
 0.4 
 
 0.8 
 
 1.2 
 
 Atoms. 
 
 1 
 
 2 
 
 3 
 
 OXIDE 
 
 OF 
 
 CALCIUM. 
 
 Parts. 
 
 0.3 
 
 0.7 
 
 1.1 
 
 4 
 
 . 
 
 . 
 
 1.6 
 
 4 
 
 
 
 
 
 1.4 
 
 5 
 
 
 • 
 
 1.9 
 
 5 
 
 
 
 
 
 1.8 
 
 6 
 
 
 . 
 
 2.3 
 
 6 
 
 
 
 
 
 2.1 
 
 7 
 
 
 . 
 
 2.7 
 
 7 
 
 
 
 
 
 2.5 
 
 8 
 
 
 . 
 
 3.1 
 
 8 
 
 
 
 
 
 2.8 
 
 9 
 
 
 . 
 
 3.5 
 
 9 
 
 
 
 
 
 3.2 
 
 10 
 
 
 • 
 
 3.9 
 
 10 
 
 
 
 
 
 3.6 
 
 BORATE OF 
 
 Atojyos of Boracic Atoms oj 
 
 ^Acid. Soda. 
 
 2 ... 1 
 
 SODA. 
 
 Paits of the 
 Borate. 
 
 . . . 1.3 
 
 Atoms. 
 
 1 
 
 OXIDE 
 
 OF 
 
 ALUMINUM. 
 
 Parts. 
 
 0.6 
 
 4 
 
 ... 2 
 
 . • 
 
 2.5 
 
 2 
 
 
 
 
 . 
 
 1.3 
 
 6 
 
 ... 3 
 
 « • « 
 
 3.8 
 
 3 
 
 
 
 
 . 
 
 1.9 
 
 8 
 
 ... 4 
 
 . • • 
 
 5 
 
 4 
 
 
 
 
 
 2.6 
 
 10 
 
 ... 5 
 
 • • * 
 
 6.3 
 
 5 
 
 
 
 
 
 3.2 
 
 12 
 
 ... 6 
 
 . • 
 
 7.6 
 
 6 
 
 
 
 
 . 
 
 3.8 
 
 14 
 
 ... 7 
 
 • 
 
 8.8 
 
 7 
 
 
 
 
 
 4.5 
 
 16 
 
 ... 8 
 
 • • • 
 
 10 
 
 8 
 
 
 
 
 
 5.1 
 
 18 
 
 ... 9 
 
 • « • 
 
 11.3 
 
 9 
 
 
 
 
 
 5.8 
 
 20 
 
 ... 10 
 
 • . . 
 
 12.6 
 
 10 
 
 
 
 
 
 6.4 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 75 
 
 PROTOXIDE OF LEAD. 
 
 Atoms. 
 
 Parts. 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 MINIUM 
 
 Atoms of Protoxide. 
 
 . 1.4 
 
 . 2.8 
 . 4.3 
 . 5.6 
 
 . 7 
 . 8.4 
 
 . 9.7 
 
 . 11.1 
 . 12.5 
 . . 14 
 
 Parts of Minium 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 . 1.4 
 
 . 2.8 
 . 4.3 
 
 . 5.7 
 
 . 7.1 
 , 8.5 
 
 . 10 
 . 11.4 
 . 12.8 
 . 14.3 
 
 The difference between minium and 
 protoxide of lead is so considerable, that 
 it may be perceived at once in any given 
 number of atoms, as will appear from a 
 comparison of the two tables. 
 
 ^ PROTOXIDE OF MANGANESE. 
 Atoms. Parts. 
 
 1 .... 1 
 
 2 .... 2 
 
 3 .... 3 
 
 4 .... 4 
 
 Atoms. 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 DEUTOXIDE OF 
 Atoms. 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 PEROXIDE OF 
 Atoms of Protoxide. 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 PEROXIDE OF 
 Atoms of Deutoxide. 
 
 1 
 
 2 
 
 Parts. 
 
 . 5 
 
 . 6.1 
 . 7.1 
 . 8.1 
 . 9.1 
 . 10.1 
 
 MANGANESE. 
 
 Parts. 
 
 . 1.5 
 
 . 2.9 
 . 4.4 
 
 . 5.9 
 . 7.3 
 
 . 8.8 
 . 10.3 
 . 11.7 
 . 13.2 
 . 14.7 
 
 MANGANESE. 
 
 Parts of Peroxide. 
 
 . 1.1 
 
 . 2.2 
 
 . 3.3 
 
 . 4.4 
 
 . 5.5 
 
 . 6.7 
 
 . 7.8 
 
 . 8.9 
 
 . 10 
 . 11.1 
 
 MANGANESE. 
 
 Parts of Peroxide, 
 
 . 1.7 
 
 . 2.3 
 
 L 2 
 
76 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 Atoms of Deutoxide. 
 
 Parts of Peroxide. 
 
 Atoms, 
 
 Parts. 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 . 5 
 
 . 6.7 
 . 8.3 
 
 . 10 
 . 11.7 
 . 13.3 
 . 15 
 . 16.7 
 
 6 .... 5.9 
 
 7 .... 6.9 
 
 8 .... 7.8 
 
 9 .... 8.8 
 
 10 .... 9.8 
 
 PROTOXIDE OF COBALT. 
 
 Atoms. 
 
 Parts. 
 
 These two latter tables show the quan- 
 tities of peroxide of manganese which are 
 necessary to produce by their decomposi- 
 tion a given number of atoms of protox- 
 ide or deutoxide. 
 
 OXIDE 
 
 Atoms. 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 9 
 
 10 
 
 OXIDE 
 
 Atoms. 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 OF ZINC. 
 
 Parts. 
 
 . 0.5 
 
 . 1 
 . 1.5 
 
 . 2.0 
 
 . 2.5 
 
 . 3 
 . 3.5 
 
 . 4 
 
 . 4.5 
 
 . 5 
 
 OF IRON. 
 
 Parts, 
 
 . 1 
 . 1.9 
 . 2.9 
 . 3.9 
 . .5 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 9 
 
 10 
 
 0.5 
 
 1.3 
 
 1.4 
 1.9 
 
 2.3 
 
 2.8 
 
 3.3 
 
 3.7 
 4.2 
 
 4.7 
 
 PEROXIDE OF COBALT. 
 
 Atoms of Protoxide. 
 
 1 
 
 
 
 Parts of Peroxide. 
 
 . 0.5 
 
 2 
 
 
 
 . 1 
 
 3 
 
 
 
 . 1.5 
 
 4 
 
 
 
 . 2.1 
 
 5 
 
 
 
 . 2.6 
 
 6 
 
 
 
 . 3.1 
 
 7 
 
 
 
 . 3.6 
 
 8 
 
 
 
 . 4.1 
 
 9 
 
 
 
 . 4.7 
 
 10 
 
 
 
 . 5.2 
 
 The table of the peroxide of cobalt 
 has been composed on the same principle 
 as that of the peroxide of manganese. 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 77 
 
 OXIDE OF CHROMIUM. 
 
 ANTIMONIC ACID. 
 
 Atoms. 
 
 Parts. 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 . 1 
 . 2 
 . 3 
 
 . 4 
 
 . 5 
 
 . 6 
 
 . 7 
 . 8 
 . 9 
 
 . 10 
 
 OXIDE OF COPPER. 
 
 Atoms. 
 
 
 
 
 
 Parts. 
 
 1 
 
 
 
 
 • 
 
 0.5 
 
 2 
 
 
 
 
 - 
 
 1 
 
 3 
 
 
 
 
 . 
 
 1.5 
 
 4 
 
 
 
 
 • 
 
 2 
 
 5 
 
 
 
 
 . 
 
 2.5 
 
 6 
 
 
 
 
 
 3 
 
 7 
 
 
 
 
 . 
 
 3.5 
 
 8 
 
 
 
 
 • 
 
 4 
 
 9 
 
 
 
 
 . 
 
 4.5 
 
 10 
 
 
 
 
 • 
 
 5 
 
 
 ANTIMONIOUS 
 
 ACID. 
 
 
 Atoms. 
 
 
 
 
 
 Parts. 
 
 1 
 
 
 
 . 
 
 . 
 
 1 
 
 2 
 
 
 
 
 
 2 
 
 Atoms of Antimonious 
 Acid. 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 Parts of Antimonic 
 Acid. 
 
 . 1 
 
 . 2.1 
 
 . 3.2 
 
 . 4.1 
 
 . 5.3 
 
 . 6.3 
 
 . 7-4 
 
 . 8.4 
 
 . 9.5 
 
 . 10.5 
 
 STANNIC ACID. 
 
 Atoms. 
 
 1 . . . 
 
 2 . . . 
 
 3 . . . 
 
 4 . . . 
 
 5 . . . 
 
 6 . . . 
 
 7 . . . 
 
 8 . . . 
 
 9 . . . 
 
 10 . . . 
 
 Parts. 
 
 0.9 
 
 1.9 
 
 2.8 
 
 3.7 
 
 4.7 
 5.6 
 
 6.5 
 
 7.5 
 8.4 
 9.3 
 
 In order that we may make no mistake in laying down the proportions of the 
 oxygen of the base to that of the acids, we must remember that these compositions 
 contain different quantities of oxygen to one atom, namely : — 
 
 1. Boracic acid 
 
 2. Alumina 
 
 3. Sesquioxide of manganese 
 
 4. Protoxide of manganese 
 
 300 parts. 
 300 „ 
 
 400 „ 
 
 300 parts 
 
78 
 
 OF THE PIGMENTS IN PARTICULAR. 
 
 5. Peroxide of manganese . . . 200 parts. 
 
 6. Oxide of iron ..... 300 ,, 
 
 7 . Stannic acid ..... 200 ,, 
 
 8. Antimonic acid ..... 500 ,, 
 
 9 . Antimonioiis acid .... 200 ,, 
 
 10. Oxide of chromium .... 300 ,, 
 
 11. The other bodies .... 100 ,, 
 
 Before we conclude the chemical part of our subject, we wish to direct the attention 
 of those who are engaged in the preparation of pigments for glass-painting to a series 
 of compositions which are capable of being used with very great advantage in the 
 art. We wish to speak of certain combinations of the colouring oxides with one an- 
 other, about which we have at present said very little. Farther back, where we were 
 speaking of the colouring substances in general, we expressed our opinion concerning 
 these kinds of compositions, which we likewise admitted into the class of salts. We 
 have already had occasion to consider a certain number of these combinations which 
 are very much used in the manufacture of the pigments, and we now intend to impart 
 what information it is in our power to give upon a few other matters less known, but 
 which seem capable of affording valuable resources to the art of painting on glass ; 
 and lastly, we intend to point out those particulars which, in our opinion, deserve to 
 be studied. We wish to open to fresh observers a fruitful field, full of objects both use- 
 ful and interesting, and we only regret that it was not our lot to explore it ourselves. 
 
 The most stable amongst the combinations which the indifferent oxides are capable 
 of entering into with the basic oxides, are the following : — 
 
 Protoxide of manganese and oxide of iron ; 
 
 Protoxide of manganese and peroxide of cobalt ; 
 
 Protoxide of manganese and oxide of copper ; 
 
 Protoxide of manganese and oxide of chromium ; 
 
 Protoxide of manganese and oxide of zinc ; 
 
 Oxide of iron and peroxide of cobalt ; 
 
 Oxide of iron and oxide of copper ; 
 
 Oxide of iron and oxide of chromium. 
 
 Amongst all the other possible combinations of the colouring metallic oxides with 
 one another, there are a few more of great stability, although certain of the oxides 
 out of which they are formed are remarkably deficient in this stability. Thus, among 
 other combinations, there ai’e a cuprate and a plumbate of silver, of which the oxide 
 of silver is reducible at less than a red heat, and further, a manganate of silver, which 
 appears to possess the same property. 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 79 
 
 PROTOXIDE OF MANGANESE AND OXIDE OF IRON COMBINED IN EQUAL ATOMS. 
 
 First process : — Two solutions, both of equal weight, according to Beaume’s 
 areometer, one of protosulphate of iron, and the other of protosulphate of manganese, 
 are mixed together ; they are then raised to the boiling point, and treated with an 
 excess of carbonate of soda. The precipitate, after it has been washed and dried, is 
 moistened with nitric acid, and exposed to a red heat in a crucible, until it is per- 
 fectly decomposed. This operation explains itself, and we need merely remark, that 
 these sulphates contain equal quantities of protoxide, and that both the protoxides 
 are converted into sesquioxides, and give an equal number of atoms. 
 
 Pi’otosulphate of Iron. 
 
 2 at. protoxide . . . 878.42 
 
 2 at. acid .... 1002.32 
 
 2 at. protosulph. iron . . 1880.74^ 
 
 Sesquioxide or Peroxide of Iron. 
 
 2 at. protoxide . . . 878.42 
 
 1 at. oxygen . . . 100.00 
 
 Protosulpliate of Manganese. 
 
 2 at. protoxide . . . 911.4 
 
 2 at. acid .... 1002.32 
 
 2 at. protosulph. mang. . 1913.72 
 
 Sesquioxide of Manganese. 
 
 2 at. protoxide . . . 911.4 
 
 1 at. oxygen . . ,100.00 
 
 1 at, peroxide . . . 978.42 1 at. sesquioxide . . 1011.4 
 
 Second process : — A stream of chlorine gas is caused to pass through water with 
 which carbonate of manganese, or the oxide obtained by precipitating sulphate of 
 manganese with potash, has been mixed. The oxide which is obtained in the state 
 of hydrate is mixed in proper proportions with hydrated, oxide of iron, and exposed 
 to a red heat. 
 
 Hydrated Peroxide of Iron. 
 
 2 at. iron .... 
 
 3 at. oxygen 
 
 Water . . . . 
 
 678.45 
 
 300 
 
 168.70 
 
 1 at. peroxide 
 
 . 1147.15 
 
 Hydrated Peroxide of Manganese. 
 
 2 at, manganese 
 4 at. oxygen . 
 W ater . 
 
