THE 
 
 CHEMISTRY OF PAINTS AND PAINTING 
 
THE 
 
 CHEMISTRY 
 
 PAINTS AND PAINTING 
 
 A. H. CHURCH, F.R.S. 
 
 M.A., D.Sc, F.S.A. 
 Professor of Chemistry in the Royal Academy of A rts in London 
 
 THIRD EDITION 
 REVISED AND ENLARGED 
 
 LONDON 
 
 SEELEY AND CO. LIMITED 
 
 38 Great Russell Street 
 
 mcmi 
 
 
THE J. PAUL GETTY CENTER 
 LIBRARY 
 
[Dedication of the First and Second Editions.] 
 
 TO 
 
 SIR FREDERIC LEIGHTON, BART., P.R.A., 
 
 WHO HAS ALWAYS SHOWN A DEEP INTEREST 
 
 IN ITS SUBJECT, AND HAS GREATLY 
 
 ENCOURAGED ITS AUTHOR, 
 
 THIS BOOK 
 
 IS, BY PERMISSION, DEDICATED. 
 
PREFACE 
 
 This handbook first appeared in the spring of 1890; two 
 years afterwards a second and revised edition was published. 
 The work having now been long out of print and a consider- 
 able amount of fresh material having accumulated, I felt 
 that the time for a corrected issue had arrived. 
 
 The plan of the book has not been altered, yet scarcely a 
 page remains without change or addition. The bibliography 
 has been augmented, while as to the body of the text, 
 important corrections have been made or paragraphs intro- 
 duced in the accounts given of paper, plaster, oil in paints, 
 resins, solvents, classification of pigments, and trials of 
 pigments. Several new pigments or new varieties of old 
 pigments are mentioned and described ; some old pictures 
 and drawings not previously noticed in my chapter on this 
 subject are critically examined for the first time. 
 
 The last six pages of the former editions of the present 
 work were occupied with a digest of an important newspaper 
 discussion on the effect of light upon water-colour drawings. 
 I have deemed it unnecessary to reprint the story at the 
 
PREFACE 
 
 present day, for no sane and observant artist, connoisseur, 
 or collector of water-colour drawings will now dispute the 
 main statements made in 1886 as to the serious fading and 
 change of hue shown in a large number of English water- 
 colour drawings which have been exposed to strong light 
 for a considerable length of time. Moreover, Chapters 
 XXIV. -XXVI. of the present volume include, I venture 
 to affirm, adequate evidence of the instability of several 
 favourite pigments largely used by painters in water-colour 
 during the eighteenth and nineteenth centuries. 
 
 To several friends and correspondents I am indebted for 
 help in the revision and improvement of this handbook. 
 Mr. J. Scott Taylor has kindly furnished me with a carefully 
 compiled series of notes and suggestions, while Mr. C. F. 
 Cross has aided me in the preparation of the account given, 
 in the first chapter, of drawing-paper. I must also express 
 my obligations to Dr. A. P. Laurie and to the authors or 
 editors of several of the books named in my Bibliographical 
 Notes. But notwithstanding all the assistance I have 
 received and my own efforts I cannot hope that I have 
 succeeded in preparing an edition of my text-book free 
 from errors and containing precisely the information in kind 
 and in extent useful to the student of painting and to the 
 artist. Yet I have tried to remove some at least of the 
 imperfections of the work, and to carry out more fully the 
 plan set forth in the preface to the First Edition, here re- 
 printed. 
 
 A. H. Church. 
 
 Kew Gardens, July, 1901. 
 
PREFACE TO THE FIRST EDITION 
 
 In the present volume the materials and methods of the 
 painter of pictures are viewed mainly from the chemical 
 standpoint. An attempt has been made to treat in orderly 
 sequence the various kinds of painting-grounds, the con- 
 stituents of vehicles and varnishes, the pigments themselves, 
 and the chief processes of painting. Although the artistic 
 side of the numerous problems discussed has not been neg- 
 lected, the book is in no way intended to teach manipula- 
 tion to art students. It has been written with the view of 
 explaining to artists, whether they be accomplished masters 
 or commencing students, the chief chemical and physical 
 characters of the materials with which they deal and of the 
 operations they practise. In many instances a sketch of 
 the processes for preparing certain pigments and varnishes 
 is given, not in order to turn the painter into a colour-maker 
 or a varnish-manufacturer, but rather that he may acquire a 
 clearer insight into the nature and properties of the most 
 important constituents entering into the composition of his 
 pictures. With regard, however, to the tests for purity and 
 genuineness which I have described in the following pages, 
 
-•' 
 
 x PREFACE TO THE FIRST EDITION 
 
 my object in introducing them has been different, for I trust 
 that (in somes cases, at least) the easy experiments I have 
 recorded will be tried, especially with suspicious pigments. 
 The operations require but little time; the pieces of apparatus 
 needed, like the chemicals, are few and inexpensive. And 
 when the ease with which these testings can be made has 
 been proved by practice, the experimenter may perhaps be 
 induced to proceed a little farther, preparing his own sicca- 
 tive oil, selecting and purifying his spirits of turpentine, and 
 so forth. That the painter should test the varnishes he 
 buys for hardness and toughness, and the pigments for 
 durability, may, I hope, be taken for granted. 
 
 ' Titian managed pretty well without chemistry, did he 
 not?' A distinguished artist asked me this question the 
 other day. But not only were the conditions under which 
 the painters of Titian's time worked simpler than those of 
 the nineteenth century, but grounds, paints, oils, and var- 
 nishes were generally prepared in the studios of the artists, 
 and under their own superintendence, so that the chances 
 of going wrong were comparatively limited. And it is not 
 to be denied that a better acquaintance with the nature of 
 the materials which many of the old masters employed 
 would have caused their works to be handed down in 
 sounder preservation to future generations. 
 
 It is possible — I hope, indeed, it is probable — that this 
 book may be found of service to students who are purposing 
 to devote themselves to certain manufacturing and technical 
 pursuits. I am aware that to those who refer to its pages 
 
PREFACE TO THE FIRST EDITION 
 
 for the revelation of all the secrets of colour-manufacturers 
 it may prove in some measure disappointing ; yet I trust 
 that, in the way of information and suggestion, the study of 
 this volume will not be unattended with advantage. It 
 must be remembered that it is confessedly an elementary 
 manual only, written with a definite aim, but covering a very 
 wide area of inquiry. And if chemists should conclude that 
 it contains too little chemistry, artists may perhaps think 
 that it contains too much. 
 
 There are repetitions in the following pages, for the topics 
 discussed in some of the chapters overlap one another. I 
 am perfectly aware of having made the same statement, 
 given the same figure, and expressed the same opinion in 
 more than one place. The scheme of the work required 
 such repetitions. I felt sure that many an artist or student 
 would turn to one section or other of the book without 
 caring to read the whole. One inquirer would like to 
 ascertain at once what pigments were safe, what dubious, 
 what fugitive, by a reference to the tables in Chapters XXI. 
 and XXII. ; while another, anxious to learn something of 
 the evidence on which the several verdicts of approval or 
 condemnation were based, would expect to find his require- 
 ments met in the pages devoted to trials of pigments. 
 Again, under the names of the individual pigments, dis- 
 cussed in Chapters XIII. to XIX., some of the changes 
 described in the last part of the work are quoted. Thus 
 it happens that there are some materials common to all of 
 those sections of the book just named. 
 
xii PREFACE TO THE FIRST EDITION 
 
 Much of the substance of the lectures which I have 
 delivered before the Royal Academy since the year 1880 
 has been incorporated with the present manual, but it is 
 necessary to state that some of the original material to be 
 found in the following pages has been long before the 
 artistic world, and has found its way into the books and 
 essays of other writers. I say this, not for the purpose of 
 making reclamations of priority, but in order to prevent 
 myself from being charged with plagiarism. For instance, 
 so long ago as 1859, I described, for the first time, some of 
 the artistic uses of solid paraffin in a paper on the processes 
 of painting, read before the Oxford Architectural Society ; 
 further details were given in a lecture to the Architectural 
 Association in 1862. On many other matters connected 
 with the chemistry of paints and painting, new investiga- 
 tions and studies were published by me between the years 
 1.867 and 1872, particularly in notes and essays entitled 
 ' Chemical Aids to Art,' and ' The Chemistry of the Fine 
 Arts.' But my statements and results, whether contained 
 in the above publications or in my Academy lectures, have 
 not been, in all instances, referred to their source, or repro- 
 duced with accuracy, while some have been overlooked or 
 forgotten. 
 
 In preparing the present volume I have made consider- 
 able use of several of the works named in my Bibliographical 
 Notes ; I have consulted also the standard chemical diction- 
 aries of Watts and of Wurtz, the treatise by Roscoe and 
 Schorlemmer, besides many special papers by other chemists. 
 
PREFACE TO THE FIRST EDITION 
 
 I wish I could have given an authority for every statement 
 not derived from my personal experience, but in an elemen- 
 tary manual treating of many diverse topics such a plan, 
 even if it could have been carried out, would have em- 
 barrassed my story with a multitude of perplexing refer- 
 ences. 
 
 I do not know of any one text-book which covers the 
 same ground as the volume now offered to the public. 
 Several small books on pigments — the most important of 
 all the materials employed by the artist — have indeed been 
 lately published, but the chemical information they afford 
 is generally meagre, and sometimes far from exact. One 
 recent little brochure, which lies before me, has, I confess, 
 caused me some amusement not wholly unshaded with 
 regret. The writer does not pose as a humourist, yet he 
 tells us, when we test for lead in cadmium red, first to mix 
 the sample with white lead before applying the usual test for 
 that metal. Chinese vermilion, he informs us, is sulphide 
 of arsenic, though it is really sulphide of mercury. The 
 presence of sulphides of baryta and lime is stated in one 
 place to lend a softness to the chromates of lead ; as these 
 sulphides instantly blacken these brilliant chromates, per- 
 haps they may be said to soften them. Cceruleum, a 
 stannate of cobalt, is directed to be made of carbonate of 
 soda, powdered flint, and oxide of copper, its two essential 
 constituents, the oxides of tin and cobalt, not being named. 
 These and many other equally preposterous statements and 
 directions may afford merriment to the chemist, but it is 
 
PREFACE TO THE FIRST EDITION 
 
 
 indeed pitiable that such teaching should be seriously offered 
 to artists and art-students. 
 
 It is satisfactory to know that several accomplished 
 chemists are now devoting themselves to the practical study 
 and improvement of pigments. Mr. A. P. Laurie, Mr. H. 
 Seward, and Mr. J. Scott Taylor, are all doing good work 
 in this direction. 
 
 It remains for me to express the hope that the readers of 
 this volume will favour me with any material at their disposal 
 which may serve for the correction and improvement of its 
 pages. I am aware of having omitted to notice many 
 interesting matters; amongst these I include certain pigments, 
 derived from coal-tar products, which have not yet been 
 sufficiently tested. Then, too, the materials and methods 
 of ceramic and glass painting have been excluded from con- 
 sideration, mainly because their adequate treatment, while 
 demanding much space, would have appealed to a com- 
 paratively limited group of students. 
 
 If painters and chemists will grant me their help, I trust 
 that I may further justify, by means of an improved edition 
 of my book, the favourable reception which I hope may be 
 accorded to the first. 
 
 A. H. Church. 
 
 KEW, March, 1 890. 
 
BIBLIOGRAPHICAL NOTES 
 
 Andes, L. E., ' Oel- und Buchdruckfarben.' Pp. viii, 271. 
 Leipzig, 1889. 
 
 Andres, E., ' Volatile and Fat Varnishes,' Brannt's transla- 
 tion. Pp. xx, 346. Philadelphia, 1882. 
 
 Bersch, J., ' Die Fabrikation der Erdfarben,' 2te Auflage. 
 Pp. viii, 222. Wien, 1893. 
 
 Blockz, J., ' Peinture a l'Huile.' Pp. iv, 98. Gand, 1881. 
 
 Cennini, Cennino, ' A Treatise on Painting in Fresco, 
 Secco, Oil and Distemper.' Written in the early part 
 of the fifteenth century, first published (in Italian) in 
 182 1 ; translated into English by Mrs. Mary P. Merri- 
 field. Pp. lxx, 177. London, 1844. 
 
 Cennini, Cennino, ' The Book of the Art.' Translated into 
 English by Mrs. C. J. Herringham, with Notes on 
 Mediseval Methods by the Translator. Pp. xxxviii, 
 288. London, 1899. 
 
 Charabot, E., Dupont, J., and Pillet, L., ' Les Huiles Es- 
 sentielles.' Pp. xvi, 1002. Paris, 1899. 
 
 Cremer, F. G., ' Untersuchungen iiber der Beginn des 
 CElmalerei.' Pp. xiv, 291. Diisseldorf, 1899. 
 
BIBLIOGRAPHICAL NOTES 
 
 Cross, C F., and Bevan, E. J., 'A Text-Book of Paper- 
 Making.' Second edition. Pp. viii, 328. London, 
 1900. 
 Eastlake, Sir C. L., • Materials for a History of Oil Paint- 
 ing.' Series I., pp. xii, 561 ; Series II., pp. xv, 432. 
 London, 1847, 1869. 
 Field, G., ' Chromotography, a Treatise on Colours and 
 
 Pigments.' Pp. xix, 276. London, 1835. 
 Field, G., ' Chromatography,' edited by T. W. Salter. Pp. 
 
 vii, 436. London, n.d. 
 Field, G., ' Chromatography,' modernized by J. S. Taylor. 
 
 Pp. viii, 207. Second edition. London, 1885. 
 Gentele, J. G, ' Lehrbuch der Farben-Fabrikation, ' 2te 
 
 Auflage. Braunschweig, 1880. 
 Halphen, G., 'Couleurs et Vernis.' Pp. vii, 385. Paris, 
 
 1895. 
 Hurst, G. H., 'Painters' Colours, Oils, and Varnishes.' 
 
 Second edition. Pp. xiii, 449. London, 1896. 
 Jametel, M., ' L'Encre de Chine.' Pp. xxx, 94. Paris, 
 
 1882. 
 Lapparent, P. de, ' Les Alterations des Couleurs.' Pp. 36. 
 
 Paris [1900]. 
 Lefort, J., 'Chimie des Couleurs.' Pp. 344. Paris, 1855. 
 Merrifield, Mrs. M. P., ' Original Treatises on the Arts of 
 Painting,' with Introduction and Notes. Two vols. ; 
 pp. cccxii, 918. London, 1849. 
 Mierzinski, S., ' Die Erd-, Mineral- und Lackfarben,' 4te 
 Auflage. Pp. viii, 500. Weimar, 1881. 
 
BIBLIOGRAPHICAL NOTES 
 
 Mierzinski, S., ' Handbuch der Farben Fabrikation,' 2 Bde. 
 
 Pp. vii, 1092. Wien, 1898. 
 Recouvreur, A., 'Grammaire duPeintre.' Pp.117. Paris, 
 
 1890. 
 Riffault, Vergnaud, and Toussaint, ' A Practical Treatise on 
 
 the Manufacture of Colours for Painting.' Revised by 
 
 M. F. Malepeyre; translated by A. A. Fesquet. Pp. 
 
 xvi, 659. Philadelphia, 1874. 
 Riffault, Vergnaud, Toussaint et Malepeyre, 'Fabricant de 
 
 Couleurs.' Nouvelle edition en deux tomes. Pp. 
 
 346 et 312. Paris, 1884. 
 Russell, W. J., and Abney, W. de W., 'Action of Light on 
 
 Water-Colours ' (Blue-Book). Pp. 78. Appendix of 
 
 14 diagrams. London, 1888. 
 Theophilus, or Rugerus, ' An Essay upon Various Arts ' 
 
 (close of eleventh century). Translated, with Notes, 
 
 by R. Hendrie. Pp. xxxviii, 447. London, 1847. 
 Vibert, J. G., ' La Science de la Peinture. Pp. viii, 332. 
 
 Paris, 1890. 
 
CONTENTS 
 
 INTRODUCTION 
 
 PAGE 
 I 
 
 PART I 
 
 PA INTING-GRO UNDS 
 
 (CHAPTER 
 
 I. PAPER, VELLUM, IVORY - - - - 
 
 II. PLASTER, GESSO, STONE, SLATE, ETC. - 
 III. PANEL ------ 
 
 IV. CANVAS ------ 
 
 PART II 
 
 VEHICLES AND VARNISHES 
 
 V. OILS ------ 
 
 VI. RESINS, WAXES, AND SOLID PARAFFINS 
 
 VII. YOLK AND WHITE OF EGG j SIZE ; GLUE 
 
 V 7 III. GUM, STARCH, DEXTRIN, HONEY, AND GLYCERIN 
 
 IX. WATER-GLASS, LIME- AND BARYTA-WATER 
 
 X. SOLVENTS AND DILUENTS 
 
 XI. SICCATIVES OR DRYERS - 
 
 XII. VARNISHES AND VEHICLES 
 
 7 
 i7 
 
 27 
 
 32 
 
 39 
 
 55 
 7i 
 78 
 
 85 
 
 90 
 
 108 
 
 112 
 
CONTENTS 
 
 PART III 
 
 PIGMENTS 
 
 CHAPTER 
 
 XIII. WHITE PIGMENTS - 
 
 XIV. YELLOW PIGMENTS - 
 
 XV. RED PIGMENTS - 
 XVI. GREEN PIGMENTS 
 XVII. BLUE PIGMENTS 
 XVIII. BROWN PIGMENTS 
 XIX. BLACK PIGMENTS 
 XX. CLASSIFICATION OF PIGMENTS - 
 XXL TABLES OF PERMANENT, FUGITIVE, AND ALTER- 
 ABLE PIGMENTS - 
 XXII. SELECTED AND RESTRICTED PALETTES 
 
 PAGE 
 127 
 
 133 
 165 
 I90 
 
 203 
 
 227 
 
 239 
 249 
 
 257 
 264 
 
 PART IV 
 
 METHODS AND RESULTS 
 
 XXIII. PAINTING-METHODS - - - " 2 75 
 
 XXIV. THE STUDY OF OLD PAINTINGS AND DRAWINGS 294 
 XXV. CONSERVATION OF PICTURES AND DRAWINGS - 310 
 
 XXVI. TRIALS OF PIGMENTS - - - 325 
 
 INDEX - 
 
 349 
 
THE CHEMISTRY 
 OF PAINTS AND PAINTING 
 
 INTRODUCTION 
 
 The materials employed by ' picture-makers ' are now very 
 numerous. Some of the old pigments, and painting-grounds, 
 and methods, have indeed fallen more or less completely 
 into disuse ; but, on the other hand, many new products, 
 both natural and artificial, have been added to the resources 
 of the artist, while several new processes of painting have 
 been introduced, or old methods modified. Nowadays it is 
 very seldom that a painter prepares for himself any one of 
 the materials which he uses, generally accepting, without 
 much hesitation and without examination, the paper, the 
 canvas, the paints, the oils, and the varnishes which his 
 colourman supplies, provided they respond, at first sight, to 
 his requirements. True he has abandoned, not without 
 regret, several of the most treacherous compounds by which 
 his immediate predecessors were seduced. ' Pure scarlet ' 
 he has given up ; he is shy of asphalt ; tobacco-juice and 
 Spanish liquorice are no longer regarded as desirable 
 water-colours. He may go so far as to reject chromate 
 of lead, but he still employs the pigment called chrome 
 green, or green cinnabar, for he does not know that the same 
 
INTRODUCTION 
 
 chromate of lead enters largely into its composition ; and he 
 still thinks that madder yellow is a sound paint, because it 
 is called madder, while he rejects the yellow lakes, which are 
 derived from the same source. His linseed oil is neither 
 made from pure linseed, nor cold-drawn ; his copal varnish 
 may not have a particle of pure copal in it ; but both are 
 taken on trust. I do not expect that artists should become 
 chemists trained to test their materials, but they will place 
 themselves in a position of comparative security by acquiring 
 an elementary knowledge of the origin, the composition, and 
 the characteristics of the various products with which their 
 works are constructed. An architect is expected to recog- 
 nise the sound or unsound quality of the timber, the stone, 
 the brick, the iron, with which the edifice he designs is con- 
 structed : why should the painter take everything on trust ? 
 The purchaser of a picture ought not to be distressed by 
 doubts as to its stability. The concentration of the artist's 
 attention on the definitely artistic side of his practice must, 
 of course, be in no wise interfered with, but time may still 
 be found for the acquisition of such knowledge of his 
 materials as shall enable him to discriminate between the 
 good and the bad. He may even try, with great advantage, 
 a few simple experiments — experiments performed in a few 
 minutes with the simplest apparatus, and with the most in- 
 nocent of reagents. These are the more necessary now that 
 painters no longer buy their raw materials, or make their 
 own paints, and oils, and varnishes, or prepare their own 
 canvases and panels. Before colourmen generally undertook 
 such work, early in the seventeenth century, painters were 
 eager after receipts, and, there can be no doubt, were 
 ignorant of reasons : there was little exact science under- 
 lying their art. Yet it would be unfair to the best colour- 
 men of the present day to assume that they do not endeavour 
 
INTRODUCTION 
 
 to provide, as far as possible, sound materials. But they 
 do not manufacture all they sell. They are not paper- 
 makers, nor, as a rule, are they manufacturers of oils and 
 varnishes. Many of the pigments they furnish are not of 
 their own make. If, for instance, you inquire the source of 
 the artificial ultramarine you purchase of your colourman, 
 you will find that it has probably been made in a factory 
 wholly devoted to the manufacture of that pigment. The 
 production of this material can indeed be properly carried 
 on only in special establishments thoroughly equipped for a 
 peculiar and difficult work. In reality, this specialization 
 ought to be, and generally is, advantageous, but it renders 
 the position of the colourman somewhat difficult. He has 
 to assume responsibility for the soundness and genuineness 
 of many products of the history and preparation of which 
 he knows little or nothing. 
 
 This difficulty confronts him in many directions. I have 
 known cases in which importers or manufacturers' travellers 
 have offered to artists' colourmen speciously prepared but 
 spurious pigments, such as madder carmine and rose madder 
 made from artificial alizarin, ultramarine ash containing not 
 a particle of the native lapis-lazuli, and a gold ochre owing 
 its colour to a basic ferric sulphate instead of a hydrate. 
 Then, too, some of the original localities of a few native 
 earths, such as terre verte and raw umber, are practically 
 exhausted, and most of the new sources yield products of 
 inferior hue. Hence the temptation to ' exalt ' the hue of 
 the commercial article by some seductive though dangerous 
 addition. 
 
 After these introductory observations, I may refer the 
 reader to the table of contents for the plan of the present 
 book, and to the prefaces for the object with which it has 
 been prepared. I would add, here, only this one remark, 
 
INTRODUCTION 
 
 that the materials with which a painting is constructed are 
 described in definite order, beginning with the ground, then 
 passing on to the medium and the pigments, not omitting 
 the final varnish, and finally closing with a brief summary of 
 methods of painting, and of the experimental studies by 
 means of which the conclusions given in the earlier portions 
 of the volume have been reached. 
 
PART I 
 PA INTING-GRO UNDS 
 
 Chapter I. — Paper, Vellum, Ivory. Chapter II. — Plaster or Intonaco, 
 Stone, etc. Chapter III. — Panel. Chapter IV. — Canvas. 
 
CHAPTER I 
 
 PAPER, VELLUM, IVORY 
 
 As paper is used as the painting-ground for the vast majority 
 of works executed in water-colours, and as this method of 
 painting offers but slight protection to the pigments em- 
 ployed against hostile influences, it becomes of the greatest 
 importance to ascertain that no unnecessary elements of 
 danger are introduced in the paper itself. We will now 
 proceed to consider briefly the sources and constituents of 
 drawing-paper. 
 
 Linen from the common flax (Linum usitatissimum), and 
 in the form of white rags, should be the basis of the pulp 
 used in the making of sound drawing-paper. In actual 
 practice the cheaper and weaker fibre of cotton (seed-hairs 
 of Gossypium sp.) has almost entirely displaced flax, although 
 during recent years a successful attempt has been made in 
 England to produce a high grade of hand-made drawing- 
 paper almost wholly composed of linen. Other vegetable 
 fibres might, no doubt, be employed for this purpose. 
 Thus, Japanese paper, prepared from the bast-fibres of the 
 paper-mulberry {Broussotietia papyri/era), were it made less 
 absorbent by the introduction of a sufficiency of size, would 
 probably become an efficient, strong, and durable substitute 
 for linen-paper ; but at present linen-papers, cotton-papers, 
 
8 
 
 CONSTITUENTS OF PAPER 
 
 and papers made from a mixture of these fibres, are the 
 only kinds with which water-colourists are practically con- 
 cerned. 
 
 The manufacture of linen-paper in Europe dates as far 
 back as the latter half of the twelfth century. Mr. W. H. 
 James Weale, formerly Keeper of the Art Library in the 
 Victoria and Albert Museum, informed me that the two 
 first paper-mills in France were set going near Ambert, in 
 the valley of the Valeyre, by men who, during their captivity 
 in the Holy Land, were forced to work at the manufacture 
 of paper at Damascus. One of these French mills was 
 called 'Damascus,' the other ' Ascalon.' This was previous 
 to the year 1189. To Mr. Weale I am also indebted for an 
 opportunity of examining two early specimens, obtained 
 from the 'Registre des Revenus de l'Eveche du Puy.' 
 As one of the sheets contains contemporary entries of the 
 year 1273 — the other entries belonging to 1289 — these 
 papers are, at least, as early as the years named. Both 
 papers present the creamy hue, the translucency, and the 
 gloss of vellum. One hundred square inches of the earlier 
 specimen weigh 127 grains; of the later, 163. Both are 
 heavily sized with paste made from wheaten starch. The 
 use of starch for sizing paper has been revived of recent 
 years, but animal size or jelly is still extensively employed. 
 Some paper is, indeed, made from felted linen pulp alone 
 without size ; but it is blotting or filter paper, and is quite 
 unfitted for water-colour work, for when a wash of pigment 
 is passed over it, the colouring matter and the water 
 partially separate, while the outline of the brush-stroke is 
 not preserved. 
 
 Before entering further into the question of what are 
 the essential and what the accidental and unnecessary con- 
 stituents of paper, I give the summarized results of six 
 
ANALYSIS OF DRAWING-PAPER 9 
 
 analyses, which show the percentage proportions found in 
 good samples : 
 
 ANALYSES OF DRAWING- 
 
 PAPERS 
 
 
 
 Water 
 
 Size 
 
 Ash 
 
 Fibre 
 
 Hodgkinson, 1869 - 
 
 6-8 - 
 
 4-6 
 
 11 
 
 87-5 
 
 English, 1876 - 
 
 io - 9 
 
 6-i 
 
 11 
 
 81-9 
 
 Dutch, 1876 - 
 
 iro 
 
 4-8 
 
 - 0-9 
 
 • 83-3 
 
 Whatman, 1885 
 
 7'4 - 
 
 6-3 
 
 I'l 
 
 ■ 85-2 
 
 Arnold, 1894 - 
 
 7-4 - 
 
 7-6 
 
 - i-5 
 
 ■ 8 3 -5 
 
 '0. W.,'1897 
 
 87 - 
 
 5'5 
 
 - 17 
 
 - 84-1 
 
 Water. — It should be noted that the percentages of 
 water shown in these analyses vary considerably by reason 
 of variations in the humidity, temperature, and pressure of 
 the atmosphere to which the different papers had been 
 exposed just before the analyses were made. There are, 
 however, slight permanent peculiarities in samples made 
 from different fibres or sized in different ways ; in conse- 
 quence the moisture-absorbing and moisture-retaining pro- 
 perties of different papers are not precisely identical under 
 identical atmospheric conditions. This hygroscopic moisture 
 does, indeed, vary inversely with the temperature, and 
 directly with the amount of water-vapour in the air ; it is 
 increased also by an increased barometric pressure. There 
 is no doubt that if it could be wholly excluded, the larger 
 number of changes which occur in the pigments of a water- 
 colour drawing would be prevented. It is most injuriously 
 active when a framed drawing is exposed to considerable 
 ranges of temperature. Under these conditions the 
 moisture of the paper is first partly turned into vapour, 
 then condensed on the glass, and, lastly, is re-absorbed by 
 the paper, and, for a time, especially by the pigments lying 
 on its surface. This temporary condensation of an excess 
 of moisture upon the coloured surface does much injury 
 
■ 
 
 ASH OF PAPER 
 
 before hygroscopic equilibrium is once more re-established. 
 Much less harm would accrue were the vapourized water 
 allowed to escape. 
 
 Size, — The size must be considered next. It may be 
 applied to the pulp or to the sheet, and may consist of 
 gelatine with a little alum, of colophony or rosin dissolved 
 in soda-lye, followed by treatment with alum or alum-cake. 
 Sometimes starch is used along with alum or alum-cake. 
 From good drawing-papers, which are sized in the sheet 
 with animal size, the greater part of the size may be ex- 
 tracted by means of boiling distilled water, the solution 
 being usually neutral or faintly acid, sometimes faintly 
 alkaline, to test-papers. Gelatine and starch, to the extent 
 of about 5 per cent, of the weight of the paper, are the 
 safest sizing materials. 
 
 Ash. — The ash or mineral matter in paper may be derived 
 from three sources, namely, traces of the original mineral 
 substances taken up by the flax plant from the soil, and 
 still remaining associated with the felted pulp ; the mineral 
 matters, such as soda and alum, introduced with the size ; 
 and, lastly, the mineral compounds used to whiten, to 
 weight, or to finish the paper, or in bleaching the fibre and 
 as ' antichlors.' In common and adulterated papers the 
 ash greatly exceeds i per cent., twelve parts per hundred 
 of paper being no unusual proportion. This ' filling ' may 
 contain or consist of the following substances : kaolin or 
 china-clay, silicate of lime or 'pearl-hardening,' chalk or 
 whitening, lead-white, baryta white or ' white dressing,' 
 artificial gypsum or ' satin-dressing,' and a mixture of alu- 
 minium hydrate with magnesium carbonate or with calcium 
 carbonate, known as 'satin-finish' or ' satin-white.' Other 
 substances which increase the amount of ash left when a 
 paper is burnt are blue colouring matters, introduced to 
 
FIBRE OF PAPER 
 
 counteract the natural yellow tint of the pulp. These 
 include artificial ultramarine, smalt or cobalt blue, and 
 Prussian blue. 
 
 Fibre. — What is put down as fibre in the analyses of 
 paper previously cited, is a substance, or group of sub- 
 stances, to which the name of cellulose is given by chemists. 
 Cellulose consists of the three elements — carbon, hydrogen, 
 and oxygen ; it is, when pure, entirely combustible, leaving 
 no ash. 
 
 The source of this cellulose is by no means without in- 
 fluence on the durability, strength, and working quality of 
 drawing-paper. The fibres of linen and of cotton present 
 distinct differences of form and resistance to strain. When 
 working on a paper with a knife so as to develop high lights, 
 the water-colour painter soon discovers the weakness and 
 fluffiness of abraded cotton, while the clear-cut surfaces of 
 linen are equally obvious. Even in washing and in taking 
 out lights from a drawing by sponging and rubbing, the 
 superiority of linen-paper to cotton-paper is very marked ; 
 in fact, papers into which a high proportion of the latter 
 fibre enters will not stand much worrying. The other 
 fibrous materials commonly forming the basis of ordinary 
 papers are, on one score or another, less desirable than 
 cotton. Nearly all of them require, in order to fit them for 
 paper-making, a very drastic treatment, which is liable to 
 leave behind it traces of injurious chemicals, or to yield 
 altered material of lessened strength and permanence. 
 Wood-pulp, esparto, and straw-pulp belong to this category. 
 
 Paper-making. — The technology of paper-making cannot 
 be discussed here, but a few references to the chemicals 
 employed in the process of manufacture may be usefully 
 given at this point. Amongst these chemical substances, 
 one or more of which will have been introduced into the 
 
TESTING PAPER 
 
 fibrous basis of the paper or into the size may be named : 
 caustic soda and caustic lime ; chloride of lime, magnesium 
 hypochlorite, moist chlorine gas, and sulphuric acid ; alum, 
 aluminium chloride, and aluminium sulphate ; sodium thio- 
 sulphate ; gelatin. Of course, it is possible to cleanse and 
 bleach the higher class of rags without having recourse to 
 any chemical treatment, but the ' souring ' with sulphuric 
 acid and the employment of some soda or sodium carbonate 
 to remove grease are usual ; while there is always a salt of 
 aluminium present in the size. Indeed, in the best and 
 purest drawing-papers, the alum, or its equivalent, is the 
 one ingredient upon which the chemist interested in paint- 
 ing will look with suspicion. But the subject of the pre- 
 sence of chemicals, injurious or innocuous, in the finished 
 product of the paper-mill may be relegated to the following 
 paragraphs. 
 