 711.5 
 
 400 
 
 150 
 
 1 at. peroxide . . . 1261.5 
 
 The following result is obtained by heating the mixture : — 
 
 Anhydrous Peroxide of Iron. 
 
 2 at. iron .... 678.45 
 
 3 at. oxygen . . . 300 
 
 Anhydrous Sesquioxide of Manganese. 
 
 2 at. manganese . . . 7H-5 
 
 3 at. oxygen . . . 300 
 
 978.45 
 
 These hydrates, it is evident, must be mixed together in equal parts. 
 
 1011.5 
 
80 
 
 OF THE PIGMENTS IN PARTICULAE. 
 
 PROTOXIDE OF MANGANESE AND PEROXIDE OF COBALT. 
 
 This combination is obtained by precipitating with an alkali, as in the case of 
 iron, from a solution of sulphate of manganese and sulphate of cobalt, in equal quan- 
 tities and of equal density, and calcining the precipitate merely at a red heat. The 
 atoms of the acids are here likewise combined in equal proportions. We have as- 
 sumed these proportions for all analogous combinations. 
 
 PROTOXIDE OF MANGANESE AND OXIDE OF COPPER. 
 
 The composition is prepared in the same way as the foregoing ; but it is better to 
 eifect the precipitation from the sulphate of copper and sulphate of manganese with 
 an alkaline carbonate, because the oxide of copper is very likely to he re-dissolved if 
 an alkali is used. Moreover, the proportions of the solutions must he equal. We 
 may proceed in the same way in the calcining ; it is as well, however, to add a little 
 nitric acid to the mixture, to render the oxidation of the manganese complete. 
 
 PROTOXIDE OF MANGANESE AND OXIDE OF CHROMIUM. 
 
 This combination arises from pouring chromate of potash into a solution of sul- 
 phate of manganese. The protoxide of manganese is oxidized at the expense of the 
 chromic acid, which is thus transformed into oxide of chromium. 
 
 PROTOXIDE OF MANGANESE AND OXIDE OF SILVER. 
 
 This combination arises from heating a mixture of peroxide of manganese and 
 metallic silver, which has been precipitated with copper from a solution of nitrate 
 of silver. 
 
 OXIDE OF IRON AND PEROXIDE OF COBALT. 
 
 This is obtained from a mixture of solutions of sulphate of iron and sulphate of 
 cobalt, which are treated with an alkaline suhcarbonate, in order that the precipitate 
 which is thus obtained may be calcined. 
 
 OXIDE OF IRON AND OXIDE OF COPPER. 
 
 The same process as before. 
 
 OXIDE OF IRON AND PROTOXIDE OF COPPER. 
 
 A mixture of oxide of copper and finely triturated iron filings are subjected to a 
 red heat The copper returns into the state of protoxide, and gives up its oxygen 
 
OF THE PIGMENTS IN PARTICULAR. 
 
 81 
 
 for the iron to form an oxide with it. Probably it would be necessary, in using this 
 compound as colouring matter, to keep it carefully from the air as soon as it passes 
 into a liquid state. We may avail ourselves of this composition for colouring glass 
 red, but it is probable that in this case there is no combination between the two 
 oxides. 
 
 OXIDE OF IRON AND OXIDE OF CHROMIUM. 
 
 This combination takes place when a solution of protosulphate of iron is treated 
 with chromate of potash. The protoxide of iron is brought into a higher state of ox- 
 idation by means of the oxygen which the chromic acid gives up, and the chromic 
 acid is thereby reduced to the state of oxide of chromium. 
 
 PROTOXIDE OF COPPER AND OXIDE OF SILVER. 
 
 This combination is obtained by heating in a crucible oxide of copper with me- 
 tallic silver in the form of powder. The same phenomena may be observed here as 
 in the case of iron and copper. 
 
 PLUMBATES. 
 
 We have already mentioned the fact, that oxide of lead to a great degree possesses 
 the property of combining with the other metallic oxides. The combinations into 
 which it enters with them are particularly valuable, although for an entirely different 
 reason from that for which the similar compounds of which we were just now speak- 
 ing are valuable : they are valuable, because the oxide of lead imparts a very slight 
 stability to them. But while it combines with the oxides, it dissolves them, sepa- 
 rates their particles, and facilitates in a remarkable manner the vitrification of those 
 pigments which are coloured by combination. 
 
 The most important of the plumbates are those of cobalt, copper, and manganese, 
 which are prepared by subjecting minium with the oxides of one or other of these 
 metals to a red heat. 
 
 M 
 
PART II. 
 
 CHAPTEK I. 
 
 THE MECHANICAL PART OF GLASS-PAINTING. 
 
 PEEPARATION OF THE COLOURS FOR USE. 
 
 We shall now distinguish the colouring materials, when combined with their fluxes, 
 by the epithet colour. 
 
 The colours must first be reduced to an extremely fine powder, by long-continued 
 levigation upon porphyry, or in a mill of porcelain biscuit, constructed expressly for 
 this purpose, which we shall describe hereafter. In order to do this it is necessary 
 to mix with it a sufficient quantity of pure water ; it is then dried and put away in 
 well-stopped bottles. 
 
 The levigated colours, at the time when they are used, are mixed with liquids 
 of various kinds, but all for the purpose, 
 
 1, of giving them sufficient stickiness and consistency, so that they may not run 
 on the surface of the glass ; 
 
 2, of causing them to adhere sufficiently, when dry, until the time when they 
 are fixed by the firing ; 
 
 3, of adapting them to the various kinds of paint-brushes which are generally 
 used in glass-painting. 
 
 These liquids are usually — water, oil of turpentine and oil of lavender, some- 
 what thickened by the substances which are to fix the colours, after they are dry, 
 upon the glass. Thus, for example, sugar-candy or borax are generally mixed with 
 water ; thickened oil of turpentine and oil of lavender to the oils of turpentine and 
 lavender. This inspissation is produced by a longer action of the air upon these 
 essential oils or essences. Among the preparations which are bought under the 
 
THE MECHANICAL PART OF GLASS-PAINTING. 
 
 83 
 
 name of thickened essence of turpentine, &c., we must distinguish between those 
 which have been really thickened by the action of the air, and those which are 
 nothing more than the residue after the distillation of the ordinary essences of tur- 
 pentine and lavender. A residue like this will never answer our purpose well, and 
 we might just as well use turpentine, or even varnish. But it will be explained 
 hereafter why liquids of this kind must be rejected. 
 
 The fat, or thickened essence, as it is called, is obtained by exposing to the air 
 and light one of the above-mentioned essential oils in a glass vessel with a wide 
 mouth, which must be covered with a woven texture that will allow the air to pass 
 through without difficulty. The contents are stirred from time to time, and the 
 essential oil has attained to the proper degree of inspissation when it is of the con- 
 sistency of a thick syrup. * 
 
 The water colours and the essential oil colours may both be advantageously 
 employed, and they are frequently used alternately in one and the same painting. 
 
 The implements with which the colours are laid on glass are various sorts of 
 paint-brushes, viz. : — 
 
 1, Marten^ s hair pencils % brushes which run to a fine point, and are generally 
 used for water-colour painting ; 
 
 % Fitch pencils^. — These are not finely pointed, but cut off abruptly at the 
 lower part, so that they present a flat surface perpendicularly to their length ; 
 
 3, Broad Badgei'’s hair pencils". — These are broad and flat brushes for softening 
 the colours ; 
 
 4, Stockfish tails **, of soft hog’s bristles, of the same form as the foregoing ; 
 
 5, Hard pencils, of the same form as the fitch-pencils, only prepared from hog’s 
 bristles ; 
 
 6, Hog’s bristle pencils ", such as are used for oil-painting. 
 
 USE OF THESE PENCILS. 
 
 In order to lay an uniform coating of colour upon the glass, a marten’s hair 
 pencil must be used, when the space which has to be covered is small ; if, on the 
 contrary, it is large, either a stockfish tail, or a cut badger’s hair pencil, must be 
 used. By the help of these implements, the colour is laid on the glass and spread 
 over its surface by being rubbed in one direction, and then in the opposite, until the 
 whole coating is uniform. Painting of this kind has generally furrows or channels 
 
 ^ Marderpinsel. ^ Iltispinsel. ® Dachspinsel. 
 
 Stockfischschwanze. ® Die pinsel ans Schweinsborsten, 
 
 M 2 
 
84 
 
 THE MECHANICAL PAET OF GLASS-PAINTING. 
 
 which are caused by the hairs of the pencil, but these may be removed when it is 
 considered necessary, by means of a fitch pencil, or, still better, by means of a cut 
 badger’s hair pencil. 
 
 The fitch pencil, as we have stated, is terminated by a flat surface, and it is used 
 for touching the glass with the ends of its hairs, but not for drawing over the sur- 
 face, as is the case with the other pencils. If this is done skilfully, and continued 
 for a sufficient length of time, not only will the streaks thereby disappear, but the 
 colour will also be diffused uniformly over the whole of the surface which is to be 
 covered. The pencil must, however, be used until the colour is almost dry, and a 
 very short time before this takes place the colour will be distributed with perfect 
 uniformity. 
 
 The fitch pencil answers very well for laying on thin coatings of very liquid 
 colour, when they are required. A little colour is taken with the pencil from 
 the palette, and lightly dabbed on those parts which are to be covered with the 
 colour 
 
 The marten’s hair pencil, on the contrary, is used for laying on those colours 
 which are required to be fused, for marking the lines, &c. 
 
 The hard pencil of the same form as the fitch-pencil, is used for removing certain 
 water-colours which were previously laid on the glass, in order to execute in this way 
 a species of painting of which we shall presently speak more fully. 
 
 For mixing up the colours properly, certain precautionary measures are necessary. 
 When a colour is to be mixed with an essential oil, for example, a little of this 
 colour, which, as w'e have before stated, must have been previously well levigated 
 and dried, is put upon a palette and mixed, by means of a spatula, with a sufficient 
 quantity of thickened essence to allow of its being worked to a stiff paste. It is then 
 diluted with more or less essential oil of turpentine, according as the colour which is 
 to be laid on is intended to be of a more or less rich tone ; it is then ground a little 
 more in the mill, and used in the manner above described. These precautions are 
 especially important towards ensuring a successful use of the fitch pencil. 
 
 The process is the same wdth regard to the water-colours, except that instead of 
 a thickened essence a thick syrup is used, and instead of essential oil of turpentine, 
 water. The object of this method of operation is to determine the proportion of sugar 
 or thickened essence without difficulty. For the borax colours, and even for those in 
 w'hich pure essence of turpentine is used, we are limited to the employment of as 
 much liquid as will yield a thick paste. As a general rule, the enamel colours 
 should not be much moistened. 
 
 It is not immaterial whether a water-colour or an oil-colour, and whether essence 
 
THE MECHANICAL PART OF GLASS-PAINTING. 
 
 85 
 
 of turpentine or essence of lavender be used. The water-colours are, generally 
 speaking, more liquid than the oil-colours, under circumstances in other respects the 
 same. They have less consistency, and consequently do not admit of being softened 
 so well with the paint-brush. On a large surface of paint, the oil-colours are much 
 better adapted to forming an uniform layer of colour, and the streaks and furrows 
 which the stockfish-tail leaves behind may be more easily removed by means of the cut 
 badger’s hair pencil. The use of the fitch pencil also ensures a far more satisfactory 
 result with oil-colours, and consequently these colours are preferred in all cases 
 which are analogous to the above. 
 
 In comparing the essence of lavender with the essence of turpentine, we find that 
 the latter dries much sooner than the former ; the former, therefoi-e, is employed 
 whenever a liquid which is long in drying is required. It is not used alone in the 
 preparation of the colours, but as much of the essence of turpentine is mixed with it 
 as is necessary to cause it to dry at the proper rate. These means are employed 
 when the fitch pencil is to be used for softening, which always requires time. In 
 the water-colours we cannot advantageously substitute for sugar other viscid sub- 
 stances, e. g., gum, &c. ; for the former has the advantage of being much softer, and 
 at the same time not so liable to peel off. 
 
 Two styles of execution essentially different from each other are adopted in glass- 
 painting. That which in former times was chiefly employed, namely, the Gothic, 
 consisted in using no enamel for colouring the glass, but in merely marking the 
 outlines and shadows with a brown opaque pigment upon glass which had been 
 coloured in the melting pot. This style of painting, or rather of drawing, notwith- 
 standing its simplicity, is susceptible of the most beautiful effects which the decora- 
 tion of panes of glass is capable of producing. To it we are indebted for the beau- 
 tiful Gothic windows which adorn our old churches. This style of glass-painting is 
 moreover the easiest of execution, for the artist need only be a skilful draughtsman, 
 and has occasion for nothing else, except one single pigment, which is easily pre- 
 pared, and not at all difficult to use. 
 
 The second style belongs to the period of the revival of glass-painting; it supposes 
 likewise the use of coloured glass, but at the same time requires the use of numerous 
 pigments, hy means of which the artist executes a real painting on the glass, which, 
 in regard to its effects, may be compared with oil-painting. The artist is therefore 
 under the necessity of having a palette covered with vitrifiable colours, which is of 
 the same use to him as a palette supplied with oil-colours is to the oil-painter. The 
 execution of this style is difficult, and requires a particular study. 
 
 Glass-painting, taking it altogether, presents numerous and considerable difficul- 
 
86 
 
 THE MECHANICAL PART OF GLASS-PAINTING. 
 
 ties, which proceed from the nature of the colours and of the glass itself, either in 
 relation to the mechanical application of the pigments, or in relation to the realiza- 
 tion of the results which the artist endeavours to obtain. We will mention the kinds 
 of manipulation which are necessary in the various cases. 
 
 The smooth and polished surface of glass is not very favourable to the laying on 
 the colours. When we are laying any colour on the glass, a second stroke of the 
 brush frequently takes off what the first had deposited ; and thence arises the im- 
 possibility of hesitating in this work. This difficulty has disposed some artists 
 to paint only on glass whose smooth surface has been removed by sandstone or 
 emery. 
 