 Paper-testing. — The simplest test of the suitability of 
 any sample of drawing-paper for water-colour work consists 
 in applying to its surface uniform and weak washes of a 
 chosen set of sensitive pigments. A sound standard paper 
 is taken for comparison; this maybe 'Whatman,' but it 
 should be first swilled in cold distilled water for five minutes, 
 and then hung up to dry. In applying this test, a strip of 
 the sample to be tested and one of the standard paper 
 should be laid side by side, and then the several colour 
 washes, made with distilled water, carried across both 
 strips by means of a broad brush. The pigments used may 
 be French ultramarine, chrome yellow, and carmine. Unless 
 they are employed in very dilute admixture, the changes 
 produced by alum and other chemicals will not be per- 
 ceptible. There should be no bleaching of the ultramarine 
 or the carmine, or any blueing of the latter, and no dulling 
 of the chrome, even after the lapse of a week from the date 
 
TESTING PAPER 
 
 >3 
 
 of the experiment. Washes of tincture of azolitmin from 
 litmus, tincture of dahlia flowers, and tincture of methyl- 
 orange may be similarly applied to paper-strips; in this 
 case it will probably be found that the two former tests will 
 show an acid reaction, and the methyl-orange a basic or 
 alkaline reaction. This seemingly strange result has been 
 found to arise from the presence of a derivative of the alum 
 in the size, namely, an aluminium sulphate which is acid to 
 some tests and basic to others. This point has been es- 
 tablished by the experiments* of Messrs. Cross and Bevan, 
 Mr. C. Beadle, and Drs. P. N. Evans and Quirin Wirtz, 
 who have proved that all the drawing-papers of well-known 
 makers which they have examined contained no free 
 sulphuric acid. Of course, the question remains, ' How far, 
 if at all, is the basic aluminium sulphate in drawing-paper 
 injurious to sensitive pigments ?' This inquiry can, I think, 
 be answered by applying the colour-tests already described, 
 not only to the suspected papers themselves, but also to 
 extracts from them made with cold distilled water and also 
 with hot. 
 
 Other useful tests are the following : 
 
 1. Burn 100 grains of paper to a white ash; not more 
 than 1 "5 grains of incombustible residue should be found. 
 
 2. Extract 100 grains of paper repeatedly with boiling 
 distilled water. The united watery extracts, evaporated to 
 dryness, should not amount to 8 grains. 
 
 3. If straw or esparto fibre be present in a paper, it will 
 become red when immersed in a boiling 1 per cent, solution 
 of aniline sulphate. 
 
 Attempts have been made to size paper with casein dis- 
 solved in ammonia, and also with 'viscose,' a modified 
 
 * Journal of the Society of Chemical Industry (1892), pp. 212, 213, 
 261. 
 
14 
 
 TESTING PAPER 
 
 cellulose made out of the substance of the paper itself by 
 means of water, caustic soda, and carbon disulphide. At 
 present, however, gelatin-sizing holds its own. The neces- 
 sity of introducing alum, or an equivalent of some other 
 aluminium salt, into this size is its chief drawback, although 
 an animal product of the group to which gelatin belongs, 
 being prone to decomposition and to the attacks of micro- 
 scopic organisms, itself constitutes a source of danger. 
 Alum is used not merely as an antiseptic, but because it 
 exerts a peculiar liquefying effect upon the size. A little 
 alum solution added to gelatin solution increases its stiff- 
 ness, but further additions up to an easily ascertained point 
 make the solution more mobile. It is absolutely necessary 
 to keep the alum percentage low ; I found in a batch of 
 one well-known make of drawing-paper that exactly twice as 
 much alum had been employed as was necessary. My re- 
 monstrance with the manufacturers had its due effect. 
 
 The roughness or smoothness of the surface of the paper, 
 or cardboard, is not without influence on the permanence of 
 water-colours. The pigments become less intimately asso- 
 ciated with the smooth surface of a hot-pressed paper than 
 with a comparatively rough natural surface. The rough 
 surface is, however, liable to wider and more rapid fluctua- 
 tions in the amount of hygroscopic moisture. 
 
 Some apparently sound papers deteriorate in strength and 
 tint on being kept. Such changes may occur even when 
 pure linen rags have been used for the pulp ; they may be 
 generally traced to the disintegrating action on the fibre of 
 the chemical bleaching agents employed. The development 
 of rust-spots, when not due to the mount or backing of a 
 drawing, arises from the presence of small particles of metallic 
 iron from the machinery having become embedded in the 
 pulp. These particles appear grey, brown, or black ; they 
 
SIZE IN PAPER 
 
 15 
 
 may be detected by placing a drop of oxalic acid solution 
 on the suspected spot, allowing it to dry, and then moisten- 
 ing the place with a drop of a freshly-prepared solution 
 of tannin. If the particle be iron an ink-stain will be pro- 
 duced. However, some dark spots consist of blackened 
 grease, or of tar, or of the paper-fungus (Myxotrichum 
 chart arum). 
 
 Naturally, there is a small quantity of oil or fat in paper ; 
 it varies from 3 to 5 parts in a thousand. The difficulty ex- 
 perienced in immediately wetting a surface, of paper caused 
 by the presence of this trace of oil, may be overcome by first 
 washing the surface with distilled water to which a drop or 
 two of caustic ammonia has been added. A solution of the 
 natural mixture of alkaline organic salts, known as oxgall, 
 effects the same purpose. The use of borax had better be 
 avoided. 
 
 As drawing-papers are sized in the sheet they occasionally 
 show a peculiar defect arising from the irregular distribution 
 of the size. In such cases, when the surface is scraped off, 
 an absorbent layer of imperfectly sized pulp is revealed 
 beneath. When such paper is used for water-colour paint- 
 ing the sinking-in and running of the pigments produce 
 disastrous results ; but it is easy to guard against accidents 
 of this sort by previously scraping and colouring a corner of 
 the sheet to be used. The peculiarity is generally owing to 
 the too prolonged and slow drying of the sheets of paper 
 after they have been removed from the warm sizing-bath and 
 pressed. The solution of size is brought to the surfaces 
 from the interior of the sheet, and remains there. More- 
 over, in very slow drying, the size is apt to decompose with 
 loss of its glutinous character and, possibly, the formation of 
 mildew. A good drawing-paper will indeed have rather 
 more size at the surface than in the interior, this result being 
 
16 
 
 VELLUM AND IVORY 
 
 secured by a rate of drying which is neither too rapid nor 
 too slow. 
 
 As to vellum, parchment, and ivory, little need be said. 
 All three contain the characteristic ingredient ossein, an 
 insoluble nitrogenous organic substance, which by long 
 boiling with water is converted into gelatin : a solution of 
 gelatin constitutes ordinary size. Water-colour paints placed 
 upon any of these materials sink either very slightly, or not 
 at all into their substance — a very few, such as aureolin, 
 strontia-yellow, and madder carmine, stain the superficial 
 layer. The old method of preparing vellum for the recep- 
 tion of water-colours consisted in rubbing the surface with 
 very finely-ground bone-ash, or with pulverized sandarac. 
 Pumice-stone or cuttle-fish, reduced to a minutely divided 
 state by pounding, grinding, and sifting, may be used for 
 this purpose ; the infusorial earth known as polishing silica, 
 or kieselguhr, may also be employed. 
 
 Ivory which has become yellowish through age and seclu- 
 sion from light may be safely bleached by contact with an 
 ethereal solution of hydrogen peroxide. The treatment is 
 best carried out in a wide-mouth stoppered bottle, care 
 being taken to immerse the sheets of ivory wholly in the 
 liquid, and not to allow them to touch each other. 
 
 Much care is necessary in selecting tinted and coarse 
 coloured papers for water-colour work. The tints of the 
 former are often obtained by the introduction of fugitive 
 pigments into the pulp ; the latter are often made of inferior 
 and mixed fibres, and sometimes contain lead-white and 
 other injurious fillings. Mill-board is often made of wood- 
 pulp, oakum and straw-pulp : its surface is primed for oil- 
 painting in the same way as canvas. 
 
CHAPTER II 
 
 PLASTER, GESSO, STONE, SLATE, ETC. 
 
 The painting-grounds to be considered in this chapter 
 consist mainly of mineral substances. However their con- 
 stituents may be varied, in accordance with the process to 
 be used in painting upon them, the wall or backing upon 
 which they are spread should fulfil certain conditions. It 
 must be naturally dry, free from soluble saline matters, and 
 not very porous. A damp-proof course above the level of the 
 ground is necessary, and the wall should be well-built, and 
 free from tremors. A double wall well-bonded has been 
 recommended : in this case the air enclosed between its two 
 divisions should not be stagnant. 
 
 Before being plastered, the wall, whether its surface be of 
 stone, bricks and mortar, roughened slate, or tiles, must be 
 thoroughly wetted with lime or baryta-water. The plaster 
 is applied in two or more coats, the coarsest and thickest 
 first. In the case of a ground for fresco the two ingredients 
 usually employed are (or rather were) pure, slaked lime and 
 clean, sharp silicious sand. The sand must be uniform in 
 grain, white, and free from soluble salts. The slaked lime 
 is so important an ingredient in the majority of plasters, that 
 it is expedient to describe its preparation once for all. 
 Before doing so we may state the relations subsisting 
 between the three compounds known generally as carbonate 
 
COMPOUNDS OF LIME 
 
 of lime, or mild lime, burnt lime, and slaked lime. The 
 first of these is neutral and nearly insoluble in pure water, 
 the second and third are alkaline and caustic. When burnt 
 lime unites with water to form slaked lime it becomes 
 slightly soluble in pure water. In chemical language these 
 three compounds are called respectively calcium carbonate, 
 calcium oxide, calcium hydrate (or hydroxide). From the 
 first substance the others are readily obtained. If calcium 
 carbonate, often called carbonate of lime, be heated to a 
 sufficient temperature, it is decomposed, being resolved into 
 carbon dioxide (carbonic acid gas) which escapes, and 
 calcium oxide (lime) which remains: from ioo parts by 
 weight of the carbonate 56 parts of lime, that is, burnt lime, 
 are obtained. Placed in water or exposed to moist air this 
 burnt lime combines with water, 56 parts of it uniting with 
 18 parts of water to yield 74 parts of slaked lime, calcium 
 hydrate. In the ordinary country atmosphere, which con- 
 tains no more than 3 measures of carbonic acid gas per 
 io,ooo, slaked lime or calcium hydrate loses its combined 
 water, slowly becoming once more the carbonate from 
 which it was originally produced : 74 parts of hydrate lose 
 18 parts of water and combine with 44 parts of carbonic 
 acid, and yield 100 parts of carbonate. Thus mild lime is 
 formed once more from caustic lime. By this change, if it 
 be effected in the presence of a sufficiency of free water — 
 that is, if the hydrate of lime be in the state of a firm paste 
 — the whole substance becomes a hard crystalline solid, 
 like an opaque marble. Advantage may be taken of this 
 hardening or cementing process to firmly incorporate other 
 substances with the lime. Silicious sand, infusorial earth, 
 pumice, marble powder, and many other mineral substances, 
 may be thus introduced. Such of these materials as are 
 silicious may contain silica in a form which is known as 
 
LIME-PUTTY 
 
 19 
 
 'soluble silica.' This substance further strengthens the 
 plaster by forming with a part of the lime an insoluble com- 
 pound called silicate of lime. To return to the preparation 
 for artistic purposes of hydrate of lime. White or black 
 marble, limestone, chalk, or other fairly pure forms of 
 carbonate of lime are first of all burnt, and then the quick- 
 lime produced is slaked with clean water. This is done in 
 a grouting box, having a sluice 1 or 2 inches from the 
 bottom. Run the thick cream of lime into a tank of slate 
 and keep it, covered loosely, for two months. At the end 
 of this time it will be ready for all the rougher purposes of 
 plastering. For finer work the grouting operation is to be 
 repeated, and the cream of lime strained through hair- 
 sieves, and preserved in screw-top stoneware jars. Some 
 water will accumulate above the lime-putty, as it may be 
 called, in these jars ; it should be poured off or drawn off, 
 from time to time. The jars are kept tightly closed to 
 prevent further carbonation of the lime hydrate. This 
 change, if carried beyond a certain point, is undesirable, 
 since the binding and hardening powers of the lime would 
 thereby be lessened seriously, or even vanish altogether by 
 its conversion into mild lime : not more than one-third or 
 at most two-fifths of the lime should be converted into the 
 carbonate. The lime-putty thus prepared may be used for 
 plaster and intonaco with the certainty that it will not give 
 rise to defects in the painting grounds made therewith. 
 Much lime paste of this kind was prepared for the works in 
 fresco in the Houses of Parliament, and was kept in the 
 cellars under that building, where probably some of it still 
 remains. I have made many experiments with samples 
 from that source, and can speak with confidence of its 
 excellent quality. 
 
 BuorH Fresco. — A good mixture for the first application to 
 
FRESCO GROUNDS 
 
 the moistened wall consists of 2 parts (by weight) of clean 
 sharp sand to one of lime-putty. When one or more coats 
 of this mixture have been duly laid and have set, then the 
 surface is ready to receive the final coat or intonaco, the 
 actual painting-ground. Before this is applied, the rougher 
 plaster below must be thoroughly wetted with distilled or 
 lime water. The sand in the intonaco is of finer and more 
 uniform grain than that previously employed ; the intonaco 
 itself is only one-eighth of an inch in thickness. All the 
 coats must be laid without having recourse to scraping or 
 ' floating '; the latter operation brings too much lime up to 
 the surface. Considerable practice and manual dexterity 
 are needed in these operations. The work of painting is at 
 once commenced when the intonaco has been laid, no 
 more being spread at one time than the artist can cover in 
 the day. Upon the wet soft plaster the cartoon is laid, and 
 the outlines and other important parts pounced in, trans- 
 ferred, or impressed by an ivory point. Rapidity and 
 firmness of execution, with the distribution of a uniform 
 thickness of pigment, are matters to which special attention 
 must be paid. The chemistry of this method of painting 
 will be discussed in Chapter XXIII. 
 
 Many modifications in the preparation, proportions, and 
 materials of fresco painting-grounds have been introduced 
 or suggested from time to time. I have found the following 
 mixture to yield an excellent plaster for this purpose : Three 
 parts of burnt lime in very fine powder are ground up with 
 2 parts of whitening or prepared chalk ; the mixture is 
 grouted, and then strained through hair-sieves ; 5 parts of 
 the putty thus obtained are mixed with 5 parts of sifted 
 crushed marble, or with 5 parts of sharp, fine, sifted sand, 
 or with 3 parts of sifted pumice, or with the same 
 quantity of infusorial (silicious) earth ; the whole being 
 
TEMPERA GROUNDS 
 
 moistened with a sufficient quantity of lime-water to render 
 working easy. For the undercoats the sand, etc., intro- 
 duced may be coarser ; while a small quantity of the most 
 silky and whitest asbestos, cut with scissors into short 
 uniform lengths, will prove a desirable addition. The 
 asbestos lessens the risk of any lack of continuity in the 
 undercoats. 
 
 Fresco-Secco and Tempera. — For fresco-secco the same 
 ground as that required for true fresco may be used, but it 
 is allowed time to dry and harden. So long as it contains 
 any caustic lime this ground is unfitted for work in tempera, 
 as its alkaline nature seriously limits the variety of pigments 
 which may be employed in this method. When carbona- 
 tion of the lime is complete it may be employed for 
 tempera-painting, the surface being first treated with warm 
 size. Many Greek and Byzantine paintings were, however, 
 executed upon a caustic lime ground, but the pigments 
 employed consisted chiefly of those natural earths which are 
 unaffected by alkalies. In these Greek tempera-grounds 
 slaked lime mixed with chopped straw, flax, or cotton, 
 formed the basis of the plaster. It is scarcely necessary to 
 remark that these vegetable materials are liable to decay 
 and to cause discoloration of the ground. 
 
 The ordinary ground for Italian and Spanish tempera- 
 paintings consisted either of whitening and size, or of burnt 
 gypsum stirred well with water so as to lose the power 
 of setting, strained, and mixed with size. Sometimes both 
 whitening and slaked burnt gypsum are found together as 
 constituents of the ground. The ground was laid directly 
 on the panel, or on the cloth which had been previously 
 glued to the wood. Great care was taken by sifting and 
 washing to secure the fineness and purity of the whitening 
 (calcium carbonate) and of the slaked plaster of Paris 
 
STEREOCHROME GROUNDS 
 
 (calcium sulphate united with two proportions of water). 
 Various kinds of size were used ; one of the best was made 
 partly from parchment, partly from the finer kind of fish- 
 glue. An excess of size will cause the ground to crack ; it 
 must never contain such a quantity as to be rendered non- 
 absorbent. All tempera-grounds of gesso were originally 
 absorbent ; in course of time they have become more so 
 owing to the decay of the size. Whether they were after- 
 wards to be painted in tempera or oil they were always first 
 sized. This sizing preserved the luminous whiteness of the 
 ground, which was unable to absorb the oil of oil-paints or 
 that present in the egg-yolks employed in tempera. A 
 proof of the existence of this layer of size above the ground 
 proper is obtained in the process of transferring old tempera 
 and oil pictures to canvas, for in such cases we find dis- 
 coloration of the ground under cracks only where both the 
 size and the paint above it have become fissured. 
 
 It will have been gathered from what has been stated in 
 the preceding paragraph that a non-caustic tempera-ground 
 is suitable for work in oils. In the latter case, however, it 
 must be perfectly dry before the painting is commenced. 
 It should be gently warmed and rubbed with a little clean 
 spirits of turpentine before laying on the first coat of oil- 
 paint. 
 
 Stereochromy. — The ground for stereochromy has been 
 modified several times since the first introduction of this 
 method of water-glass painting. Originally it was re- 
 commended to use an undercoat containing 2 parts of 
 sharp sand, 2 parts of fine sand, and one part of slaked 
 lime in fine powder. Upon this was laid an intonaco of 
 one-tenth to one-eighth of an inch in thickness, made of 3 
 parts of fine sand and 1 part of slaked lime. The fineness 
 or coarseness of the sand in the intonaco must, however, 
 
SPIRIT-FRESCO GROUNDS 
 
 23 
 
 be regulated by the nature of the surface required by the 
 artist. I see that nearly thirty years ago I recommended* 
 the employment of sifted white marble powder, and of 
 several other substitutes for sand, recommendations which, 
 within the last few years, have been again brought forward 
 by Herr Adolph Keim. Oxide of zinc may be advantage- 
 ously substituted for a part of the lime in the intonaco, and 
 it may be added to the pigments. Keim recommends the 
 wall to be first coated with a mixture of 1 part of burnt 
 lime (which is to be slaked with distilled water), and 4 parts 
 of a composition consisting of coarse quartz sand, infusorial 
 earth, and powdered marble. The actual painting-ground, 
 which is from one-eighth to a quarter of an inch in thick- 
 ness, is made of 1 part of slaked lime, and 8 parts of a 
 mixture of the finest quartz sand, marble sand, marble 
 meal, and infusorial earth. Fine asbestos paper, wetted 
 with lime-water, and firmly pressed by rolling into a soft 
 freshly-laid lime and sand-plaster, makes an excellent ground 
 for stereochrome painting ; but as a single breadth only of 
 this paper can be used, the size of the work that can be 
 executed upon it is somewhat limited. All the precautions 
 as to dryness of the wall and purity of the materials, already 
 noted in the case of fresco grounds, must be observed in 
 reference to those intended for stereochrome painting. 
 
 Spirit-Fresco. — The ground recommended by the late 
 Mr. Gambier Parry for that modified form of varnish-paint- 
 ing to which he gave the name of ' Spirit- Fresco ' is 
 identical with that required for true fresco. All the usual 
 precautions as to the dryness of the backing, and its freedom 
 from soluble salts, must be taken. The plaster must be 
 allowed to dry completely before the operation of saturating 
 it with the medium is commenced; ihe lime in it should 
 
 * ' Chemistry of the Fine Arts' in Cassell's 'Technical Educator.' 
 
24 
 
 SPIRIT-FRESCO GROUNDS 
 
 also have become mild — that is, carbonated. (See Chapter 
 XXIII. for tests for alkalinity and moisture.) Syringing 
 the plaster with distilled water previously charged under 
 pressure with carbonic acid gas, though it delays the drying, 
 hastens the carbonation of the lime materially. To com- 
 plete the preparation of the ground, it should, when quite 
 dry, be soaked with a mixture of two parts of the medium 
 (Chapter XII.), and three of turpentine. After two days, 
 this treatment must be repeated. A third application may 
 be needed for very porous grounds. Another period of 
 forty-eight hours having elapsed, the surface receives a coat 
 of white paint, made of equal parts of white lead and 
 gilder's whitening, ground up with the medium diluted with 
 one-fourth or one-third its bulk of turpentine. This prim- 
 ing is repeated when the first coat is dry. After three 
 weeks, the painting may be commenced. Stone and terra- 
 cotta, if sufficiently porous, may be primed in the same way 
 as plaster. Under no circumstances should cements con- 
 taining plaster of Paris be introduced into the grounds used 
 for spirit-fresco. 
 
 During the last decade a considerable number of large 
 mural paintings have been executed either in Gambier 
 Parry's medium or in the paraffin-copal medium. Some of 
 these works have been painted directly on plastered walls, 
 some on canvases which have been afterwards affixed by 
 maronflage to the surfaces prepared to receive them. To 
 the latter category belong nearly all the paintings in the 
 Ambulatory of the Royal Exchange, London. Each of the 
 compartments has been very carefully arranged with a view 
 to secure dryness and freedom from soluble saline matter. 
 In front of the wall itself has been fixed a slate slab slightly 
 inclined forwards at the top and having a ventilated air- 
 space behind it. Upon the slate the finished picture has 
 
SLATE AND STONE 
 
 25 
 
 been attached (or maroufle) by means of a thick paste of 
 white-lead, oil, and copal-varnish, spread not only upon the 
 slate, but simultaneously upon the back of the canvas. It 
 may be affirmed that paintings so secured are free from all 
 risk of injury from the back. In an atmosphere like that of 
 London the surface of the painting must either be protected 
 by glass or be periodically cleansed from deposits of dust, 
 soot, tarry matters, and the other impurities which are 
 described in Chapter XXV. of this handbook. 
 
 Several fresh materials have been recently employed as 
 painting-grounds. They are either patent or secret pre- 
 parations, dependent in general for their solidification upon 
 reactions between insoluble earthy and alkaline earthy 
 matters, such as china-clay, asbestos, and compounds of 
 lime and magnesia, with solutions of such salts as mag- 
 nesium chloride, aluminium sulphate, and alum. There is 
 sometimes a lack of tenacity, and always a lack of toughness 
 in these mixtures, but some artists find them to possess 
 precisely the texture and absorptive character they desire in 
 grounds not only for tempera, but also for oil-painting, and 
 they may be spread on canvas as well as on more rigid 
 supports. There is some danger of want of adhesion 
 between the paint and the ground. It is also necessary to 
 make sure that the materials of the ground do not affect 
 sensitive pigments such as ultramarine. The hardening or 
 petrifying liquids which in most cases are used in associa- 
 tion with solid preparations to make the grounds in question, 
 are invariably acid to test-paper, unlike the alkaline silicates 
 described in Chapter IX. 
 
 Slate may be used as the ground for spirit-fresco and oil- 
 painting ; but its freedom from crystals of iron-pyrites, 
 which present a brass-yellow colour, must be first ascer- 
 tained. The firm adhesion of any priming, or other layers 
 
26 
 
 SLATE AND STONE 
 
 of oil-paint which may be applied subsequently, to slate may 
 be secured in the following manner. The slate is slowly 
 warmed in a water-oven, and thus becomes quite dry. 
 While still warm, it receives a very thin coat of oil-copal 
 varnish, largely diluted with turpentine or with toluol, and 
 applied warm. When this film is hard, the painting may be 
 carried out as in the ordinary way of using oil-colours ; a 
 priming of flake- white ground in oil and mixed with a little 
 copal-varnish and turpentine, may be first applied, if desired. 
 Terra-cotta and stone may be treated in the same way j but, 
 being more absorbent than slate, the process recommended 
 on p. 24 is preferable. 
 
CHAPTER III 
 
 PANEL 
 
 Wood, as a backing for the painting-ground of works in 
 tempera and oil, presents some advantages over plaster and 
 canvas. Its chief merit lies, perhaps, in its comparative 
 immunity from mechanical injuries. The wood selected 
 must be hard, that its surface may resist blows and abrasion ; 
 and it must not contain much resin, gum, colouring-matter, 
 or other ' extractives,' as they are called, or else discolora- 
 tion of the painting-ground, or priming, may occur. Wood 
 grown in poor soils, in temperate climates, and felled in 
 winter, is the best. The Flemings used oak ; the Italians 
 white poplar. But oak often proves treacherous, through 
 irregular shrinkage ; while poplar is too soft. Italian painters 
 employed, also, the wood of the stone pine. Leonardo 
 da Vinci recommended cypress, pear, and service-tree. 
 Mahogany, which was unknown to the old painters, is 
 now generally employed. Teak and cedar, and also 
 American or black walnut, deserve further trial. 
 
 The specific gravity of wood varies from 0-3 to 1*3 ; the 
 lighter kinds contain large volumes of interstitial air. The 
 longitudinal contraction of wood is much less than the 
 transverse; the distribution, form, and number of the 
 cracks in old panel-pictures is often to be traced to this 
 cause. 
 
28 
 
 PANEL 
 
 Wood contains (i) water, (2) ligno-cellulose, (3) extrac- 
 tives, (4) ash or mineral matter. The water, in thoroughly- 
 seasoned and air-dried wood, generally constitutes about 
 one-eighth part of its weight. The main constituent of 
 wood is the so-called ligno-cellulose, which is present to the 
 extent of from 75 to 85 per cent. It may be resolved into 
 two substances, which, for convenience' sake, are here called 
 cellulose and lignose. The extractives belong to two groups 
 — one, soluble in alcohol and ether, consists chiefly of 
 resins ; the other, soluble in cold or hot water, or else in 
 very dilute alkalies, includes tannin, albuminoids, gum, and 
 colouring-matters. The following analyses of three kinds of 
 wood in an air-dried state will convey a fair idea of their 
 constitution in 100 parts : 
 
 
 Mahogany 
 
 Oak 
 
 Pine 
 
 Water - 
 
 - I2'4 - 
 
 ■ I3-I " 
 
 ■ I2'9 
 
 Cellulose 
 
 - 49-0 - 
 
 - 39"5 ■ 
 
 - 53'3 
 
 Lignose • 
 
 - 27-6 - 
 
 - 34'3 - 
 
 - 28-2 
 
 Ash 
 
 Pi - 
 
 I "2 - 
 
 ■ 0-3 
 
 Resin 
 
 I"0 - 
 
 ■ 0-9 - 
 
 - i-6 
 
 Water-extract - 
 
 - 8-9 - 
 
 - 1 1 "0 - 
 
 • 37 
 
 The preparation of panels for painting requires much 
 time and trouble. The directions given by ancient authori- 
 ties are numerous, and not always accordant. One author 
 tells us to boil the wood ; another says we are to coat it 
 with mastic dissolved in twice-distilled turpentine and 
 mixed with white. Then it is to be treated twice or thrice 
 with spirits of wine, in which some white arsenic or corro- 
 sive sublimate has been dissolved ; coats of boiled oil, of 
 liquid-varnish* and white, and of verdigris and yellow are 
 subsequently mentioned. Probably the best method of 
 
 * Made by boiling 1 part of sandarac in 3 parts of linseed-oil. 
 
PREPARATION OF PANELS 
 
 29 
 
 treating the harder woods intended for pictures is, after 
 thorough seasoning, first of all to reduce the panel, by 
 planing and glass-papering both sides equally, to the desired 
 thickness. The panel is then soaked in water heated to 
 50 C, and then steamed. When dry, it receives a wash 
 on both sides of a solution of corrosive sublimate in 
 methylated spirit ; it is again dried and seasoned in a warm 
 air-chamber. After these operations, the panel should not 
 require more than a slight rubbing with fine glass-paper, in 
 order to render both surfaces plane. For panels to be used 
 for oil-pictures, a priming is now applied, consisting of 
 white lead, a little copal-varnish, and drying linseed-oil 
 prepared by means of borate or oxalate of manganese. 
 Allow this coat, which is intended to fill up the cavities and 
 pores of the wood, to dry thoroughly, and then apply 
 another coat in the transverse direction ; subsequent coats 
 should contain nothing but white lead (or other pigment) 
 and the drying oil. Repeated smoothings of each coat, 
 when hard, with fine pumice-powder are necessary ; the last 
 coat may consist of zinc-white and drying-oil. Both sides 
 of the panel should be treated, as far as possible, alike, so 
 that they may be equally loaded, and equally protected ; 
 but the pumice-rubbings are, of course, not required for the 
 back of the panel. The object of priming the back is two- 
 fold — the prevention of decay and of the attacks of insects ; 
 and the avoidance of that gradual curvature whereby the 
 protected front becomes convex, and the unprotected back 
 concave. This change occurs through the slow loss of 
 water from the back of the panel — a loss which is generally 
 accompanied by a loss of some of the organic constituents 
 of the wood through oxidation. Here it may be mentioned 
 that the original steaming of the panel removes some of the 
 extractives, and coagulates the albuminoids present, which 
 
3o 
 
 PREPARATION OF PANELS 
 
 are generally the first cause of decay. This decay is not 
 primarily a chemical and spontaneous one, but is com- 
 menced by certain minute organisms, the growth and 
 increase of which is, in part, dependent upon the presence 
 of available albuminoids, but which involves also the de- 
 struction of some of the other extractives, and even of the 
 ligno-cellulose itself. The corrosive sublimate employed 
 helps to sterilize the wood, and to prevent the inroads of 
 animal organisms. 
 
 In order to avoid the disastrous effects of transverse 
 shrinkage upon compound panels, the old painters glued 
 linen cloth, or vellum, or parchment, or tinfoil to the front 
 surface of the wood, and on this they spread their gesso or 
 painting-ground. Gesso, made of plaster of Paris and size, 
 or of whitening and size, often lost its cohesion through the 
 decay of the binding material, and in consequence became 
 fragile and powdery ; the panel itself decayed, and thus at 
 last the linen or parchment remained as the best preserved 
 element of the composite structure. Were we to avoid 
 gesso and use lead-primed canvas glued to panel, we should 
 really be painting upon canvas backed or protected by wood. 
 Panel is to be recommended for modern work only when a 
 single piece of uniform and well-seasoned wood of sufficient 
 size can be secured. However, an excellent cement for 
 joining panels together was sometimes used with success. 
 It consisted of lime and cheese, both in fine powder, the 
 latter having been grated, and then washed with water. 
 These materials intimately mixed and then ground into a 
 paste with water, yield a tough and adhesive cement which 
 becomes of rocky hardness. 
 
 In order to prepare a panel for tempera work, it should be 
 treated in the manner above described, substituting for the 
 priming with oil, white lead and copal-varnish, a mixture 
 
PREPARATION OF PANELS 
 
 3* 
 
 consisting partly of parchment-size, partly of fish-glue, and 
 whitening. 
 
 It is very probable that some of the hard, fine-grained 
 woods of British India and of North Borneo will furnish 
 excellent materials for picture-panels. At present experi- 
 ments in this direction cannot be regarded as more than 
 tentative and promising. 
 
CHAPTER IV 
 
 CANVAS 
 
 The usual, and probably the best fibre for the manufacture 
 of canvas for painting is unbleached flax — that is, linen ; 
 hemp and cotton are decidedly inferior. The material is 
 woven in different ways, and with strands of different degrees 
 of fineness, so as to produce cloths of various degrees of 
 thickness and fineness, and having several kinds of texture 
 and surface. 
 
 The canvas is first treated with size or a solution of glue ; 
 this should be as free from colour as possible. The 
 priming consists of two coats, the first containing whitening 
 and size, the second lead white and linseed-oil. Fuller 
 primings are often given where it is not desired to allow the 
 texture of the canvas to remain evident. Such primings are 
 put on alternately in directions at right angles to one 
 another, and are treated in the same way as the primings of 
 panel. If before the last priming be dry it be dusted with 
 zinc white, or if a final priming of zinc white and drying oil 
 (free from lead) be given, the usual discoloration of the 
 canvas which occurs on keeping it, especially in the dark, will 
 be avoided. But such discoloration can always be removed 
 by leaving in contact with the priming a piece of blotting- 
 paper saturated with a solution of hydrogen peroxide : a 
 slight warmth greatly hastens the bleaching process. 
 
CANVAS 
 
 33 
 
 Some painters in oil have employed with success a tempera- 
 priming on their canvases. This priming may be prepared 
 with a mixture of a strong, though elastic, size, with whiten- 
 ing. A good composition of this sort may be made by taking 
 equal weights of fine whitening and of fine plaster of Paris, 
 which has been slaked in and soaked with abundance of 
 clean water, or of the preparation called satin-finish, an 
 artificial gypsum, used by paper-makers : the warm size is 
 incorporated with this mixture. When the priming coats 
 are dry the surface is dressed with a layer of pure size, 
 and allowed to harden thoroughly before the picture is 
 begun. 
 
 An ordinary primed canvas was examined with the 
 following results. The amount of moisture present was 
 5*5 per cent, of its weight, the priming 25 per cent., and the 
 dry substance of the size 15. The dry fibre which con- 
 stituted the remaining part would weigh, therefore, about 
 54 parts. It was further found, with the same canvas, in a 
 dry heat of ioo° C. (212 F.) continued for twenty minutes, 
 that a strip 20 inches long became shorter by a quarter 
 of an inch, changing in colour from a creamy white to a pale 
 buff. After immersion in boiling water for twenty minutes 
 a piece of this canvas 20 inches square was found to have 
 shrunk rather more than 1 inch in one direction, and in 
 the other direction rather more than half an inch. The 
 piece was somewhat crinkled, and had become yellow in 
 patches. 
 
 A few remarks as to the bearing of the above observa- 
 tions on some of the phenomena presented by oil-paintings 
 on canvas may be here introduced. The water present in 
 canvas varies with the temperature, and in consequence the 
 dimensions of the canvas vary. As the contraction on 
 drying and the expansion on taking up moisture are not the 
 
 3 
 
 V 
 
34 
 
 PRESERVATION OF CANVAS 
 
 
 \ 
 
 o 
 
 same in the direction of the warp as in that of the woof, 
 there is an unequal strain upon the layers of paint upon the 
 surface. These may, therefore, become irregularly fissured, 
 and even loosened. The importance of selecting a canvas 
 so woven as to expand nearly equally in both directions is 
 evident, but the maintenance of a uniform temperature, and 
 of a suitable degree of moisture in the atmosphere where 
 pictures are hung, is also obvious. The absorption of 
 moisture by canvas occurs through the back, unless that be 
 also protected by paint. With the moisture deleterious 
 gases may also be absorbed, and these may easily pass 
 through and affect the priming, even the picture. Canvas 
 protected by panel behind, or coated at the back with 
 a layer of white lead which has been ground up with starch 
 paste, escapes this injury in great measure, as the sulphuretted 
 hydrogen, etc., are then intercepted. The colouring-matter 
 of the fibre and size of the canvas may move towards the 
 front and discolour the priming and even the picture. An 
 excess of damp and a high temperature are the chief causes 
 of this movement. When the first priming coat contains 
 size, though it may adhere firmly to the sized canvas, it may 
 not hold the subsequent oil-painting quite so tenaciously. 
 Canvas is liable to accidental injuries from mechanical 
 causes : a double canvas mitigates the evil. The elasticity 
 of the priming may not suffice, when the canvas is rolled up, 
 to prevent cracking. A small addition of a non-drying oil, 
 such as almond or olive oil, to the linseed oil used in the 
 priming coats, proves useful, but such addition should not 
 exceed i part of non-drying oil to 20 of drying oil. 
 
 There are two methods of preserving canvas from decay 
 by the application of solutions to the back after the priming 
 has been completed on the front. One of these solutions 
 contains corrosive sublimate (mercuric chloride) dissolved 
 
 
0^ 
 
 'WILLESDEN CANVAS' 
 
 35 
 
 in methylated spirit : a 5-per-cent. solution is sufficiently 
 strong. The other solution is made by dissolving tannin in 
 methylated spirit. One or other of these solutions should 
 be applied once to the back of the canvas by means of a 
 broad stiff varnish-brush. When the spirit has evaporated, 
 the coating of white lead ground in starch paste previously 
 recommended in this chapter may be applied. The two 
 solutions we have named act by coagulating some of the 
 size in the canvas : the tannin turns it into leather. Corro- 
 sive sublimate prevents the development of mould or mil- 
 dew, and is a good preservative against the attack of animal 
 organisms. 
 
 It may be observed that the employment of size in the 
 first preparation of canvas constitutes an element of weak- 
 ness. Many attempts have been made to substitute a less 
 hygroscopic and changeable substance. A plain collodion 
 containing a little ceresin has been used for the purpose in 
 question. It is, however, very difficult to secure the 
 adhesion to the canvas of the film left behind when the 
 collodion dries. I have found that oil-paintings executed 
 upon collodionized canvas cannot be rolled up without 
 damage. It would probably be found that the formation of 
 a viscose film (see the account previously given of paper- 
 sizing) would prove a good substitute for ordinary size in 
 the first treatment of canvas. 
 
 ' Willesden canvas ' appears to resist the attack of moisture 
 and of animal organisms : the copper-compounds which it 
 contains do not interfere with its use as a painting-ground, 
 but the absence of soluble salts (chiefly sulphates) from it 
 should be ascertained. This test is easily made by soaking 
 a piece of the canvas weighing 50 grains in distilled water 
 overnight, pouring off the clear liquid next morning, heating 
 it to boiling, and adding a few drops of barium chloride 
 
 3—2 
 
36 
 
 ' WILLESDEN PAPER' 
 
 solution. If a distinct precipitate be formed the canvas 
 cannot be employed safely, but a mere cloudiness may be 
 disregarded. It is just as well to test the watery extract for 
 free acid by means of litmus paper, because an attempt has 
 been made to remove the green colour of Willesden canvas 
 by a bath of dilute sulphuric acid, the presence of which is, 
 on all accounts, to be avoided. 'Willesden paper' pos- 
 sesses properties similar to those of Willesden canvas, and 
 may sometimes be found serviceable for work in oil- 
 colours. 
 
PART II 
 
 VEHICLES AND VARNISHES 
 
 Chapter V. — Oils. Chapter VI. — Resins, Waxes, Paraffin-Waxes. 
 Chapter VII.— Yolk and White of Egg, Size, Glue. Chapter VIII.— 
 Gums, Glycerin, Honey. Chapter IX. — Water-Glass, Lime- and 
 Baryta- Water. Chapter X. — Solvents and Diluents. Chapter XI. — 
 Siccatives and Dryers. Chapter XII. — Varnishes and Oleo-Resinous 
 Vehicles. 
 
n 
 
CHAPTER V 
 
 OILS 
 
 The common usage of the term ' oil ' is wider and less 
 definite than that sanctioned by chemists. We must ex- 
 clude from the category of true oils petroleum and the 
 liquid paraffins, spirits of turpentine and the volatile essences 
 of plants, the hydrocarbons of coal naphtha, as well as a 
 number of other liquids which present certain superficial 
 resemblances to the oils proper. Fats, however, belong to 
 the same group, their solidity at ordinary temperatures 
 being, so to speak, an accidental rather than an essential 
 difference. 
 
 The true oils are often called fixed oils, for they cannot 
 be boiled and distilled without change, thus differing from 
 really volatile liquids. They are glycerides — that is, com- 
 pounds from which glycerin, on the one hand, and fatty 
 acids, on the other, are obtainable. These glycerides are 
 named after the fatty acids which they yield. Thus olein 
 is the glyceride of oleic acid, linolein the glyceride of linoleic 
 acid. In reality three kinds or varieties of glycerides of 
 each fatty acid are possible, but the oils used by painters 
 consist almost entirely of one of these kinds. The forma- 
 tion of one of these glycerides may be expressed in words 
 thus : One molecule of glycerin, reacting with three mole- 
 cules of a fatty acid, yields one molecule of the glyceride in 
 
40 
 
 DRYING OILS 
 
 question and three molecules of water. Conversely, under 
 other conditions, one molecule of a glyceride, reacting with 
 three molecules of water, produces one molecule of glycerin 
 and three molecules of fatty acid. If, in this last reaction, 
 we substitute for the water three molecules of an alkali, 
 such as potash, we obtain glycerin as before ; but, in lieu of 
 the free fatty acid, we find that an alkaline salt of the fatty 
 acid has been formed — such salt is a soap. Alkaline soaps, 
 namely, those of potash, soda, ammonia, are soluble in 
 water, which fatty acids — at any rate, those with which we 
 are here concerned — are not. There are, however, other 
 soaps which are insoluble in water, namely, the lime, 
 lead, copper, and many similar metallic salts of fatty 
 acids. 
 
 Oils, though insoluble in water, are easily soluble in spirit 
 of turpentine, benzene, chloroform, liquid paraffins, and 
 volatile plant essences ; they are, in fact, miscible in all 
 proportions with these liquids. There are other liquids in 
 which the oils are less soluble, such as alcohol, acetone, 
 and glacial acetic acid. 
 
 Oils are divisible into two classes, one of which includes 
 those which dry up and harden, forming a kind of elastic 
 varnish, by exposure to the air. The oils of the other class 
 do not harden, but become sticky, and rancid in smell ', 
 these oils, however, if submitted to the temperature of boil- 
 ing water for some time, do in some instances become dry 
 and hard, but the varnish they yield under these circum- 
 stances is dark in colour and brittle. The painter's concern 
 is almost exclusively confined to the oils of the first group, 
 generally known as drying oils. To the most important of 
 these attention will be directed presently, but the general 
 methods of extracting them first demand a few words of ex- 
 planation. There are two different processes in use. In 
 
LINSEED OIL 
 
 4i 
 
 one of these, which has been practised widely from very 
 early times, the oil is obtained by pressure ; in the other 
 process, invented some sixty years ago, the oil is extracted 
 by means of an appropriate solvent. We may dismiss this 
 latter process almost summarily, for the product which it 
 yields, though much greater in quantity, is decidedly inferior 
 to that obtained by pressure. It is less fluid, and contains 
 a larger proportion of solid fats. The solvent commonly 
 employed to dissolve out the oil from oil-yielding materials 
 is carbon bisulphide (CS 2 ), a compound of carbon and 
 sulphur, which may be prepared cheaply by passing the 
 vapour of sulphur through red-hot charcoal. Of the 
 pressure-process for obtaining fixed oils there are two 
 modifications. In the more usually adopted of these, the 
 oily seed or other material is first heated, and then pressed 
 while still hot ; in the other modification the pressure is 
 applied to the cold seed, etc. Heat and pressure give a 
 more abundant yield of oil, but the product is less pure and 
 less well fitted for use in painting. The bulk of the oils of 
 commerce are thus obtained. Cold-pressed oils remain 
 clear in cold weather, are more fluid than hot-pressed oils, 
 and contain a smaller proportion of solid fats and of free 
 fatty acids. 
 
 The most important drying oils are those of linseed, 
 poppy-seed, and walnut kernels ; others are obtained from 
 niger-seed, sunflower-seed, and hemp-seed. The first place 
 is due to linseed oil. 
 
 Linseed oil is obtained from the seed of the common 
 cultivated flax [Linum usitatissimuni). Linseed varies in 
 size and colour. The usual colours are a purplish-brown 
 and a reddish-brown, but there is a nearly white sort — a 
 mere sport or variety — which may be said to be straw- 
 coloured. It is grown along with the brown variety in 
 
42 
 
 LINSEED OIL 
 
 some parts of the North- West Provinces of India, particularly 
 in Nagpur, but no pains are taken to keep the strain pure. 
 Through the kind offices of the Director of the Royal 
 Gardens, Kew, the Government of India were good enough 
 to obtain a specially pure sample of some hundredweights of 
 white Nagpur linseed, and to place it at my disposal. At- 
 tempts to grow it for seed in this country and in Belgium 
 failed, but a large quantity of oil was expressed for trial and 
 analysis. Messrs. Bell and Co., of 225, Oxford Street, 
 obtained several gallons of oil by cold-pressure ; many 
 artists have expressed their approval of the product. One 
 advantage of this white seed is the ease with which the 
 purity of a sample may be recognised by the eye, any 
 accompanying weed-seeds differing widely in colour from 
 the white linseed. The skin of the seed is, moreover, thin, 
 the cold-drawn oil is nearly colourless, and the seed is 
 particularly rich in oil, containing no less than 45 per cent, 
 of its weight, although, of course, much less than this pro- 
 portion is obtainable by cold-pressure. In a hand-press about 
 25 per cent, was the average yield. Of the common or 
 brown linseed our chief supplies come from Russia and 
 India. The Russian seed is generally finer than the East 
 Indian ; it is, moreover, imported in a less mixed and 
 impure condition. By screening, the greater part of the 
 impurities are or may be removed, but it is sold on a basis 
 of 4 per cent, impurity. The impurities consist of dirt, 
 other oil-seeds, such as mustard, rape, and gold of pleasure, 
 and non-oily weed-seeds. The presence of the last-named, 
 though it reduces the yield, is not otherwise objectionable,* 
 but the same remark does not apply to the foreign oil-seeds. 
 Most of these contain non-drying oils, which mingle with 
 
 * Occasionally these weed-seeds give up, under pressure, certain 
 matters which deepen the colour of the expressed oil somewhat. 
 
LINSEED OIL 
 
 43 
 
 the linseed oil when the sample is pressed and reduce its 
 siccative character. 
 
 The percentage of oil in linseed varies between 28 and 
 45 : by cold-pressure 20 per cent, is the average yield; by 
 hot-pressure, 27 per cent. ; by extraction with carbon di- 
 sulphide, 33 per cent. The linseed oil in common use by 
 artists is hot-pressed oil, and is very rarely, if ever, obtained 
 from absolutely pure seed. The seed should be kept three 
 months before it is pressed. The expressed oil should be 
 exposed to light in covered glass vessels or tanks, and kept 
 at a temperature of 8o° or even ioo° F. for some time. It 
 thus loses colour and becomes clear, a slimy deposit being 
 formed. When thus bleached and clarified, the oil should 
 be preserved in corked bottles filled quite full ; the longer 
 it is kept the better it becomes for painting, provided the 
 access of air is prevented. The specific gravity of good 
 linseed oil varies very little. At 6o° F. (i5'6° C.) it is '935 ; 
 a bottle which will hold 1,000 grains of water at this tem- 
 perature will therefore hold but 935 grains of linseed oil. 
 It expands considerably with heat, its specific gravity at 
 50 C. being "913 only. One part of linseed oil requires 36 
 parts of cold absolute alcohol for solution, but only 4 parts 
 of boiling alcohol. It may be purified by solution in boil- 
 ing alcohol or in petroleum ether. Other methods of 
 purification are generally employed. Amongst these may 
 be named the following : Filtration through felt or carded 
 cotton and charcoal, and then through pyrolusite ; agitation 
 with a solution of common salt, followed by washing with 
 water, and drying by a heat of 220 F. ; treatment with one 
 four-hundredth part of oil of vitriol, addition of hot water, 
 washing, and drying. Various other processes and reagents 
 have been employed for purifying and bleaching linseed oil. 
 Aqueous solutions of sulphurous acid, green vitriol, potas- 
 

 44 
 
 LINSEED OIL 
 
 sium permanganate, potassium bichromate, and peroxide of 
 hydrogen may be included in this list. The addition of i 
 per cent, of oil of turpentine to the oil, and then passing a 
 mixture of air and steam through it, has also been tried. 
 Whatever process be adopted, no acid, saline matter, or 
 moisture must be left in the oil. The general and usual 
 result of all the very different kinds of treatment to which 
 linseed oil is subjected, in the above-named and in many 
 other processes, seems to be the more or less complete 
 removal of impurities. The effect on the properties of the 
 purified oil is chiefly seen in its greatly increased rate of 
 absorbing oxygen and consequent hardening. 
 
 The chemical composition of linseed oil may now engage 
 our attention. Its ultimate analysis shows it to vary accord- 
 ing to the method of extraction adopted, cold-pressed oil 
 containing about 78 per cent, of carbon, n per cent, of 
 hydrogen, and 1 1 per cent, of oxygen ; while the hot-pressed 
 oil contains nearly 3 per cent, less carbon, and nearly 3 per 
 cent, more oxygen — linseed oil, extracted by carbon di- 
 sulphide, is still poorer in carbon, and richer in oxygen. It 
 appears that linseed oil consists chiefly of four glycerides, 
 called, respectively, linolein, linolenin, isolinolenin, and 
 olein. A small, but variable, amount of free fatty acids is 
 also present. The empirical formulas of the four fatty acids 
 of the above-named glycerides are, respectively : 
 
 Linolenic Acid\ 
 Isolinolenic J 
 Linoleic- 
 Oleic - 
 
 Ci8H 80 O a . 
 
 Ci8H 32 2 . 
 
 C 18 H 34°2- 
 
 Linolein, which is present in linseed oil to the extent of 
 about 20 per cent., is the glyceride of linoleic acid, and has 
 the formula, (C^H^O^CgH^Og ; or, as it may be written, 
 C 3 H 5 (0,C 18 H 31 0) 3 . The relation of this glyceride to 
 
LINSEED OIL 
 
 45 
 
 glycerin may be seen when the latter body is expressed by 
 the formula, C 3 H 5 (OH) 3 . It is probable that the two other 
 main constituents of the oil — linolenin and isolinolenin — 
 are similarly constituted glycerides, and that they closely 
 resemble linolein in physical and chemical properties. 
 When iao parts of linseed oil are saponified by an alkali, 
 they yield from 9-4 to 10 parts of glycerin. 
 
 The most important chemical property of linseed oil, 
 from a painter's standpoint, is its behaviour with oxygen. 
 Under certain circumstances, it absorbs oxygen to the extent 
 of 13 or even 14 per cent, of its weight, becoming converted 
 into a mixture of substances for which it is convenient to 
 retain the old name linoxine. Linoxine is solid, and not 
 liquid ; it is far less soluble than linseed oil in any solvent, 
 and in many liquids it is insoluble. Linoxine is, moreover, 
 denser than the original oil; 100 grains of linseed oil 
 produce about 109 or no grains of linoxine. Notwith- 
 standing the greater density of linoxine, when compared 
 with the original oil, its formation is attended by a con- 
 siderable expansion. In consequence, a layer of raw linseed 
 oil spread upon glass becomes wrinkled during the drying 
 and oxidizing process. During the oxidation of linseed oil, 
 the small quantity of olein it contains remains unoxidized — 
 its presence confers elasticity upon the product. The 
 changes which occur during this oxidation are complex and 
 ill-understood ; but there is some formic acid formed, so 
 that the product is sour — carbonic acid gas and water are 
 also produced. There are many ways of bringing about 
 this oxidation. A very common one is to heat the oil to a 
 temperature of at least ioo° C, and to blow air through it, 
 or air containing ozone. Many substances favour the 
 absorption of oxygen by linseed oil under the above condi- 
 tions. Amongst these may be named manganese dioxide, 
 
wSar 
 
 46 
 
 SICCATIVE LINSEED OIL 
 
 borate, oxalate, or linoleate ; red-lead, litharge, or lead 
 acetate ; green vitriol, iron in the presence of water, etc. 
 It is better to use one of the manganese compounds, and 
 an excellent result is obtained with the borate of this metal. 
 On the small scale, the operation may be thus carried out : 
 Tie up in a small piece of muslin 20 grains of dry and 
 powdered manganese borate. Suspend the bag in a glass 
 quart flask, into which a pint of linseed oil has been placed, 
 so that the bag is just covered by the oil ; lightly plug the 
 mouth of the flask with some carded cotton. Stand the 
 flask in a warm place, where the temperature does not fall 
 below 40 C.j nor rise above ioo° C. In a fortnight's time, 
 the oil will have become strongly siccative, so that when it 
 is spread in a thin layer on glass, or paper, it will dry up to 
 a tough varnish within twenty-four hours. If the oil and 
 manganese borate be maintained, by means of a water-bath, 
 at a temperature of ioo° C, the change will occupy less 
 time, and the product will be just as good ; but it is not 
 advisable to boil the oil with the borate, although the 
 change may be thus effected in less than an hour. The 
 oxidation may be further hastened by occasionally blowing 
 a little air into the oil through a glass tube kept permanently 
 in the flask. When the rapid-drying quality of the oil has 
 been proved, by experiments made with a drop or two with- 
 drawn for that purpose, the flask is allowed to get cold, and 
 the oil poured into a corked glass bottle, so as to fill it. In 
 the course of the next few weeks, a slight deposit will be 
 formed in the bottle ; when this has occurred, the clear oil 
 should be poured off into other bottles, and preserved for 
 use. According to the purpose for which the prepared oil 
 is to be afterwards used, the treatment with the borate must 
 be more or less prolonged ; but care should be taken not to 
 carry it so far that the oil becomes ropy or viscous, unless 
 
SICCATIVE LINSEED OIL 
 
 47 
 
 it is intended to make linseed oil varnish. In the subse- 
 quent chapters of this book, we shall often refer to this 
 siccative linseed oil as 'manganese oil.' To the above 
 directions for preparing this oil may be added the remark that 
 if the operations be conducted in a strong light, the oil will 
 be bleached, as well as rendered highly siccative. No 
 satisfactory explanation of the action of the manganese 
 borate (and of many other substances used for the same 
 purpose) has been offered. But it seems probable that the 
 absorption of oxygen by the oil is favoured by the removal 
 of certain impurities, and this the borate of manganese may 
 effect. 
 
 The increasing specific gravity of the ' manganese oil,' 
 as the process is prolonged, may be used as an indication of 
 the point at which the heating may be discontinued. When 
 the oil has acquired a specific gravity of "945, it is generally 
 sufficiently siccative for grinding with non-drying pigments, 
 and as an addition to certain varnishes. For these purposes 
 it may even attain a specific gravity of "96 ; but when it 
 shows '99, or '995, it constitutes a thick varnish, which 
 needs dilution with a suitable solvent. It may be well to 
 remark here that the various processes for rendering linseed 
 oil more rapidly-drying may be regarded as resulting in two 
 actions, partly consecutive, partly simultaneous. The first 
 action, if it could, or did, occur alone, would yield a purified 
 oil apt to dry quickly, but very slightly altered in composi- 
 tion ; the second action is more profound, and gives rise to 
 a thickened, denser product, in which the drying process 
 has already commenced. In practice, the first action occurs 
 almost, but not quite, uncomplicated with the second, when 
 linseed oil is warmed with borate of manganese in a vessel to 
 which atmospheric air has very limited access ; the second 
 action, which is of necessity associated with the first, takes 
 
4 8 
 
 TESTING LINSEED OIL 
 
 place when a stream of air is blown through warm linseed 
 oil, even in the absence of manganese borate, but far more 
 quickly in its presence. 
 
 The superiority of the highly siccative oils prepared with 
 borate of manganese (or the oxalate, or the linoleate) over 
 those in the manufacture of which lead compounds are 
 used, is so decided that all description of the older and less 
 satisfactory methods will be omitted. But there are two 
 other ways of rendering linseed oil more siccative, which 
 deserve a passing notice. Into a clear-glass quart-bottle an 
 ounce of distilled water and an ounce of clean iron brads 
 are first placed, and then one pint of raw linseed oil, agita- 
 tion being avoided. The next day, the bottle, placed in as 
 strong a light as possible, is to be shaken frequently, the 
 shaking being repeated every day, until a drop of the oil, 
 when tested, shows a sufficient degree of drying character. 
 Finally, the liquid part of the mixture in the bottle is poured 
 into a separating-funnel, and the aqueous part allowed to 
 run away. The oil may require drying and filtration. In 
 another similar process green vitriol is substituted for the 
 metallic iron, the other directions being identical. 
 
 The most important property of linseed oil, and some 
 methods for the further development of this property having 
 been discussed, we may now describe the remaining 
 characters of this oil. The cold-pressed oil is very pale 
 straw-coloured, or pale yellow, with occasionally a faint 
 greenish hue ; the hot-pressed oil is a darker yellow or 
 brown. The cold-pressed oil, when considerably cooled, 
 remains clear long after the hot-pressed oil has become 
 turbid. The fluidity of the oil is less than that of water in 
 the ratio of i : 10. The hot-pressed oil has a much stronger 
 taste and odour than the cold-pressed oil. 
 
 The adulteration of linseed oil with other oils may be 
 
TESTING LINSEED OIL 
 
 49 
 
 recognised with more or less precision by means of several 
 different tests. Most of these tests (oil of vitriol test, 
 nitric acid test, etc.) produce reactions in which the oil and 
 the acid acquire varied colours characteristic of different 
 oils. These tests must be applied under exactly similar 
 conditions of temperature, agitation, lapse of time, strength 
 of acid, etc. ; and even then, unless the experimenter is 
 well-versed in the work, the indications obtained are some- 
 times perplexing and difficult to interpret. The amount of 
 bromine absorbed by a given weight of linseed oil, or better, 
 of the fatty acids obtained from it, affords a valuable test 
 of purity. This amount of bromine is unusually high, 
 much higher than that absorbed in the case of the oils 
 likely to be used as adulterants. But such quantitative 
 determinations can be properly performed only by the 
 skilled chemist. There is another test known as Valenta's 
 acetic acid test, which has been used for the detection of 
 non-drying oils in linseed oil. It is based upon the less 
 solubility of the former oils in glacial acetic acid. It is, 
 however, not easy to secure constant results with this test. 
 Determinations of volatile matters, of unsaponifiable sub- 
 stances, and of insoluble bromine derivatives, afford valuable 
 indications as to the purity of samples of this oil. 
 
 The specific gravity of linseed oil also affords a valuable 
 means of testing its purity. At 15 "6° C. (6o° F.) it is denser 
 than most other vegetable oils : 
 
 Name of Oil 
 Linseed 
 
 Gold -of- Pleasure - 
 Hemp-seed - 
 *Cotton-seed - 
 Walnut 
 
 Spec. Grav. 
 •935 
 •93i 
 •930 
 •930 
 •929 
 
 Name of Oil 
 Poppy-seed 
 Sunflower-seed 
 
 *Black Mustard-seed 
 
 *Ground-nut 
 
 *Colza-seed 
 
 Spec. Grav. 
 - '926 
 
 •925 
 •921 
 
 •918 
 •914 
 
 The four oils marked with an asterisk are non-drying. 
 
So 
 
 POPPY OIL 
 
 Poppy Oil. — This oil is obtained from the seed of the 
 opium-poppy, Papaver somniferum. It is of a very pale 
 straw-colour, often almost colourless, and is nearly free from 
 taste and smell. By filtration through hot animal charcoal 
 it may be completely decolourized. If the fluidity of water 
 be represented by 1,000, that of poppy oil at 15 "6° C. is 74. 
 Its specific gravity at the same temperature is "926. Its 
 chemical composition is near that of linseed oil ; it contains 
 the same four glycerides, but in different proportions, for 
 it is mainly made up of linolein and olein. The large 
 quantity present of olein causes poppy oil to be a less 
 rapidly drying oil than linseed. Wolffen, in 1640, stated 
 that poppy oil dries throughout in four or five days, while 
 linseed oil forms a pellicle upon the surface. Joseph Petitot, 
 writing from Geneva under date January 14, 1644, stated 
 that umber is a siccative for poppy oil. Poppy oil was 
 introduced into painting in the beginning of the seventeenth 
 century, after linseed and nut oil. Later on in the same 
 century the Dutch painters acquired greater confidence in 
 this more slowly drying oil, employing it not only in the 
 painting process, but also for grinding their pigments, 
 especially whites, blues, and pale tints. 
 
 Nut Oil. — This oil is obtained from the kernels of the 
 common walnut, Juglans regia. Leonardo da Vinci directs 
 it to be made from the peeled kernels in order to avoid the 
 chance of darkening its colour, and also causing the subse- 
 quent alteration of the tone of the pictures painted with it. 
 The kernels were to be soaked in water first, before being 
 peeled and pressed. The introduction of nut oil into 
 painting followed that of linseed oil, and preceded that of 
 poppy. Cold-pressed nut oil is much paler in colour, and 
 has much less taste and smell than the hot-pressed oil; it 
 also differs in composition much in the same way that cold- 
 
ACTION OF PIGMENTS ON OILS 
 
 5i 
 
 pressed differs from hot-pressed linseed oil. The con- 
 stituent glycerides of nut oil are the same in kind as those 
 of linseed oil, but a larger proportion of linolein is present. 
 Nut oil closely resembles linseed oil in its physical characters; 
 its specific gravity, "929, is intermediate between that of 
 linseed and poppy oil : cold-pressed oil from the Black 
 walnut (Juglans nigra) has the specific gravity "922, and is 
 quite as good for painting purposes as oil from the common 
 walnut. Besides the three drying oils already described we 
 may name that expressed from niger-seed, Guizotea ohifera. 
 It is occasionally employed in grinding artists' colours as a 
 substitute for linseed and poppy oil. Tea-seed and camellia- 
 seed oils, and the oils extracted in Japan from the seeds of 
 Perilla ocimoides and from the kernels of Torreya nucifera, 
 are not of sufficient importance to demand description. 
 
 A few observations may now be offered as to (1) the 
 action of certain pigments on oils ; (2) the different amounts 
 of oil needed for grinding with different pigments. 
 
 1. Action of Pigments on Oils. — The most common action 
 is a physical one, in which the opacity of a pigment is 
 gradually lessened in course of time by the more complete 
 interpenetration of the oil between the particles. Thus 
 yellow ochre and raw sienna, for example, darken in colour 
 because they become more translucent, just as a piece of 
 oiled cream-laid paper is darker and yellower than the same 
 paper when dry. The light which falls upon it plunges into 
 it more deeply, and on reflection is more highly coloured. 
 In the case of such pigments as we have named, and several 
 others, another cause is at work darkening and modifying 
 the colour : this is the yellowing of the oil itself. And it 
 is the pigments which require the largest proportion of oil 
 for grinding which exhibit in a marked degree the pheno- 
 mena in question. 
 
 4—2 
 
52 
 
 OIL IN PAINTS 
 
 A second action between a pigment and the oil with 
 which it has been ground is the peculiar gelatinous or 
 ' livery ' condition quickly assumed by some oil-paints. 
 This change is particularly noticeable with the cochineal and 
 madder lakes. I have succeeded in obviating it, by care- 
 fully drying the pigments at a temperature just under ioo° C, 
 before grinding them with oil, and by substituting for raw 
 linseed oil a mixture of the ' manganese oil,' described in 
 the present chapter, with some poppy oil. Those pigments 
 which dry easily should be ground with more of the latter 
 oil, those which dry with difficulty with more of the former. 
 Sometimes pigments harden quickly in the tube itself; this 
 change is due either to the siccative character of the 
 pigments, or to the introduction of an actual ' dryer,' or to 
 the too copious use of a strongly siccative oil with those 
 pigments which are naturally slow in drying. 
 
 The third action between a pigment and the oil with 
 which it has been ground is of a distinctively chemical 
 nature. The most striking example of it known occurs 
 with flake-white. The lead hydrate in normal lead-white 
 saponifies the oil, forming lead-soaps with the fatty acids 
 which it contains, and, at the same time, setting free a small 
 quantity of glycerin. References to this curious action will 
 be found in Chapters XIII. and XXIII. 
 
 A fourth action between a pigment and the oil with which 
 it has been ground is occasionally observed with certain 
 colours of organic origin, which actually dissolve in and 
 stain the oil. Bitumen, gamboge, and several alizarin pre- 
 parations exhibit this phenomenon. 
 
 2. The different amounts of oil required by different pig- 
 ments may now be considered. As a rule, the densest or 
 heaviest pigments require the least oil. A few pigments 
 require an excess of oil in order to protect them from 
 
OIL IN PAINTS 
 
 53 
 
 moisture or other injurious agents. Different authorities do 
 
 not agree at all closely as to the amount of oil needed to 
 
 make a workable oil-paint from the same pigment. The 
 
 following list gives the weight required by ioo parts in 
 
 weight of 22 pigments : 
 
 According to 
 Name of Pigment C, Roberson and Co. 
 
 (1901) 
 
 - 16 - 
 
 - 19 - 
 
 - 71 - 
 
 • 35 - 
 
 • 37 - 
 
 • 59 - 
 
 . 147 - 
 
 White Lead • 
 Zinc White 
 Aureolin - 
 Chrome Yellow 
 Cadmium Yellow 
 Yellow Ochre - 
 Raw Sienna 
 
 Vermilion - - - — 
 
 Light Red - 69 
 
 Madder Lake - - - 103* 
 
 Terre Verte - - - 49 
 
 Viridian - - - - 56 
 
 Prussian Blue - - - 72 
 
 Cobalt Blue - - - 50 
 
 Ultramarine (artificial) - 34 
 
 Raw Umber - - - 97 
 
 Burnt Umber - - - 97 
 
 Bitumen . - - - — 
 
 Brown Madder - - 81 
 
 Vandyke Brown - - 72 
 
 Burnt Sienna - - - 138 
 
 Ivory Black - - - 88 
 
 The discrepancies between the corresponding figures in 
 the vertical columns are due, amongst other causes, to differ- 
 ences in the modes of preparation of the dry pigments ; to 
 natural variations in the native earths employed, to the dis- 
 similar standards of solidity or fluidity aimed at in the finished 
 paint, and to several other causes which it is needless to 
 particularize, but amongst which may be named different 
 * Figure for rose madder. 
 
 According to 
 
 Winsor and 
 
 Neivton (1901) 
 
 - 15 
 
 - 23 
 • 49 
 
 - 56 
 
 - 67 
 
 ■ 63 
 
 - 240 
 
 - 23 
 
 - 7o 
 
 ■ 55 
 
 - 87 
 
 - 52 
 
 - 78 
 
 - 90 
 
 - 43 
 
 - 95 
 
 - 87 
 
 - 127 
 
 - 93 
 
 - 94 
 
 - 150 
 
 - 112 
 

 54 
 
 OIL IN PAINTS 
 
 modes of grinding and the employment of different kinds 
 of oil. 
 