 But the greatest obstacle to the painter arises from the nature of the vehicle, 
 which does not easily admit of the several coatings of colour being laid one over 
 the other, which, on account of the substances that are used, do not even adhere 
 after the first coating is thoroughly dry. As the vehicle for fixing on the first coat- 
 ing retains its solubility, it is capable of being softened and removed from the surface 
 by the succeeding coatings. To meet this difficulty it was happily suggested that 
 the vehicle should he changed in every coating of colour which was laid on over 
 another. Thus, for example, we paint with water-colour upon an oil-colour, and 
 vice versa, with oil-colour upon a water-colour. The fixing substances of the one 
 colour being insoluble in the liquid of the other, there is no danger of removing, by 
 a second application of colour, that which has been produced by a first. 
 
 The inconvenience, however, which accompanies the employment of colours pre- 
 pared in different ways, gave rise to the discovery of a method by which we may 
 paint with the same vehicle. This discovery was arrived at by observing the follow^- 
 ing fact. An oil-colour rendered viscid with thickened essential oil of turpentine, or 
 V enice turpentine, retains its solubility in this liquid, if it has been dried by exposure 
 to the air ; hut if the painted pieces of glass have been submitted to a moderate 
 temperature in a drying-oven, the colour loses its easy solubility, bears the friction 
 of the pencil very well, and the fresh coatings may be laid on without difficulty. 
 
 In proceeding according to the method which we have just described, the painter 
 will sometimes have occasion to interrupt his work, in order to dry the painted 
 pieces of glass in the oven ; and this circumstance was so disagreeable to many 
 artists, that they considered how they might avoid the necessity of doing so, and at 
 length they succeeded in painting on glass with water or oil-colour, as is the practice 
 in painting on canvass, without being obliged to dry the first painting. We must 
 observe, however, that this is to he attributed more to their skill and dexterity, than 
 to the method itself to which they ascribe this invaluable superiority in practising 
 
THE MECHANICAL PART OF GLASS-PAINTING. 
 
 87 
 
 their art. In order to explain their method of proceeding, we will consider a paint- 
 ino- with water-colours. The artist first of all makes up his colour, and mixes with 
 it no more sugar than is necessary to cause it to adhere. This colour laid on, he 
 paints upon the first coating with colours which contain more dissolved sugar, with- 
 out being thereby of a thicker consistency. The increasing solidification of the 
 vehicle prevents its solvent action upon the colour which was originally laid on. 
 
 If this is dexterously performed, it admits of the painting being impaste, to use a 
 technical expression. But nothing but long experience and perfect dexterity will — 
 we repeat it — enable us to employ this method with advantage. 
 
 For the execution of paintings on glass, particularly Gothic, a method as simple 
 as it is ingenious, is frequently had recourse to, which enables the artist to work with 
 the greatest certainty of success. This mode of painting is designated by the 
 French term, peinture par enlevage, and consists in drawing the outlines with an oil- 
 colour, and painting over the whole with a water-colour, which, after it is perfectly 
 dry, is to be removed with a hard paint-brush. By a dextrous use of this paint- 
 brush, portions of colour of different degrees of thickness are removed, according as 
 shadows, half-tints or lights are required. Wherever the glass is left bare by a com- 
 plete removal of the colour, we get the lights ; the places which the brush has spared 
 give the shadows, and the half-tints are produced by an imperfect removal of the 
 colour. In this way the process of laying on the ground-colour of the picture 
 is performed, and after the latter has undergone the firing, it is again painted over, 
 and retouched with a colour which has been made up with sugar or thickened 
 essence. 
 
 The colour proper for the peinture par enlevage is an enamel colour, with which 
 a little borax is mixed, and which is then levigated with enough water to give a 
 thick paste. The colour is laid on by means of a stockfish-tail, and softened 
 uniformly with a cut badger’s hair pencil, with the assistance of which the colour is 
 easily spread over the glass. The small quantity of borax which has been mixed 
 with the colour causes a sufficient adhesion of the latter to the glass, so that the hard 
 pencil may be fearlessly applied to the removal of the water-colour. 
 
 The majority of the pigments of the second class are well adapted to the 
 employment of this method. There are, however, among the pigments of the first 
 class, some whose colouring matter is acted upon by borax, so that a combination 
 arises which imparts to the colour which has been laid on too much adhesiveness to 
 admit of its being removed with the hard pencil. Among these colours are ochre 
 yellow and all those pigments which contain oxide of zinc. 
 
88 
 
 THE MECHANICAL PART OF GLASS-PAINTING. 
 
 This unpleasant circumstance may, however, be certainly obviated by fritting 
 these pigments before they are levigated for mixing with borax. 
 
 To frit a pigment is to heat it to that point at which it coagulates, and, by reason 
 of an incipient fusion, forms a mass of the consistency of dough. 
 
 Pigments of the second class are seldom used for the peinture par enlevage. As 
 this kind of painting only has in view a simple sketch upon a previously coloured 
 ground, it requires in most cases merely an opaque pigment coloured by mixture. 
 That which is best adapted to this purpose, consists of a flux of flint glass and of 
 brown or violet oxide of iron in the usual proportions, with a mixture of calcined 
 borax, whose weight is equal to the eighth part of that of the flux. The proportions 
 of the borax and the flux are calculated for the preparation of flux No. 3 of the 
 pigments of the first class. 
 
 The method which we have just described is capable of an important modifica- 
 tion with respect to the preparation of the colour proper for peinture par enlevage. 
 Instead of dissolved borax, merely the oil of turpentine of commerce is used. In 
 this case, the drawing is first sketched with a pen in water-colour, and a coating of 
 oil-colour is laid on over it. This modification is based upon the property which 
 essence of turpentine possesses of giving sufficient firmness for the enlevage pencil to 
 be used. The essence of turpentine owes this property to a small quantity of resin 
 which it contains, but which is not to be found in it after it has been rectified by a 
 new distillation. Hence it follows that this method is the opposite to the former. 
 Certain precautionary measures, however, ought not to he neglected, to obtain a suc- 
 cessful result. The water-colour must accordingly be properly mixed with sugar, so 
 that the oil-colour may be incapable of softening it. Moreover, after the oil-colour 
 is laid on, it must be submitted in the drying oven to a temperature sufficient to pro- 
 duce the requisite firmness. It is also necessary to avoid adding essence of turpen- 
 tine frequently to the same colour, because the proportion of resin is likely to be in- 
 creased by that means, and the consequence would be too strong an adhesion of the 
 pigment to the glass, so that it could not then be easily removed with the enlevage 
 pencil. 
 
 Circumstances arise in which this method is rather complicated, and this is the 
 case when it is required to paint upon glass which has not been coloured. In order 
 to paint a head, for example, a light tint is laid on for the colouring of the lights, 
 and upon this a coating of colour suited to the enlevage, in order to form the shadows 
 and half- tints. Thus, upon a drawing prepared with water-colour, the first coating 
 must be laid on with a colour mixed with thickened essential oil, and the second with 
 
THE MECHANICAL PART OF GLASS-PAINTING. 
 
 89 
 
 a colour mixed with borax ; but if the drawing has been executed in colour mixed 
 with thickened essential oil, the first coating of paint must be laid on with colour 
 mixed with sugar water, and the second with colour moistened with pure essential 
 oil, in conformity with the directions we have given above. 
 
 The peinture p>ar enlevage is not only simple, but is also executed in a very 
 short time. It is peculiarly adapted to decoration, especially to the execution of 
 such designs as stand out in light colours from a dark ground, and to the representa- 
 tion of the embroidered parts of drapery. In this case the enlevages are executed 
 in a different way. To make the drawing clean and correct, wooden scrapers of 
 various forms must be substituted for the hard pencils. The colour which is here 
 operated upon is of no particular kind, but may be any pigment whatever that has 
 been levigated with thickened essential oil. 
 
 Finally, glass-painting justifies every possible artifice, the object of which is to 
 lessen difficulties, or to enable us to obtain results which are not to be obtained in 
 any other way. Thus, for example, it is not uncommon to paint both sides of the 
 glass, in order to obviate the unpleasant results of laying on one colour over the 
 other. The same method is adopted in the case of yellow from silver, because the 
 substances by which it is produced ought not to be brought into immediate contact 
 with the colouring enamels. In this way a green is obtained, that is to say, by giving 
 a yellow stain to the back of a piece of glass which has been painted blue. 
 
 The same method is also followed in order to impart brilliancy and a remarkable 
 freshness to the brownish red colours from iron ; that is to say, a yellow is applied 
 to the opposite side to the brown. 
 
 Whatever method be adopted, the employment of the colours is always, however, 
 subject to certain restrictions. Care must be taken to use as few mixtures as pos- 
 sible. The colours are by means of the latter mutually destroyed at the temperature 
 at which they are burnt in, while at the same time new combinations take place. 
 By avoiding a mixture of the pigments we obtain purer, less perishable and much 
 more certain colours. It is better to lay one colour over the other, instead of mix- 
 ing them. In order, therefore, to produce an effect similar to that which may be ob- 
 tained with ochre yellow and red from iron, the yellow is first laid on and then tem- 
 pered with red. 
 
 It is also of consequence to lay on the pigments as thin as possible, and there are 
 several reasons for so doing. Thus if the colours are laid on too thick, the adhesive sub- 
 stances that are in them form a mass which possesses too little softness and flexibility. 
 The motions caused by expansion, which the glass undergoes in the changes of tem- 
 perature, unless they are shared by the painting, at length overcome the adhesion 
 
 N 
 
90 
 
 THE MECHANICAL PART OF GLASS-PAINTING. 
 
 of the colours and loosen them from the surface of the glass. This always takes 
 place when water-colours and oil-colours are laid on in alternate coatings, for the he- 
 terogeneous qualities of the substances by which those colours are fixed are still more 
 conducive to this result. The mere drying of itself is often sufficient to produce this 
 unpleasant result in consequence of the unequal contraction of these substances. 
 
 On the other hand the water-colours certainly part with the water they contain, 
 in drying on the glass, but then they retain the sugar which was mixed with them ; 
 the oil-colours give up the volatile part of their vehicle, whilst the thickened essence 
 which is in the latter has lost the power of being converted into vapour, and conse- 
 quently remains upon the glass. Hence it follows, that these substances must be 
 consumed in the firing, and leave a certain quantity of carbon lying between the par- 
 ticles of the pigment. This body re-acts upon certain combinations, e. g., the oxides 
 of iron and lead, which it turns black by robbing them of their oxygen, which it does 
 so much the more, as the carbon being protected by a thick coating of colour resists 
 combustion the longer. This circumstance is at least of importance with regard to 
 the flesh colouring. This co7itretemps which we have just pointed out would not take 
 place if a firm substance, and one perfectly volatile at a certain temperature were in- 
 variably used as a means of fixing on the colour, as, for example, camphor, or 
 borax, which contains no carbon at all. But the former substance is yet to be tried, 
 and the latter could not always be conveniently used. Nevertheless, it follows from 
 what we have already stated, that, of the substances which are adapted to fixing the 
 painting upon the glass, the preference should be given to those whose combustion 
 leaves the least carbon behind, and which at the same time preserve a certain ductility, 
 as a security against cracking and splitting. Perhaps wax would answer very well 
 with regard to these two particulars, for a portion of it volatilizes when it is exposed 
 to heat, and it possesses moreover great ductility. For this purpose we have only 
 to dissolve it in essential oil of turpentine. 
 
 It would be a waste of time to describe the various manipulations used here, 
 which are purely artistical ; and we would rather therefore confine ourselves to some 
 few particular cases. Painting on glass is always done by copying oil-paintings, or 
 original designs expressly prepared, which are called cartoons. The original de- 
 sign is traced by means of transparent paper, and this is used for transferring the 
 drawing to the glass. For this purpose the piece of glass is laid upon the tracing, 
 which has been first spread out upon a table. The transparency of the glass makes 
 it easy to follow the outlines and shadows of the tracing ; but if the glass is very 
 much coloured and destitute of transparency, it becomes necessary to use a perforated 
 pattern for finding out the drawing through the glass. This is a kind of tracing. 
 
THE MECHANICAL PART OF GLASS-PAINTING. 
 
 91 
 
 the outlines of which are drawn through numerous contiguous punctures of the size 
 of a needle’s point. The paper which lies on the glass is then struck with a hag of 
 powdered charcoal, and the outlines appear marked with sufficient distinctness. It 
 is best to begin by drawing in Indian ink the object to he painted, when it is in our 
 power to correct and modify the sketch, just as we think proper, and then the paint- 
 ing may be executed according to it with the greatest certainty. If corrections are 
 made after the pigments have been laid on, a want of uniformity and completeness 
 will always be observed in the work. Besides, correcting is then much more difficult. 
 In other respects the same rules and precautions are applicable to glass-painting as 
 to painting on canvass. The easel and the maulstick are used equally in both. The 
 easel is constructed in a particular manner, which we shall describe hereafter. The 
 pieces of glass that are placed upon it must be fastened with a soft adhesive wax pre- 
 pared solely for this purpose. In order to take advantage of the transparency of the 
 glass, the painter places his picture between himself and the light, and can at once 
 judge of the effect of his work, as he proceeds, 
 
 A paint-brush or a goose-quill is used for drawing on glass with a pigment. A 
 water-colour is best adapted to the goose-quill. Oil-colours, which are preferred for 
 painting upon a flat surface, because they admit of being diffused more uniformly 
 with the pencil, are not suited so well to the quill and do not adhere so well to the glass ; 
 nevertheless they are frequently used. A large quantity of sugar facilitates the 
 drawing ; still it is necessary to define the amount which should be mixed with the 
 colour. Six grains of sugar to one drachm of colour produce a sufficiently strong 
 adhesion, but for the quill at least seven grains of sugar must be mixed with the 
 colour. A mixture of twelve grains would cause the colour to peel off. It is a very 
 good precaution, when it is intended to paint with a quill, to wash the glass beforehand 
 with essential oil of turpentine. Drawing in Indian ink is likewise more easily exe- 
 cuted if this plan he adopted. 
 