 The great differences in the above amounts of oil do not 
 cause such serious results in the conduct of the process of 
 oil-painting as might have been expected at first, for they 
 correspond in a measure to the relative bulks of the several 
 pigments. We can use more copal or amber varnish to 
 balance the excess of oil in some pigments, and so secure a 
 uniformity of structure, texture, and rate of drying in the 
 different parts of the work. It is, however, often convenient 
 to remove some of the excess of oil from a pigment before 
 using it, especially with the colours prepared by some 
 makers.* This can be done by leaving the oil-paint on a 
 pad of blotting-paper ; but 3-inch cubes of plaster-of-Paris 
 afford a far cleaner and surer method for the absorption of 
 oil. It may be further remarked that the quantities of oil 
 required by some of the pigments in the above table may be 
 reduced by grinding them under greater pressure. Raw 
 sienna, burnt sienna, and ivory black should be dried at 
 ioo° C. just before grinding and then yield workable paints 
 with less oil. The subsidence of vermilion from the oil in 
 which it has been ground may in some measure be pre- 
 vented by using ' manganese oil ' instead of raw linseed oil, 
 and adding to it a small quantity of linoleate or oleate of 
 alumina, or of hard paraffin wax or ceresin, having a melting- 
 point not under 65 C. Some artists find it a good plan 
 to keep their tubes of vermilion and of other heavy pigments 
 in an inverted position — that is, with the cap downwards. 
 
 * Dr. H. Stockmeier, of JNurnberg, found the following percentages 
 of oil in certain oil-paints from different sources which he analysed : 
 
 Flake-White (Roberson and 
 Co.) .... 16-2 
 
 Light Red (Winsor and 
 Newton) - - - 41 "9 
 
 Burnt Sienna (Dr. Schoen- 
 
 feld) .... 59-2 
 Chinese Ochre (G. B. 
 Moeves)- - - - 45 
 
CHAPTER VI 
 
 RESINS, WAXES, AND SOLID PARAFFINS 
 
 In commercial parlance resins are incorrectly termed gums. 
 The true gums (Chapter VIII.) are either soluble in water 
 or swell up in that liquid, but resins are not acted on by 
 water. The term resin is used throughout the present 
 volume in its proper sense, so that 'copal resin,' 'mastic 
 resin' are spoken of, not 'gum copal,' 'gum mastic' All 
 the resins used for making vehicles and varnishes are of 
 vegetable origin ; they contain besides carbon and hydrogen 
 a not inconsiderable proportion of oxygen. They are 
 related to the hydrocarbons known as terpenes, present in 
 many essential oils, but are of more complex constitution. 
 Some resins, such as gamboge, contain gum and are called 
 gum-resins ; others contain a hydrocarbon (or terpene, see 
 Chapter XI.) or an aromatic acid, and are called balsams ; 
 others are true resins, but even these rarely, if ever, consist 
 of a single definite compound, but are mixtures of at least 
 two, often of three, four, or five different bodies. Generally 
 these constituents of true resins differ as to their degree of 
 solubility in various liquids, such as alcohol, ether, spirit of 
 turpentine, benzene, petroleum spirit, and heated fixed oils. 
 They contain carbon, hydrogen, and oxygen, with occa- 
 sionally a little sulphur, and are usually of an acid character, 
 and are capable of forming soaps, called resinates, with the 
 
56 
 
 AMBER 
 
 alkalies. Resins differ much from one another, not only in 
 solubility but also in hardness and in the temperature at 
 which they melt. Those which are least soluble are gener- 
 ally those which are hardest, and which require the highest 
 degree of heat to bring them into fusion. Most true resins 
 contain, besides their proper resinous constituents, small 
 quantities of colouring-matter, of water, of crystalline aromatic 
 acids, and of a volatile hydrocarbon or terpene. All these 
 impurities, save the first, may be removed, generally with 
 advantage, by the following treatment. The powdered resin 
 is thoroughly mixed with a little water and placed in a large 
 glass retort. A current of steam is then passed into the 
 mixture until the terpene and volatile acids present have 
 distilled over. To the contents of the retort carbonate of 
 soda is added (i part for each ioo of resin). The mixture 
 after agitation is allowed to cool and then filtered through a 
 fine cotton cloth. The purified resin is then washed on the 
 filter with distilled water, then dried in the air and finally in 
 the water-oven: the air-bath and a temperature of no to 
 i2o° C. may be used for the desiccation of the harder 
 resins. 
 
 It might be thought that the subject of resins would be 
 sufficiently discussed from the painter's standpoint by a 
 description of three kinds — amber, copal, mastic. But it 
 will be shown presently that copal and mastic are names 
 given to several distinct substances, and that there are some 
 other resins which cannot be excluded from our view. 
 
 A?nber is the most familiarly known of all the resins on 
 account of its long use in its natural state for ornamental 
 purposes. Amber beads have not infrequently been found 
 in early British graves ; on the Continent these and other 
 ornaments of amber have often been obtained from ancient 
 interments. At Naples I was shown some years ago a very 
 
AMBER 
 
 57 
 
 large number of antique fibulas carved out of this substance : 
 they had just been disinterred from Etruscan tombs. Such 
 amber has often become brittle and far more soluble in the 
 usual solvents, especially so far as regards the surface layers; 
 but in other instances the preservation of the properties of 
 this resin has been complete. The chief localities where 
 amber is found are the Prussian shores of the Baltic Sea 
 (particularly between Konigsberg and Memel) and the neigh- 
 bouring plains ; it has been found in veins, and is regularly 
 quarried. Some amber, much of it having a dark colour, 
 is found near Catania, Sicily. Near Lemberg (Galicia in 
 Austria) nodules of amber occur in rock. It occurs in 
 several places in Denmark, Sweden, Norway, and France. 
 In the British Museum collection of minerals there is a fine 
 mass from Cambridge. Excellent specimens occur in com- 
 parative abundance on the seashore at Southwold in Suffolk, 
 and at several other places on the Suffolk, Norfolk, and 
 Essex coasts. The dark fossil resin found in Birma, often 
 in large masses, is not identical with Baltic and English 
 amber. The same observation may be made with respect 
 to the so-called ambers of Travancore in the East Indies, 
 and of the Isle of St. Louis, Senegambia, Africa. In fact, 
 amber, instead of being, as commonly stated, the fossil resin 
 of a single species of tree of Tertiary age, has obviously 
 been derived from no inconsiderable number of different 
 plants. Goppert, so long ago as 1853, satisfied himself 
 that at least eight species of plants besides Pi?iites succinifer 
 have afforded this fossilized resin : he also enumerated 163 
 species of plants as represented by remains in amber ; many 
 others have been since recognised. 
 
 Amber has a specific gravity of about 1*07 ; its hardness 
 is 2\ on the ordinary mineralogical scale. In most of the 
 usual solvents of resins it is either insoluble, or but partially 
 
MM 
 
 58 
 
 AMBER 
 
 soluble. When heated quickly on a spatula it splits up and 
 then fuses into a viscous liquid, the drops which are 
 formed rebounding as they fall upon a cold surface : this 
 behaviour serves as a distinguishing test between amber and 
 copal. When crushed amber is heated in a retort it fuses 
 at about 280 C. (536 F.), gives off water, succinic acid, 
 marsh gas, a mixture of liquid hydrocarbons (known as oil 
 of amber), and, finally, at a very high temperature, a yellow 
 substance having a wax-like consistence. Sulphuretted 
 hydrogen and other sulphur compounds are also evolved in 
 small quantity, for amber, like several other fossil resins, 
 contains a little sulphur (sometimes | a part in 100) in 
 organic combination. Amber breaks with a conchoidal 
 fracture. When fragments of amber are being ground or 
 powdered they emit an aromatic odour. On being rubbed 
 amber becomes negatively electric in a high degree. 
 
 It is probable that true amber consists mainly of a single 
 resin (85 to 90 per cent, of the whole) represented by the 
 empirical formula «C 10 H 16 O. Small quantities of two other 
 resins which are soluble in alcohol and ether, of a liquid 
 hydrocarbon, and of succinic acid are associated with the 
 main constituent, which has received the mineralogical 
 name ' succinite.' 
 
 The classical names for amber were r/Ae/cTpov, lyncu'rium, 
 electrum and succinum. In early mediaeval times amber was 
 called vernix, a term which at first was applied also to 
 sandarac, and later in the fifteenth century to sandarac only, 
 when amber was designated as glas, or glassa. In modern 
 French amber is distinguished from ambre gris as ambre 
 jautie, although it is also known as karab'e and succin. It is 
 the Bernstein of the Germans. The word ' amber ' is prob- 
 ably derived, through the Spanish, from the Arabic anbar, a 
 term applied to ambergris. 
 
COPAL 
 
 59 
 
 Copal is a name given to a number of hard resins which 
 vary not only in their degree of hardness, but also in their 
 degree of solubility : they are the produce of many different 
 species, and even genera of trees, while the origin of several 
 of the kinds still remains unknown. One of the hardest, 
 palest, and best of all is known as Sierra Leone copal, from 
 the port of collection and shipment. It has been identified 
 as the resin produced by a tree, Copaifera Guibonrtia?ia, 
 which belongs to the sub-order Cassalpinese of the order 
 Leguminosse. It is probable that the hard West African 
 pebble copal is the resin of the same tree, but it occurs in 
 rolled pebbles with an abraded surface, and is at least semi- 
 fossil : it is collected from the beds of streams. Pebble 
 copal has more colour than Sierra Leone copal, but yields 
 as strong a varnish. The latter resin occurs in irregular 
 rounded lumps or masses, generally varying in size from 
 that of a hazel-nut to that of a walnut. It is hard and 
 elastic. It consists of at least two resins, one of which, 
 present to the extent of 33 per cent., is soluble in 
 absolute alcohol and in spirits of turpentine. The other 
 resin constitutes nearly the whole of the remaining part of 
 the copal and becomes soluble in most of the usual solvents, 
 as well as in hot linseed oil, when it has been previously 
 heated to its melting-point or to a temperature of 180 to 
 221 C. (360 to 430 F.). Another process for rendering 
 this and other kinds of copal soluble is reduction to a fine 
 powder in the presence of water and the subsequent expo- 
 sure of this powder to the air for several months or even a 
 whole year. The time requisite for this change may be 
 shortened by keeping the powdered copal at a temperature 
 higher than that of the ordinary atmosphere. More will be 
 said as to this and other methods of increasing the solu- 
 bility of copal in the chapter on Varnishes. 
 
6o 
 
 COPAL 
 
 Other species of the genus Copaifera yield similar but 
 inferior resins to that produced by C. Guibourtiana, but 
 C. Gorskiana is the source of Inhambane (near Mozam- 
 bique) copal ; Benguela copal, Angola copal, and Gaboon 
 copal are other sorts, varying in hue from straw-colour to a 
 dull reddish-orange, produced in all probability by different 
 species of Copaifera. 
 
 Zanzibar copal is another hard and valuable resin of 
 African origin : it is often called anime. It is produced by 
 another leguminous tree, Trachylobium Hornemannianum, 
 which belongs to the same sub-order, Caesalpineae, as Copai- 
 fera. Most of this Zanzibar copal occurs in a fossil or semi- 
 fossil state in the earth near the roots of the trees, or in 
 places where the trees have formerly stood. This fossilized 
 resin is covered when dug up with a semi-opaque, rough, 
 and dull-brown crust ; when this powdery coat is removed 
 the remainder of the mass appears of a transparent yellow 
 colour, with a surface covered with small rounded elevations 
 like those on the rind of an orange : this is spoken of as 
 ' goose-skin.' Many of the pieces are flat and tabular, with 
 a thickness of a quarter of an inch or more. The same 
 resin, when occurring on the bark of the living trees of the 
 same species of Trachylobium, presents a smooth and glossy 
 surface ; it is not so hard as the fossil variety. Zanzibar 
 copal melts at a higher temperature than Sierra Leone 
 copal, and is very hard. In order to render it soluble it 
 may be treated in the same manner as the Sierra Leone 
 copal. Its chemical nature requires further study. The 
 varnish made with Zanzibar copal, though darker in colour, 
 must be regarded as at least equal in strength and durability 
 to that prepared with Sierra Leone copal. 
 
 A third resin, sometimes designated as copal, sometimes 
 as anime, is produced by another leguminous tree, Hymencea 
 
DAMMAR 
 
 61 
 
 courbaril, a native of Brazil and other countries of South 
 America. It is rather softer and more soluble than Zan- 
 zibar copal. The copal of Madagascar comes from another 
 species of the same genus, H. verrucosa. A Mexican copal 
 is probably the resin of an allied species. The resin from 
 H. courbaril is generally known as West Indian copal ; fine 
 specimens have been received from Demerara. 
 
 The Bungo tree of Sierra Leone, Daniellia thurifera, 
 affords a resin of inferior quality. It is probable that the 
 same leguminous tree is the source of some of the Niger 
 and Sudan copals. 
 
 A rather hard resin of comparatively recent introduction 
 is Kauri or Cowdi copal, produced by the Cowdi pine of 
 New Zealand, Dammara australis. This is a coniferous 
 tree belonging to the tribe Araucarise. The largest masses, 
 some of them occasionally over ioo pounds in weight, are 
 found in the earth in many places far from those in which 
 the trees now grow. Kauri resin usually becomes more 
 transparent and yellower by keeping. It is generally some- 
 what whitish, or streaked with opaque bands, when first 
 found. It is cleaned and scraped and then sorted into 
 several qualities. Its use has greatly extended of recent 
 years. It is now largely employed as the basis of most of 
 the so-called copal varnishes, on account of its abundance, 
 its low price, and its easy manipulation. But the varnish 
 which it yields, or of which it constitutes the chief resinous 
 component, is inferior in hardness, toughness, and dura- 
 bility to that made from Sierra Leone copal or Zanzibar 
 copal. 
 
 Kauri resin is sometimes spoken of as dammar, but this 
 name properly belongs to the resins produced by other trees, 
 not by Dammara australis. White or Singapore dammar 
 is the resin of Dammara orientalis. It is soft, and may be 
 
62 
 
 SANDARAC 
 
 scratched even by mica. ' Sal dammar ' is produced by 
 Shorea robusta, the sal tree, widely distributed in India. 
 This resin, though soft, yields a good flexible paper varnish. 
 The tree belongs to the Dipterocarpeas. Vateria indica, 
 another Dipterocarp, yields piney resin or white dammar : a 
 similar resin is produced by another species, V. acuminata, 
 a Ceylon tree. Several kinds of Hopea (H. micrantha, 
 H. odorata, etc.), which belong to the same natural order, 
 yield pale, transparent resins which are a trifle harder than 
 that of the sal tree. Black dammar or Tinnevelly resin is 
 produced by Canarium strictum ; it is of very inferior 
 quality. This tree belongs to the Burseraceas : several 
 kinds of elemi resin are also furnished by plants belonging 
 to the same natural order. These elemis are soft, sticky 
 resins, occasionally employed in varnishes to prevent them 
 from becoming brittle and cracking. They contain essential 
 oils and other aromatic bodies, and vary very much in com- 
 position and properties, although they resemble one another 
 in their solubility in boiling alcohol and in their easy alter- 
 ability. They are unsatisfactory resins. 
 
 The resin first known as sandarac was probably juniper 
 resin, although the name was also applied to amber. It is 
 spoken of by the older authorities on painting as having a 
 red colour. Its hue is a dull reddish orange, and it yields 
 a dark-brown varnish when dissolved by the aid of heat in 
 a drying oil. The effect of this varnish in imparting an 
 agreeable warm tone to pictures painted in tempera is very 
 evident, when the cold aspect of an old Italian unvarnished 
 tempera picture is compared with the glowing colour of a 
 painting which still retains its original sandarac varnish. 
 The resin now called sandarac is produced by another 
 coniferous plant {Callitris quadrivalvis), a native of Algiers. 
 It is a pale yellow resin, when fresh resembling mastic in 
 
MASTIC 
 
 63 
 
 colour, but becoming yellower with age. It is soft and 
 brittle. When finely powdered and sifted it forms one of 
 the kinds of pounce used in preparing the surface of parch- 
 ment and vellum for writing and illuminating. It melts at 
 130 C. (266 F.), exhaling an aromatic odour. It partly 
 dissolves in alcohol, and is wholly soluble in oil of spike 
 and in several terpenes ; acetone also dissolves it. 
 
 There is one more resin which requires mention. This 
 is mastic. The best and most important sort of mastic is 
 produced by a small tree (Pistacia Lentiscus), belonging to 
 the cashew-nut order or Anacardiaceae. This tree occurs in 
 Scio and other islands of the Greek Archipelago. Mastic 
 exudes in the form of tears from incisions made in the bark. 
 It occurs in small pea-like masses, and presents when fresh 
 a very pale straw colour. It is so fragile that it may be 
 crushed to powder between the fingers. It has an aromatic 
 odour, and dissolves completely in boiling alcohol and in 
 spirits of turpentine. Its melting-point is low. It contains, 
 besides its resinous constituents, a small quantity of a volatile 
 essential oil (a terpene) and of moisture. It yields a tender 
 but glossy varnish, largely employed for the final protection 
 of pictures in oil. This varnish yellows with age, and 
 becomes fragile and fissured. 
 
 Resins, sometimes called mastics, are produced by other 
 trees of the same genus. These resins, which are of no 
 value for artistic purposes, are : — 
 
 Indian mastic from Pistacia cabulica. 
 Bombay mastic from P. Khinjak. 
 Pistachio mastic from P. Terebinthus. 
 
 In the following table, compiled from the results of 
 Bottler, are comprised some particulars concerning twelve 
 of the resins commonly called ' copals.' In the first 
 
6 4 
 
 TURPENTINES 
 
 column the names are given, in the second the melting- 
 points, in the third the relative hardness (12 being the 
 hardest), and in the fourth and last column the degree of 
 solubility (xii. being the least soluble). The specific gravity 
 of these copals depends so much upon the relative freedom 
 of the several kinds from cavities and bubbles that the 
 figures for this character are not included in the table. It 
 may, however, be mentioned that all these resins are rather 
 heavier than water, their specific gravities ranging from 
 1-035 to i"°7- 
 
 Name of Copal 
 
 Melting-point 
 
 Hardness 
 
 Solubility 
 
 Zanzibar - 
 
 - 275° C. 
 
 12 
 
 xii 
 
 Red Angola 
 
 - 3i5 - 
 
 11 
 
 ix 
 
 Pebble Copal - 
 
 - 230 - 
 
 10 
 
 xi 
 
 Sierra Leone - 
 
 ■ 195 - 
 
 9 - 
 
 V 
 
 Yellow Benguela 
 
 - 180 - 
 
 8 - 
 
 vii 
 
 White Benguela 
 
 - 185 - 
 
 7 - 
 
 X 
 
 Congo 
 
 - 190 
 
 6 - 
 
 iv 
 
 Manila - 
 
 - 145 - 
 
 5 ■ 
 
 ii 
 
 White Angola - 
 
 - 245 - 
 
 4 - 
 
 i 
 
 Kauri 
 
 ■ 150 - 
 
 3 - 
 
 iii 
 
 Demerara 
 
 - 90 - 
 
 2 
 
 viii 
 
 Brazilian - 
 
 - 95 - 
 
 1 
 
 vi 
 
 All these numbers are approximative only ; and the 
 valuation of these resins for varnish-making ought to take 
 into account other properties not here recognised, such as 
 toughness after as well as before heating and solution, 
 liability to darkening in colour by lapse of time, and dura- 
 bility. 
 
 Turpentines, Oleo-Resins, and Balsams. — There is a group 
 of substances, many of them derived from coniferous plants, 
 which are, or have been, included under the term balsam. 
 Strictly speaking, this designation should be limited to 
 those resinoid exudates which contain benzoic or cinnamic 
 
VENICE AND STRASBURG TURPENTINE 
 
 65 
 
 acid, while the term oleo-resin, or, better still, the term 
 turpentine, should be given to those soft and semi-liquid 
 natural exudates which consist of terpenes associated with 
 bodies of resinous character. The word turpentine is, how- 
 ever, so generally connected with the volatile hydrocarbons 
 (terpenes) distilled from these exudates, that it should be 
 clearly understood that the three vegetable products here- 
 under described are of natural, not artificial, origin. It is 
 in consequence of the preservative influence upon certain 
 pigments which has been assigned, not without experi- 
 mental confirmation, to these bodies that they are noticed 
 here. 
 
 Venice Turpentine. — Under this name the resin of the 
 common larch is now known. It comes chiefly from Tirol. 
 Recent examination has shown it to consist mainly of three 
 groups of compounds, namely, about 63 per cent, of 
 resinous acids, 20 per cent, of terpenes, and 14 per cent, of 
 resins. The best specimens are never quite so clear and 
 free from colour as those of the next product to be de- 
 scribed. 
 
 Strasburg Turpentine is derived from Abies pectinata, the 
 silver-fir, the best quality coming from the Italian side of 
 the Tirolese Alps. It contains about 57 per cent, of 
 resinous acids (not identical with those in larch-turpentine), 
 28 per cent, of terpenes, and 13 per cent, of resins. This 
 turpentine is the true Olio d'Abezzo of Italian writers, and 
 when dissolved in a terpene was used as a varnish for 
 pictures in tempera and oil, and for the special protection 
 of verdigris and of some other dangerous pigments. Some 
 specimens of this turpentine are beautifully clear and 
 colourless. It is decidedly superior to larch turpentine, 
 with which it has no doubt been often confused, and to 
 Bordeaux turpentine, obtained from Pinus pinaster. The 
 
 5 
 
 ^ 
 
66 
 
 WAX 
 
 chemical study of the olio d'abezzo has at present thrown 
 no light upon the specially protective or locking-up 
 qualities which are claimed for this turpentine. 
 
 Canada Balsam, from Abies balsamea, much resembles 
 Strasburg turpentine. The resinous acids which constitute 
 three-fifths of its weight are said to be different from those 
 already mentioned as existing in the turpentines from the 
 larch and silver-fir. 
 
 Wax. — The true waxes, unlike the oils described in 
 Chapter V., are not glycerides, and do not therefore yield 
 glycerin when they are saponified — that is, turned into soaps 
 by the action of alkalies. Ordinary beeswax is the best 
 known, and probably the most important of all the different 
 kinds ; but very few experiments have been made as to the 
 utilization of exotic and vegetable waxes in the processes of 
 painting. Crude beeswax requires purification and bleach- 
 ing in order to fit it for artistic use. The first operation 
 consists in melting the wax at nearly the lowest temperature 
 possible, and then pouring it in a slender stream into a cold 
 saturated solution of alum, agitating the latter all the time. 
 The granulated wax thus prepared may be bleached by 
 exposure for several days on linen cloths to the action of 
 the sunlight and dew ; or it may be treated with dilute 
 chromic acid solution, or with hydrogen peroxide. All 
 these processes succeed better when the wax is in the form 
 of thin sheets or ribbons. The bleached wax, after 
 thorough washing and drying, is to be re-melted. Its 
 hardness is increased and its melting-point raised by the 
 above treatment. 
 
 Bleached beeswax melts at 62 or 64 C. (144 or 147 F.). 
 It consists of four distinct substances, not present in all 
 samples in the same proportions. By boiling wax with 
 strong alcohol a substance called myricin (myricyl palmitate) 
 
WAX 
 
 6 7 
 
 is left undissolved. The dissolved portion is the larger ; 
 the bulk of it, which crystallizes out as the alcohol cools, was 
 formerly called cerin. It is a mixture of two fatty acids. 
 The cold alcohol still retains a small quantity of a fourth 
 substance. 
 
 Beeswax, by long-continued exposure to atmospheric in- 
 fluences, disintegrates and partially perishes by oxidation. 
 It is a constituent of Gambier-Parry's spirit-fresco medium, 
 into which it is introduced in order to impart a matt appear- 
 ance to the painting. Excellent examples of the use of 
 melted wax as a binding material for pigments may be seen 
 in the National Gallery and the Victoria and Albert 
 Museum. They are encaustic portraits, executed probably 
 in the second and third centuries of our era, and were dis- 
 covered by Mr. W. M. Flinders Petrie, in the Hawara 
 Cemetery, Fayum, Egypt. The pigments were mixed with 
 wax and laid on in the melted state. The wax having 
 become disintegrated in the course of centuries has been 
 re-melted, some fresh wax having been added in several 
 instances. 
 
 Wax is abundantly distributed in the vegetable world ; its 
 production is, in many cases, stimulated by the attacks of 
 insects. Thus, Chinese wax is produced by the puncture 
 of Coccus Pela, living on Ligustrum lucidum and Fraxi?ius 
 chinensis. Chinese wax, which melts at 82 C. (180 F.), 
 consists almost entirely of cerotyl cerotate. Brazilian or 
 Carnauba wax occurs naturally in thin films on the leaves of 
 a palm (Copernicia cerifera); it melts at 84 C. (183 F.). 
 Japanese or Ibota wax is probably produced by the attacks 
 of a coccus on Ligustrum Ibota ; it melts at 42 C. 
 (108 F.). 
 
 Paraffin wax, hard paraffin, solid paraffin, and ceresin, 
 are names given to certain mixtures of hydrocarbons 
 
 5—2 
 
68 
 
 PARAFFIN WAX 
 
 occurring in native petroleum and in the ' mineral wax ' 
 called ozokerite, and also in the tars produced by the 
 destructive distillation of wood, peat, lignite, bituminous 
 shales, and coals. The liquid hydrocarbons which 
 accompany the paraffin wax are described so far as neces- 
 sary in Chapter XI. under the head of Solvents. 
 
 Paraffin wax, so far as its main or fundamental con- 
 stituents are concerned, contains no oxygen, and is a 
 mixture of several of the least alterable of all organic com- 
 pounds ; very few chemical reagents have any action at all 
 upon it. On this account it presents for artistic purposes a 
 marked superiority over beeswax or any vegetable wax. Of 
 the hydrocarbons occurring in large quantity in paraffin wax 
 the best known are those to which the chemical formulas 
 
 ^22"46: 
 
 ^od-H-sr 
 
 ^26 "52' 
 
 C 27 H 56 , C 2S H 5S , and C 30 H r , belong. 
 
 The melting-point of paraffin wax oscillates within wide 
 limits, say, from 30 to 8o° C. The higher the melting- 
 point the harder, the heavier, and the less crystalline is the 
 material. For artistic purposes, hardness and the absence 
 of a tendency to separate from solution in the form of large 
 crystals are desirable properties. Unfortunately the hardest 
 paraffin waxes of high melting-point are much less soluble 
 in oils, terpenes, and varnishes than the softer varieties, and 
 thus their usefulness is limited; they are also somewhat 
 yellowish in hue. I have, however, found that a pure 
 paraffin wax from the Bathgate shale, having the melting- 
 point of 65 *5° C. (150 F.), answers every purpose. It is 
 sufficiently hard and but indistinctly crystalline, and yet 
 may be dissolved in fair abundance by the usual solvents. 
 It is convenient to preserve it for use in the form of small 
 flattened globules, which are easily prepared by melting the 
 substance and pouring it drop by drop on to the surface of 
 a large sheet of glass previously moistened by breathing 
 
PARAFFIN WAX 
 
 69 
 
 upon it. When these drops are shaken in a bottle they 
 rattle like small pebbles, and do not mark the glass; when 
 the softer solid paraffins are thus treated, they fall with 
 a thud, and leave streaks and spots upon the interior 
 surface of the vessel. This difference of deportment 
 affords a ready means of distinguishing between a paraffin 
 wax suitable for artistic uses and one which had better be 
 rejected. 
 
 The manufacture or isolation of hard paraffin and its 
 purification are not described here. The processes em- 
 ployed — distillation, treatment with oil of vitriol, fractional 
 crystallization from solvents, etc. — involve the use of com- 
 plex apparatus. It may, however, be here stated that 
 commercial hard paraffins vary somewhat in purity. Those 
 obtained from mineral wax or ozokerite are nearly free from 
 oxygen compounds ; while those derived from the products 
 of the destructive distillation of shales, coal, etc., sometimes 
 contain as much as 3 per cent, of oxygen, indicating the 
 presence of other bodies besides hydrocarbons. Some of 
 these bodies are of an acid nature ; these may be separated 
 by repeatedly boiling the commercial paraffins in question 
 with a 5 per cent, solution of caustic potash. The following 
 table shows the relations subsisting between the melting- 
 point and the specific gravity (at 20 C.) of six different 
 samples of hard paraffin, generally known as ceresin, from 
 ozokerite : 
 
 No. of 
 
 Melting- 
 
 Specific 
 
 No. of 
 
 Melting- 
 
 Specific 
 
 Sample 
 
 point 
 
 Gravity 
 
 Sample 
 
 point 
 
 Gravity 
 
 1 
 
 - 56° c. - 
 
 - 0-912 
 
 4 - 
 
 - 72 <J. - 
 
 ■ 0-935 
 
 2 - 
 
 - 6i° - - 
 
 - 0'922 
 
 5 - 
 
 - 76 - - 
 
 - 0-939 
 
 3 
 
 - 67 - - 
 
 - - 927 
 
 6 - 
 
 ■ 82 - - 
 
 - 0-943 
 
 A sample of ceresin made from ozokerite was furnished 
 to me at my request by Mr. J. Calderwood, of Price's Patent 
 
7o 
 
 PARAFFIN WAX 
 
 Candle Company. It has a setting-point of about 156 F. 
 (69 C.)j and is almost non-crystalline in appearance. It 
 possesses, however, a somewhat greasy feel and a slight 
 yellowish hue. I find by experiment that this ceresin, with 
 a small admixture of a refined paraffin (from the same manu- 
 facturers) having a melting-point of 147 F., forms an ex- 
 cellent substitute for the hard paraffin wax (melting-point 
 150 F.), from Bathgate shale, described on a preceding 
 page, and unfortunately no longer to be met with in com- 
 merce. 
 
 Hard paraffin wax may be used in the preparation of 
 painting mediums as a substitute for beeswax ; for prevent- 
 ing the separation of heavy pigments, such as vermilion, 
 from the oil in which they are ground ; and for the prepara- 
 tion of certain painting-grounds. 
 
CHAPTER VII 
 
 YOLK AND WHITE OF EGG; SIZE; GLUE 
 
 The materials described in the present chapter owe their 
 peculiar properties — at least, in great measure — to the 
 presence of chemical compounds which contain the element 
 nitrogen. Now, this element is not a constituent of any of 
 the artists' materials already described, nor, indeed, of any 
 others, except a few pigments, such as aureolin, Prussian 
 blue, and indigo. The presence of nitrogen in an organic 
 compound is very often accompanied by a measure of 
 instability, or proneness to change ; the nitrogenous con- 
 stituents of eggs, and of size, afford illustrative examples. 
 Another source of weakness in the composition of the 
 nitrogenous constituents, both of the white and of the yolk 
 of eggs, lies in the presence of another element — namely, 
 sulphur. Part of this sulphur readily leaves the original 
 substance, yielding simpler compounds, such as sulphuretted 
 hydrogen, and ammonium sulphide, which possess the 
 objectionable property of discolouring many of the metallic 
 pigments used by artists. On the other hand, all these 
 nitrogenous bodies are susceptible of coagulation, whereby 
 they become insoluble, and very much less prone to change. 
 Indeed, the majority of them may be turned into a substance 
 which is virtually leather, a material which resists decay in 
 the most marked manner. This tanning operation may be 
 

 /"* A^ 
 
 I 
 
 D 
 
 <\, 
 
 \ 
 
 ,y> 
 
 72 
 
 WHITE OF EGG 
 
 readily effected by treating the substances in question with a 
 solution containing tannin, the active ingredient of oak-bark, 
 sumach, nut-galls, etc. 
 
 We will first consider the composition of the yolk and 
 white of ordinary hen's eggs. The percentage proportions 
 are, on the average : 
 
 
 Yolk 
 
 White 
 
 Water - 
 
 ■ 51-5 - 
 
 - 84-8 
 
 Albumen, Vitellin, etc. • 
 
 - 15-0 - 
 
 - I2"0 
 
 Fat or Oil - 
 
 - 22*0 - 
 
 CT2 
 
 Lecithin 
 
 - 9-0 - 
 
 - trace 
 
 Mineral Matter 
 
 I'O - 
 
 • 07 
 
 Other Substances - 
 
 - i'S - 
 
 - 2-3 
 
 The white, it will be seen, is characterized by the presence 
 of 12 parts per hundred of albumen, which is in solution 
 in the ropy liquid. When this solution is heated to a 
 temperature considerably below that of boiling water, the 
 albumen becomes insoluble, and is said to be coagulated ; 
 it is not capable of being again dissolved. Solutions of 
 tannin, corrosive sublimate, and many other compounds, 
 inorganic and organic, produce a similar effect. But egg- 
 white is not a pure solution of albumen. For all practical 
 purposes in the arts, it may be sufficiently freed from ex- 
 traneous matters in the following manner : The necessary 
 number of ' whites ' are mixed in a wide-mouth stoppered 
 bottle, with twice their bulk of water, and shaken up 
 thoroughly ; then a slip of yellow turmeric-paper is dropped / 
 
 into the mixture. Drop by drop weak acetic acid is poured 
 in, until the reddened turmeric-paper has just, or nearly, ; V 
 regained its original yellow hue. In this way the alkaline >\Ia 
 
 reaction of the liquid is almost neutralized, and it becomes ' f . 
 
 thinner. After further agitation, the mixture is poured t 
 upon a piece of well-washed muslin in a funnel. The clear V 
 
 >'. 
 
COAGULATION OF ALBUMEN 
 
 73 
 
 liquid which drops through has been freed from membranes, 
 etc., and contains nearly 4 per cent, of albumen. It may 
 be concentrated by cautious evaporation at a temperature 
 not exceeding 50 C. The albumen which it contains is a 
 very complex substance, containing, besides carbon, hydrogen, 
 nitrogen, and oxygen, about i*6 per cent, of sulphur. A 
 solution of albumen spread upon glass, and allowed to dry 
 slowly at the ordinary temperature, leaves a residue of 
 albumen in the form of a nearly-transparent film. This, 
 when quite dry, is brittle, and easily cracks. If, before it 
 be quite dry, it be heated to 70 or 75 C, it cannot be 
 again dissolved by water, having been converted into the 
 insoluble form. In this condition it is much less prone to 
 change. It will now be seen how powdered pigments, if 
 ground up with albumen solution and then used in painting, 
 may be made to cohere, and also to adhere to the painting- 
 ground of cloth, paper, or plaster, on which they have been 
 spread. And afterwards, by simply heating the work suffi- 
 ciently, the whole coloured layer may be rendered insoluble 
 and irremovable by water. Advantage may also be taken 
 of the action of tannin on albumen to secure the same 
 result — the coagulation of the albumen. We may coat a 
 piece of fine linen cloth with albumen-solution, and before 
 it is quite dry we may paint upon it with pigments which 
 have been previously ground up with a weak solution of 
 tannin. If the work be carefully done, the colours will, 
 when dry, be found to have been fixed by the reaction 
 between the tannin and the albumen. If, however, the 
 pigments be laid on somewhat thickly, it may be found 
 necessary to give the whole surface a final coat of albumen- 
 solution. We have dwelt at some length upon this employ- 
 ment of tannin, or of heat, to secure the coagulation of 
 albumen, because it serves to illustrate the way in which 
 
 J* 
 
74 
 
 YOLK OF EGG 
 
 paintings, executed with egg-yolk, or size, as a medium, may 
 be fixed. For, as we shall now proceed to show, egg-yolk 
 and size possess many characters in common with albumen- 
 solution. 
 
 But the yolk of an egg contains other substances besides 
 albumen. First of all, the albumen present is accompanied 
 by another similar compound called vitellin, which resembles 
 it in composition and properties, and which, for our present 
 purpose, we need not further describe, except so far as to 
 state that, unlike albumen, it is not soluble in water. Of 
 albumen and vitellin, taken together, egg-yolk contains, as 
 we have seen, not less than 14 or 15 per cent. But egg-yolk 
 is something more than a solution of these two similar 
 bodies. It is, in fact, an oily emulsion, in which innumerable 
 minute globules of a thick, fatty oil are suspended in an 
 albuminous solution. And, moreover, the amount of this 
 oil is large ; there is about 22 per cent, of it, and associated 
 with this oil there is no less than 9 per cent, of a curious 
 compound called lecithin, which has many of the physical 
 properties of a fat, and may be resolved into stearic acid, 
 glycero-phosphoric acid, and a base called choline. This 
 fatty body contains, therefore, two elements not found in 
 ordinary fats, namely, nitrogen and phosphorus. Its con- 
 stituents are shown in the empirical formula assigned to 
 lecithin, C 44 H 90 NPO 9 . Although this substance resembles 
 oils and fats in its behaviour to most solvents, it yet differs 
 from them in this one particular, that it is very hygroscopic 
 and swells up in water, forming a kind of emulsion. Now, 
 9 parts of lecithin with 22 parts of oil make up nearly one- 
 third of egg-yolk, or 31 parts of oily or fatty matter per 
 100, as against 15 parts of albuminoid matter, or vitellin 
 and albumen taken together. Hence it happens that egg- 
 yolk, the usual vehicle for pigments in the best kind of 
 
SIZE AND GLUE 
 
 75 
 
 tempera-painting, must be regarded as essentially an oil- 
 medium. As it dries, the oil hardens, and remains in- 
 timately commingled with the albuminous substances left 
 behind on the evaporation of the water present. These 
 albuminous substances coagulate and become insoluble in 
 the lapse of time — a change greatly accelerated by the old 
 practice of exposing the finished tempera picture to sunshine 
 previous to varnishing it. 
 
 Size and glue may be considered together. They consist 
 of two distinct yet similar compounds, known respectively 
 as gelatin and chondrin. These bodies consist of carbon, 
 hydrogen, nitrogen, and oxygen ; and, when pure, they 
 contain no sulphur. They are soluble in hot water, yet are 
 coagulable by tannin and by some other compounds, organic 
 and inorganic. Chondrin is thrown down from its solution 
 by alum, and, indeed, by several compounds which do not 
 precipitate gelatin. The latter body is obtained from skin, 
 tendons, and bones. These organized structures contain a 
 substance called ossein, or collagen, which, under the 
 influence of boiling water, dissolves, becoming changed into 
 gelatin. This conversion occurs more quickly when the 
 process is performed under a pressure somewhat greater 
 than that of the atmosphere, and, therefore, at a temperature 
 rather higher than ioo° C. In this way the transformation 
 of the organic tissue of ivory, bone, vellum, parchment, 
 fish-bladder, etc., into gelatin may be readily effected. The 
 purity of the product depends, in part, upon the care with 
 which the raw materials have been selected and cleansed, in 
 part upon the temperature and the duration of the extraction. 
 If the temperature be too high, or the boiling be much 
 prolonged, the gelatin produced is transformed partially into 
 a substance which does not gelatinize when its aqueous 
 solution is cooled. Chondrin is obtained from cartilage, 
 
76 
 
 SIZE AND GLUE 
 
 which consists mainly of cartilagin, or chondrigen, by the 
 same process which changes collagen into gelatin. A hot 
 solution of chondrin gelatinizes on cooling just like one of 
 gelatin ; but it does not yield, with the same amount of 
 substance, so firm a jelly. Size, glue, and commercial 
 gelatin, consist of mixtures of gelatin, chondrin, and the 
 non-gelatinizing substances produced by the long-boiling or 
 the over-heating of their solutions. Isinglass, vellum, and 
 ivory-dust yield a size which contains nothing but gelatin 
 and a little mineral matter ; the darker and stickier kinds of 
 glue contain many impurities, having been made from very 
 varied materials, such as ox-hoofs, horseflesh, old leather, 
 etc. ; they often contain sulphuric acid. 
 
 In selecting a size for artistic usage, the special purpose in 
 view will indicate whether an insoluble (in cold water) and 
 strongly-gelatinizing, or a partially soluble and very adhesive 
 one should be selected. The former is less liable to crack 
 when dry than the latter. The very fine gelatins used in 
 photography will often be found suitable. A few experi- 
 ments, with cold water and then with hot, will soon reveal 
 the peculiarities of the samples submitted to examination. 
 As caustic lime, caustic soda, chloride of lime, sulphurous 
 acid, and certain mineral acids, are frequently employed in 
 the manufacture of size, glue, and gelatin, it is absolutely 
 necessary to ascertain, before using these materials in any 
 process of painting, their freedom from free acids, free 
 alkalies, or bleaching agents. A hot-water solution of the 
 material must not redden blue litmus-paper, nor bleach 
 dahlia-paper, nor embrown turmeric-paper. 
 
 Glue and size may sometimes be purified and improved 
 by cutting up the solid or gelatinous mass into small pieces, 
 soaking them in distilled water for a few hours, and then 
 pouring off the liquid before dissolving them. 
 
PRESERVATION OF EGG-YOLK 
 
 77 
 
 The temporary preservation from putrefaction of the solu- 
 tions of the substances described in the present chapter, 
 may be effected in several ways. A lump of camphor, or a 
 few drops of eugenol (from oil of cloves), is generally suffi- 
 cient. I have preserved the egg-yolk medium for tempera- 
 work for many days in an agreeable condition for use by the 
 following plan : A saturated solution of eugenol in 5 per 
 cent, acetic acid is first made, then this is added, drop 
 by drop, with constant agitation, to the required number of 
 yolks in a wide-mouth bottle, the point at which to stop 
 further addition being learnt by the change of colour of a 
 slip of turmeric-paper. When this paper just regains its 
 original yellow colour, which was turned brownish-red by 
 the yolks, no more acetic acid is wanted. Any water 
 needed for thinning the medium may now be added, 
 together with a lump of camphor, which will remain floating 
 on the surface. 
 

 CHAPTER VIII 
 
 GUM, STARCH, DEXTRIN, HONEY, AND GLYCERIN 
 
 The term gum is properly applied to a number of non- 
 crystalline, structureless substances, of vegetable origin. 
 They consist essentially of so-called hydrates of carbon, and 
 are either soluble in cold water, or swell up when left therein 
 for some time. The only gum of any importance in paint- 
 ing is gum-arabic. This name is not, however, exclusively 
 applied to one variety only ; it is given to the gums which 
 exude from several pieces of Acacia. For instance, Acacia 
 arabica furnishes the Morocco, Mogador, Brown Barbary, 
 and East Indian gums of commerce. But it should be 
 noted that, although A. arabica is a native of India, and 
 is grown to some extent in many parts of that empire, the 
 gum it yields is rarely, if ever, exported thence, the so-called 
 East Indian gum-arabic being really taken from Red Sea 
 ports to Bombay, and thence re-shipped to Europe. Acacia 
 arabica, however, does not furnish a strong and durable 
 gum, and it is from another species, A. Senegal, that we 
 ..obtain the gum employed as a binding material for water- 
 colours. This gum is known commercially as Kordofan, 
 picked Turkey, white Sennaar, and Senegal gum. The tree 
 which yields it is a native of Senegal and the Sudan ; it 
 grows to a height of twenty feet. The supplies which come 
 from Kordofan are of the finest quality, but all the grades of 
 
GUM SENEGAL 
 
 79 
 
 gum from A. Senega/ are superior to the produce of A. 
 arabica in their greater dryness, density, and adhesiveness, 
 as well as in the smaller amount of mineral matter which 
 they contain. It may be added in this place that, according 
 to some authorities, a part of the gum Senegal of commerce 
 is produced by other species of Acacia besides A. Senegal, 
 such as A. Adansonii, A. albida, A. dealbata, A. nilotica, A. 
 Verek, etc., and even from species of Kaya, Spondias, and 
 Sterculia. 
 
 Gum consists mainly of arabin, a mixture of the salts of 
 an acid called arabic acid, and of the free acid itself. The 
 salts are those of the three bases — potash, lime, and 
 magnesia ; water is also present. It is probable that, in all 
 varieties, even of the finest gum Senegal, other organic acids, 
 besides arabic acid, are present. An analysis of a fine 
 specimen of picked 'Turkey gum' gave 15 per cent, of 
 water, and 2 - 8 per cent, of ash, leaving 82*2 per cent, for 
 the arabic and other allied acids and organic matters. 
 The arabic acid was formerly expressed by the formula 
 C 12 H 22 O n , but the experiments of O'Sullivan indicate a 
 much more complex composition (C 89 H 142 74 ). 
 
 Gum from Acacia Senegal, the only sort which ought to be 
 employed in painting, should be nearly free from colour, and 
 should dissolve in cold water without leaving an appreciable 
 residue. Its watery solution should be clear, and should give 
 no colour with tincture of iodine, but an abundant precipi- 
 tate with ammonium oxalate solution. If iodine produce a 
 purplish colour, adulteration with dextrin is indicated ; the 
 white precipitate thrown down by the oxalate shows the 
 presence of calcium, a constant constituent of the genuine 
 gum. I have found that the samples of gum sold to me as 
 gum Senegal were of a more pronounced yellowish colour 
 than those bought as gum-arabic and best Turkey : the lumps 
 
GUM TRAGACANTH 
 
 varied more in size, often contained air-bubbles, and were 
 less fissured. The adhesiveness and toughness of these 
 samples, moreover, compared favourably with these pro- 
 perties as exhibited by the finest and whitest ' Turkey gum ' 
 obtainable. 
 
 For the preparation of water-colours, and for occasional 
 use in the operations of painting, it is convenient to have at 
 hand a standard solution of gum. This may be prepared 
 by dissolving i ounce of the selected gum reduced to fine 
 powder in 2 measured ounces of boiling distilled water. 
 The powdered gum should be very slowly added, with 
 constant stirring, to the boiling water. When the whole is 
 dissolved, the liquid is allowed to stand for at least a day ; 
 then it is decanted from any sediment that may have been 
 deposited into a wide-mouth bottle without cork or stopper, 
 but covered with a glass cap. It is well to allow a lump of 
 camphor to float in it, or to add to it a couple of drops of 
 eugenol, the active antiseptic constituent of oil of cloves : a 
 still more effective preservative is /3-naphthol. 
 
 Gum tragacanth is produced by certain leguminous shrubs 
 belonging to the genus Astragalus. Amongst these may be 
 named: A. gummifer, A. eriostylus, A. brachycalyx, and A. 
 adscendens. Its constituents include a small quantity of a 
 gum soluble in cold water, a little starch and cellulose, and 
 a large proportion of a mucilaginous body which swells up 
 in cold water, but does not dissolve. The substance having 
 these properties is a compound of carbon, hydrogen and 
 oxygen of very complex constitution, which has been called 
 bassorin. Gum tragacanth contains from 12 to 15 percent, 
 of water, and leaves 2 to 3 per cent, of ash when burnt. 
 A mucilaginous medium made with gum tragacanth may 
 be used for painting on linen : it is not very easy to pre- 
 pare so as to be of uniform consistency. A fairly good 
 
STARCH 
 
 81 
 
 plan is to place the finely-powdered tragacanth in a bottle, 
 and to add enough spirit of wine to moisten it : then 
 add the required amount of water and shake the mixture 
 gently at intervals. Water containing no more than 3 or 
 4 per cent, of the gum constitutes a moderately thick 
 mucilage. 
 
 Other gums are of small importance. They commonly 
 contain much bassorin and but little arabin. The Australian 
 wattle gums from several species of Acacia are perhaps thus 
 constituted ; but if this be the case, the bassorin present in 
 them seems to present some points of difference from the 
 bassorin of tragacanth. Cape gum is produced by Acacia 
 horrida : A. stenocarpa yields Suakin gum. So far as I 
 know, no use has at present been made, in the fine arts, 
 of these gums. 
 
 Starch comes next in our list. This important food- 
 substance occurs in commerce in a condition so nearly pure 
 that there is no need to describe its character. For the 
 limited uses to which it is put in artistic practice the 
 uncoloured or white starch should be selected. The starch 
 from rice, wheat, maize, or potatoes may be employed 
 indifferently. Arrowroot may also be used. The prepara- 
 tion of starch-paste does, however, require some care. The 
 best plan is to thoroughly agitate 50 grams of the dry 
 powdered starch with enough cold water to produce a liquid 
 of creamy consistence, and then to pour this mixture slowly / 
 into a vessel in which about 300 cubic centimetres of 
 distilled water is kept in steady ebullition. All but 2 per 
 cent, of the starch will dissolve into a nearly transparent 
 homogeneous paste : the quantity of starch must be reduced 
 if a thin liquid be required. 
 
 Starch contains carbon, hydrogen, and oxygen only, and 
 is a carbohydrate having the empirical formula «C G H 10 O . 
 
 6 
 
82 
 
 HONEY 
 
 It is a stable compound. Commercial starch always contains 
 some water, generally from 12 to 18 per cent. 
 
 Dextrin, or British gum, as met with in commerce, is 
 prepared from starch in one or other of several different 
 ways, and is a variable mixture of at least three varieties of 
 true dextrin, soluble or modified starch, starch, a sugar called 
 maltose, and certain minor ingredients and impurities. It 
 will suffice for the purpose now in view, if we select a 
 commercial dextrin, free from acidity, dissolving nearly 
 completely in cold water, and then yielding a solution 
 which, even when strong, has only a light yellowish or 
 brownish colour. When a filtered cold-water solution of 
 commercial dextrin is allowed to evaporate on a glass plate, 
 and the residue becomes air-dry, the film of dextrin left 
 differs from one of true gum by being less friable. A 
 solution of dextrin is, however, far less adhesive than one 
 of true gum of the same strength. 
 
 Honey now claims our attention. It is a common 
 ingredient in moist water-colours, and was often employed 
 in size-painting. It is used to counteract the brittleness of 
 gum or of size when dry, or, by its absorption and retention 
 of water, to keep a paint moist. Honey consists of nearly 
 equal quantities of two sugars known as dextrose and 
 laevulose, a little sucrose or common sugar, small quantities 
 of non-saccharine compounds, and about 20 per cent, of 
 water. As the useful properties of honey depend entirely 
 upon its laevulose, a solution of this sugar should be 
 employed instead of the raw honey : this may be easily 
 prepared in the following way : Pure pale honey, kept 
 until it has become crystalline and semi-solid from the 
 separation of dextrose, is mixed gradually with four times 
 its bulk of proof spirit, and thoroughly shaken at intervals 
 for a few hours. The pale yellow alcoholic solution is 
 
GLYCERIN 
 
 83 
 
 then filtered : the filtrate is a solution of lsevulose, accom- 
 panied by small quantities of the other sugars of honey and 
 of harmless impurities, and for some artistic purposes is 
 at once available. Should it be desired to obtain a more 
 concentrated solution of this substance, the liquid may be 
 evaporated to the desired consistency in a porcelain basin, 
 or it may be submitted to distillation in a retort. The 
 aqueous solution of laevulose may be decolourized by 
 filtration through warm animal charcoal. 
 
 Ldevulose, when free from water, forms a glassy solid ; 
 but it is usually obtained as a thick syrup. Although this 
 sugar is capable of assuming the crystalline form, it never 
 does so under ordinary conditions. It has a strong attrac- 
 tion for moisture ; on this property its usefulness as a con- 
 stituent of certain paints depends. 
 
 Glycerin was discovered in 1779 by Scheele as a by-pro- 
 duct in the preparation of lead-plaster ; for a long time the 
 comparatively small quantity of glycerin met with in com- 
 merce was obtained in this way. It is now prepared from 
 oils and fats by distilling them in a current of superheated 
 steam ; sometimes by first saponifying them with alkalies, or 
 decomposing them with sulphuric acid, and then submitting 
 them to this distillation treatment. 
 
 Glycerin generally occurs as a thick syrup with a sweet 
 taste : when pure, it may be obtained in deliquescent 
 crystals. Its empirical formula is C 3 H s 3 . It is a strongly 
 hygroscopic or water-attracting substance, the pure water- 
 free glycerin being capable of absorbing more than one- 
 third its weight of water from the air. Commercial glycerin 
 always contains water : the specific gravity of the liquid 
 affords a rough method of estimating the amount. For 
 pure glycerin at 15 "6° C. has the specific gravity i'263, 
 while that which contains 20 per cent, of water is reduced 
 
 6—2 
 
84 
 
 GLYCERIN 
 
 ^ 
 
 to i'2 1 ; with 30 per cent, it is i'i83, and with 40 per cent. 
 ri56. The presence of sugar, a not uncommon adulterant, 
 may be recognised by the turbidity caused by mixing the 
 glycerin, after evaporation to remove water, with chloroform. 
 Glycerin containing lead darkens when sulphuretted-hydro- 
 gen water is added to it, while the presence of acids may 
 be recognised by blue litmus-paper, which is not reddened 
 by pure glycerin. 
 
 The water-attracting property of glycerin induced me to 
 use it as a substitute for honey in preparing moist water- 
 colours so long ago as 1856, but I am given to understand 
 that it was employed even in 1847 by Messrs. Winsor and 
 Newton. Even in cake-colours a trace of glycerin may be 
 introduced with advantage, as it renders them less friable 
 and more easily rubbed down with water. It prevents size, 
 glue, and white of egg from becoming brittle on drying, 
 and on this account may be used in the preparation of 
 linen, canvas, etc., as painting-grounds. Care must, how- 
 ever, be taken in every case not to add more glycerin than 
 is necessary to effect the purpose in view. It is a useful 
 addition to gum-water, 1 dram to each ounce of gum 
 present being sufficient ; some copying -inks contain it. 
 Modelling clay may be kept moist by means of glycerin. 
 
CHAPTER IX 
 
 WATER-GLASS, LIME- AND BARYTA-WATER 
 
 The name water-glass appears to have been first applied to 
 those silicates of potash and of soda which are soluble in 
 water by Professor J. N. von Fuchs, in 1825 ; but Glauber, 
 so early as 1648, made a soluble potash silicate, which he 
 termed fluid silica. Von Helmont had prepared a similar 
 compound in 1640. The actual manufacture on a com- 
 mercial scale of these salts dates, however, from 1825 only, 
 and the credit of originating their production belongs to 
 Von Fuchs. They differ from the compounds constituting 
 ordinary and insoluble glass by containing no lime, baryta, 
 alumina, or other earthy base. They are made in several 
 ways. The purest sand obtainable is fused with carbonate 
 of potash, or carbonate of soda, or a mixture in the desired 
 proportions of these two carbonates, in the presence of a 
 little powdered charcoal. The fused mass dissolves by long 
 continued boiling in water, and yields a heavy syrupy liquid 
 of strongly alkaline reaction. By evaporating this liquid to 
 dryness, and fusing the residue, the water-glass may be 
 obtained in a solid form, and then closely resembles 
 ordinary glass in appearance. Water-glass may also be 
 made by heating flints red-hot, quenching them in water, 
 and then digesting the powdered silica thus obtained with 
 soda-lye or potash-lye under pressure. 
 
86 
 
 WATER-GLASS 
 
 Three kinds of water-glass have been used in water-glass 
 painting or stereochromy. One of these is a potash silicate, 
 another is a soda silicate, the third is a mixture of these 
 two, or a potash-soda silicate, called double water-glass. 
 The solutions of the two former silicates as met with in 
 commerce vary a good deal in their relative proportions of 
 silica and alkali ; it is not desirable that they should contain 
 so much silica as was recommended in the original papers 
 of Von Fuchs, the inventor of stereochromy, and of Kuhl- 
 mann, who subsequently modified the process. Indeed, it 
 has often been found useful to add a little pure caustic 
 potash or caustic soda-solution to the commercial solutions 
 of water-glass before diluting them with distilled water for 
 use in this process of painting. 
 
 A solution of water-glass, if allowed to dry upon a piece 
 of ordinary glass, leaves an opaque white irremovable 
 stain. Water-glass alters or destroys, in virtue of its strong 
 alkalinity, the great majority of organic pigments. On the 
 same account it cannot be used with flake-white, aureolin, 
 the chromates, vermilion, and several other mineral pig- 
 ments. It hardens zinc-white, some of the ochres, earths, 
 and terre verte, forming with them, or with some of their 
 constituents, double silicates, which are quite insoluble in 
 water. The fixative power of water-glass in stereochromy 
 depends indeed mainly upon actions of this order which 
 occur between it and ingredients of the plaster or painting- 
 ground, and of the pigments. It was formerly supposed 
 that when an alkaline silicate acted upon carbonate of lime 
 a double decomposition occurred, of which the only pro- 
 ducts were an alkaline carbonate, and lime silicate. But 
 subsequent investigation has proved that the change in 
 question is more complex, a considerable quantity of a 
 double and insoluble silicate of lime and alkali being pro- 
 
LIME-WATER 
 
 87 
 
 duced. Similar double silicates of potash or soda and 
 zinc, of potash or soda and baryta, and of potash or soda 
 and alumina, have been proved to exist in stereochromic 
 work ; doubtless, many others are also present. They are 
 not only insoluble in water, but are harder than the materials 
 out of which they are formed. 
 
 Commercial solutions of water-glass contain from 28 to 
 60 per cent, of the alkaline silicate or silicates. They 
 should be carefully preserved from access of air, the 
 carbonic acid of which produces much alkaline carbonate 
 (often separating in crystals in the case of soda), and finally 
 causes the separation of gelatinous silica hydrates. The 
 entrance of calcareous matters, gypsum, zinc-white, etc., 
 should also be guarded against. 
 
 The subject of water-glass is here treated very briefly, 
 partly because the various processes of stereochromy, even 
 with their latest improvements, are very little used in this 
 country, and partly because the preparations of water-glass 
 specially made for the use of painters may be trusted. To 
 this latter observation I might add the remark that the 
 problem of thoroughly examining a commercial water-glass 
 solution, for strength, purity, and due proportion of silica to 
 alkali, is too complex to be undertaken except by a trained 
 chemist. 
 
 Lime-water is the name given to the solution in water of 
 slaked lime, called in chemical language hydrate of lime, 
 calcium hydrate, and calcium hydroxide. To prepare it, 
 quicklime, which has been made by burning (as it is com- 
 monly called) a pure marble, is slaked with distilled water. 
 The calcium hydrate formed is placed in a wide-mouth 
 stoppered bottle, and covered with several times its bulk of 
 distilled water. The object of this treatment is to dissolve 
 soda and some other soluble impurities, the major part of 
 
3&s 
 
 LIME-WATER 
 
 which will be removed when the watery liquid in the bottle 
 is decanted from the undissolved excess of calcium hydrate 
 which should then be again covered with distilled water 
 which has been recently boiled. The stopper should be 
 well ground and smeared with vaseline. The bottle should 
 be shaken at intervals in order that the water may take up 
 as much calcium hydrate as it can dissolve. After all, this 
 amount is very small, not exceeding, at 15 C, 0*172 part 
 by weight per hundred measures of lime-water. Thus a 
 gallon of lime-water, saturated at about 6o° F., could not 
 contain more than 120 grains of calcium hydrate, corre- 
 sponding to 90 grains of pure lime or calcium oxide, CaO. 
 In ordinary practice such a perfectly saturated solution is 
 not attainable, while the most carefully prepared and 
 strongest solution is sure to become weakened each time 
 the stopper of the containing vessel is withdrawn by the 
 removal of some of the lime in solution in the form of 
 carbonate of lime. The clearest lime-water, from this cause 
 and from its action on glass, always appears turbid after a 
 time. 
 
 Although so dilute a solution, lime-water gives the most 
 marked reactions of an alkali : it turns red litmus paper 
 blue, embrowns yellow turmeric paper, and imparts a 
 crimson hue to colourless phenolphthalein paper. It acts 
 energetically upon many organic and some inorganic pig- 
 ments, owing to its alkaline or basic properties. The ease 
 with which the lime in lime-water unites with carbonic acid, 
 forming carbonate of lime ( = calcium carbonate), and the 
 bearing of this action, and of other properties of caustic 
 lime upon the materials and processes of painting are dis- 
 cussed in Chapters II. and XXIII. 
 
 Baryta-water may sometimes advantageously replace lime- 
 water in fresco-painting. It is a solution of hydrate of 
 
BARYTA -WATER 
 
 baryta, barium hydrate, barium hydroxide, for these names 
 all belong to the compound, in distilled water. The 
 distilled water used should have been recently boiled and 
 then cooled out of contact with the carbonic acid of the air. 
 The barium hydrate used may be purchased in the form 
 of colourless crystals having the formula Ba0 2 H 2 + 8 aq. 
 These, if not sufficiently pure, may be washed with cold 
 distilled water, or recrystallized from boiling water, in which 
 they dissolve very abundantly. A saturated cold solution 
 is made by placing rather more than i ounce of these 
 crystals in a bottle containing a pint of distilled water : the 
 bottle should be almost full, the stopper should be smeared 
 with a little vaseline. If the crystals dissolve completely, 
 after repeated agitation, a few more should be added so as 
 to leave a small excess at the bottom of the bottle. If the 
 solution be clear it may be used directly from the bottle, as 
 required; if filtration be needed, a glass plate should be 
 placed on the funnel during the operation to prevent free 
 access of air, and the clear filtrate should be received at 
 once in the bottle in which it is to be preserved. A solu- 
 tion of barium hydrate saturated at 15 C, contains nearly 
 2*9 grams of BaO in 100 cubic centimetres, or 2,023 grains 
 per gallon. It is thus very many times stronger than a 
 solution of calcium hydrate saturated at the same tempera- 
 ture. Baryta-water, as it is called, is a powerfully alkaline 
 liquid, becoming covered with a film of white barium car- 
 bonate on exposure to the air. By blowing air from the 
 lungs through a glass tube into baryta-water, a dense white 
 precipitate is formed. 
 
CHAPTER X 
 
 SOLVENTS AND DILUENTS 
 
 The liquids to which attention is directed in the present 
 chapter are, with very few exceptions, not miscible with 
 water. Of water itself it is not necessary to say anything 
 beyond this, that distilled water is best adapted for almost 
 every purpose to which this liquid is applied in the prepara- 
 tion of pigments, as a solvent for gum, honey, etc., and in 
 the practice of painting in water-colours. Next to distilled 
 water may be ranked rain-water collected in the open 
 country, then the softer kinds of water yielded by some 
 streams, springs, and wells. Waters containing more than 
 20 or 30 grains per gallon of solid matters in solution should 
 be avoided as far as possible. It should be noted that very 
 hard waters tend to curdle or precipitate the particles of 
 colouring matter in the water-colour paints which they may 
 be used to dilute. 
 
 Before considering the chief solvents and diluents, a list 
 of the most important of those which have been obtained 
 in a pure state or isolated may be given. Most of these 
 are artificial or laboratory products, the natural liquids em- 
 ployed in the processes of painting being mixtures, not in- 
 frequently both variable and complex. In the following 
 table the several definite compounds included are arranged 
 according to their boiling-points, those which boil at low 
 
SOLVENTS 
 
 91 
 
 temperatures being placed first : an asterisk indicates that 
 the liquid is miscible with water : 
 
 TABLE OF SOLVENTS 
 
 f- 
 
 Name 
 
 Boiling-point 
 
 Specific 
 Gravity 
 
 Forvni I a 
 
 Ether - 
 
 35° C 
 
 = 95° F. 
 
 - 719 - 
 
 C 4 H 10 O. 
 
 Carbon bisulphide - 
 
 46° 
 
 = 115° 
 
 - I '271 - 
 
 CS., 
 
 *Acetone 
 
 56° 
 
 = 133° 
 
 - 798 ■ 
 
 c :i ii fi O. 
 
 Chloroform - 
 
 6i° 
 
 = 142° 
 
 - I -500 - 
 
 CHC1 :V 
 
 * Wood-spirit - 
 
 66° 
 
 = i5'° 
 
 - 798 - 
 
 CH 4 0. 
 
 *Alcohol 
 
 7S 
 
 = 172° 
 
 • 794 - 
 
 C 2 H 6 0. 
 
 Benzene 
 
 81° 
 
 = 178° 
 
 - -884 - 
 
 C 6 H 6 . 
 
 Toluene 
 
 iii° 
 
 = 232° 
 
 - -869 - 
 
 C 7 H 8 . 
 
 Epichlorhydrin 
 
 117 
 
 = 243° 
 
 - IT91 - 
 
 C 8 H 5 C10 
 
 Amyl alcohol - 
 
 131° 
 
 = 268° 
 
 - -814 ■ 
 
 C 5 H la O. 
 
 - Pinene - 
 
 155° 
 
 = 3"° 
 
 - -86o 
 
 Cl0"i6- 
 
 Cineol = eucalyptol 
 
 173° 
 
 = 343° 
 
 - -92s 
 
 QoHisO. 
 
 Cymene 
 
 175° 
 
 = 347° 
 
 - -858 
 
 CioH 14 . 
 
 Sylvestrene - 
 
 176 
 
 = 349° 
 
 • -851 ■ 
 
 CioH 16 . 
 
 Limonene 
 
 177° 
 
 = 351° 
 
 - -850 
 
 ^10^16* 
 
 - Dipentene 
 
 180 
 
 = 356° 
 
 - -850 
 
 Q0H16. 
 
 Citral 
 
 228 
 
 = 442° 
 
 - -897 
 
 ■ C 10 H 16 O 
 
 Geraniol 
 
 230 
 
 = 446° 
 
 - -887 
 
 - Q H 18 O. 
 
 The pinene, sylvestrene, limonene and dipentene named 
 in the above table are examples of what are now called 
 terpenes. Mixtures of these and of a few other terpenes of 
 less importance constitute what is generally known as oil or 
 spirit of turpentine. Terpenes are very frequent and often 
 very abundant constituents of the volatile, ethereal or 
 essential oils extracted from plants. Some, however, of 
 these volatile and strong-smelling essences consist mainly 
 of liquids containing oxygen, such as cineol or eucalyptol, 
 C 10 H 18 O, which occurs to a large extent in the oils distilled 
 from many species of eucalyptus. Besides the compounds 
 in our list and a certain number of essential oils from plants, 
 
92 
 
 ETHER 
 
 we shall have to consider some of the more volatile liquid 
 constituents of natural petroleum and of artificial paraffin 
 oils. The fixed or fatty oils, which are constantly used in 
 painting and in the manufacture of varnishes, have been 
 already discussed in Chapter V. 
 
 Ether, often called sulphuric ether, is a very mobile 
 liquid of extreme volatility, and possesses a penetrating 
 odour. Its vapour, given off freely at ordinary tempera- 
 tures, forms with air a highly inflammable and explosive 
 mixture. Great care is therefore required in using this 
 liquid ; no light must on any account be brought near it. 
 It does not mix with water, but floats on the surface, 
 although it dissolves in water to the extent of about 10 per 
 cent. Commercial ether contains water and alcohol along 
 with traces of other impurities. It is seldom necessary to 
 remove the alcohol from it (for varnish-making, etc.), but it 
 can be got rid of by repeatedly shaking the crude ether with 
 water, whereby much ether also is dissolved away. The 
 water present interferes seriously with the use of ether as a 
 solvent for resins, etc., but it may be removed by careful 
 rectification with fused calcium chloride, that substance 
 having previously been allowed to remain in contact with 
 the liquid for a day. A final distillation from a little 
 metallic sodium completes the drying of the ether and also 
 removes, if used in sufficient quantity, the alcohol present. 
 Great care is necessary in distilling ether to secure, by a 
 current of ice-cold water in the condenser, the condensation 
 of the vapour. 
 