 Should it devolve upon a glass-painter to paint a church-window of large dimen- 
 sions, he must begin by dividing it into more or fewer compartments which are sur- 
 rounded by iron bars properly disposed and firmly united, so that all parts may be 
 equally firm. He first determines the direction which is to be given to the iron bars and 
 lead casing which are intended to unite the different parts of the picture. In doing 
 this- he must study to make these parts follow the outlines as much as possible, and to 
 hide them in the shadows in such a way that they may not injure the effect of the 
 picture. He ought not to be afraid of giving them a proper thickness, and increasing 
 their number when necessary for the sake of greater firmness ; this is of the greatest 
 importance for the duration and preservation of a work of art which is always exposed 
 
 N 2 
 
THE MECHANICAL PART OF GLASS-PAINTING. 
 
 92 
 
 to the violence of the winds. It is a necessary condition which fetters the author of 
 the original design himself in his composition. He must always take care that 
 the execution of the painting will not require pieces of glass which are too large to 
 admit of being durably fixed by means of iron bars and leading. 
 
 If the artists of the present day understand not only how to ensure firmness to a 
 painting on glass, hut also at the same time how to satisfy the demands of the art as 
 far as is necessary, this, whatever may be said of it, is an improvement which we owe 
 to the modern style of painting, and to which the manufactory at Sevres has greatly 
 contributed. As for the rest both these conditions may be satisfied at once 
 without much difficulty. The presence of the iron bars and of the leading does 
 not disturb the harmony of the painting neaidy so much as would be supposed. Can 
 this be a magical result of this kind of human creation ? The human mind has the 
 power of dismissing these obstructions, and the largest of them always appear like ob- 
 jects which are outside the picture. Now whether the ancients sacrificed everything 
 to solidity, or were deficient in mechanical skill, their church- windows afford frequent 
 instances in which the painting is far from harmonizing with the materials which 
 support it. Thick iron bars are frequently carried across the figures or abruptly cut 
 the masses in the finest centre of light. Every one, therefore, will certainly coincide 
 in our opinion, namely, that this is granting too much to the demand of solidity and 
 too little to the effect of the painting. But did not a very simple principle of 
 economy frequently predominate in this matter ? This hypothesis seems at least 
 reasonable, the construction of the arming being one of the most expensive parts of the 
 construction of painted church-windows. When we come to work the iron bars into 
 complicated forms, this, as every one must see, can only be done at a great expense. 
 It is a consideration of some importance, why the ancients thought themselves 
 obliged to restrict the claims of the art to limits marked out by economy. 
 
 After we have explained the various manipulations of the proper art of glass- 
 painting, we must not omit to speak of a branch of industry which has something 
 in common with the art with which we are at present engaged. We mean the 
 manufacture of the mousseline glass, which consists in covering panes of ordinary 
 window-glass with a coating of opaque white enamel, upon which a transparent 
 sketch is drawn by enlevage, which seems to be executed upon a faintly-polished 
 ground. To obtain this result, a fitch pencil must be used, whose form we have 
 already described. This is dipped into thickened oil of lavender, and the surface 
 of the glass is touched perpendicularly with it until the whole is covered with an 
 uniform coating. As soon as this layer has acquired a proper consistency, a powder 
 composed of one part of oxide of tin and three parts of a fiux of the second class, 
 
THE MECHANICAL PART OF GLASS-PAINTING. 
 
 93 
 
 is sifted over it. The thickened essence retains a proper quantity of this enamel. 
 This coating is then dried for six or eight hours, and after it has become sufficiently 
 hard, the excess of enamel powder is removed by means of a badger’s hair pencil. 
 
 Now, in order to draw upon a plate of glass like this lines which shall possess the 
 polish and transparency of glass, we lay under the glass a pattern whose lines are 
 sufficiently conspicuous even through the layer of powder. The pattern having been 
 previously well secured, the artist removes by means of an etching tool the colour 
 from those places which are indicated by the drawing. This painting is now exposed 
 to a proper degree of heat, that it may adhere or become burnt in. There is little 
 in this operation that admits of the application of the proper art of glass-painting, 
 the use of the wooden etching tool alone being accidentally borrowed from this art. It 
 is an exceedingly convenient tool for executing transparent drawings in imitation of em- 
 broidery ; it is also much better adapted tg enlevages than the steel scraper. The 
 method which is employed in producing white enamel is preferred on account of its 
 succeeding in a very short time, but is better adapted to white enamel than to the 
 other colours. Laying on by means of the fitch pencil ensures greater uniformity, 
 and enables us to obtain the requisite tone of colour with certainty. 
 
 THE BURNING IN OF THE PAINTING. 
 
 The glass, after it has been painted, must be exposed to a temperature at which 
 the pigments liquefy, and are thereby united to the glass. For this purpose the 
 pieces of glass are arranged in a kind of box of fire-clay, called the mvjfle, which is 
 placed in a furnace and there heated until the colours which have been laid on are 
 liquefied. 
 
 DESCRIPTION OF THE FURNACE. 
 
 The furnace consists of four walls formed by bricks standing on their ends ; these 
 bricks enclose a space which is again subdivided into three parts. The upper com- 
 partment contains the muffle, which is open in front for the purpose of putting the 
 glass in and taking it out. This aperture must be walled up, after the muffle has been 
 filled. The intermediate space contains the fire-place ; the lower space contains 
 the ash-pit. A cast-iron grate separates the fire-pot from the ash-pit ; it is 
 composed of single cast bars, in order that it may be more easily repaired. These 
 bars are merely laid by the side of one another. Two or three arches span the 
 fire-pot transversely, and are placed at equal distances from each other ; they serve 
 for the support of the muffle. An arch of burnt clay is perforated with several 
 
94 
 
 THE MECHANICAL PART OF GLASS-PAINTING. 
 
 holes to allow the escape of the flame and the products of combustion. The mufile 
 has a wide aperture in front for the purpose of putting in and taking out the glass, 
 and another one of a small size under the arch for the escape of the gases which are 
 evolved in the interior of the mufile. The door which closes the large aperture is 
 usually provided with a sort of pipe in the middle, through which the experimental 
 pieces of glass or the pyrometer are introduced into the mufile. By means of the 
 latter we are enabled to observe the temperature. It is better, however, to have two 
 apertures of the same kind, as we shall presently see on a closer examination. 
 
 MANAGEMENT OF THE PAINTED PIECES OF GLASS IN THE MUFFLE. 
 
 As the colours which have been laid on are to be melted, the plates of glass should 
 not be placed in immediate contact with one another, or they would necessarily bake 
 into one mass. They are therefore laid apart from one another by means of fire- 
 proof earthenware shelves, (in France, by means of slabs of lava from Auvergne,) or 
 plates of cast-iron, which are ranged horizontally in parallel layers, so that a 
 small space is always left between them. These shelves are kept apart by the 
 insertion of small parallelopipeda of baked clay in the four corners. The shelves 
 are also laid upon cross-bars of iron, of which two are used for every shelf, and are 
 inserted at both ends of the mufile into notched bars ; the former method, however, 
 is preferred. Before the glass is put into the mufile, the shelves must be covered 
 with a stratum of Spanish chalk mixed up with water, so that the glass, if it should 
 happen to become soft when heated, may not adhere to the surface of the shelves. 
 This coating of the shelves must be carefully dried, and then the pieces of glass 
 must be laid side by side, but without touching one another ; moreover, a clear space 
 must be left at each corner of the shelves for the little supports which we have 
 already mentioned. After the mufile has been filled, the aperture is hermetically 
 sealed by being plastered over with clay which is proof against fire, and the front of 
 the furnace is walled up with bricks. Thus shut up, the glass may be heated with- 
 out the colours being exposed either to the action of the flames or the vapours which 
 arise from the fire-pot. 
 
 According to Dr. M. A. Gessert, to whom we are indebted for an excellent history 
 of glass-painting, the introduction of the painted pieces of glass into the muflBie is 
 efiected in the following way in Germany ; — Well-calcined lime is first of all slaked 
 with water, and when it has crumbled to powder, is properly dried over the fire. 
 The bottom of the mufile to the thickness of an inch is covered with this powder, as it 
 falls through a coarse hair-sieve ; this substratum is carefully levelled, otherwise the 
 
THE MECHANICAL PART OF GLASS-PAINTING. 
 
 95 
 
 pieces of glass might become distorted in the firing ; these pieces of glass are then 
 laid side by side, but in such a manner that they may not be in contact either with 
 one another or with the sides of the mufile. A thin layer of lime is then sifted over 
 them, other painted pieces of glass are disposed in a second series, and the process is 
 continued, until we reach the centre of the muffle, at least the aperture for drawing 
 out the tests, which consist of strips of glass from 6 to 7 inches in length and 1 inch in 
 breadth, painted over with patterns of the colours which are to be burnt in. These, like 
 the painted pieces of glass, are laid upon a stratum of lime, and sprinkled over with a 
 coating of the same, but are so arranged that one end of them reaches to the centre 
 of the muffle, while the other projects half an inch out of the test aperture, to admit 
 of their being taken hold of and drawn out by the pincers. The artist then continues 
 introducing the other pieces of glass, and strewing line, until all have been arranged 
 in their places in the manner above described, or the muffle is full. If only one has 
 to undergo the burning in, the muffle is filled with ordinary pieces of glass instead of 
 painted glass, and the only piece which is to be fused is introduced into one of the 
 interior layers of the muffle. The latter is then covered up. 
 
 The furnace must be heated with wood, inasmuch as no other kind of fuel will 
 answer the purpose, at least for the species of furnace of which we are now speaking, 
 because the heating of the muffle is effected less by radiation from the fire-pot than 
 by contact with the flames. Consequently that kind of wood should be selected 
 which gives a long and bright flame, e. g., the wood of the aspen, birch or poplar, 
 which, moreover, must previously be seasoned as thoroughly as possible. The fire 
 must be made to burn up slowly, in order that the muffle may acquire the same degree 
 of temperature in all its parts. The ignited matter must therefore have time to pro- 
 pagate itself. Were we to proceed otherwise, the glass which lay next to the sides 
 of the muffle would have already endured a degree of heat which would not only af- 
 fect the pigments but would even bring the glass itself into a state of fusion, whilst 
 the plates of glass which were situated in the centre of the muffle had only attained 
 the proper degree of temperature. The better to escape so unpleasant an occurrence, 
 we must proceed in the following manner : — 
 
 The fire must be constantly kept at a moderate temperature, until the muffle has 
 attained a lively red heat, when the temperature must be lowered. The heat pene- 
 trates into the interior, and the muffle at last becomes of a dull red heat ; the fire is 
 now stirred, and as soon as the muffle is again at a lively red heat, is lowered a 
 second time. This is continued until the centre of the muffle is at the requisite 
 temperature. According to this method it can never happen that the exterior of the 
 
96 
 
 THE MECHANICAL PART OF GLASS-PAINTING. 
 
 muffle has already attained a high temperature before the interior is properly 
 heated. 
 
 The temperature which it is intended to arrive at is generally a moderate cherry 
 red heat ; this is determined by looking into the various apertures of the muffle. 
 But these observations are very liable to error, because we are not always in the 
 same condition with regard to light. Suppose, for instance, that the room in which 
 the furnace stands is very well lighted, then the red-hot muffle is not nearly of so 
 bright a colour. In a more subdued light, the red appears much more intense ; so 
 that one day’s experience is frequently fallacious. It is therefore necessary to hang 
 curtains before the windows, in order to obtain a tolerably uniform light for this ex- 
 amination. 
 
 The temperature is also determined by painted pieces of glass for testing, which 
 are laid in the apertures of the muffle ; but such tests as these are not conclusive, 
 inasmuch as they only indicate a local temperature. An experiment made in one 
 part of the muffle affords no clue towards determining the state of the other parts. 
 But if after all the artist should be disposed to use this test, he must endeavour to 
 keep always below the requisite temperature, and to lower the fire before the test- 
 glass has actually arrived at the proper degree of fusion ; for he may be sure that the 
 temperature will increase towards the centre. Carmine is generally employed in ex- 
 periments of this kind. The changes of colour which it undergoes in mass, when 
 it is raised to a higher temperature, render it peculiarly adapted to this purpose. 
 When not much heated it has a dirty violet colour, it then passes over into pure 
 carmine ; and when at length it is heated too much, it appears yellow in reflected 
 light, and violet in refracted light, that is to say, upon an opaque body, e. g., a piece 
 of porcelain, it will appear yellow ; upon a piece of glass, on the contrary, in trans- 
 mitted light, it will appear violet. 
 
 Finally, the temperature may he determined by means of particular instruments 
 contrived on purpose to measure the heat of the furnace. Among these are the 
 jyyrometers of Wedge wood and Brogniart. The former is constructed on the prin- 
 ciple that clay contracts in proportion to the heat to which it is exposed. It 
 consists of a plate of copper, on which two or three rulers, likewise of copper, 
 are fixed. Between these is inserted a cylinder of clay baked in the fire, which has 
 been exposed to the degree of heat which is to be determined. The more it has 
 diminished in bulk the greater was the degree of heat which was applied. The in- 
 strument is divided into 240 parts. The zero answers to 580.55° Centigrade ; every 
 degree is equivalent to 72.22° Centigrade. This pyrometer is therefore adapted to 
 
THE MECHANICAL PART OF GLASS-PAINTING. 
 
 97 
 
 the measurement of very high temperatures, hut does not answer well in the case 
 before us, in which the other is preferable. This latter is constructed on the prin- 
 ciple of the expansibility of the metals by heat, and consists of an apparatus of baked 
 clay, along which a groove runs longitudinally, but stops short of one of the ends. 
 A bar of metal and another of baked clay lie in this groove in such a way that their 
 ends touch one another. The other end is furnished with a dial-plate, in the centre 
 of which a finger moves, one end of which is in contact with the earthenware bar in 
 the groove. 
 
 That part of the instrument which contains the bar of metal is introduced into 
 the muffle in such a way that the bar shall be completely in the muffle. As it ex- 
 pands by the heat, it must necessarily, since it lies at the end of the groove, push 
 forward the earthenware bar ; the latter again communicates the impulse to the 
 finger, which then indicates upon the dial-plate the expansion which has taken place. 
 The metallic bar must he made of a metal whose point of fusion is far beyond the 
 temperature necessary for burning in the painting ; it must not even become too soft 
 at this degree of heat. Iron and silver may be employed for this purpose, but silver 
 is generally preferred, because it becomes less oxidized. If a metal still more dif- 
 ficult of fusion were required, a bar of platinum might be used. 
 