 Carbon Bisulphide. — This heavy, oily but volatile liquid 
 readily gives off vapour at ordinary temperatures. It is 
 poisonous, and the same care in manipulating it must be 
 taken as that insisted upon in the case of ether. The 
 smell of the ordinary commercial bisulphide is most offen- 
 
ACETONE 
 
 93 
 
 sive, but it is now possible to purchase a specially purified 
 sort from which a particularly disagreeable sulphur-com- 
 pound of nauseous odour has been removed. Carbon 
 bisulphide sinks in water : it is a powerful solvent for many 
 resins, and mixes perfectly with the fixed and essential oils 
 in all proportions. 
 
 Acetone also occurs in crude wood-naphtha. It has a 
 penetrating but agreeable odour. It is miscible with water, 
 alcohol, oils, etc., and dissolves many resins, camphor, fixed 
 oils, and allied bodies. It is sometimes serviceable as a 
 solvent for discoloured varnishes on pictures. Commercial 
 acetone is very impure, containing wood-spirit, empyreumatic 
 oils, and water. 
 
 Chloroform is another powerful solvent of resins. It has 
 a pungent but sweet taste, is not miscible with water, and is 
 very heavy. Commercial chloroform often contains alcohol 
 and other foreign matters, from most of which it may be 
 purified by redistillation from a little oil of vitriol followed 
 by a second distillation from fragments of quicklime. For 
 making varnishes neither water nor alcohol should be 
 present in chloroform, but there are other impurities 
 which do not interfere with its employment for such a 
 purpose. 
 
 Wood-spirit, or methyl-alcohol, is a constituent of wood- 
 naphtha, a product of the destructive distillation of wood. 
 It rarely occurs in commerce in a state even approaching 
 to that of purity. It is miscible with water in all proportions, 
 but not with fixed oils. When free from water it may be 
 used as a solvent for some resins, and for removing dis- 
 coloured varnish from oil-paintings. Methylated spirit is 
 spirit of wine, to which some crude wood-spirit has been 
 added. 
 
 Alcohol, or pure spirit of wine, is met with in commerce 
 
94 
 
 ALCOHOL 
 
 practically free from all impurities save water. Proof spirit, 
 rectified spirits of wine, and methylated spirit, though of 
 service in cleaning oil-pictures and for many other purposes, 
 ought not to be used in the preparation of varnishes. For 
 this purpose pure alcohol, often called absolute alcohol, is 
 required ; but provided that it contains no water the presence 
 of wood-spirit is no drawback to its use. In commerce, 
 nearly absolute alcohol, made both from spirits of wine and 
 from methylated spirit, is obtainable; but it may be pre- 
 pared by operating upon the strongest available spirits of 
 wine in the following manner : The spirit is distilled in a 
 water-bath until no further strengthening of the alcoholic 
 distillate is secured by repetition of the process ; then a dry 
 retort is half- filled with small, clean, hard fragments of quick- 
 lime, the strong spirit is poured upon these so as to some- 
 what more than cover them, and then the whole is left 
 over-night; distillation from a water -bath is then com- 
 menced, when it will be found that a spirit comes over which 
 contains no more than one part of water in two hundred. Even 
 this small proportion may be removed by redistilling the 
 alcohol from a very little metallic sodium. The last distil- 
 late, when a small portion of it is shaken up with its own 
 bulk of benzene, should mix perfectly with the latter, causing 
 no turbidity. But it should be borne in mind that absolute 
 alcohol is a very hygroscopic liquid, greedily absorbing 
 water from the air ; it must, therefore, be kept in well- 
 stoppered bottles, filled almost completely. In absolute 
 alcohol some of the more intractable resins, even some 
 kinds of copal, readily dissolve. The specific gravity of 
 absolute alcohol at 15° C. is '794, while, if it contains but 
 1 per cent, of water, its specific gravity is distinctly higher, 
 namely, 797. 
 
 Benzene is employed not only as a solvent, but as a 
 
BENZENE 
 
 95 
 
 diluent of the medium or oil employed in painting. It is 
 obtained from the lighter naphtha separated in the fractional 
 distillation of coal-tar. The benzene (also called benzol) of 
 commerce is rarely pure. The presence of small quantities 
 of higher hydrocarbons of the same series is of little 
 moment, but it also contains about one half per cent, of a 
 sulphur compound called thiophene (C 4 H 4 S), to which the 
 offensive odour of ordinary benzene is partly due. Thio- 
 phene is, however, much more soluble in cold oil of vitriol 
 than is benzene, and may be removed by several treatments 
 of the benzene with small quantities of this powerful acid. 
 Benzene thus purified can now be purchased. Benzene is a 
 mobile liquid, not miscible with water, but dissolving readily 
 in all proportions in most if not all of the liquids now being 
 described. It dissolves oils and very many of the harder as 
 well as all the softer resins. 
 
 Toluene much resembles benzene, and may be used for 
 the same purposes, although it is less volatile. Commercial 
 toluene has a disagreeable smell, arising from the presence 
 of a sulphur compound (thiotolene), which is more diffi- 
 cult to remove from the liquid than the thiophene from 
 benzene. 
 
 Toluene of good quality and at a moderate price may 
 be obtained from Kahlbaum of Berlin. It constitutes a 
 useful diluent and solvent when used with the spirit-fresco 
 medium. 
 
 Epichlorhydrin has been employed as a solvent for some 
 of the copals and other intractable resins in the manu- 
 facture of varnishes. Without further trials it would be 
 unwise to employ this liquid in artistic painting, yet the 
 resins dissolved in it seem to retain much of their original 
 toughness and hardness. 
 
 Amyl alcohol, the chief constituent of fusel-oil, is used by 
 
9 6 
 
 TERPENES 
 
 picture-cleaners for the removal of discoloured varnish. Its 
 vapour is suffocating and even poisonous. 
 
 Pinene, Sylvestrene, Limonene, and Dipentene, with several 
 other similar compounds, are the main constituents of the 
 various liquids to which the ordinary name of turpentine, 
 or, rather, spirit or oil of turpentine, is applied. All these 
 liquids are hydrocarbons, having the same composition in 
 ioo parts, expressed by the empirical formula C 10 H 1G . But 
 these liquids — of which about ten are known — differ from 
 one another in some of their chemical and physical char- 
 acters, such as oxidizability, boiling-point, specific gravity, 
 and action on light. The extreme importance of turpentine 
 in the process of oil-painting, and in the manufacture of 
 varnishes, warrants a full consideration of its several con- 
 stituents. 
 
 Turpentine, properly so called, is not a liquid, but the 
 solid or semi-solid resinous secretion of many trees, chiefly 
 coniferous. Some exudes naturally, but much more is 
 obtained by artificial incisions. It consists of a mixture of 
 one or more true resins and resinous acids in which oxygen 
 is present, with one or more liquid hydrocarbons which 
 contain (as the name imports) nothing but carbon and 
 hydrogen, and therefore no oxygen. These hydrocarbons 
 are called in chemical language terpenes, a term by which 
 they will be designated henceforth in the present chapter. 
 On distilling the crude turpentine or resins alone or with 
 water, or in a current of steam, the terpenes distil over while 
 the solid part remains behind ; this, on fusion, is called rosin 
 or colophony. It need not be further considered, as it is of 
 no value in painting, being friable and more or less strongly 
 coloured. We confine our attention, therefore, to the 
 distillate or terpenes. It should be added, however, that 
 the leaves, cones, and other parts of many coniferous trees, 
 
TERPENES 
 
 97 
 
 themselves yield various terpenes when submitted to distil- 
 lation, and that many of the volatile or essential oils of 
 aromatic plants other than conifers comtain or consist of 
 terpenes. The oils expressed from the rimds of lemons and 
 oranges afford illustrations of this remark. 
 
 Terpenes differ from one another in seweral obvious and 
 in several obscure ways. Even now the chemistry of these 
 liquids is not by any means clearly and completely un- 
 ravelled. We need not here concern ouirselves with those 
 minute differences in chemical and physiical properties by 
 which the identity of individual terpenes iis established, but 
 may confine our attention to their most salient characteristics. 
 Of these none is more important than the behaviour of 
 terpenes with regard to atmospheric oxygen, Some of 
 these liquids absorb oxygen readily, and to a large extent, 
 from the air, becoming thereby resinified — in fact, they thus 
 yield sticky, resinous, semi-solid bodies, closely resembling 
 the crude turpentine from which they have been prepared. 
 Everyone who has had occasion to use spirits of turpentine 
 frequently must have noticed the production of a sticky 
 substance about the neck of the bottles in which this liquid 
 has been kept. Moreover, the spirit of turpentine itself 
 will often have been noticed to have become cloudy, viscid, 
 or almost solid, especially if it has been contained in a 
 bottle frequently opened, and not quite full. Besides these 
 observations another will have been made — different speci- 
 mens of spirits of turpentine will have been found to 
 differ much as to the rate at which these changes have 
 taken place. Some samples, even in half-full bottles, remain 
 clear and limpid for long ; others become thick, opaque, 
 and sticky in a few weeks. Such changes are undesirable 
 in a solvent, diluent, or painting medium, on many grounds. 
 The resin formed is an unsatisfactory one — soft, sticky, and 
 
 7 
 
9 8 
 
 TERPENES 
 
 contractile. The liquid decreases so greatly in mobility, 
 and increases so greatly in viscosity, that its utility in 
 thinning oil pigments, and in making fine touches, is greatly 
 impaired. And this thickening of the liquid is accompanied 
 by the production of acid substances and of water, which 
 affect injuriously the ease of working and the stability of 
 the picture. Spirits of turpentine should disappear by 
 evaporation quickly and completely from the painting into 
 which it has been introduced. Now, if it be easily oxidizable, 
 even if it be kept from experiencing change before it is 
 actually employed, it will, during the very time in which it 
 is being used, attract oxygen ; so that though a great part 
 of it will escape by evaporation, the remainder will resinify 
 on the very canvas itself, adding a sticky deposit to the 
 drying oils and hard resins which may have been used as 
 the painting medium. It is clear, from all the above con- 
 siderations, that the greatest care ought to be taken in 
 selecting, in the first instance, such a sort of spirits of 
 turpentine as will resist oxidation under ordinary conditions. 
 Even an inferior spirit may be used, with a minimum of 
 disadvantage, if immediately after distillation it be poured 
 into a number of small bottles, so as to fill each of them 
 completely; they should be at once closed with sound 
 corks. In this way the contents of a bottle may be used 
 up very soon after it has been opened. Another precaution 
 may be taken : A few small fragments of hard quicklime 
 may be placed in each bottle to absorb any moisture pro- 
 duced by oxidation, and also the acid bodies which are 
 formed at the same time. Even with the choicer samples 
 of spirits of turpentine, which pass much less easily into 
 resins, this use of quicklime is desirable \ but in this case 
 the employment of many small bottles is unnecessary, and 
 it will suffice to put a few hard pieces of lime, free from 
 
TERPENES 
 
 99 
 
 powder, into a pint or quart bottle, and then to fill it with 
 the spirit. The clear liquid may be poured off as required 
 for use, any disintegrated particles of lime sinking readily to 
 the bottom of the vessel. 
 
 Before giving details as to the sources and characteristics 
 of the best terpenes, it may be useful to mention that com- 
 mercial samples of spirits of turpentine may be tested and 
 compared by means of a very simple experiment. Obtain 
 the required number of small, flat-bottomed, conical glass 
 flasks with wide mouths, one flask for each sample ; these 
 flasks are known as Erlenmeyer's. Into the flasks pour 
 enough of the several samples to cover the bottom to the 
 depth of one-eighth of an inch ; label each flask to corre- 
 spond with the sample, and lightly close each mouth with 
 a plug of carded cotton— the date of the experiment should 
 be added on the label. Shake each flask so as to cause a 
 number of bubbles to be formed in the liquid ; the more 
 rapidly these bubbles break, the better is the sample. Repeat 
 the experiment of shaking the samples at short intervals for 
 a few weeks — notable changes in the viscosity of the oils 
 will be observed sooner or later. Any sample which after 
 one month remains clear, and in which the bubbles formed 
 on agitation break almost as quickly as at first, may be 
 accepted as of good quality. Another test for discriminating 
 between the samples, so far as their state at the time of the 
 experiment is concerned, is the very simple one of placing 
 one drop of each oil upon a sheet of writing-paper, and 
 gently warming the translucent stain it forms ; with a good 
 oil the mark completely disappears. 
 
 Two other obvious characteristics of different samples of 
 spirits of turpentine may now be noticed— namely, odour 
 and boiling-point. Some samples have a much more agree- 
 able scent than others \ the vapour of these seems to have 
 
 7—2 
 
ioo TERPENES 
 
 a less marked tendency to produce headache than that of 
 the pungent and cruder-smelling varieties. The range in 
 boiling-point is not very extensive ; but it may be taken 
 as about 25 C, the figures ranging from 155 to 181 . 
 Samples having lower boiling-points evaporate more quickly 
 than those which enter into ebullition at higher tempera- 
 tures. The solvent power on resins differs with different 
 kinds ; this is a property which is of importance in varnish- 
 making, but very little accurate knowledge exists on this 
 point. 
 
 A few of the more important turpentine oils may now be 
 named : 
 
 Russian and Swedish oils, chiefly from Pinus sylvestris 
 
 and P. kdebourdii. 
 Austrian oil, partly from Pinus Laricio, partly from 
 
 P. Pamilio. 
 American oil, chiefly from Pinus australis and P. tceda. 
 French oil, from Pinus Pinaster. 
 German oil, from Pinus sylvestris, P. Cembra, P. Abies, 
 
 P. vulgaris, etc. 
 Strasburg oil, from Abies pectinata. 
 Juniper oil, from Juniperus commimis. 
 
 The above-named turpentine oils are accompanied by 
 small amounts of various resins, camphor, and other 
 oxygenated bodies, from which they may be separated by 
 treatment with caustic potash, metallic sodium, and fractional 
 distillation. 
 
 From the above-named liquids a number of terpenes have 
 been isolated. Among the better known of these the 
 following may be mentioned. 
 
 1. Pinene, with a boiling-point of 160 C. It forms the 
 chief constituent of German and American oil of turpentine, 
 
TERPENES 
 
 101 
 
 and occurs in considerable quantity in the volatile oils of 
 wormwood, sage, rosemary, and juniper. It is an easily 
 alterable and resinifiable terpene, and should not be em- 
 ployed either in thinning paints, or as an ingredient of 
 varnishes. 
 
 2. Phellandrene. — Boiling-point 171 to 172 . This 
 terpene has been separated from eucalyptus oil, that is, 
 from the oil obtained by the distillation with water of 
 the leaves of one of the numerous species of eucalyptus, 
 E. amygdalina. It is one of the most alterable of all 
 terpenes, and the oils containing it should be avoided. 
 
 3. Limonene. — This terpene, like most of the others, 
 occurs in two forms or varieties, having opposite actions 
 on polarized light. It is sometimes called citrene. It 
 boils at 1 7 7 . It is best prepared from orange-peel oil, 
 which yields over 90 per cent, of dextro-limonene when 
 distilled from caustic potash. When pure it is less alter- 
 able than pinene and phellandrene, though it resinifies after 
 a time. 
 
 4. Sylvestrefie. — Boiling-point i76°to 17 7 . When pure 
 it has the smell of bergamot, but generally presents the 
 odour of fir-wood. It is dextro-rotatory, and forms the 
 chief constituent of Russian and Swedish oil of turpentine, 
 and of some of the German oils. On exposure to air it 
 leaves a sticky resin. 
 
 5. Dipentene, which boils at about 180 C, is optically 
 inactive, and may be made by heating some of the other 
 terpenes to 250 — 270 for some hours, or by mixing 
 dextro- and lasvo-limonene together. The only natural 
 product in which dipentene is known to occur is the vola- 
 tile oil which accompanies common camphor. Its odour 
 resembles that of citron oil : it resinifies to about the same 
 extent as limonene. 
 
a j gS g ^ P ^ P Pm 
 
 TERPENES 
 
 From the preceding descriptions it may be gathered that 
 of all the above terpenes limonene and dipentene are the 
 least alterable. They have, however, somewhat high boiling- 
 points, and evaporate more slowly than most of the other 
 terpenes. 
 
 Here it may be mentioned that the presence of water 
 in a terpene, or a mixed essential oil, may be detected by 
 the cloudiness which it shows when mixed with thrice its 
 volume of benzene or of petroleum-spirit. To remove 
 traces of water from any of the less volatile liquids we have 
 been considering, without having recourse to distillation 
 from caustic potash, or from quicklime, the following simple 
 procedure may be adopted : A glass flask is three-fourths 
 filled with the liquid, and then it is kept at a temperature of 
 ito° to i2o° C, so that the moisture present is disengaged 
 as vapour without the terpene or essential oil itself boiling : 
 drops of moisture will condense in the neck of the flask, 
 and may be removed from time to time by means of a roll 
 of blotting-paper. The mouth of the flask should be loosely 
 plugged with carded cotton. Of course this process is 
 applicable only to liquids which boil at temperatures con- 
 siderably over i2o°, like the terpenes. 
 
 In connection with the terpenes two other liquids and 
 one solid remain to be mentioned. The liquids are ' oil of 
 amber' and 'oil of copal.' These are obtained by strongly 
 heating the resins in question. They are employed as 
 efficient solvents for the harder resins. Oil of amber may 
 be obtained in commerce at a moderate price. Its offensive 
 smell, partly due to compounds of sulphur, may be lessened 
 by adding to it some white lead and solid caustic potash, 
 and afterwards distilling it. It contains amongst other liquid 
 constituents at least one terpene. Its boiling-point rises, as 
 distillation proceeds, from no C to 260° Camphor is 
 
PETROLEUM-SPIRIT 103 
 
 expressed by the formula C 10 H 16 O, and is obtained chiefly 
 from Cinnamomum camphora, a tree of Formosa, China and 
 Japan. It is a tough crystalline solid of penetrating odour 
 and pungent taste. It is soluble in all the liquids named 
 in the present chapter. Although it boils at so high a 
 temperature as 204 C, it readily and rapidly volatilizes at 
 ordinary temperatures. It is used to aid the solution of 
 some of the harder resins in the making of varnishes, but its 
 presence in a varnish is objectionable, for it slowly escapes 
 after the apparent drying-up of the varnish, and thus causes 
 a deterioration of the lustre and continuity of the resinous 
 film. Q» wJhl&xSbJT l/v,' EouxTFTcVvr, Ouw, cCs ? )| 
 
 Petroleum-spirit. — When native petroleum and the similar 
 materials obtained in the distillation of bituminous shales, 
 etc., are submitted to fractional distillation, the more volatile 
 portions which come over first constitute the liquids variously 
 known as gasoline, benzoline, ligroine, petroleum-naphtha, 
 petroleum-ether, and petroleum-spirit. This liquid consists 
 entirely of hydrocarbons, some of which belong to the 
 paraffin series, while others are naphthenes. Their boiling- 
 points are all under 170° C, while some of them boil as 
 low as 50 • indeed, commercial samples of petroleum-spirit 
 often begin to enter into ebullition at a lower temperature 
 even than this. The series of petroleum products may be 
 roughly grouped thus : 
 
 Petroleum-spirit boils below 1 70 C. ; specific gravity, 
 o'6 to c'7. 
 
 Lamp-oil, kerosene, photogen, or paraffin-oil, boils be- 
 tween 180 and 220 , and has a specific gravity of 0-78 
 to o - 82. 
 
 Solar-oil, lubricating-oil, vaseline, and paraffin-wax, are 
 heavier products, with a range of specific gravity from 0-83 
 up to o"94. Their viscosity increases with their density 
 
HHHHff 
 
 104 
 
 PETROLEUM-SPIRIT 
 
 until the semi-solid vaseline and the solid paraffin-waxes are 
 reached. The latter substances have been described already, 
 the former are not available in painting : in fact, their pre- 
 sence even in traces in petroleum-spirit — an extremely useful 
 solvent and diluent— should be carefully guarded against. 
 They neither escape by evaporation nor harden in the lapse 
 of time. Thus petroleum-spirit remains alone for further 
 consideration. 
 
 As a solvent for resins, and as an extremely volatile and 
 very thin liquid for diluting oily vehicles and paints in the 
 process of oil-painting, the variety of petroleum-spirit which 
 boils between 50 and 70 C. is the most suitable. It con- 
 tains hydrocarbons represented by the formulas C 6 H 12 and 
 C G H 14 . It must be used with great caution on account of 
 its easy inflammability and the readiness with which it gives 
 off a vapour, which, when mingled with atmospheric air, is 
 highly explosive. It may be used for many purposes in lieu 
 of benzene (from coal-tar naphtha), being much cheaper 
 and quite as efficient. A drop of this variety of petroleum- 
 spirit on paper evaporates very quickly, leaving no greasy 
 stain. 
 
 Another variety of this petroleum-spirit is obtained by 
 collecting apart the fractions which boil between ioo° C. 
 and 130 . These contain heptane (C 7 H 16 ), octane (C S H 1S ), 
 heptylene (C 7 H 14 ), and octylene (C 8 H 1G ), and other hydro- 
 carbons. This mixture is less volatile than that just de- 
 scribed, it dries more slowly, and is a less energetic 
 solvent. 
 
 A third variety boils between 130 and 170 and is avail- 
 able for many of the purposes for which turpentine oil is 
 employed. It is not advisable, in my opinion, to use frac- 
 tions having a higher boiling-point than 170 C. as additions 
 to the pigments and vehicles of oil-painting, for, though 
 
OIL OF SPIKE LA VENDER 
 
 io5 
 
 their slow drying is sometimes an advantage, there exists the 
 danger of their incomplete evaporation from the painted 
 surface. If they remain even in traces in the finished work 
 after it has been varnished, they may give rise to the same 
 accidents as are caused by the treacherous though seductive 
 asphaltum. 
 
 It should be remembered that the various petroleum 
 liquids just described do not resinify, nor do they leave any 
 permanent stain or mark upon paper which has been moist- 
 ened with them. 
 
 In the Table of Solvents on p. 91 three liquids con- 
 taining oxygen and related to the terpenes find a place. 
 Two of these, cineol or eucalyptol, and geraniol, represented 
 by the empiric formula C 10 H 18 O, are alcoholic in constitu- 
 tion ; while the third, known as citral, belongs to the 
 aldehydes. These and several other allied oxidized com- 
 pounds, as well as a few ethereal salts known as esters, enter 
 largely into the composition of certain essential oils occa- 
 sionally used in oil-painting. We will introduce a few 
 remarks concerning some of these compounds under the 
 names of the essential oils of which they are important 
 components. 
 
 Oil of Spike Lave?ider is obtained by distillation from the 
 flowers of a species of lavender, Lavandula spica. Its 
 specific gravity varies from "905 to "918 : it dissolves in 
 three volumes of 70 per cent, alcohol. It contains about 
 30 to 40 per cent, of an alcohol, linalol (C 10 H 18 O), about 
 the same amount of an ester, linalyl acetate, a considerable 
 quantity of cineol (eucalyptol), and only a small proportion 
 of terpenes. It is often adulterated with rosemary oil. 
 When spike oil is exposed for a long time to the air, the 
 part which does not evaporate gradually thickens, owing 
 to the oxidation of its constituents. This thickened oil, 
 
io6 
 
 OIL OF ORANGE 
 
 although usefully employed in the application to porcelain 
 of enamel colours, is useless in oil and spirit-fresco painting. 
 To preserve spike oil in its thin and mobile state, the pre- 
 cautions recommended in the case of turpentine (p. 98) 
 should be taken. Spike oil is a powerful solvent of resins ; 
 it is one of the components of Gambier-Parry's spirit-fresco 
 medium. 
 
 Oils of Eucalyptus are derived from many species of euca- 
 lyptus, and differ from one another widely as to the relative 
 proportions in which their components exist, and also in 
 their odour. Cineol, or eucalyptol, is the chief and most 
 characteristic constituent of the majority of them, occurring 
 to the extent of 50 to 65 per cent, in the oil from E. globulus, 
 the commonest of all kinds. On the other hand, the oil 
 from E. metadata, var. citriodora, sometimes contains no 
 less than 95 per cent, of citronellal, an alcohol. This oil is of 
 particularly agreeable odour, as are also the oils of E. cneori- 
 folia, E. corymbosa, and E. dealbata. For a diluent in oil- 
 painting it is probable that any one of these oils may be 
 chosen with equal propriety, our choice being guided by the 
 odour of the sample. 
 
 Oil of Lemon. — Though the terpenes known as dextro- 
 and lsevo-limonene constitute the main portion of this oil, 
 yet its characteristic odour is partly due to the presence 
 of 6 to 9 per cent, of the aldehyde known as citral. This 
 compound is occasionally separated from lemon oil ; by its 
 removal the remainder becomes richer in terpenes and more 
 fitted for the use of the painter. 
 
 Oil of Orange. — This essential oil, which, like that of 
 lemon, is obtained by expressing the rind of the fruit, is re- 
 markably rich in limonene (dextro-limoncnc). This, with 
 small quantities of other terpenes, makes up over 95 per 
 cent, of the oil. Although the expressed oil possesses a 
 
CYMENE 
 
 107 
 
 yellow colour, it may be obtained absolutely free from colour 
 and of agreeable odour, by distillation under reduced 
 pressure. 
 
 Oil of Rosemary. — This oil varies in specific gravity be- 
 tween -9 and -9 18. It contains about 20 per cent, of an 
 ester, bornyl acetate (C 12 H 20 O 21 ), and 6 per cent, of borneol. 
 Its other constituents include lineol and two terpenes. 
 
 Cymene. — There are twenty or more varieties of the 
 hydrocarbon expressed by the empirical formula C 10 H 14 . 
 The best known of these is the agreeable lemon-scented 
 liquid contained in cumin oil from the seeds of Cuminum 
 cyminum. Its full scientific name is paramethylisopropyl- 
 benzene, while its constitution is shown by the formula 
 CH 3 .C 6 H 4 .CH(CH 3 ) 2 . This hydrocarbon serves the same 
 purpose as a diluent as the terpenes, but is too costly for 
 general use. Doubtless some of the other forms of the 
 C 10 H U hydrocarbon might be similarly employed. The 
 range of their boiling-points lies between 168 and 204 C. 
 Some are solid at ordinary temperatures. 
 
■■HI 
 
 CHAPTER XI 
 
 SICCATIVES OR DRYERS 
 
 The terms ' siccatives ' and ' dryers ' are applied to three 
 classes of substances. Perhaps the most correct or appro- 
 priate application of these words is to those metallic com- 
 pounds which are used in order to increase the rate at 
 which the drying oils harden, but in the literature of the 
 subject we often find that drying oils which have been thus 
 treated, and likewise certain resinous solutions, are spoken 
 of as siccatives. In the present chapter we describe the 
 dryers proper only, referring our readers to the chapters on 
 oils and on varnishes for the necessary particulars concerning 
 the other materials which may be included in the group 
 under discussion. 
 
 Lead and several of its salts have been long and widely 
 used as dryers. Metallic lead in the form of foil, litharge 
 or lead protoxide, minium or red lead, lead peroxide, sugar 
 of lead or lead acetate, the basic lead acetate, and white 
 lead itself, have all been used in this way, chiefly for the 
 purpose of making linseed or other painting oil dry more 
 quickly. Some of these compounds, particularly sugar of 
 lead, have been introduced into the very picture itself. It 
 was a common practice to employ powdered sugar of lead 
 or a solution of this salt in water to hasten the drying of 
 vehicles and of slow- drying pigments which have been ground 
 
MANGANESE DRYERS 
 
 109 
 
 in oil. I have seen one of the results of this commingling 
 of sugar of lead with the medium or the paint in the pro- 
 duction of an immense number of small spots in the picture, 
 sometimes appearing through the surface-varnish in the 
 form of a white efflorescence. This efflorescence consists at 
 first of lead acetate in crystals, but these soon attract car- 
 bonic acid from the air and become lead carbonate, which, 
 in its turn, is changed into lead sulphide by the action 
 of sulphuretted hydrogen. This tendency of the lead com- 
 pounds to yield brown or black lead sulphide is, indeed, the 
 great drawback to any use of these substances as dryers. 
 When oil is left in contact with them, and especially when 
 heat is applied to the mixture, some of the lead dissolves, 
 forming, with the fatty acids of the oil, lead-soaps. These 
 soaps are distributed uniformly throughout the oil, and help 
 to make it dry and harden quickly. The same action 
 occurs when white lead is ground as a paint with oil, and 
 has been urged as an objection to the use of those white 
 leads which contain hydrate of lead, a compound which 
 acts upon oil more quickly and thoroughly than the car- 
 bonate of lead. 
 
 It will be seen, however, that while there may be 
 reasons for permitting the use of a single lead pigment 
 which possesses this peculiar property, there can be none 
 for introducing into every part of a picture oils or other 
 materials which contain a metal, like lead, so liable to 
 cause discoloration and darkening, when other and per- 
 fectly innocuous substances are available for producing the 
 same siccative effects. On this account we omit further 
 reference to the lead compounds, which have been and are 
 still employed in the preparation of strongly-drying oils, etc., 
 but pass on to the 
 
 Manganese compounds, of which the di - oxide, the 
 
MANGANESE DRYERS 
 
 hydrated protoxide and sesquioxide, the borate, the oxalate, 
 and the linoleate are the most important. 
 
 Manganese dioxide, the black oxide, Mn0 2 , is used in 
 the form of a powder obtained by grinding the mineral 
 pyrolusite. As the effectiveness of this compound is made 
 complete only by the use of oil of vitriol, which needs 
 subsequent neutralization with lime, it cannot be recom- 
 mended as a material for rendering linseed oil intended for 
 painting, or for making picture-varnish, more drying. The 
 difficulty of preparing the manganese hydrates above men- 
 tioned constitutes an objection to their employment for 
 this purpose. But the borate, the linoleate, and the oxalate 
 of manganese may be obtained in commerce in a state of 
 sufficient purity for our present purpose, and it is to them 
 that we wish to direct attention. Borate of manganese 
 may, moreover, be so easily prepared, that it is worth while 
 to give here the necessary directions. One pound of pure 
 manganese sulphate is dissolved in six pints of distilled 
 water, the solution being filtered if cloudy. A few drops of 
 the liquid are now to be tested with caustic soda solution — 
 the precipitate formed should be white ; if it show a 
 greenish, yellowish, or grayish hue, iron is probably present, 
 and it will be necessary to treat the whole of the solution 
 with caustic soda until a white precipitate falls, and then to 
 filter it again. In order to produce manganese borate, a 
 boiling saturated solution of pure borax is added to the 
 manganese sulphate solution until no more precipitate falls. 
 The precipitate is collected on a filter and washed with hot 
 distilled water until the wash-waters show no turbidity when 
 a solution of barium chloride and a few drops of dilute 
 hydrochloric acid arc added to the last portion coming 
 through the paper. The borate of manganese is then dried 
 in a warm place, and finally in the water-oven. One grain 
 
DRYERS 
 
 of it, warmed with linseed oil, is sufficient to render an 
 ounce of the latter highly drying (see Chapter V.). The 
 oxalate or the linoleate of manganese may be used in the 
 same way, and there are also met with certain manganese 
 1 resinates ' which may be employed similarly. 
 
 Borate of lime and borate of zinc have been employed 
 not only for rendering oils more quickly drying but also 
 in admixture with some of those oil-paints which dry with 
 difficulty. Being colourless they are well adapted for use 
 with white pigments, such as oxide of zinc. Several of the 
 siccative materials sold under various fancy names consist 
 of mixtures of these borates with carbonate of zinc or oxide 
 of zinc, manganese compounds being also sometimes added. 
 Another dryer in common use is white vitriol or sulphate of 
 zinc. Its siccative character is very slight. Most of the 
 other siccatives employed by artists owe their efficacy to 
 lead, or are resinous preparations. Siccatif de Courtrai is 
 a very dangerous mixture, heavily loaded with compounds 
 of lead ; Siccatif de Haarlem is a resinous preparation, | 
 which produces, on drying, a hard, brilliant, and tough film. 
 This acquires, in course of time, a deep yellow hue, which, 
 however, hardly affects the colour of the paints with which 
 the siccative has been employed, because of the small pro- 
 portion used. 
 
IHHBJI 
 
 CHAPTER XII 
 
 VARNISHES AND VEHICLES 
 
 When an oil, such as linseed, walnut, or poppy, has been 
 purified and made more quickly drying by one or other of 
 the methods already described, it is often called ' varnish.' 
 It has acquired the property of rapidly solidifying, when 
 spread as a thin layer, into a tough transparent substance, 
 endowed with a considerable degree of cohesiveness and 
 elasticity, yet rather soft withal. Now oil of this character, 
 although it has many uses in painting, is not quite hard 
 enough for some of the purposes for which a true varnish 
 may be required, but its defects may be amended by 
 associating with it one or more of the resins described in 
 Chapter VI. One class of varnishes is compounded in 
 this manner of two materials, oil and resin, both of which 
 are fixed or non-volatile. A second group of varnishes 
 consists of a resin dissolved in a volatile solvent. And 
 there are also mixed varnishes which contain at least three 
 ingredients— namely, a drying oil, a volatile solvent, and a 
 resin. As the varnishes which consist wholly of oil and 
 resin are thick and intractable, it is usual to thin these, 
 according to the purpose for which they are intended, with 
 varying amounts of some volatile liquid or solvent, spirits 
 of turpentine being most frequently thus employed. In 
 order to avoid too elaborate a classification, it will be 
 
MASTIC VARNISH 
 
 "3 
 
 advisable to describe those varnishes which contain oil as 
 oil or fat varnishes, and those which consist wholly of a 
 resin and a volatile solvent as spirit-varnishes. We de- 
 scribe the latter first, as their manufacture is easier and 
 their constitution simpler. In order to avoid repeated 
 references to the descriptions already given of the several 
 materials employed in making varnishes, it will be con- 
 venient to state once for all that the oils used are described 
 in Chapter V., the resins in Chapter VI., and the solvents 
 in Chapter X. 
 
 Mastic Varnish. — This is usually prepared by dissolving 
 mastic in spirits of turpentine, although other volatile oils 
 and even absolute alcohol may be employed. In order 
 to prevent the mastic from agglutinating together, warm 
 powdered glass, or warm fine white quartz sand, may be 
 added to the resin before it is mixed with the solvent. The 
 spirits of turpentine should be absolutely free from moisture, 
 the mastic may be in tears, or, preferably, have been 
 purified and dried as before directed. The materials are 
 introduced into a capacious glass flask fitted with a cork, 
 tube and condenser so arranged that, when the flask is 
 heated in a water-bath, the vapours given off from the 
 solvent may be condensed and return to the vessel. The 
 temperature of the water-bath may be ioo° C. if oil of 
 turpentine be used, but should not be allowed to rise 
 beyond 7 8° C. if absolute alcohol or 96 per cent, alcohol 
 (specific gravity "806) be substituted for the oil of turpen- 
 tine. The following receipt gives a varnish which contains 
 nearly 25 per cent, of its weight of mastic, but the propor- 
 tion may easily be increased or diminished : 
 
 14 ounces of mastic, 
 44 „ „ spirits of turpentine, 
 6 ,, ,, powdered glass, or fine sand. 
 
 8 
 
ii 4 
 
 MASTIC VARNISH 
 
 When the mastic has dissolved the varnish is allowed to 
 cool, and then poured off into a closed glass vessel, in 
 which it is allowed to rest until perfectly clear. Or it may 
 be clarified by filtration through a plug of dried carded 
 cotton fitted into a funnel. The funnel should be closely 
 covered with a ground-glass plate, but a specially contrived 
 filtering apparatus has been designed for the purpose of pre- 
 venting any escape of vapour during the process of filtration. 
 
 The varnish prepared according to this receipt is nearly 
 colourless, and leaves a brilliant glassy film when it evapor- 
 ates on a smooth surface. But this film is very brittle, and 
 easily abraded by gentle friction even with the finger, in 
 fact it consists of little more than the original mastic resin, 
 the fragility of which is well known. To obviate this brittle- 
 ness many plans have been devised. Sometimes Venice 
 turpentine, Canada balsam, or Elemi resin is introduced in 
 small quantity, not exceeding one-seventh in weight of the 
 mastic used. In consequence of such admixture of a 
 natural soft turpentine the varnish produced dries more 
 slowly, and leaves a less brittle, tougher, more adhesive, 
 and more elastic film on evaporation. Ultimately, how- 
 ever, these balsams become brittle like mastic itself. This 
 remedy is, therefore, of a temporary character, but, at the 
 same time, these additions do not interfere with the ease 
 with which the varnish, when old and discoloured, can be 
 removed from a painting by means of solvents or of friction, 
 without injuring the glazing pigments which may lie im- 
 mediately below it : they also render the varnish more easy 
 of application. The other classes of substances added to 
 toughen the resinous film left by the drying of a spirit 
 varnish, are fixed oils, and those liquid paraffins which boil 
 at temperatures above 170 C. A very small proportion of 
 ' manganese ' linseed oil is, perhaps, the more effective and 
 
COPAL VARNISH 
 
 "5 
 
 safer toughener of the two, but its introduction involves 
 the disadvantage just named. In many French mastic 
 varnishes camphor is introduced for the same purpose to 
 the extent of 5 to 8 parts for each 100 of mastic. The 
 camphor, however, gradually escapes by volatilization, the 
 varnish losing its fine lustre and becoming brittle and 
 fissured. It should be mentioned here that the more 
 easily resinified varieties of oil of turpentine, when used as 
 solvents for mastic, also toughen the resinous film left on 
 the drying up of the varnish, although the effect is not per- 
 manent. If alcohol, benzene, light petroleum ether, or 
 other non oxidizable solvents be substituted for any kind of 
 essence of turpentine in making mastic varnish, there is no 
 doubt that the brilliant films they yield are more brittle and 
 less adhesive. 
 
 Sandarac and the various kinds of soft pale dammar may 
 be substituted wholly or in part for the mastic mentioned 
 in the receipt for spirit varnish above given. But if these 
 dammars be used great care must be taken that they are 
 themselves free from moisture, and that the oil of turpentine 
 or other solvent be also perfectly dry. It has been recom- 
 mended to employ oil of spike lavender instead of oil 
 of turpentine in making mastic varnish. The spike oil 
 in this case must be free from water, and freshly distilled : 
 mastic varnish thus prepared has less tendency to ' bloom ' 
 than the ordinary kind, but if pictures are varnished in 
 a perfectly dry atmosphere and kept therein till the surface 
 has hardened, the formation of bloom is minimized. 
 
 A copal spirit varnish may be made by the use of acetone, 
 or of ether (both water-free), or of absolute alcohol, light 
 petroleum-ether, or benzene. The copal to be dissolved 
 may be either Sierra Leone copal, Zanzibar copal, or 
 Demerara copal, the first two yielding the harder varnish, 
 

 - 
 
 n6 
 
 C0P.4L VARNISH 
 
 but the last-named being easier of solution, or, rather, dis- 
 solving less incompletely. The powdered copal, prepared 
 as directed previously (by exposure to the air, and heating), 
 or first fused, or at least heated till it has lost from 10 to 
 20 per cent, of its weight, is kept in contact with four 
 times its bulk of the solvent until it is nearly dissolved. 
 Three measures of dry oil of turpentine are then added, and 
 the mixture submitted to distillation from a water-bath until 
 three measures of the acetone or other original solvent have 
 been drawn over : an efficient condenser must be used. If 
 it be desired to prepare a mixed varnish (partly oil or fat 
 varnish), 1 measure of ' manganese ' oil, and 2 measures of 
 oil of turpentine may be used in lieu of the quantity of 
 turpentine above mentioned, the distillation being then pro- 
 ceeded with as before. 
 
 In another method of preparing copal (and amber) spirit 
 varnishes the resins duly prepared and powdered are heated 
 with the selected solvent under pressure — that is, at a 
 temperature above that at which the particular solvent used 
 boils under ordinary conditions. With purified oil of 
 amber, oil of copal, oil of turpentine, oil of spike, or the 
 heavier petroleum spirit, and on a small scale, glass tubes 
 hermetically sealed and heated to 200 C. may be used, but 
 if a higher temperature or more volatile solvents be em- 
 ployed, copper tubes with screw stoppers are necessary. 
 But operations of this order can be carried out safely and 
 successfully only in a well-equipped laboratory or factory by 
 skilled operators, and it is therefore unnecessary to furnish 
 further particulars in a work like the present. 
 
 The preparation of fat or oil varnishes with the harder 
 resins is generally attended with considerable difficulty ; 
 but there is, as we have already mentioned, one way in 
 which the difficulty may be lessened. By the aid of one of 
 
COPAL VARNISH 
 
 117 
 
 the powerful and very volatile solvents previously named, 
 we prepare a spirit copal or amber varnish : we then add 
 the required amount of ' manganese ' oil and draw off the 
 volatile solvent by distillation, thinning the resinous solution 
 obtained with so much oil of turpentine as is necessary. 
 If the copal or amber employed has been first roasted or 
 fused, the varnish produced will be more or less dark in 
 tint; it is on this account that the exposure of the powdered 
 resin to the air in a flat porcelain dish for seventy-two 
 hours, at a temperature (of 220 C.) which does not cause 
 discoloration, is recommended. But if, on the other hand, 
 the copal or amber be merely powdered, some part of it, 
 and that a considerable part, will probably remain undis- 
 solved though swollen, and will therefore be wasted. The 
 following process, in the main identical with one recom- 
 mended in the American edition of Mr. Erwin Andres' 
 work on varnishes, yields a pale and durable varnish when 
 Sierra Leone copal or other hard copal is employed, and is 
 doubtless well adapted for the preparation of amber varnish 
 also. As will be seen, it is based upon the preliminary 
 partial solution of the hard resin in chloroform, or in light 
 petroleum spirit of about the same boiling-point. It may 
 be stated at once that the proportions of the five ingredients 
 used are approximately 10 parts by weight of copal or other 
 hard resin ; 5 parts by weight of dried powdered glass or 
 sand ; enough chloroform to cover the above substances ; 
 35 parts by weight of oil of turpentine, and 10 parts by 
 weight of ' manganese ' oil. The following is an outline 
 only of the process. The copal, after having been powdered 
 and heated to 220 C. for seventy-two hours, is mixed with 
 the glass or sand, and introduced into a retort ; chloroform 
 in quantity sufficient to cover the mixture is added. After 
 the lapse of twenty-four hours the dry oil of turpentine is 
 
u8 
 
 COPAL VARNISH 
 
 poured in, and an upright condenser is attached to the 
 retort. The retort is then heated to 50 or 6o° C. for two 
 hours, so that the chloroform continually returns to the 
 mixture. Then the contents of the retort are allowed to 
 cool, and the condenser slanted downwards to allow of the 
 chloroform being distilled over. This removal of the 
 chloroform having been effected at a temperature so low 
 that very little turpentine has come over, the remaining 
 mixture in the retort is heated once more with the con- 
 denser in an upright position. The heat used must suffice 
 to bring the oil of turpentine into vigorous ebullition — in 
 an hour the whole of the copal should have dissolved. The 
 'manganese ' oil wanted should now be heated to ioo° C, 
 and then the copal mixture, when it has cooled to 70 C, 
 added little by little to it with constant stirring, the tempera- 
 ture of the oil being maintained at 90 to ioo°. When the 
 mixture is complete the source of heat is withdrawn, but the 
 varnish is still stirred for twenty minutes. Then it is allowed 
 to settle, until quite clear, in glass bottles, or, if an appro- 
 priate filtering apparatus is available, it is filtered. In the 
 latter case a little hot oil of turpentine may be used to 
 extract any copal solution which may remain with the 
 powdered glass or the sand in the retort. 
 
 The older plan of preparing oil or fat varnishes with hard 
 resins is still that usually adopted ; but it yields products 
 which are darker in colour than those obtained by the 
 method just described, as the copal or amber used has 
 been previously heated or even fused, whereby it has lost one 
 quarter of its weight. One way of carrying out this plan 
 consists in melting the copal in one vessel, and heating the 
 oil until it commences to give off small bubbles in another ; 
 then half the oil is poured in a very thin stream into the 
 melted resin, and incorporated therewith by constant stirring. 
 
COPAL VARNISH 
 
 119 
 
 Complete union having been effected between the two 
 materials, the mixture is incorporated with the remainder 
 of the hot linseed oil, any portions adhering to the vessel 
 being afterwards dissolved by means of oil of turpentine ; 
 30 parts of melted copal, 100 parts of linseed oil, and 70 
 parts of oil of turpentine, are proportions often employed 
 in carrying out the process we are describing. This process 
 may now be completed by adding to the solution of copal 
 in linseed oil £ of a part of manganese borate, stirring con- 
 tinually, and heating for two hours, or until the solution has 
 acquired the character of a thick gold-coloured syrup which 
 can be drawn out into threads. This point having been 
 reached, the heating is discontinued, and the contents of 
 the boiler allowed to cool to 6o° or 70 C, and then is 
 added the warm oil of turpentine which has been used to 
 dissolve out any of the copal solution clinging to the vessel 
 in which that resin was melted. Finally, the remainder of 
 the oil of turpentine is very gradually introduced with con- 
 stant stirring. Copal varnish prepared in the above manner 
 ought to dry in twelve hours or sooner. It is scarcely 
 necessary to say that this method of preparing varnish with 
 copal or other hard resin is one that no inexperienced 
 person should attempt ; not only is there some chance of 
 partial or total failure, but there is serious risk of fire. An 
 easier and less dangerous process requires a specially con- 
 structed heater, which is kept hot by a water-bath. Melted 
 copal, copal or amber oil, ' manganese ' oil, and oil of tur- 
 pentine, are the materials used. They are all introduced 
 together, and, as the temperature during the process of co- 
 hobation does not exceed ioo° C, the time required is 
 greater than in the previously described process. 
 
 A good copal or amber varnish ought to leave a film (on 
 a sheet of glass) which combines the qualities of hardness 
 

 1 20 MEDIUMS FOR OIL-PAINTING 
 
 and toughness. The toughness is given by the oil, the 
 hardness by the resin. Such a film should not become 
 fissured even when it has been exposed to sunshine during 
 a year. Much of the copal varnish of commerce is not 
 made from true copal or anime at all, kowdi or kauri resin 
 (from Dammara australis), which is much easier to dissolve, 
 being employed instead — the product, however, is decidedly 
 inferior. Sometimes several resins are mixed together in 
 the preparation of a so-called copal varnish. A guarantee 
 of genuineness, in which the name or names and propor- 
 tions of the resin or resins employed is inserted, should 
 always be demanded when buying copal varnish. This 
 ought to be furnished by the varnish-maker himself, for 
 artists' colourmen rarely prepare oil-varnishes themselves. 
 
 For the general use of painters in oil nothing more is 
 wanted than true copal or amber oil-varnish, a drying oil, 
 and a diluent. Of these three liquids a mixed medium in 
 general use is compounded by taking equal measures of the 
 three — varnish, oil, spirits of turpentine — and mixing them 
 together in small quantities as required. But considering 
 the large quantity of oil already associated with oil-pigments 
 and present in copal or amber oil-varnish, one-third of oil 
 in the medium seems a somewhat high proportion. I have 
 proved by numberless experiments that it may be reduced 
 with perfect safety to the permanence of the picture, although 
 the manipulation and technique of a painter may demand 
 the peculiar quality in a medium which oil in considerable 
 proportion can alone supply. A formula which answers well 
 is this : 
 
 2 measures of copal oil-varnish made from Sierra Leone 
 or Zanzibar copal ; 
 
 1 measure of poppy oil ; 
 
 2 measures of oil of turpentine or oil of spike. 
 
MEDIUMS FOR OIL-PAINTING 
 
 By substituting linseed oil for the poppy oil a more quickly- 
 drying medium is obtained ; still more rapid drying is 
 secured by means of ' manganese ' oil. With the same 
 object in view, benzene may be used instead of oil of 
 turpentine. This latter ought, of course, in all cases, to be 
 one of the least resinifiable varieties obtainable. 
 
 If an amber or copal varnish containing no oil be avail- 
 able, a good medium may be prepared by mixing 3 measures 
 of it with 2 measures of poppy or linseed oil, and 1 measure 
 of oil of turpentine or of spike. 
 
 Bell's medium contains no resin, but consists of thickened 
 linseed oil dissolved in oil of spike. To prepare it, pure 
 linseed oil may be oxidized by having a current of warm, 
 moist air passed through it until it has acquired the con- 
 sistence of fresh honey : this change occurs slowly when a 
 layer of oil is exposed to the air in a large flask, the mouth 
 of which is lightly plugged with carded cotton. The flask 
 should be shaken occasionally to mix its contents, and 
 to prevent the formation of a pellicle on the surface of 
 the oil. 
 
 Paintings executed with this thickened oil medium do 
 not acquire the hardness and solidity of those carried out 
 with a vehicle containing a hard resin. 
 
 Roberson's medium has now been in use for something 
 like sixty years. It has been and is a favourite vehicle with 
 many distinguished artists. A substitute for it is sometimes 
 prepared in the studio by mixing and warming together strong 
 copal varnish, poppy oil or linseed oil and a trace of white 
 wax. 
 
 Of megilp — a mixture of linseed oil and mastic varnish — 
 it is only necessary to say this : that however agreeable as a 
 medium with which to work, it contains a poor and weak 
 resin, which becomes in course of time yellow and brittle, 
 

 llllsh •'<%%&* 
 
 122 SPIRIT-FRESCO MEDIUM 
 
 and is liable to be injuriously affected when a picture, in 
 which it has been used freely, is cleaned. 
 
 For painting in oil on plaster, slate, or stone, a perfectly 
 sound and convenient medium is made by warming 1 2 ounces 
 of oil of spike, or of non-resinifiable oil of turpentine in a 
 glass flask plunged in water heated to the boiling-point, and 
 then pouring into it in a slender stream 4 ounces by 
 weight of paraffin-wax (melting-point about 58 to 62 C), 
 or of ceresin, or of a mixture of these materials. The mix- 
 ture becomes perfectly clear if it be thoroughly agitated and 
 maintained at a temperature of 8o° C. Then 20 measured 
 ounces of ' picture '-copal varnish, or 16 ounces of oil-copal 
 varnish, are slowly added, with constant shaking, in the 
 same way. It is of the highest importance that the copal- 
 varnish used should contain a sufficiency of oil. If a thin 
 varnish with much terpene be employed in preparing this 
 medium the pigments may lack coherence. I have found 
 this defect counteracted by using pigments ground in in- 
 spissated or blown linseed oil, rather than in the medium 
 itself. The ' paraffin-copal ' medium thus obtained may be 
 diluted with oil of turpentine exactly to the same extent as 
 recommended by the late Mr. Gambier-Parry, in the case 
 of his ' spirit-fresco ' medium, and may be used in the same 
 way and for the same purpose. Paintings executed with 
 this medium present a perfectly dead or matt surface without 
 the least shine. This medium is superior to that used in 
 spirit-fresco, for it contains neither elemi-resin nor wax, the 
 two doubtful constituents of the latter preparation. 
 
 Mr. Gambier-Parry's medium, to which reference has just 
 been made, is prepared with five ingredients. The original 
 instructions are unnecessarily complicated, and may be 
 simplified while keeping to the original proportions, and 
 without modifying the nature of the product in the slightest 
 
SPIRIT-FRESCO MEDIUM 
 
 123 
 
 degree. Eight ounces of oil of spike are warmed in a glass 
 flask to 8o° C, then 2 ounces by weight of elemi are added, 
 the mixture being warmed and shaken till the elemi has 
 dissolved. Some dirt and woody fragments are sure to be 
 introduced with the elemi, and so the solution (still warm) 
 must be filtered. Upon the filter, when all the liquid has 
 run through, 2 ounces by measure of oil of turpentine, 
 heated to 8o° C, are now poured, and the united filtrates 
 are thoroughly mixed. The liquid is then introduced into 
 a flask, and heated to 8o° C. ; then 4 ounces by weight of 
 pure white wax (previously melted) are poured in a thin 
 stream into the solution of elemi and thoroughly shaken. 
 When the commixture is complete, 20 ounces by measure 
 of 'picture '-copal varnish, or 16 ounces of oil-copal varnish, 
 are gradually introduced with constant agitation. The 
 water surrounding the flask is now made to boil, and kept 
 boiling for five minutes. The flask is withdrawn, wiped 
 dry, and allowed to cool. As the cooling proceeds the 
 flask is gently agitated from time to time. When the 
 mixture begins to get treacly in consistence it is at once 
 poured into the bottles (bottles with wide mouths, holding 
 4 ounces apiece, are convenient) in which it is intended to 
 preserve the medium for use. The dilution of this medium 
 and the mode of using it are described in Chapter XXIII. 
 on Painting Methods. 
 

 ■ 
 
PART III 
 
 PIGMENTS 
 
 Chapter XIII. —White Pigments. Chapter XIV.— Yellow Pigments. 
 Chapter XV. — Red Pigments. Chapter XVI. — Green Pigments. 
 Chapter XVII.— Blue Pigments. Chapter XVIII.— Brown Pig- 
 ments. Chapter XIX. — Black Pigments. Chapter XX. — Classifi- 
 cation of Pigments. Chapter XXI. — Tables of Permanent and 
 Fugitive Pigments. Chapter XXII. — Selected and Restricted 
 Palettes. 
 
lunH 
 
CHAPTER XIII 
 
 WHITE PIGMENTS 
 
 Flake- White : White Lead— Ceruse — Blanc d 'Argent — 
 Blanc de Plomb — Bleiweiss — Kremserweiss. 
 
 White lead was known to the ancients. A face-powder or 
 cosmetic, found, in its original pottery-box of about B.C. 400, 
 in the neighbourhood of Athens, proved to be a mixture 
 of white lead and whitening. Theophrastus, Pliny, and 
 Vitruvius describe its manufacture from lead and vinegar. 
 It was designated by several names, such as cerusa, cerussa, 
 cerosa, psimuthion. In the first half of the fourteenth 
 century it is mentioned as ' minium album.' It has been 
 called by divers names after the place or method of its 
 manufacture, or after persons who have devised special pro- 
 cesses for preparing it. 
 
 White lead still continues to be made for the most part 
 by processes which are essentially identical with the old 
 method, now generally known as the ' Dutch ' process. 
 This consists in attacking metallic lead, in the form of 
 ' crates,' ' grids,' or spirals, simultaneously by acetic acid, 
 carbonic acid, atmospheric oxygen, and water-vapour. The 
 metal is gradually converted into a mixture or compound 
 of lead carbonate and lead hydrate. Other processes, 
 generally yielding an inferior product containing more 
 carbonate and less hydrate, have been used. One of these 
 
rara&sit' 
 
 .; 
 
 
 S3 ■;:/•'<":' .''• 
 
 '■■■■"■-■■—■•■••■•- 
 
 128 
 
 FLAKE-WHITE 
 
 consists in passing a current of carbonic acid gas through 
 a solution of lead subacetate ; in another, 4 parts of litharge, 
 1 part of common salt, and 16 parts of water, are kept in 
 contact for some hours with constant agitation, and then 
 carbonic acid gas is led into the mixture until it becomes 
 neutral to test-papers. 
 
 The best white lead contains two molecules of lead 
 carbonate intimately associated with one molecule of lead 
 hydrate, and is represented by the formula 2PbC0 3 ,PbH 2 2 . 
 This formula corresponds to about 70 per cent, of lead 
 carbonate, and 30 per cent, of lead hydrate. If the propor- 
 tion of hydrate rise above this percentage, the opacity of 
 the paint is lessened seriously; if it fall much below the 
 above-named figure, the binding-power and working quality 
 of the white lead are impaired. It is scarcely necessary to 
 say that the metallic lead used in the manufacture should 
 be as nearly pure as possible, such, for instance, as the lead 
 from the Upper Hartz, which contains but 2 parts of 
 foreign metals per 1,000. These foreign metals, the presence 
 of any one of which in sensible quantity may cause a dis- 
 coloration of the product, are copper, bismuth, silver, 
 cadmium, antimony, nickel, and, more particularly, iron. 
 But not only must the raw material be pure, but it is 
 necessary to guard against the contamination of the white 
 lead, during its manufacture, by dust or sulphuretted 
 gases. 
 
 The impurities and defects of white lead are (1) accidental, 
 (2) intentional. 
 
 (1) Of the accidental impurities and defects of white lead 
 made from pure metal, the following are the chief : 
 
 a. Metallic lead, imparting a gray hue to the product. 
 
 b. Massicot or litharge, the yellow oxide of lead. 
 
 c. Minium or red lead, which gives a rosy hue. 
 
WHITE LEAD 
 
 129 
 
 d. Excess of lead hydrate, which causes translucency. 
 
 e. Excess of lead carbonate. 
 / Lead acetate. 
 
 A simple experiment will suffice to show whether lead 
 acetate be present in objectionable proportion in any sample. 
 Some of the dry pigment is to be ground with distilled water 
 into a paste, thrown on to a wetted filter and then washed 
 with freshly-boiled distilled water. The clear filtered liquid 
 should give nothing more than a slight cloudiness on the 
 addition of a little dilute sulphuric acid. Some samples of 
 flake-white which had been insufficiently washed contained 
 from 2 to 1 1 per cent, of lead acetate removable by distilled 
 water. In order to ascertain whether the lead carbonate 
 and lead hydrate exist in due proportion in a sample of 
 white lead, a weighed portion of the dry pigment, after 
 having been dried at 2 1 2 F., should be carefully roasted in 
 a current of dry air, and the water evolved (2 to 3 per cent.) 
 intercepted by means of a weighed calcium chloride absorp- 
 tion tube. This operation, however, requires much manipu- 
 lative experience, and, unless accurately performed, may 
 lead to erroneous conclusions. 
 
 (2) Of the intentional adulterations of white lead the 
 following are the most usual : 
 
 a. Heavy spar, that is, native barium sulphate ; or 
 
 the same compound artificially prepared (per- 
 manent white, blanc fixe). 
 
 b. Gypsum. 
 
 c. China-clay. 
 
 d. Whitening or chalk. 
 
 e. Lead sulphate. 
 
 The first of these adulterations is by far the most usual. 
 
 9 
 
aM H § g i i gS| 
 
 mm '" >: Hw WHWi 
 
 130 
 
 WHITE LEAD 
 
 Barium sulphate, in the form of finely-ground barytes, or 
 heavy spar, is the material employed on the large scale for 
 cheapening the cost of production of ordinary white lead ; 
 precipitated, that is, artificially-prepared, barium sulphate is 
 used in the case of the finer makes of this pigment. In 
 either case the sophistication is very readily recognised. 
 Pure flake-white, for example, loses 14^ per cent, of its 
 weight when strongly heated so as to drive off its carbonic 
 acid and water, but ' Venice ' white, which is white lead and 
 barium sulphate mixed in the proportion of equal parts, 
 loses, under such treatment, no more than 7*3 grains per 
 100. 'Hamburg' white, with 33 per cent, only of white 
 lead, loses 4/8 per cent., and ' Dutch ' white, of which three- 
 fourths are barium sulphate, gives off no more than 3-8 per 
 cent. ' Crems,' or ' Cremnitz ' white, is, or ought to be, pure 
 white lead. The complete solubility of pure white lead in 
 dilute nitric acid may also be made use of to detect the 
 presence of barium sulphate, which will remain undissolved 
 as a dense white powder. The adulterations with gypsum, 
 china-clay, whitening and lead sulphate, can be recognised 
 only by further tests. Gypsum, for instance, gives off water 
 when heated, and 1 part of it dissolves in 420 parts of water. 
 China-clay also gives off water when heated, but is insoluble 
 in water, and only slightly soluble in nitric acid. Whitening 
 dissolves in all mineral acids, but lead sulphate is practically 
 insoluble. After all, the detection of barium sulphate is the 
 only point with which the painter need concern himself. It 
 will therefore suffice if he ascertain that a sample of white 
 lead is of first-rate colour and body, contains no sensible 
 quantity of lead acetate, loses when heated 14^ per cent, of 
 its weight, and dissolves perfectly in dilute nitric acid. 
 
 It has been observed that white lead is less liable to be 
 blackened by sulphuretted hydrogen and by other sulphides 
 
WHITE LEAD 
 
 131 
 
 when it contains a small quantity of baryta-white, or of lead 
 sulphate thoroughly incorporated with it by grinding. This 
 observation opens the door to adulteration, it is true : and it 
 is perhaps wiser to rely upon the protection furnished by 
 resinous mediums and a final coat of mastic varnish rather 
 than upon any admixture with other white substances. 
 
 The drawbacks attendant upon the use of white lead as 
 a paint are its poisonous character, its sickly and noxious 
 smell when used with oil, and its liability to discolour when 
 exposed to sulphuretted hydrogen or any sulphide soluble 
 in water. On the other hand the quality of the whiteness 
 of the best flake-white is unimpeachable : the paint works 
 admirably in oil, and has great body ; moreover, flake-white 
 not only mixes perfectly and safely with the majority of 
 permanent pigments, but it serves to impart to slow-drying 
 colours its own strongly siccative character. Besides all 
 these merits white lead possesses a valuable property, which 
 has scarcely been clearly recognised or duly appreciated. 
 For when an old oil-picture is carefully examined, it will 
 generally be found that if any portion of its surface (of the 
 paint, not the varnish) show decided contractions and 
 cracks, these are precisely those portions into which white 
 lead has entered in smallest proportion, if at all. The most 
 translucent parts, the rich glazings and the deepest shadows 
 may be fissured, but not the high lights : examples illustra- 
 tive of this point are referred to in Chapter XXIV. of the 
 present volume. This property of white lead seems to 
 depend upon a combination taking place between a part 
 of the oil with which it is ground and a part of the lead 
 hydrate which it contains. A kind of lead-soap (lead lino- 
 leate) is thus formed ; this compound imparts a degree of 
 toughness and elasticity to those films of oil paint into 
 which lead-white enters to any considerable extent. A very 
 
 9—2 
 

 
 132 
 
 WHITE LEAD 
 
 pretty and instructive experiment which has been adduced 
 to prove the formation of this lead-soap is made thus. On 
 a sheet of glass a smear of flake-white in oil is spread ; then 
 a few drops of weak sulphuric acid (10 per cent, of the real 
 acid) are mixed thoroughly with it by means of a glass rod 
 or glass spatula. The whole may be easily incorporated 
 into a cream-like mixture, for the acid decomposes the lead- 
 soap and destroys the oily or hydrofuge character of the 
 paint. No such commixture of acid can be made with zinc 
 white in oil, or baryta-white in oil, for in these paints the 
 oil has not been saponified. 
 
 Although the above experiment appears to confirm the 
 opinion that a lead-soap is really present in flake -white 
 ground in oil, yet the existence of such a combination has 
 been disputed on what I believe to be insufficient grounds. 
 
 Flake-white becomes brown, grey or black when exposed 
 to the action of sulphuretted hydrogen, ammonium sulphide, 
 or any metallic sulphide soluble in water. This discolora- 
 tion, which is due to the formation of lead sulphide, occurs 
 more readily in the presence of moisture : it is favoured by 
 darkness to such an extent that a piece of perforated card- 
 board laid upon a dry oil-painted surface of white lead will, 
 after a few weeks' exposure, give a white pattern on a buff 
 ground. But, after the removal of the perforated card and 
 subsequent exposure of the painted surface to strong light, 
 this pattern will disappear, the coloured sulphide of lead 
 being oxidized into the white sulphate. The same change 
 may be more speedily brought about by means of a solution 
 of hydrogen peroxide. By laying a sheet of white filter- 
 paper soaked in this liquid upon the discoloured lead- 
 priming of a prepared canvas the original colour of the paint 
 may be gradually brought back, especially by the aid of a 
 moderate degree of warmth. This method is not available 
 
LEAD SULPHATE 
 
 133 
 
 in the case of drawings or water-colour paintings in which 
 flake-white has blackened ; but even these may often be 
 successfully treated by exposure to moist ozone, or by light 
 touches of a solution of hydrogen peroxide in ether. Old 
 silver-point drawings, in which the lights were heightened 
 with lead-white, may sometimes be thus restored to their 
 pristine state. 
 
 The specific gravity of the best flake-white is 6"6; 100 
 parts by weight of it require from 11 to 15 parts of linseed 
 oil in order to form an oil-paint of suitable consistence. It 
 is sometimes ground with poppy oil when a particularly 
 pure white product is demanded. The yellowish tint of 
 some makes of white lead is occasionally neutralized by the 
 addition of a trace of indigo or of artificial ultramarine. 
 Burnt or roasted white lead is sometimes used as a pigment. 
 It is of a cream-colour, a buff, or a pale yellowish salmon, 
 according to the temperature at which it has been prepared, 
 or the length of time during which it has been heated. 
 
 Lead Sulphate. — Many attempts have been made to 
 utilize the sulphate of lead (PbS0 4 ) as a pigment. This 
 compound, which is nearly insoluble in water and in dilute 
 acids, is almost, if not entirely, destitute of poisonous pro- 
 perties owing to this insolubility, although as ordinarily pre- 
 pared it possesses neither the pure whiteness nor the body 
 of white lead. But under the name of Freeman's white 
 lead, or non-poisonous white lead, a paint has been intro- 
 duced which may prove a rival to ordinary white lead. It 
 is essentially lead sulphate, and is prepared by precipitating 
 lead acetate solution with sulphuric acid. But this precipi- 
 tate is subjected to a special process of grinding with small 
 quantities of zinc white and barium sulphate, and acquires 
 thereby a considerable increase of density and opacity. 
 Being, when ground in oil, not only destitute of the dis- 
 
E|Mj^^i^^^^5^p 
 
 wBSSSS&S&B i 
 
 134 
 
 ZINC-WHITE 
 
 agreeable smell of white lead, but much less readily darkened 
 by sulphuretted hydrogen, Freeman's white possesses dis- 
 tinct advantages in these respects over the more common 
 paint. It may be mixed with other permanent pigments 
 without injuring them : it is practically non-poisonous. On 
 the other hand, it does not possess the remarkable harden- 
 ing and drying powers of white lead. 
 