 In order that we may use this instrument efiectually, the following conditions 
 must be complied with ; — The door of the muffle must be furnished with two aper- 
 tures, one of which must be made in the lower part, and the other in the middle, or 
 rather about the upper third of its height. A pyrometer is prepared for each 
 aperture. When the lower one indicates a dull red heat, the fire is not allowed to 
 increase, hut is stirred in proportion as the heat has been reduced below that tem- 
 perature. The artist proceeds generally according to the directions above given, 
 until the upper pyrometer indicates a proper temperature. 
 
 In beginning to light the fire, it is important to cause a feeble current of air to 
 pass through the muffle, in order to allow the gases, which are formed in the latter 
 by the combination of the substances which are used for fixing the painting with 
 those which come out of the fire-pot, and penetrate through the sides of the muffle, 
 to escape with rapidity. For this purpose one of the apertures in front, as well as 
 that of the upper part, is left half open. Upon the latter is also placed a stove 
 chimney, a few decimetres in length, which when heated draws the air out of the in- 
 terior of the muffle, and accelerates its upward motion. It is only when the muffle is 
 being first heated that the most injurious of the external gases penetrate in larger 
 quantities. After it has arrived at a red heat, they become more completely dissi- 
 
 0 
 
98 
 
 THE MECHANICAL PART OF GLASS-PAINTING. 
 
 pated on the exterior. These gases always exercise a pernicious influence upon the 
 painting, which it is necessary to guard against. 
 
 The creating the current of air of which we have just been speaking, is not less 
 useful as a means of obviating an unpleasant occurrence, which, without this precau- 
 tion, frequently takes place, viz., the cracking of the painting. This may be ex- 
 plained as follows : — When the muffle is being first heated, a large quantity of smoke 
 often penetrates through the hole at the top. The glass is still cold, whilst the sides 
 cf the muffle are hot ; consequently the aqueous vapour of the smoke condenses in 
 small drops upon its surface. As soon as the glass begins to grow hot, the water 
 which lies upon it begins to boil before it is converted into steam, and at last affects 
 the painting with which it is in contact. The consequence of this is, that a peculiar 
 kind of cracking takes place, similar to that which varnish undergoes when it is laid 
 on an oil painting just finished. The possibility of this accident is diminished by 
 creating a draught of air at the commencement of the heating ; but this draught should 
 not be so strong as to chill, and consequently to crack the objects with which it comes 
 in contact. If this be avoided, it seems to be attended with no other prejudicial 
 results. 
 
 There is also another source of moisture, viz., in the clay with which the door of the 
 muffle is plastered over. It is customary, therefore, to heat for a short time the 
 mufile, with its contents, before plastering on the clay, and to close the furnace. The 
 muffle being already hot at the time the clay is laid on, its contents are not so likely 
 to condense the vapour. 
 
 That kind of glass-painting which is executed with coloured fused pigments, is 
 not finished after the first firing. The fusion of the colours gives in general 
 too feeble a tone of colour. The pigments of the first class especially lose some of 
 the intensity of their colour when they are exposed to too high a temperature. It 
 becomes necessary after the first firing to give expression to those parts which are 
 deficient in this particular, and generally to impart the requisite harmony to the 
 whole. It is even sometimes useful to re-touch the work after the second burning-in, 
 and in this case a third burning- in becomes neeessary ; but the painting is not ca- 
 pable of bearing more than this, for a large portion of the pigments would be consi- 
 derably damaged and even entirely destroyed by the repeated action of heat. When 
 a painting is to he burnt-in a second time, and it becomes necessary to restore har- 
 mony to the various parts of which it consists, the artist generally lays them together 
 in the position which they are afterwards intended to occupy, in order that he may 
 be enabled to judge of their combined effect. For this purpose he fixes them in 
 
THE MECHANICAL PART OF GLASS-PAINTING. 
 
 99 
 
 their respective places upon the glass plate of the easel, or upon a plate of glass of a 
 proper size, which is placed in a frame. 
 
 There are two ways of holding the pieces of glass together. They may 
 be fastened upon the glass plate with wax, which is spread out between the fingers 
 and rolled upon a flat surface. The wax takes the place of the leading, and fills up 
 all interstices. The pieces of glass may also be encased in lead. Fastening with 
 wax has the advantage of being materially cheaper than leading, only it is deficient 
 in solidity. When it is warm, the wax becomes so soft that the pieces do not hold 
 together well, and numerous accidents are the result. A work which has occupied 
 much time may be ruined in a single moment. It is also difficult to free the glass 
 entirely from the wax which adheres to it without a considerable loss of time, and if 
 any wax remains behind, it is injurious to the painting. Besides, the idea that lead- 
 ing is more expensive is merely illusory, when it is the painter himself who fastens 
 the pieces with wax ; for the cost of the leading is more than compensated for by the 
 value of his time, because the former is done by a glazier, who only solders together 
 the ends of the strips of lead. Fastening with wax is only practised at Sevres ; at 
 Munich leading is preferred. 
 
 OF ENGRAVING UPON GLASS WITH HYDROFLUORIC ACID. 
 
 This style of decoration, which has nothing in common with the proper art of 
 glass-painting, is nevertheless frequently and advantageously employed as an assistant 
 to this art. It is generally used for overlaid glass “, as it is called, (white glass, upon 
 which a coating of coloured glass is fixed in the blowing.) It consists of a kind of 
 white drawing upon a coloured ground, and it is obtained by removing the coating 
 of coloured glass in all those places where it is intended to lay bare the white stratum, 
 according to the form of the drawing. The process of engraving is as follows : — 
 The glass is first covered with a coating of oily copal varnish, or, what is better, with 
 merely linseed oil which has been boiled with litharge, in order to preserve from the 
 action of the acid the parts which are not to be etched. This layer is dried in the 
 drying-oven, and the varnish is then removed by means of a graver or needle, and a 
 scraping instrument, from those parts where the glass is to be acted upon by the 
 acid. As soon as this operation is finished, the plate of glass is laid horizontally 
 upon a table, and a raised border of wax is carried round the edge which is capable 
 of containing the acid, which is then poured upon the glass. The acid is allowed to 
 remain upon the glass as long as is necessary to destroy the coloured stratum wherever 
 
 ^ Ueberfanwolas. 
 
100 
 
 THE MECHANICAL PART OF GLASS-PAINTING. 
 
 it is exposed. After this, the piece of glass is washed and freed from the border 
 of wax and the wax ground. The engraving is clean and fine in proportion to the 
 thinness of the coating of glass, and the diluted state of the acid. If the acid is very 
 much concentrated, its action extends over the etching ground, and the lines seem 
 undermined. This kind of drawing is frequently employed for exhibiting silver em- 
 broideries upon coloured dresses. It is white at first, but may be coloured yellow, so 
 as thus to imitate gold ornaments. 
 
 Glass may be etched by means of hydrofluoric acid, because the latter has the 
 property of dissolving silica. But on account of the exceedingly pernicious effect of 
 this acid upon the health of those who employ it, it has been hitherto almost impos- 
 sible to use it. In order, therefore, to apply the art of etching on glass to the arts 
 and sciences, it became necessary to find out another means of etching perfectly harm- 
 less, and a suitable etching ground. Dr. Bromeis, of Hanau, a clever young chemist, 
 and after him the celebrated professor, Dr. Bottger, of Frankfort-on-the-Maine, 
 each however by himself, and without being acquainted with the researches of the 
 other, have now discovered such a method of etching, and by means of it have etched 
 plates of glass of any thickness, and have prepared them for giving impressions in 
 the presses which have been hitherto generally employed. 
 
 Professor Bottger gave a full account of this invention, which is called hyalo- 
 graphy by the inventors, in a lecture delivered at a meeting of the Physical Society of 
 Frankfort. At the same time he pointed out the advantages which were associated 
 with this discovery, of which we shall only particularise the following : — 
 
 1 . The snbstance used for etching is perfectly harmless, and no vapours or gases 
 are evolved, which, as is the case in copperplate engraving, are in the habit of pro- 
 ducing an injurious effect even upon the plate ; moreover, it does not lose its strength, 
 the same quantity can he used for etching several hundreds of lines in glass. 
 
 %. Glass admits of an exceedingly delicate treatment, and the lines are more 
 perfectly developed than in engraving on steel or copper. 
 
 3. All kinds of porcelain and flint-glass may he very easily supplied with colour- 
 ing and glittering ornaments, by rubbing in the drawings that are etched upon them 
 with vitreous porcelain colour, which is not difficult of fusion, and then burning it in 
 in the muffle. 
 
 The inventors intend to make known their method, which, independently of 
 hyalotypy, promises to be of great interest, for a very moderate remuneration, as 
 soon as at least fifty persons in the district of the Zollverein will combine to purchase 
 it. 
 
THE MECHANICAL PART OF GLASS-PAINTING. 
 
 101 
 
 DESCRIPTION OF THE EASEL PROPER FOR GLASS-PAINTING. 
 
 The easel consists of an oblong wooden frame, whose greatest dimension is its height. 
 Its interior edge is furnished with grooves for the reception of a plate of glass. This 
 frame is placed in a larger frame, and may be raised or lowered in grooves at pleasure. 
 We have an exact representation of it in the old sash-windows. The exterior frame 
 has a series of holes in the direction of its height, on both sides, and the interior 
 frame can thus be supported at any given height by means of pegs which are in- 
 serted into these holes on either side. This apparatus is placed obliquely on a table,, 
 and supported in this position by two props at the back, which are joined to the 
 upper part of the large frame by means of two hinges. These two pieces are joined 
 together by a cross-bar, and held at a proper distance from the frame by means of 
 moveable iron hooks ; a contrivance precisely similar to what we find in step-ladders, 
 for, like them, when it is not wanted to be used, it can be shut up, so as to occupy 
 less room. 
 
 mill’' for GRINDING THE PIGMENTS. 
 
 The mill is a circular vessel of porcelain, which receives the runner ° and the sub- 
 stances to be ground. The bottom of it, towards the centre, rises in the form of a co- 
 nical or rounded projection, which forms with the lower part of the side a wide groove 
 in which the runner moves. The runner consists of a thick crown of porcelain, 
 formed out of the segment of a cylinder. It is placed perpendicularly in the vessel, 
 projecting above it. Its lower edge is situated in the groove. As it is supported 
 by the bottom of the vessel, it is capable of revolving on its axis in a horizontal di- 
 rection. The levigation of the pigments is therefore effected by the rubbing of the 
 lower edge of the runner upon the surface of the groove. This groove is intended to 
 retain the runner in its position, and to cause the substances which are to be ground 
 to collect at the points where the grinding takes place. The upper edge of the runner 
 is level. It has two holes situated opposite to one another, and bored perpendicularly 
 from the surface : they serve to fasten on the piece which is destined to communicate 
 motion to the runner. 
 
 A tin plate, of the width of the runner, closes the opening at the top. It 
 has two pegs, which are inserted into the above-mentioned holes. By this con- 
 trivance the runner is made to follow every motion which is communicated to the 
 plate. 
 
 There are two ways of causing the motive power to act by the help of the plate 
 of metal. We may act upon a point in the circumference by means of a revolving 
 handle, which is let into a wooden plate that serves as a cover. This is the 
 a StafFelei. Miilile. Laufer. Furcbe. 
 
102 
 
 THE MECHANICAL PART OF GLASS-PAINTING. 
 
 simplest method : but as in this case the runner moves at liberty in its receptacle, as 
 soon as ever it meets with any check in its circular motion, it suddenly quits its path, 
 and the moving it then becomes very troublesome. This might be entirely obviated 
 by means of a pin passing through the centre of the runner and of the outer vessel ; 
 hut it is better to produce motion by means of a crooked handle which is made to 
 work in the following manner : — The upper surface of the metallic plate has in its 
 centre a circular iron bar, well secured. This bar or spindle serves as an axis, and 
 turns in a hole which is bored in a horizontal cross-piece, or rather in the centre of 
 the lid of a box which covers the runner. The handle is fastened on just where the 
 axis projects out of the box. By this means the centre of the runner is always re- 
 tained in the same place. It assists the action of the handle, which thus distributes 
 the impulse it receives to all parts at the same time ; consequently the runner cannot 
 suffer any concussion, as in the foregoing case. 
 
 When the pigments are being ground, it is often advisable to increase the weight 
 of the runner at the commencement of the operation. This is done by placing upon 
 the tin plate another plate of lead of the same diameter, whose weight may be 
 determined at pleasure. It is moveable, and can be easily laid on the plate, and at 
 the same time as easily removed, for which purpose it is merely necessary to take 
 the handle off. 
 
 OF THE DRYING OVEN ^ IN WHICH THE PAINTED PIECES OF GLASS ARE DRIED. 
 
 The drying oven is constructed of baked bricks, and at the bottom of it is a cast- 
 iron plate. This cast-iron plate lies over the fire, from which the necessary 
 temperature is conveyed to the interior of the oven. The interior is provided with 
 wire sieves, fixed in frames lying horizontally at short distances one above the other, 
 which admit of a free circulation of air. In front of the oven there is a door, which 
 is closed as soon as the pieces to be dried have been laid in their places. The 
 heating apparatus is similar to that of a common oven which is heated with charcoal 
 or coal. 
 
 FURNACE 
 
 The furnace consists of a wall of baked bricks ; 
 
 A fire-pot, the interior of which is lined with fire-bricks, as well as with a coating 
 of clay which is proof against fire ; 
 
 Grating ; 
 
 Ash-pit ; 
 
 Pipe through which the air is conveyed from a pair of bellows into the ash-pit ; 
 
 “ Kurbel. tj Trockenschrank. ' Sclimelzofen. 
 
THE MECHANICAL PART OF GLASS-PAINTING. 
 
 103 
 
 and grating perforated with several holes, in order to distribute the wind of the 
 bellows uniformly throughout the interior. A good smith’s bellows should be used 
 for this furnace. 
 
 This kind of furnace is preferred to the common draught-furnace for the prepara- 
 tion of the pigments, because it is capable of producing a very high temperature, and 
 by that means shortening the operation. 
 
 WAX FOR FASTENING THE PLATES OF GLASS UPON THE EASEL. 
 
 This wax is similar to modelling-wax, and consists of 
 
 Bees’-wax* .... 4 parts. 
 
 Burgundy-pitch ... 1 part. 
 
 It owes its ductility to the Burgundy-pitch, and its adhesive property principally 
 to the greasy matter which the bees’-wax of commerce almost always contains. If this 
 is found to be wanting, the deficiency should be supplied by mixing with it tallow in 
 small quantities. 
 
 CHAPTER II. 
 
 THE WORK OF THE GLAZIER. 
 
 The work of the glazier consists — 
 
 1. In cutting out the various pieces of glass which are to be painted, and in giving 
 them exactly the form which the drawing requires. 
 
 2. In encasing the glass in lead when the painting is finished, and forming it 
 into the panels of which the whole picture is composed. 
 
 3. Lastly, in arranging it permanently in the arming. 
 
 In the two first operations the glazier is guided by a cartoon prepared expressly 
 for this purpose. Upon this the outlines of the pieces of glass are indicated by a mere 
 line, which at the same time determines the arrangement of the strips of lead. The 
 irons by which the glass is fixed in the window are likewise drawn here in their 
 natural dimensions. 
 
 OF THE CUTTING THE GLASS. 
 
 The cartoon having been placed on a table, the glazier lays upon the drawing a 
 plate of glass whose colour has been determined to a nicety by the painter. He draws 
 the outline of the piece with a brush containing white paint, and then cuts it with 
 
 Gelbem Wachs. Felder. 
 
104 
 
 THE MECHANICAL PART OF GLASS-PAINTING. 
 
 the diamond, after which he brings it to the exact form by means of the riesel-iron^. 
 Among other things he takes care to leave a space between each piece of glass, which 
 is determined by the thickness of the interior of the strip of lead by whose edges the 
 pieces of glass are afterwards to be united. The colour with which the glazier draws 
 the outline of the pieces which are to be cut out, is composed merely of Spanish 
 white and weak gum- water ; the paint-brush which he employs for this purpose consists 
 of long, flexible hairs attached to a thin cylindrical stick. The painter on porcelain 
 also uses this pencil, and it has the advantage of yielding a line of uniform width. 
 
 Although the diamond and its use are well known, we shall, however, mention a 
 few interesting particulars in relation to the properties of this instrument. The 
 diamond which cuts with its natural edge is preferable to that which comes from the 
 hands of the lapidary ; for such a diamond only cuts by means of an angle artificially 
 produced. The latter may be very easily seen, when looked at with a magnifying 
 glass, to possess level sides, and to form a rectilineal edge where these planes intersect. 
 That of the natural diamond is not perfectly rectilineal, but always convex ; and this 
 is just the form which is best adapted to cutting glass. When the diamond acts 
 upon the glass by means of one of its edges, it either cuts or furrows it. But in 
 this there is an essential difference, for a piece of glass which has been merely 
 furrowed can never be so well divided. The diamond leaves a scarcely visible trace 
 upon well-cut glass ; on furrowed glass, on the contrary, a very distinctly fringed 
 groove may be observed. When the diamond is cutting well, a low, monotonous 
 sound may be heard ; if it is furrowing, the sound which it produces is very per- 
 ceptible to the ear and even to the hand of the glazier. When a line has been drawn 
 with the diamond, and the endeavour which is made to break off the piece of glass is 
 fruitless, the attempt must not be obstinately continued, for it is only necessary to 
 strike gently with the handle of the diamond or some other hard body upon the side 
 opposite to the cut, in order to cause it to begin to separate ; only a little more 
 trouble is then required to carry on the separation along its whole length. In this 
 way we avoid breaking the glass. When it is necessary to cut a piece of glass of 
 such a form that it would be difficult to cut it with the diamond, and the attempt 
 would probably fail, recourse may be had to the action of fire. 
 
 After the outline of the piece which is to be cut off has been drawn, a little 
 incision is made with the diamond in any part of the line, the glass is then heated 
 with a hot coal at those points through which the separation is to be continued, the 
 heating beginning at the point where the diamond has commenced the separation. 
 If the coal is carried in this way slowly over the glass, in proportion as the separation 
 
 ^ Krosel-oder Rieseleisens. Iw'Exewch, grugeoir. 
 
THE MECHANICAL PART OF GLASS-PAINTING. 
 
 lOJ 
 
 takes place, the whole piece is at last disengaged. The glazier would do well, how- 
 ever, to draw the piece rather larger than it ought properly to he, for fear that any 
 deviations which might take place as the crack is being continued should spoil the 
 whole piece. The riesel-iron is used as a finishing tool to give the requisite form to 
 the glass. 
 
 To prevent the necessity of blowing incessantly upon the coal, in order to keep it 
 burning and sufficiently hot, pieces of white wood saturated with subacetate of lead 
 are used, which possess the property of continuing to burn without further assistance, 
 as soon as it has once been ignited at one of its ends. These pieces of wood are 
 generally cut from the willow or poplar, and are then steeped for several days in a 
 solution of the above-mentioned salt, after which they are dried. They are very 
 convenient for hot coals. 
 
 The glazier must be supplied with rectilineal and also with curvilinear rulers of 
 various kinds, for cutting the glass. Suppose he has to cut a piece of glass of com- 
 plicated form — he removes, first of all, from the plate of glass by a rectilineal cut, 
 the glass which lies outside the proper outline, and then, by several cuts in succession, 
 he penetrates into the corners, so that at last it is only necessary to use the riesel- 
 iron. 
 
 THE RIESEL-IRON. 
 
 This tool consists of a blade of soft steel lines’" in thickness, and about 5 inches 
 5 lines in length. At each end is a shallow notch in the direction of its thickness ; 
 and by means of these notches a number of small fragments are chipped off the glass 
 one after another, so that those parts which are outside the outline are removed with 
 tolerable rapidity. The glass to be operated upon is held in one hand, and the riesel- 
 iron in the other ; the edge of the glass is then inserted without any difficulty into a 
 notch of the riesel-iron, and by gentle pressure downwards and upwards, the part 
 which lies in the notch is broken off. This action is rapidly and continually re- 
 peated, hut the use of this instrument requires some skill. The riesel-iron must he 
 made of soft steel, and thus possess sufficient flexibility to hold fast the corner of the 
 glass, and at the same time must be hard enough to last a long time for this continuous 
 work. Iron would be too soft. 
 
 A rwsel-iron of a somewhat different construction is also used, which is suited to 
 glass of any strength, and which can he easily repaired. It consists of two per- 
 fectly level rulers, 5 inches 5 lines in length, at one end of each of which there is a 
 rectangular projection a little more than a line in length. These rulers fit one upon 
 
 ® The line is yU of an inch French. 
 
 P 
 
i06 
 
 THE MECHANICAL PART OF GLASS-PAINTING. 
 
 the other in such a way that that end of the one which is without a projection is re- 
 ceived by the angle of the other, so as to form the notch of the riesel-iron. The two 
 rulers slide upon one another, and are joined together by a band, by the binding screw 
 of which they can be fixed in any position. By means of this apparatus, the proper 
 width may be given to the notch, and the instrument may be easily repaired by being 
 taken to pieces. 
 
 OF THE LEADING A 
 
 After the various parts of a painting on glass have been burnt in, the parts them- 
 selves must be united, so as to form a whole. This operation is performed by means 
 of strips of lead in the following manner : — 
 
 These strips of lead consist of two narrow ribbons joined together lengthwise, by 
 one narrow slip of the same metal running along the centre of both. The arrange- 
 ment of these three pieces produces a groove ^ in each side of the strip of lead, for the 
 purpose of receiving the edges of the two pieces of glass, which border on one 
 another, and which are thus separated by the middle slip and covered by the over- 
 lapping parts of the leading. The length of the strips of lead is determined at 
 pleasure, and the breadth should be from two to six lines, so that the overlapping 
 part may be from two to four lines in breadth. We shall afterwards explain how 
 the strips of lead receive their proper form. 
 
 The cartoon, according to which the pieces of glass have been cut out, is also 
 used for putting them together and leading them. The glazier begins as nearly as 
 possible in the centre of any of the pannels which are to be made up. As soon as 
 the first piece which is to be fixed has been laid in its proper place, it is fastened in 
 several places by pegs which are driven into the table. These pegs or nails without 
 heads accomplish this purpose by the help of small pieces of milled lead, which are 
 laid between the pegs and the glass. One of the sides of the piece of glass is then 
 inclosed in a piece of lead. After this piece has followed the whole outline of the 
 piece of glass, during which pressure has been applied by means of the lead-jack ^ 
 the superfluous breadth is cut off with the lead-knife. A second piece of glass is 
 then fitted on, which, like the first, is fixed with pegs, until a strip of lead has been 
 fastened on. The edges of the lead are pressed down with the lead-jack, and the 
 operation is continued until the pannel is finished. 
 
 The glazier then proceeds to the soldering, which consists in applying the solder® 
 to the joinings, which unites the various pieces of lead and imparts a greater 
 firmness to the net which they form. 
 
 ^ Verbleiung. Falz. ® Kern. Bleiknechtes. ® Loth. 
 
THE MECHANICAL PART OF GLASS-PAINTING. 
 
 107 
 
 The solder is an alloy of lead and tin, less flexible than the pieces of lead them- 
 selves, consequently it imparts to them a greater power of resistance. In this alloy 
 the tin and the lead are united in equal quantities. Before the solder is used, it 
 must be previously prepared in such a way that it may be conveniently applied. 
 Lead is melted in an iron bason or pot, and as soon as it has become liquid, an equal 
 quantity of tin is added. This done, it is kept at a moderate temperature, and 
 a small quantity of resin or grease is thrown into it, which deoxidizes the metal, and 
 thus restores it to a perfectly liquid state. The oxide and the foreign bodies which 
 float upon the surface are then removed, and the metal is poured out. It is best to 
 cast it in thin ribbon, which on account of its form and its pliability can he much 
 more easily handled. This ribbon may be obtained by pouring a small quantity of 
 solder upon a grooved plate, and inclining the latter a little in the act of 
 pouring. The inclination of this mould must be such that the ribbons or strips 
 which arc thus obtained shall be sufliciently pliable, without being too thin. As 
 soon as the glazier has provided himself with a sufficient quantity of solder, he sets 
 to work. The solder is applied by means of the soldering iron’'. This imple- 
 ment consists of a piece of copper in the form of a cone, the base of which is 
 prolonged and serves as a handle. The latter is held in the hand by means of two 
 concave and moveable pieces of wood which completely surround the hand in their 
 junction. The soldering-iron might also be made of iron, and then it would 
 probably be more durable ; but iron does not seem so ivell adapted to receiving the 
 solder as copper. The soldering-iron must be previously tinned at its point. For 
 this purpose it is necessary to have a tin plate rather concave in form. After the 
 soldering-iron has been heated in a proper furnace, it is rubbed over a piece of 
 sal-ammoniac, in order to clean it, and then over the before-mentioned tin plate, upon 
 which a little resin has been sprinkled for the purpose of deoxidizing the tin. The 
 soldering-iron then receives a portion of tin from the tin plate, and becomes thereby 
 tinned. It is advisable to clean the tinned end of it, whenever it is taken from the 
 fire, by passing it over the tin plate, the metal of which must be rene^ved as soon as 
 it becomes necessary. 
 
 The soldering-iron having been properly heated and tinned, is brought near to the 
 lead, upon which a small quantity of resin has been previously sprinkled. In this 
 position, the solder, which is applied with the other hand, is melted. It is then 
 diffused uniformly and regularly by the point of the soldering-iron being made to 
 pass over the whole surface of the lead. The soldering-iron must be heated to the 
 proper temperature. If it is too hot, it will melt the lead ; if it is too cold, it gives 
 
 Lothkolbens. 
 
 P 2 
 
108 
 
 THE MECHANICAL PART OF GLASS-PAINTING. 
 
 the soldering a wrinkled appearance, which proceeds from the imperfect fusion of the 
 alloy. The lead is soldered on one or both sides, according to the degree of strength 
 which is to he given to the leading. As soon as the soldering is finished, the lead is 
 cleansed from the resin that remains, by being rubbed with a piece of linen which 
 has been dipped in oil of turpentine. 
 
 The furnace for heating the soldering-iron is nothing more than a circular tin 
 box with neither grate nor draught. This box is generally placed on three feet, suffi- 
 ciently high to allow of its being conveniently used. The coals are made to burn 
 up merely by a pair of hand-bellows. 
 
 PREPARATION OF THE GLAZIER’S LEAD. 
 
 The bars of lead are cast in a mould, and when in a rough state hear some 
 resemblance in shape to the strips we have already described, for the production of 
 which these bars are used. The mould is a sort of frame consisting of two 
 parts, each of which is from 1 inch 6 lines to 1 inch 10 lines in breadth, from 
 5 to 7 lines in thickness, and from 1 foot to 1 foot 6 inches in length. These two 
 pieces have each three longitudinal grooves, which, when they are joined with those 
 of the opposite side, form the cavities in which the bars are cast. The parts of the 
 mould are united at one end by a hinge which admits of the grooves of the frame being 
 shut and opened at pleasure. At the other end of one of these parts is a bifurcated* 
 handle which moves on a hinge, and which is capable of clasping the opposite piece 
 with its fork and holding it fast. The grooves of the frame are terminated by a 
 transverse groove near the handle, into which the metal is poured. The frame 
 being shut is held perpendicularly by the handle with one hand, while the melted 
 lead is poured in with the other. As soon as the lead has solidified, it is taken out 
 of the frame in order to make room for other castings. 
 
 After the casting is finished, the bars are smoothed, that they may be subjected 
 to the milling machine, whereby they are converted into what is called glazier’s 
 lead^. 
 
 THE MILLING MACHINE ^ 
 
 The milling machine consists, first, of two vertical cheeks which are parallel 
 to one another, and are held together by strong cross-pieces, by means of screws 
 and burrs. Each cheek is furnished with two wide holes between the cross-pieces, 
 in which there are as many revolving cylinders ®, which we shall presently describe 
 more fully. The corresponding holes in each cheek are at the same height from 
 
 Gabelformigen. Glaserblei. ® Bleizug ; in French tire-plomb. Wangen. ® Wellen. 
 
THE MECHANICAL PART OF GLASS-PAINTING. 
 
 109 
 
 the bottom of the machine. At the bottom of each of the cheeks also there are two 
 horizontal projections chamfered off, and furnished with holes to receive the iron 
 bolts with which they are fastened to a bench. Two iron cylinders pass hori- 
 zontally through the intermediate space between the cheeks, and their ends are 
 let into the above-mentioned corresponding holes at each side. The upper cylinder 
 projects beyond the hinder cheek, and at the end of it is a tooth- wheeT of 12 teeth, 
 which is held in its place by a burr. The other end of the cylinder only extends to 
 the outer surface of the cheek. The lower cylinder projects beyond the cheeks at 
 both ends. At one end there is a tooth- wheel similar to the one we have already 
 mentioned, into which it fits ; the other end is squared to receive a handle. On 
 each of the cylinders, at an equal distance from either of the cheeks, there is a 
 wheel, or disk^ which is capable of being disengaged from or fastened to the 
 cylinder. These two disks are thus situated opposite to one another, without how- 
 ever coming in contact. The bar of lead which is to be drawn out by the revolving 
 motion of the disks in opposite directions, when the cylinders are set in motion by 
 means of the handle, must pass between these two disks. Their thickness deter- 
 mines the breadth of the groove, and the distance at which they are apart the 
 thickness of the interior strip. On the circumference of these disks there are a few 
 lines engraved, like the scratches of a file, and these are for the purpose of holding 
 the lead more securely. 
 
 To each of the cheeks between the cylinders there is attached a heavy piece, of 
 complicated form, which is called the die". The die, which is let into a morticed 
 hole in its corresponding cheek, presents an angular surface on its opposite side which 
 is bounded at the top and the bottom by a rectilineal part called the nagelemsatz. 
 
 The two planes of the angular surface bear the name of engorgeures in French, 
 the broader one being the engorgeur di’ entree, the other the engorgeur de sortie. At 
 the top and at the bottom of each die there is a semicircular groove corresponding to 
 the adjacent cylinder. It is now evident that the dies, in their mutual relations to one 
 another, in conjunction with the disks, complete the mill which is to give the proper 
 shape to the lead. They serve to form the outer surfaces and the sides of the lead, just 
 as the disks form the core and the grooves. In order to draw the lead, the end of 
 the bar is placed between the two disks in the intermediate space between the dies ; 
 the handle being now turned, the bar must pass through the rolling-press, and receive 
 the form and dimensions of the latter. In this operation the lead is considerablv 
 lengthened ; a bar one foot long will give a strip of lead of more than four feet in 
 length. It is impossible to obtain milled lead of various dimensions without having 
 ^ Getiiebe. ^ Sclieibe. Lager. 
 
110 
 
 THE MECHANICAL PART OF GLASS-PAINTING. 
 
 several pairs of wheels and dies of proper sizes ; consequently, if the disks are 
 fixed to the cylinders, it is necessary to have just as many cylinders as disks. 
 
 The bench of the machine consists of a simple piece of wood, the ends of which 
 are supported by three legs fixed in the ground. 
 
 Before the lead is placed in the machine, it must be smoothed, and then con- 
 densed''. The latter operation is performed in the following manner : — one end of a 
 bar of a lead is bent into the form of a right angle, which is placed under the foot, 
 while the other end is wound upon a piece of wood, by which means the lead is 
 forcibly drawn out ; it is thus considerably lengthened, and becomes more rigid. 
 When it is to he used, the lead jack is passed between the overlapping edges to sepa- 
 rate them from one another, so that the glass may he more easily pressed into the 
 groove. 
 
 OF THE ARMING. 
 
 The chief object of the arming is to impart sufficient firmness and power of resist- 
 ing external violence to church windows. The net of lead which holds the pieces of 
 glass together is by no means capable of doing so for any length of time, unless it is 
 of very small dimensions or supported at certain distances by iron bars. But this 
 iron work contributes sometimes even to the decoration of the window ; Gothic church 
 windows afford an example of this, which consist of numerous pannels containing 
 forms of various kinds artistically disposed, so that the whole presents a very pleasing 
 appearance. Here the ai'ming pays its tribute to the art by affording the requisite 
 strength to the window ; it isolates the pannels, and renders their agreeable outlines 
 conspicuous, whilst at the same time by its complicated pattern it forms a drawing 
 so much the more powerful and effective, as it appears black upon a transparent 
 ground. In those windows, on the contrary, where the arming is evidently of no 
 use to the painting, but is merely for the sake of rendering the glass secure, its 
 presence cannot be otherwise than prejudicial to the effect; therefore, in that case, 
 it must be our object to conceal it as much as possible in the shadows, unless we 
 prefer presenting it to the eye as a piece of trellis work independent of the picture, 
 just as is generally the case in church windows. The ancients did this very fre- 
 quently, from a principle of economy. 
 
 There are several other methods of constructing the iron armings ; sometimes, for 
 example, as in the case of Gothic windows, simple iron bars, which have been bent 
 into the form of the outline of the pannels, are used, and the latter are fastened to the 
 bars by means of pins disposed at equal distances throughout the whole extent of the 
 
 ^ Verdichtet. 
 
OF THE INGREDIENTS FOR COLOURED GLASSES. 
 
 Ill 
 
 former ; sometimes there are iron bars which in certain modern church windows 
 receive the pannels in grooves in which they are fixed by nails running transversely 
 through them. Sometimes there are merely thin iron bars disposed at the back of 
 the painting, which, by means of bands of the same metal laid on the lead on one 
 side, carried round it and twisted together on the other, render the leading com- 
 pact. 
 
 Armings which are furnished with grooves are difficult of construction ; the bars 
 are composed of two plates, which are connected longitudinally at right angles, one 
 in the centre of the other, by means of clenched rivets ; or they may be made of a 
 single strip of tin bent at right angles, and then bent back again, so as to form two 
 right angles, which constitute the groove. This kind of arming is exceedingly ex- 
 pensive, and will always increase the cost of those church windows to which it is 
 applied. The Gothic arming, although simpler, is nevertheless always expensive, on 
 account of the great strength of the iron and the splints which belong to this kind of 
 arming. The arming which is constructed with thin bars and with ribbons of lead 
 is much more easily prepared, but is less durable, and presents no pleasing appear- 
 ance. 
 
 After the glazier has arranged the pannels in the arming with splints, nails, or 
 ribbons of lead, he cements all the places through which the rain is capable of pene- 
 trating, and thus finishes his work. 
 
 CHAPTER III. 
 
 OF THE INGREDIENTS FOR COLOURED GLASSES. 
 
 The preparation of the glass which is coloured in mass is, strictly speaking, no part 
 of glass painting, but belongs properly to the art of making glass. Since, however, 
 such kinds of glass are frequently used by glass-painters, we shall here briefly state 
 the ingredients proper for the various kinds of coloured glass. 
 
 If we mix with glass, at the time of its manufacture, certain metallic compounds, 
 we impart various colours to it, the shades of which we are capable of varying to any 
 extent by following the general rule, viz., that according as it is required to increase 
 
 ® Versatzen. 
 
112 
 
 OF THE INGREDIENTS FOR COLOURED GLASSES. 
 
 or diminish the intensity of the colour, a small quantity of the colouring metallic oxide 
 must be either added to or taken from the mixture. The colour thus imparted is not 
 superficial, as in the case of porcelain and enamel painting, but is diffused throughout 
 the whole mass, the colouring matter having become a real constituent part of it. 
 In other respects, the same substances are applied to this purpose as are used for the 
 colouring of the pigments in general. 
 
 OF THE PURPLE GLASS. 
 
 Gold is employed to give a purple colour to glass, similar to that of ruby, for such 
 glass is the most perfect imitation of the ruby in colour, and resembles it almost in 
 brilliancy and liveliness. There is no other substance which is capable of imparting 
 a red of so beautiful a tone to the pot metal ; but extremely delicate manipulation is 
 required in the management of the gold, and a variety of precautionary measures are 
 necessary to ensure success. The precipitate of Cassius is the preparation of gold, 
 which is most frequently employed for colouring glass purple. We have already 
 described the methods of obtaining it, and we shall now state the reason why it is 
 generally preferred to the rest. 
 
 The precipitate of Cassius is one of those combinations containing gold which 
 possesses the greatest stabilty. It resists a high temperature, and if the reduction of 
 the gold, as we believe it to he, takes place after it has united with the glass, this will 
 only happen at the moment when it can be held by the whole mass in the state of 
 division in which it exists when united with the tin. This combination is less dis- 
 posed than any other preparation of gold to pass over into violet or blue. The 
 purple of Cassius absolutely requires, in order to be used, to be levigated in a 
 gelatinous state with pulverized glass, borax, or any other substance which is capable 
 of entering into combination with glass, and this with a view to prevent a conglome- 
 ration of the particles of the gold. Its power of colouring is such, that one part of 
 the purple of Cassius is capable of colouring 1000 parts of glass. In using this 
 purple it is customary to mix with it the sixth part of its weight of the white oxide 
 of antimony, in order to give the glass a faint tinge of yellow, which reduces the red 
 that slightly approximates to violet to a lively purple. In other respects, all that we 
 have said about the pigments coloured by means of the purple of Cassius applies just 
 as well to the colouring of glass in the melting-pot. 
 
 Fulminating gold is also used for colouring glass purple. It is one of those com- 
 binations which are obtained by precipitation with ammonia from chloride of gold. 
 
OF THE INGREDIENTS FOR COLOURED GLASSES. 
 
 113 
 
 Its property of exploding at a very low temperature renders it unsafe to use. In 
 order to deprive it of this property, it is customary to mix it with silica, lime, &c. 
 The same result is obtained with a fixed alkali, the mixture being exposed to a 
 gentle heat. It is also sufficient for the purpose to levigate the mixture with essential 
 oil of turpentine. But the precautionary measures which we are under the necessity 
 of adopting, in order to prevent an explosion, are at the same time indispensable to 
 success in colouring, and that too on the same principle which guides us in the pre- 
 paration of the purple of Cassius. I mean that the fulminating gold, while moist, 
 must be mixed with a substance which will deprive it of its explosive property, and at 
 the same time hold it in a state of the most minute division. 
 
 The purple colour of glass may also he produced by using chloride of gold, sul- 
 phuret of gold, and even from aurates*, if the operator proceeds according to the 
 method which prevails in the other preparations of gold. 
 
 OF THE RED GLASS. 
 
 The red glass receives its colour from copper, if not in the metallic state, at least 
 at the degree of strongest oxidation. To make red glass, a mixture of sulphuret of 
 copper and oxide of iron is added to the melted mass of glass ; or, after a green has 
 been first produced in the mass by means of oxide of copper, the metal is deoxidized 
 by the mixture of a substance containing carbon, and the colour is thus made to pass 
 over into red ; this deoxidizing substance is usually bitartrate of potash It has been 
 found that any other combination which contains carbon would produce the same 
 effect. 
 
 Carmine is obtained from copper only ; a darker red from a mixture of iron 
 and copper, in which the former is to the latter as three to one. The quantity of 
 iron is diminished, if it is intended that the tone of the colour shall approach nearer 
 to that of carmine. The glass must be worked as soon as the proper red colour 
 makes its appearance, otherwise it would speedily disappear. 
 
 The red which is obtained from copper is so intense that it is necessary to con- 
 duct the operation with the greatest care, in order that the glass may not lose its 
 transparency, for it is often in danger of becoming perfectly opaque. Our object 
 must therefore be, to find out a method by which this risk may be obviated. Now 
 this method consists in overlaying the white glass with an extremely thin coating of 
 red glass {flashed glass') ° it is only in this way that transparency can be com- 
 bined with a beautiful colour. 
 
 “ Goldsauren Salzen. ^ Saures weinsteinsaures Kali. Ueberfangglas. 
 
 Q 
 
114 
 
 OF THE INGEEDIENTS FOE COLOUEED GLASSES. 
 
 The ancients only mixed crude tartar, soot, or other deoxidizing bodies with the 
 mass which had been coloured by copper, for the sake of obtaining the red. But 
 it is best to use protoxide of tin, in order to obtain copper in the state of protoxide. 
 The action of protoxide of tin is not so transient as that of the vegetable substances, 
 whose action naturally terminates with their combustion, and in using which we are 
 liable to a double disappointment ; for if they are not sufficiently consumed, the glass 
 will not be so clear, nor the colour so bright, and as soon as the colour has come out 
 properly we must proceed to work up the glass as quickly as possible, because the 
 colour is exceedingly liable to disappear. But all this is avoided by using protoxide 
 of tin. According to Dr. Engelhardt’s experiments, the red continued equally fine 
 throughout the whole process, and he never found himself obliged to add deoxidizing 
 bodies. He also met with oxide of tin in all the ancient kinds of glass wffiich he 
 examxined, and this oxide was for the most part present in greater quantities than the 
 protoxide of copper itself. 
 
 Now, since the colour imparted by protoxide of copper is too intense to admit of 
 its being worked up alone, and the plate which has been coloured throughout would 
 be opaque and appear dark brown, and since it would be necessary to blow it ex- 
 ceedingly thin, in order that the red may become transparent, we can only obtain 
 manageable red plates of glass by flashing a white plate with a very thin coating of red 
 glass. There is, moreover, this advantage in flashed glass, viz.; that the red coating 
 may be ground off in different places; thus we obtain white sketches, or, by melting 
 other colours on the surface, sketches of various colours. 
 
 That this was the method employed by the ancients is apparent from all the 
 painted windows of the middle ages. 
 
 In order to make flashed glass two crucibles are necessary, one containing the 
 red and the other the white glass ; the workman first dips his pipe into the red 
 mass and brings up a small globule at the end of it ; he then covers this with a 
 proper quantity of white glass. The cylinder which is produced by blowing will ex- 
 hibit a flashed glass of a beautiful red colour. It is necessary for the purpose of 
 thoroughly uniting the red coating to the plate of white glass, and preventing it from 
 peeling off in the cooling, as happened in Dr. Englehardt’s first attempts, that the 
 composition of white glass should be similar to, if not the same as, that of the red 
 glass ; but it is best to make the red glass a little more fusible than the white. 
 
 Moreover the ingredients of the red glass must contain no oxidizing sub- 
 stances. 
 
 Dr. Engelhardt, who has satisfied himself upon this subject at the glass-houses, 
 proceeds as follows ; — He places between the large crucibles for the red glass a small 
 
OP THE INGREDIENTS FOR COLOURED GLASSES. 
 
 115 
 
 crucible, and into this he introduces 4 oz. of protoxide of copper and 4 oz. of protoxide 
 of tin in addition to the usual ingredients, for every 5 lbs. of the latter, if they hap- 
 pened to contain minium. 
 
 But if they do not contain minium, he takes 3 oz. of protoxide of copper, and 3 
 oz. of protoxide of tin for every 2 lbs. of salt which the ingredients contained. If the 
 protoxide of copper is not immediately added to the frit*, but is introduced into it 
 afterwards, when the latter is beginning to become clear, a much smaller quantity 
 must be added. 
 
 For scarlet he uses for every (25 lbs. of frit ^Ib. of protoxide of tin and li^ oz. of finely 
 levigated protoxide of iron: these are added just at the beginning of the operation. 
 
 As soon as the glass has become clear, he mixes with it 1^ oz. of protoxide of 
 copper, and the whole is well stirred up together. Especial care must he taken to avoid 
 bubbles, which are extremely liable to be formed, and specks of sand as also that the 
 white and the red mass be ready at the same time to admit of their being worked up 
 together. 
 
 It is clear from what we have just stated, that to succeed in obtaining a beautiful 
 plate depends very much upon the workman, for the overlaid glass always remains 
 thicker at the mouth of the tube than at the opposite end of the hulb of glass ; the 
 plate is therefore always darker on one side than on the other, and only the middle is uni- 
 form ; indeed the flashing is sometimes so thin at one end, that the colour disappears and 
 passes over into white. Dr. Engelhardt has in his possession several ancient pieces 
 of glass in which this transition from dark to light has been made of the greatest 
 use in producing certain effects ; among others, in the satin drapery of a Judith. 
 However, the workman may with some practice acquire the knack of making tolerably 
 uniform plates of glass, and Dr. Engelhardt hopes soon to obtain this result in a glass- 
 house with which he has become connected for this particular purpose. 
 
 A frit containing lead seems more likely to preserve the red than any other frit ; 
 Herr Engelhardt, however, says that his experiments are not decisive upon this 
 point. 
 
 OF THE YELLOW GLASS. 
 
 There are several compounds with which glass may be coloured yellow, if they are 
 mixed with it at the time of its manufacture. Among these are sulphuret of anti- 
 mony, antimonite of lead, and chloride of silver. The method of colouring with the 
 
 ^ Glassatze. 
 
 Korner, lit. grains. 
 
 Q 2 
 
116 
 
 OF THE INGREDIENTS FOR COLOURED GLASSES. 
 
 latter has, in this case, nothing in common with the production of the silver yellow. 
 The employment of chloride of silver, however, requires a very well refined glass 
 which does not contain an excess of alkali. Without this precaution the chloride 
 would be decomposed, the silver which is in the melted mass of glass, being now re- 
 duced to the metallic state, would suffer a rapid agglomeration of its minute particles, 
 and the colour would in consequence disappear. Chloride of silver is not used on ac- 
 count of its being very expensive. Sulphuret of antimony and antimonate of lead * 
 are the only colouring materials in general use. But as the yellow which is burnt in 
 gives a fresher and clearer colour, yellow pot-metal is not much manufactured. W"e 
 merely wish to mention one other yellow here, which is obtained by an admixture of 
 a carboniferous substance with the pot-metal. This imperfect method, which gives a 
 glass of a disagreeable shade of colour and full of small bubbles, has now fallen en- 
 tirely into disuse. 
 
 In order to colour the glass blue, black oxide of cohalt is employed, which causes 
 the formation of the protosilicate. 
 
 Violet glass is obtained by means of peroxide of manganese with or without an 
 admixture of oxide of cohalt. 
 
 A green is imparted to glass with oxide of copper, oxide of chromium, or a mix- 
 ture of antimonite of lead and oxide of cobalt. Oxide of chromium gives a less trans- 
 parent colour than oxide of copper. 
 
 Black glass is prepared from oxide of manganese, oxide of iron, oxide of copper, 
 and oxide of cobalt, in combination with one another. This colour depends upon the 
 mixture of the three colours which are produced by these oxides; that is to say, the 
 mixture of green, blue, and violet, which in proper proportions will give a black. 
 
 Finally, glass is made white and opaque with stannic acid or phosphate of lime, 
 obtained by calcining bones. 
 
 Phosphate of lime, or calcined bones, is also used in the manufacture of opalescent 
 glass. The exact receipt for the mixture will be given below. Opalescent glass is 
 employed with advantage in every case where the direct rays, or even the reflected 
 light of the sun, is prejudicial to workmen. This, for instance, is the case in the 
 workshops of goldsmiths, jewellers, &c., in government offices, banking offices, &c., 
 which are situated on the ground floor, where it is often necessary to use ground 
 glass. So also this glass is of great service for all kinds of lamp-glasses, since the 
 
 a Antimonsaures Blei, probably put by mistake for antimonigsaures Blei (antimonefe of lead), which oc- 
 curs a few lines above. 
 
 Opalescirenden. 
 
OF THE INGREDIENTS FOR COLOURED GLASSES. 
 
 117 
 
 grinding of concave or convex surfaces is attended with difficulty, and mahes such 
 glass expensive. 
 
 We will now give several receipts for the ingredients of coloured glasses ; — 
 
 MIXTURE FOR ROSE COLOURED GLASS. 
 
 White sand 
 Potash . 
 
 Slaked lime** . 
 
 Purple of Cassius 
 Peroxide of manganese 
 Or, 
 
 White sand 
 Minium . 
 
 Caustic potash 
 Nitrate of potash 
 Purple of Cassius 
 Peroxide of manganese 
 Sulphuret of antimony 
 
 RED GLASS. 
 
 White sand 
 Minium . 
 
 Caustic potash 
 Nitrate of potash 
 Purple of Cassius 
 Peroxide of manganese 
 Sulphuret of antimony 
 
 YELLOW GLASS. 
 White sand 
 
 Potash .... 
 Slaked lime 
 
 Antimony-yellow, coloured 
 with oxide of lead 
 Or, 
 
 White sand 
 Potash . 
 
 100 parts. 
 48 „ 
 
 8 „ 
 h . 
 
 4 „ 
 
 100 parts. 
 78’ „ 
 
 35 „ 
 
 7 „ 
 
 8 „ 
 
 4 „ 
 
 4 „ 
 
 6 
 
 6 
 
 100 parts. 
 50 
 8 
 
 
 6 „ 
 
 100 parts. 
 
 40 .. 
 
 Lime .. . . .10 parts. 
 
 Antimony-yellow, coloured 
 
 with oxide of lead . 10 „ 
 
 Or, 
 
 White sand . . .100 parts. 
 
 Minium . . , . 80 „ 
 
 Caustic potash . . 36 „ 
 
 Crystallized nitrate of potash 12 „ 
 
 Antimony-yellow, coloured 
 with oxide of lead 
 
 BLUE GLASS. 
 
 White sand 
 Minium . 
 Caustic potash 
 Calcined borax 
 Oxide of cobalt 
 
 100 parts. 
 
 Or, 
 
 60 „ 
 
 White sand 
 
 30 „ 
 
 Potash . 
 
 5 0 
 
 Slaked lime 
 
 12 „ 
 
 Oxide of cobalt 
 
 Or, 
 
 White sand 
 Minium . 
 Caustic potash 
 Nitrate of potash 
 Oxide of cobalt 
 
 GREEN GLASS 
 
 White sand 
 Refined pearlash 
 Slaked lime 
 
 Green oxide of chromium 
 
 8 
 
 100 parts. 
 150 „ 
 
 35 „ 
 
 10 „ 
 
 4 „ 
 
 100 parts. 
 50 „ 
 
 6 „ 
 
 1 part. 
 
 100 parts. 
 80 „ 
 40 „ 
 
 8 „ 
 
 1 part. 
 
 100 parts. 
 50 „ 
 
 8 „ 
 
 2 „ 
 
 ** An der Luft zerfallener Kalk, i. e., lime slaked in 
 slaked lime, here and elsewhere in this table. 
 
 the air, which, for the sake of brevity, we have called 
 
118 
 
 OF THE INGREDIENTS FOR COLOURED GLASSES. 
 
 Or, 
 
 White sand . . , 100 parts. 
 
 Refined pearlash . . 50 „ 
 
 Slaked lime . . . 9 ,, 
 
 Yellow oxide of antimony 4 „ 
 
 Oxide of cobalt, or zaffre 2 „ 
 
 Or, 
 
 White sand 
 Minium . 
 
 Calcined potash® 
 
 Nitrate of potash 
 Green oxide of chromium 
 
 100 
 
 75 
 
 38 
 
 4 
 
 parts. 
 
 yf 
 
 yy 
 
 yy 
 
 2 
 
 yy 
 
 Or, 
 
 White sand 
 
 100 parts. 
 
 Minium . . . . 
 
 60 „ 
 
 White pearlash 
 
 40 „ 
 
 Oxide of arsenic 
 
 6 „ 
 
 Glass of antimony . 
 
 9 „ 
 
 Oxide of cobalt 
 
 5 
 
 Or, 
 
 Whitewashed sand . 
 
 100 parts. 
 
 Minium .... 
 
 85 „ 
 
 Calcined potash 
 
 38 
 
 Nitrate of potash 
 
 8 „ 
 
 Yellow oxide of antimony 
 
 4 „ 
 
 Oxide of cobalt 
 
 2 „ 
 
 VIOLET GLASS. 
 
 White sand 
 
 100 parts. 
 
 Pearlash 
 
 48 „ 
 
 Slaked lime 
 
 n n 
 
 Oxide of manganese 
 
 4-10 
 
 Or, 
 
 Whitewashed sand . 
 
 100 parts. 
 
 Minium .... 
 
 78 „ 
 
 Calcined potash 
 
 35 „ 
 
 Crystallized nitrate of potash 8 „ 
 
 Peroxide of manganese . 
 
 1-2 „ 
 
 BLACK GLASS 
 
 White sand 
 
 100 parts. 
 
 White pearlash 
 
 66 
 
 yy 
 
 Slaked lime 
 
 8 
 
 yy 
 
 White glass, pulverized 
 
 70 
 
 yy 
 
 Oxide of arsenic 
 
 6 
 
 yy 
 
 Oxide of cobalt 
 
 10 
 
 yy 
 
 Peroxide of manganese 
 
 10 
 
 yy 
 
 Acetate of iron, or even 
 iron in the highest state 
 
 of oxidation 
 
 5 
 
 yy 
 
 Or, 
 
 White sand 
 
 100 
 
 parts. 
 
 Pearlash . . . . 
 
 48 
 
 yy 
 
 Lime .... 
 
 6 
 
 yy 
 
 Oxide of cobalt 
 
 4 
 
 yy 
 
 Peroxide of manganese 
 
 3 
 
 yy 
 
 Oxide of copper 
 
 3 
 
 yy 
 
 Black oxide of iron 
 
 4 
 
 yy 
 
 Or, 
 
 White sand 
 
 100 
 
 parts. 
 
 Minium . . . . 
 
 82 
 
 yy 
 
 Calcined potash 
 
 38 
 
 yy 
 
 Nitrate of potash 
 
 8 
 
 yy 
 
 Oxide of cobalt 
 
 8 
 
 yy 
 
 Peroxide of manganese 
 
 8 
 
 yj 
 
 Black oxide of iron . 
 
 12 
 
 yy 
 
 Oxide of copper 
 
 12 
 
 yy 
 
 OPALESCENT GLASS. 
 
 
 White sand 
 
 100 
 
 parts. 
 
 Refined pearlash 
 
 50 
 
 yy 
 
 Slaked lime 
 
 16 
 
 yy 
 
 Oxide of silver 
 
 3-6 „ 
 
 Phosphate of lime, or cal- 
 
 cined bones . 
 
 6 
 
 yy 
 
 Or, 
 
 White sand 
 
 100 parts. 
 
 Purified soda . 
 
 450 
 
 yy 
 
 Anotlier name j^earlash. 
 
OF THE INGREDIENTS FOR COLOURED GLASSES. 
 
 119 
 
 Slaked lime . . .160 parts. 
 
 Calcine^, or white broken 
 
 glass .... 500 „ 
 
 Hydrochlorate of silver . 10 „ 
 
 Phosphate of lime from 
 
 mutton bones . . 60 „ 
 
 Oxide of arsenic . . 30 ,, 
 
 WHITE OPAQUE GLASS. 
 
 White sand 
 White pearlash 
 Slaked lime 
 White glass, pulverized 
 
 parts. 
 
 Oxide of lead . 
 
 100 parts. 
 
 Oxide of arsenic 
 
 3 „ ■ 
 
 Or, 
 
 
 White sand 
 
 100 parts. 
 
 Calcined potash 
 
 50 „ 
 
 Slaked lime 
 
 16 „ 
 
 Oxide of tin 
 
 60 „ 
 
 Or, 
 
 
 White sand 
 
 100 parts. 
 
 Minium .... 
 
 78 „ 
 
 Calcined potash 
 
 30 „ 
 
 Nitrate of potash, in crystals 
 
 8 „ 
 
 White oxide of tin . 
 
 62 „ 
 
 ^ A calcined mixture of oxide of lead and oxide of tin in 
 the latter, — (Author’s Note.) 
 
 the proportion of 4 of the former to 1 of 
 

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