 Lead Oxychloride. — Pattinson's white (PbClHO) does not 
 possess any advantage, as a white pigment for artists' use, 
 over the ordinary flake-white. Similar verdicts may be pro- 
 nounced as to the eligibility of several other white com- 
 pounds of lead, such as the sulphate, the antimonite, the 
 antimoniate, and the tungstate of this metal. 
 
 The blanc d'argent of the French is supposed to be pure 
 lead carbonate free from any hydrate, but the great majority 
 of the specimens which I have examined are nothing but 
 flake- white of good quality. For general use as a white pig- 
 ment, both alone and in admixture, the best flake-white, 
 with all its defects, presents distinct advantages over pure 
 lead carbonate free from lead hydrate. 
 
 Zinc-white : Chinese white — Blanc de Zinc — Zinkweiss. 
 
 The substitution of carbonate of zinc for white lead seems 
 to have been first suggested by Courtois of Dijon in 1787. 
 After several unsuccessful attempts to introduce either the 
 carbonate or the oxide as an oil paint, the latter began to 
 be used about 1849-50, shortly after Leclaire had shown 
 how to prepare an oil suitable for making the paint dry. 
 We believe that it had been frequently employed as a water- 
 colour many years before 1849. So early as 1834 Messrs. 
 VVinsor and Newton prepared a peculiarly dense form of 
 this pigment under the name of Chinese white. 
 
ZINC- WHITE 
 
 135 
 
 For the preparation of the best zinc-white it is essential 
 that the zinc be pure ; especially should it be as free as 
 possible from the metal cadmium. The zinc is heated to 
 the distilling-point in crucibles or retorts set in a furnace ; 
 the vapour, meeting with air, burns into the white oxide, 
 which condenses in a series of chambers. The contents of 
 these chambers vary somewhat in purity of tint; the presence 
 of some metallic zinc generally imparts a greyish hue to the 
 zinc oxide nearest the crucibles or retorts. By selecting the 
 densest and whitest product, and then submitting this to 
 powerful mechanical compression when red-hot, an excellent 
 pigment having a dense body is obtained. Zinc-white pre- 
 pared in the wet way, as by the action of lime-water upon 
 zinc chloride, is inferior in substance to that made as above 
 described, while that obtained directly from blende is of bad 
 colour. 
 
 As an oil-paint, zinc-white is a bad dryer. Instead of 
 being ground in raw poppy or linseed oil, an oil rendered 
 highly siccative by borate of manganese should be employed. 
 In spite of its unquestionable merits, zinc-white in oil can- 
 not be recommended as a complete substitute for flake-white. 
 When used freely, it often shows a tendency to crack and 
 scale, besides becoming with age more translucent, or rather, 
 less opaque. For water-colour painting, tempera, and for 
 fresco, zinc-white is practically perfect, being unchangeable 
 in hue or opacity under the most adverse influences. Paper 
 washed with zinc-white, either alone or tinted with a coloured 
 pigment, affords a good ground for silver-point, platinum- 
 point, or pencil drawings. There is a peculiar ' tooth ' in 
 the zinc-white which freely brings off the metal or graphite 
 from the pencil, and serves to fix it on the prepared surface. 
 
 The purity of zinc-white is easily tested. Heated in a 
 tube, it should yield no volatile product, and should suffer 
 
i|p^^ ||§|||§| w* : ^m WbBBHsBw ^^H 
 
 136 
 
 BARYTA-WHITE 
 
 no permanent change of hue. It should dissolve completely 
 without effervescence in boiling dilute nitric or hydrochloric 
 acid. If, on heating, it acquires a permanent yellowish hue, 
 giving off moisture at the same time, white lead is probably 
 present. If it does not dissolve completely in acid, it pro- 
 bably contains barium sulphate ; if effervescence occurs 
 during solution, either whitening, . or white lead, or zinc 
 carbonate is present. Zinc carbonate, however prepared, is 
 inferior in whiteness and body to the oxide. 
 
 Zinc sulphide has been prepared as a paint ; its liability 
 to evolve sulphuretted hydrogen renders its use as an 
 artists' pigment dangerous, for there are several other 
 colours upon which it would exert a deleterious action. It 
 has very considerable body. 
 
 
 Baryta-white: Permanent white- 
 . Weiss. 
 
 -Blanc Fixe — Permane?it 
 
 The mineral known as heavy spar, or barytes, has been 
 used as a white paint, particularly as an adulterant for white 
 lead. However finely it may be ground, it is always very 
 inferior in body and covering-power to the artificially-pre- 
 pared barium sulphate. To make this, a cold solution of 
 barium chloride of specific gravity 1*19 is prepared, and to 
 it is gradually added in the cold, and until no further pre- 
 cipitate is formed, dilute sulphuric acid of 1*245 specific 
 gravity. The barium sulphate is washed with cold water 
 until the wash-waters are entirely free from acid ; for many 
 purposes to which the product is applicable (fresco and 
 tempera painting) it should be kept under water. 
 
 Baryta-white is absolutely unalterable by an impure at- 
 mosphere, and is without action upon other pigments. It 
 does not work well in oil, but a mixture of flake-white 
 and baryta-white, in the proportion of 2 to 1, presents the 
 
MINOR WHITE PIGMENTS 
 
 137 
 
 advantage of being very much less affected by sulphuretted 
 hydrogen than flake-white. 
 
 The artificial baryta-white may be distinguished from the 
 natural by its much finer state of division, by its greater 
 body, and by the purity of its whiteness. Baryta-white is 
 not adulterated, but its almost absolute insolubility in hydro- 
 chloric or nitric acid enables it to be at once distinguished 
 from zinc-white or white lead. 
 
 Several mixtures of barium sulphate and zinc sulphide 
 have been introduced as pigments ; they are not suitable 
 for the palette of the artist. The reaction by which the 
 majority of them are formed is brought about by mixing to- 
 gether solutions of two soluble salts, barium sulphide (BaS) 
 and zinc sulphate (ZnS0 4 ), when two new salts are pre- 
 cipitated, both insoluble, namely zinc sulphide (ZnS) and 
 barium sulphate (BaS0 4 ). 
 
 Other white compounds used in painting are lime, 
 whitening, gypsum and China-clay. These have been con- 
 sidered in the chapter on Painting-Grounds. Amongst 
 white pigments which we need not describe are antimonious 
 oxide, antimonious oxychloride, lead sulphite, lead tungstate, 
 lead antimonite, and lead antimoniate. Not only are these 
 compounds difficult to prepare in a satisfactory condition of 
 purity and whiteness, but they are liable to turn yellow or 
 dull in impure air. 
 
 It should be stated here that the tests described in the 
 present chapter, and in all the other chapters on pigments, 
 can be tried only after the removal of the vehicle with which 
 they have been ground. Oil may be removed by means of 
 benzene or turpentine-spirit, gum by treatment with distilled 
 water. 
 

 CHAPTER XIV 
 
 YELLOW PIGMENTS 
 
 Yellow Ochre : Roma?i Ochre — Golden Ochre — Mineral 
 Yellow — Broivn Ochre — Oxford Ochre — Ocre jaune — 
 Gelber Ocker. 
 
 The distinction between the yellow ochres and the red 
 ochres, whether natural or artificial, depends upon a per- 
 fectly definite chemical difference. The colour of every one 
 of these pigments is due, indeed, to iron, and to iron in the 
 same state of oxidation ; but the iron oxide in the yellow 
 and brown ochres is chemically united to water, while in the 
 red ochres it is nearly or quite anhydrous — that is, dry. In 
 chemical language, then, we may say yellow ochre is a ferric 
 hydrate, red ochre a ferric oxide. But, when we proceed to 
 examine a number of samples of yellow ochre, we find, not 
 merely different proportions of ferric oxide to combined 
 water — that is, different ferric hydrates — but we find also 
 very variable proportions of intruding or accessory consti- 
 tuents. In fact, yellow ochre represents not less than three 
 mineral species, and it occurs associated with many im- 
 purities, the latter consisting mainly of silica, of clay, of 
 rocky debris, with traces of gypsum, of iron or copper pyrites, 
 and of humus or peaty acids. There are, moreover, ochres 
 in which other compounds occur, as barium sulphate to the 
 extent of 75 per cent, in some American varieties. The 
 
YELLOW OCHRE 
 
 139 
 
 three fundamental minerals, in order of frequency, which 
 may be traced in various yellow ochres, are these : 
 
 Brown haematite, or limonite, consisting of two molecules 
 of ferric oxide combined with three molecules of water, and 
 represented by the formula 2Fe 2 3 , 3H 2 ; 
 
 Yellow Haematite, or xanthosiderite, consisting of one 
 molecule of ferric oxide combined with one molecule of 
 water, and represented by the formula Fe 2 3 , H 2 ; 
 
 Bog-iron ore, or lymnite, consisting of one molecule of 
 ferric oxide and three molecules of water, and represented 
 by the formula Fe 2 3 , 3H 2 0; the separate existence and 
 permanence of a hydrate having this formula are, it must 
 be owned, doubtful. 
 
 It is probable that all the numerous varieties of yellow 
 ochre, from the countless localities of this substance, belong 
 essentially to one or other of the above species of iron 
 minerals, although the frequent presence of such impurities 
 or accessories as silica, iron silicates, and clay renders the 
 identification very difficult. Moreover, there are reasons 
 for suspecting, in some ochres at least, the presence of 
 another and more complex compound, namely, a distinct 
 double iron-aluminium hydrate. 
 
 An analysis of a fine sample of yellow ochre, from a pit 
 on Shotover Hill near Oxford, gave the following percent- 
 ages : 
 
 Hygroscopic moisture 
 
 - 7-i 
 
 Magnesia 
 
 - 0-3 
 
 Combined water 
 
 - 9-0 
 
 Silica 
 
 • 61 -5 
 
 Ferric oxide 
 
 " 1.3 "2 
 
 Calcium sulphate 
 
 - 1*4 
 
 Alumina - 
 
 - 6-3 
 
 Undetermined 
 
 ■ I '2 
 
 The varying hues of yellow ochres depend mainly upon 
 two differences of composition. One of these is the amount 
 of white clay, silica, calcium sulphate, or barium sulphate 
 
■...;:,.-.;-,,.: 
 
 ■ 
 
 140 
 
 YELLOW OCHRE 
 
 present in them — this lightens the colour ; the other is the 
 presence of ferric oxide, which gives them a ruddier or 
 warmer hue. All, when burnt — that is, calcined — lose their 
 essential water, and become converted into various kinds of 
 red ochre, light red, etc. The varieties which contain much 
 silica and clay (ingredients which, even in good yellow 
 ochres, often amount to two-thirds of their weight) yield the 
 less translucent and paler tints of some of the burnt red 
 ochres. India furnishes a great variety of hues of yellow 
 ochre, but our chief supplies come from France, Italy, 
 Germany and Spain. More recently excellent ochres have 
 been obtained from the district of Dubbo in New South 
 Wales. Some of the English ochres (from Oxfordshire, 
 Derbyshire, etc.) are of fine quality. 
 
 Yellow ochre is generally prepared for use as a pigment 
 first of all by careful selection of the best pieces, and then 
 by the familiar process of elutriation, or washing over. 
 Thus it is at once freed from sand or other coarse particles, 
 and from any soluble salts which it may contain. Immedi- 
 ately before being ground in oil, it should, however, be 
 dried at a temperature a little below that of boiling water, as 
 it is liable to contain hygroscopic moisture in addition to its 
 necessary constitutional water. 
 
 Yellow ochre is one of the most ancient pigments, having 
 been used by the Egyptians, the Greeks, and the Romans. 
 It is the oichra of Theophrastus. Pots of yellow ochre were 
 found at Pompeii. It has stood, with very little change, the 
 test of centuries. It certainly does become, in all media, 
 but especially in oil, slightly darker and warmer in hue after 
 prolonged exposure to light. The change, however, is 
 slight ; moreover, it soon comes to a stop. It is probably 
 due in part to a slight loss of constitutional water from the 
 ferric hydrate, and in part to increased translucency. Yellow 
 
YELLOW OCHRE 
 
 141 
 
 ochre, so long as it is exposed to air and light, is not 
 darkened by sulphuretted hydrogen. It is without action 
 on other pigments, although the statement has often been 
 made, on quite insufficient grounds, that paints which are 
 damaged by contact with metallic iron are likewise damaged 
 by yellow ochre and by the red oxide of iron. For instance, 
 true Naples yellow is undoubtedly spoilt by contact with a 
 steel spatula, because the metal of the latter takes away 
 oxygen from, or ' reduces,' the lead antimoniate of which 
 the former consists. But such an action is impossible with 
 yellow ochre, for this iron compound is a stable substance, 
 containing already all the oxygen it can take up. It is 
 possible, notwithstanding, that ochre may injure the hue 
 of some lakes, such as yellow lake and crimson lake, by 
 replacing in part some of the alumina with which the 
 colouring matter is united. But as such lakes are worthless, 
 from their extreme instability when exposed to light, when 
 used alone, such probable action of ochre upon them need 
 scarcely be considered. With reference to the darkening 
 or embrowning of yellow ochre in oil, this change is in part 
 due to the change of the oil, of which this paint usually 
 contains as much as 43 per cent., and in part to an increase 
 in the translucency of the mixed paint. 
 
 Yellow ochre is little subject to adulteration, for it is too 
 cheap a pigment to make it worth while to substitute other 
 substances for it. But sometimes the golden and richer 
 coloured varieties have been found to have had their colour 
 enhanced by the addition of turmeric, or of certain other 
 fugitive or semi-permanent yellows of organic origin. The 
 majority of such additions may be detected by pouring a 
 little liquor amnionic mixed with spirits of wine upon some 
 of the ochre placed on a filter paper in a funnel : the liquid 
 passing through will be colourless if the ochre be genuine. 
 
.-■ : "■ - 
 
 tttwBUB 
 
 ■:'■' : '■ ■ .• :■:'■■■' / f g '■ - t jgffi 
 
 IgSSEBaEl 
 
 142 
 
 CADMIUM YELLOW 
 
 
 An ochre which when heated in a test-tube gives off, besides 
 water, fumes which partially condense into a coloured or 
 tarry matter on the glass, contains organic matter, naturally 
 present or artificially added, and is generally of inferior 
 permanence. Of late years a far more frequent adulteration 
 of yellow ochre is the addition of chrome-yellow — that is, 
 lead chromate. This adulteration may be detected by 
 boiling the suspected ochre with sodium carbonate solution, 
 filtering, and adding to the filtrate enough acetic acid to 
 neutralize it, and then a few drops of lead-acetate. A yellow 
 precipitate indicates the presence of a chromate. An arti- 
 ficial yellow ochre is made by acting upon solutions of iron 
 salts with metallic zinc, and thoroughly washing the precipi- 
 tate obtained. 
 
 Brown ochre is an approximately pure limonite : raw 
 sienna is very nearly related to it (see further on), but cologne 
 earth, raw umber, Caledonian brown and vandyke brown are 
 distinct substances. An artificial brown ochre is prepared 
 by heating yellow ochre with 4 per cent, of common salt to 
 a low red heat. 
 
 Under the name of cyprusite a peculiarly bright lemon- 
 coloured earth has been imported from Cyprus as a pig- 
 ment : it consists essentially of a hydrated ferric sulphate : 
 it is not likely to prove a safe pigment for artistic use. 
 
 Cadmium Yellow : Orient Yellow — Aurora Yellow — 
 Daffodil — Orange Cadmium — Sulphide of Cadmium — 
 Jaune Brillant—Jaune de Cadmium — Cadmium Gelb. 
 
 The metal cadmium, which is nearly related to zinc both 
 chemically and physically, was discovered by Stromeyer in 
 the year 181 7. To one compound only of cadmium, the 
 sulphide, are due all the hues and tints from the palest 
 lemon cadmium to the fiery orange-red. This compound is 
 
CADMIUM YELLOW 
 
 143 
 
 represented by the formula CdS, and contains 112 parts by 
 weight of cadmium to 32 parts of sulphur. As commonly 
 prepared, cadmium yellow is of an orange hue ; when this 
 compound separates slowly from a solution, or is made in 
 any way to take a dense or aggregated form, it becomes of 
 a decided reddish orange. The orange-yellow variety, when 
 very finely ground, becomes less red and more inclined to 
 yellow. Some of the palest cadmium yellows contain white 
 pigments, or flour of sulphur, added to reduce their depth 
 of colour : the presence of free sulphur is sufficient to make 
 any pigment ineligible. 
 
 There are two well-known processes for making cadmium 
 yellow. In one of these pure cadmium oxide is heated in a 
 covered crucible with pure sulphur in excess. In the other 
 process, which yields pigments of greater brilliancy and 
 beauty, a soluble salt of cadmium, such as the chloride or 
 sulphate, is precipitated in the presence of a little free acid, 
 by means of a solution of sodium sulphide, or preferably, of 
 a stream of sulphuretted hydrogen. The hue of the product 
 inclines to red when the solution is strong, hot and faintly 
 acid ; to yellow when it is weak, cold, and neutral. It is 
 necessary to state that all the materials used must be pure. 
 Iron, lead, bismuth, and any metals giving a coloured 
 sulphide, even in traces, are seriously detrimental to the 
 beauty of the product. The precipitate of cadmium sul- 
 phide, after having been thoroughly washed with boiling 
 distilled water until the wash-waters no longer redden blue 
 litmus paper, is collected on filter-papers and dried in the 
 water-oven. In order to remove any free sulphur that may 
 be present the dry cadmium yellow may now be digested 
 in a suitable vessel with pure carbon disulphide. After this 
 treatment the pigment is once more dried, and is then ready 
 for grinding in oil or other vehicle. Cadmium yellow, pre- 
 
WmmmmB mm HHH m 
 
 144 CADMIUM YELLOW 
 
 pared by the process last described, presents a satisfactory 
 degree of permanence, and has no action on white lead 
 when both pigments are ground together in oil. But a 
 curious change has been noticed when the orange-red 
 variety of this pigment, ground in oil, was kept some time 
 in the ordinary metallic collapsible tubes, which formerly 
 contained some lead, although of late years they have been 
 made of nearly pure tin. The interior surface of the tube 
 became darkened, sometimes almost black, from the forma- 
 tion of lead sulphide. It is certainly strange that a similar 
 action does not occur between white lead and these deep 
 cadmiums. For I found that the same sample of cadmium- 
 red in oil which had blackened the metallic tube, when 
 some of it was laid upon flake-white in oil, and kept for 
 years, had not darkened the lead compound anywhere, 
 even at the surface of contact. Moreover, cadmium yellows 
 mixed with flake-white prevent, as do many other substances, 
 such as baryta-white, lead sulphate, etc., the ready darken- 
 ing of this lead paint by sulphuretted hydrogen. On the 
 other hand, the cadmium yellows act with great energy 
 upon some of the pigments containing heavy metals. 
 Emerald green, for example, is rapidly ruined by cadmium 
 sulphide, both in water and in oil ; cadmium yellow and 
 emerald green (Schweinfurt green) are absolutely incom- 
 patible. Chrome yellow and true Naples yellow are also 
 darkened by admixture with cadmium yellow, at least after 
 a time. With oil colours, a sample of yellow ochre, which 
 was afterwards found to have been adulterated with chrome 
 yellow to the extent of 8 per cent., became yellowish-grey 
 after admixture with some cadmium yellow. 
 
 While the stability of what may be called the normal 
 cadmium yellow or orange is pretty well assured, both as 
 an oil and a water colour, a very different verdict must be 
 
CADMIUM YELLOW 
 
 145 
 
 pronounced upon pale and lemon cadmium when used in 
 water-colour painting. When thus used these pigments do 
 not merely fade, but acquire a somewhat greyish hue. The 
 following observations throw some light upon these changes. 
 During the year 1876 I prepared a number of samples of 
 cadmium yellow and orange. All were obtained by the 
 action of sulphuretted hydrogen upon solutions of cadmium 
 chloride. The products ranged in hue from a lemon colour 
 to a deep orange, according to the strength of the solution, 
 the presence or absence of free acid, and the temperature 
 at which the precipitation of the pigment took place. 
 After due washing and drying the various samples were 
 put into bottles and preserved in my laboratory. They 
 were never exposed to direct sunshine. On examining 
 them from time to time it was noticed that the specimens 
 of medium depth, having a yellowish orange hue, kept their 
 hue perfectly, while two or three of the orange-red varieties 
 exhibited a curious phenomenon of alteration. The loose 
 friable lumps into which the powder had aggregated were 
 distinctly paler on the outside than in the interior, while 
 the parts of the contents of the bottles which had been 
 most exposed to light were paler than those which had been 
 comparatively shaded. But a still more marked change 
 had taken place in the samples to which the term ' pale ' 
 cadmium might be applied. These had generally become 
 still paler, almost straw-coloured, especially where most ex- 
 posed to light ; but in some of the specimens orange specks 
 were observed, resembling in hue what is usually called 
 ' middle ' cadmium. From the above observations it would 
 seem that there is a tendency in differently tinted cadmium 
 yellows to return to what we may call the normal or medium 
 hue, but that the palest varieties are most subject to change. 
 This change seems to arise m part from oxidation and hydra- 
 
 10 
 
 
 ^ 
 
b^^P' lilslli 
 
 146 
 
 CADMIUM YELLOW 
 
 
 
 > r f 
 
 
 
 tion, for the bleached specimens gave indications of contain- 
 ing some white cadmium hydrate, when heated giving off a 
 little water, and becoming brownish from the formation of 
 the brown oxide of cadmium. Such a bleaching of pale 
 cadmium, if my explanation be correct, is in a measure 
 explicable if we recollect that this variety occurs in a very 
 fine state of division, and on this account is more liable to 
 chemical change. In water-colour painting, where there is 
 no effective protection through the presence of a hydrofuge 
 medium, this fading of pale cadmium is notorious. In oils 
 this cadmium, like the others, is practically permanent. I 
 regard the passage of the pale and of the deep cadmium 
 yellow when in powder into the normal or middle variety as 
 dependent chiefly, if not entirely, upon molecular changes. 
 Moreover, the pale cadmiums are rarely found free from 
 admixture, and their alterability may be in part owing to 
 the foreign ingredients they contain. More recent researches 
 by G. Buchner and N. von Klobukoff confirm the conclu- 
 sions drawn from my early experiments. There can be no 
 doubt that cadmium sulphide exists in two if not in three 
 molecular states, differing not only in colour but in crystal- 
 line form and in specific gravity. Thus pale cadmium has 
 the specific gravity 3^9 to 4/5, while the red modification is 
 denser — 4*5 to 4*8. And when the pale variety, dry and in 
 powder, is rubbed strongly with a piece of agate, its colour 
 deepens and reddens in a very decisive manner. The same 
 change occurs when a water-colour wash of cadmium yellow 
 is exposed for a year or so to sunlight in a perfectly dry 
 atmosphere. This phenomenon is clearly analogous with 
 that shown when the yellow mercuric iodide is altered into 
 the scarlet form by pressure. It is perhaps safer to employ 
 an ivory palette knife rather than one of steel in manipula- 
 ting the cadmium pigments. 
 
 
CADMIUM YELLOW 
 
 147 
 
 Aurora yellow is a bright and beautiful pigment consisting 
 essentially of cadmium sulphide. It has more opacity than 
 most of the other varieties of cadmium and possesses a pure 
 yellow hue. Its stability is greater than that of many other 
 varieties of this pigment. Daffodil yellow is the name given 
 to another variety of cadmium sulphide, prepared at a red 
 heat and containing a small quantity of magnesia. Neutral 
 orange is a mixture of cadmium yellow with Venetian red. 
 
 Cadmium yellows are sometimes adulterated with Indian 
 yellow, baryta and strontia chromates, and chromates of 
 lead. Indian yellow shows its presence by blackening and 
 giving off tarry fumes when the pigment, in the state of dry 
 powder, is strongly heated in a test-tube. The chromates 
 may be detected by the green colour produced when the 
 sample is warmed with alcohol and dilute sulphuric acid. 
 The lead chromates or chrome-yellows, and the orange and 
 red basic chromates of the same metal will blacken when 
 the substance in which they are present is moistened with 
 weak ammonium sulphide. Free sulphur in pale cadmium 
 yellows comes off as a vapour when the sample is heated, 
 but it may be better detected by the solvent action upon it 
 of carbon bisulphide. Baryta-white may be detected by its 
 insolubility in hot strong hydrochloric acid, in which cad- 
 mium sulphide dissolves. 
 
 Cadmium red and cadmium orange are slightly translucent 
 when compared with the paler and yellower varieties of this 
 pigment, and possess very full and glowing hues. They 
 work well as oil and water colours. Mixed with zinc-white 
 or flake-white, deep and middle cadmiums yield several 
 beautiful colours, some of which closely resemble the different 
 varieties of true Naples yellow, and are now employed very 
 largely in lieu of the latter pigment. Pure cadmium yellow, 
 when heated moderately, becomes orange-red or red, but 
 
:. BSSgJ 
 SBsKH 
 
 WS&k 
 
 iBBli&Il 
 
 
 148 A UREOLIN 
 
 regains its pristine hue on cooling. If, however, the heat 
 be considerably raised in the presence of air, some of the 
 sulphur in the compound burns, and the residual mass pre- 
 sents a dull brown colour. ' Manganese oil ' accelerates the 
 drying of the cadmium colours, which is sometimes incon- 
 veniently slow. 
 
 Aureolin : Cobalt Yellow — Jaune de Cobalt — Kobaltgelb. 
 
 Origin and Composition. — This remarkable artificial yellow 
 pigment was discovered by Fischer. It is a compound of 
 the nitrites of cobalt and potassium. Usually it is free 
 from water, but it sometimes contains three molecules, 
 and is then represented by the formula K 6 Co 2 (N0 2 ) 12 , 
 3H.,0. Other proportions of water also occur; but when 
 the compound contains four molecules, its hue is somewhat 
 greenish. The dry or anhydrous variety is best made by 
 mixing a solution of a cobaltous salt, strongly acidified with 
 acetic acid, with a concentrated solution of potassium nitrite, 
 and keeping the mixture warm. Perhaps a pigment of finer 
 hue is obtained by passing a stream of nitric oxide gas 
 mixed with air into a solution containing nitrate of cobalt 
 and a little acetate of potassium ; from time to time a little 
 potassium carbonate is added. 
 
 Another method of preparing a variety of aureolin having 
 a singularly bright yellow hue consists in adding a solution 
 of sodium cobaltinitrite acidified with acetic acid to a dilute 
 solution of potassium acetate or nitrate. I have tried the 
 experiment in accordance with the instructions given by 
 Messrs. Adie and Wood (in the 'Transactions of the 
 Chemical Society,' vol. lxxvii., 1900, p. 1076), but I have 
 used sometimes other cobalt salts instead of the acetate 
 and have also so arranged the constituents of the two solu- 
 tions that the precipitate of aureolin is intimately associated 
 
A UREOLIN 
 
 149 
 
 with barium sulphate precipitated at the same time. By 
 this means a mixed pigment of bright and light yellow hue 
 is obtained. The aureolin obtained by this process contains 
 sodium as well as potassium, and is represented by the 
 formula K 2 NaCo(N0 2 ) 6 ,H 2 0. Its value as a pigment is 
 at least equal to that of the better-known varieties of 
 aureolin. The pure pigment prepared in the way indicated 
 by Messrs. Adie and Wood requires less oil than usual and 
 dries well ; in water-colour painting it shows one distinct 
 advantage over the older varieties of aureolin, for it is less 
 soluble in water and does not sink into the paper. The 
 several varieties of aureolin are not much affected by caustic 
 potash solution or by dilute hydrochloric or nitric acid, 
 and are very slowly attacked and blackened by solution 
 of sulphuretted hydrogen, but are at once destroyed by 
 ammonium sulphide. Ordinary aureolin is slightly soluble 
 in cold water. 
 
 Aureolin is of a pure yellow colour, and is almost trans- 
 parent whether used in water or oil painting. In oil some 
 samples dry with great difficulty, and become very dirty if 
 exposed to the air during the progress of desiccation ; other 
 samples dry and harden too quickly — the exact cause of 
 this difference of deportment has not been ascertained. 
 Moreover, as ordinarily ground in oil, some varieties require 
 a very large proportion of the medium. These defects may 
 be easily remedied by heating the slow- drying variety of the 
 ground pigment to 212 F. immediately before the addition 
 of the oil, and by using, instead of raw linseed oil, the 
 siccative linseed oil, prepared by means of borate of man- 
 ganese. Thus prepared, aureolin not only dries quickly, 
 but it retains its purity of hue ; moreover, a surface of the 
 dried oil pigment will yield nothing to a wet cloth passed 
 over it instead of staining it yellow. The reason why this 
 
k mm ■' ■■■■■'■ mm s s ■■ im ■ ■■■ : bbm ■ ■ • 
 
 iSo 
 
 A UREOLIN 
 
 staining occurs with ordinary aureolin ground in oil, even 
 when it has at last become dry, is that the oil does not 
 suffice to protect the particles of pigment from the solvent 
 action of moisture. The quick-drying variety of aureolin 
 should be ground in poppy oil. 
 
 I find that the variety of aureolin which contains sodium 
 as well as potassium (see above) dries perfectly well when 
 ground in purified linseed oil, even when the latter has not 
 been made siccative by special treatment. 
 
 Aureolin properly prepared in oil, as described above, 
 does not fade by exposure to sunlight, nor does it darken, 
 except so far as the admixed oil is concerned. As a water- 
 colour aureolin is practically permanent, even in sunlight, 
 as the following figures show : 
 
 Original intensity ... 
 After two and five years 
 After ten years 
 
 10 
 
 10 
 
 9 
 
 In the Burlington Club trials it was found that aureolin 
 stood perfectly for four years when exposed in an ordinary 
 frame or in air kept dry, but that it lost somewhat by 
 exposure, during the same time, in a hermetically sealed 
 tube in the presence of ordinary moist air. 
 
 The fading of fugacious organic pigments, such as the 
 lakes from cochineal, is accelerated by their commixture 
 with aureolin, which particularly hastens the destruction of 
 indigo, even in oil. The aureolin cannot so act without 
 being itself likewise affected; it generally becomes, under 
 such circumstances, of a brownish hue. 
 
 It is easy to learn whether a sample of aureolin is free 
 from combined water by heating a small portion somewhat 
 strongly in a long test-tube ; dew will condense upon the 
 upper part of the tube if water be present in the pigment. 
 
LEMON YELLOW 
 
 I5i 
 
 The presence of yellow organic matters in imitative or adul- 
 terated aureolins may generally be detected by mixing some 
 powder of the suspected sample with spirits of wine and a 
 few drops of strong ammonia ; the liquid becomes red 
 orange, or yellow if the aureolin be not pure. Aureolin 
 containing chrome yellow is blackened by a solution of 
 sulphuretted hydrogen. 
 
 Aureolin is the first pigment described (in the presen 
 manual) which illustrates the remarkable colouring power 
 of the element cobalt. The hues derived from this meta 
 acting as a chromogen range from yellow to green, blue and 
 violet or purple ; there is also a rose cobalt. Various 
 oxides, themselves colourless, serve as chromophores. 
 
 Lemon Yellow : Baryta Yellow — Barium Chr ornate — 
 Yellow Ultramarine — Permanent Yellow— Jamie d 'Outre 
 mer. 
 
 Of all the chromates which have been used in painting, 
 barium chromate is the most stable. It has a pure yellow 
 colour, with a not inconsiderable degree of opacity. It 
 works smoothly. 
 
 Lemon yellow is often made by mixing solutions of 
 neutral potassium chromate and of barium chloride, both 
 liquids having been previously heated to ioo° C. A still 
 better plan is to take equivalent proportions — namely, 
 25I parts by weight of pure crystals of barium chloride and 
 2i| parts of pure crystals of neutral potassium chromate— of 
 these two compounds, and to grind them together to very 
 fine powder. Continue the grinding, and then add gradu- 
 ally sufficient pure water to convert the mixture into a thin 
 paste. The paste is then heated to ioo° for fifteen minutes, 
 thrown on a filter, washed with abundance of pure water, 
 dried, and ground. 
 

 
 sBuBy 
 
 152 
 
 GAMBOGE 
 
 Properly prepared lemon yellow may be mixed with most 
 other stable pigments without suffering change. It is not 
 blackened like the lead chromes by sulphuretted hydrogen, 
 but it has a tendency, as a water-colour, to become greenish 
 when long exposed to this gas or to impure air. In oils it 
 is very useful, for although some organic pigments may give 
 it a greenish cast by reducing it in part to green chromic 
 oxide, yet it may be safely associated with aureolin, with 
 madder carmine, and with Prussian blue. Lemon yellow 
 may be used in fresco. 
 
 Strontium chromate is very often — we may say generally — 
 substituted for true lemon yellow, but it is less stable, and has 
 the further defect (for water-colour work) of being decidedly 
 soluble even in cold water, so that light washes of it may be 
 found to sink into the paper and to partially disappear. 
 The most common adulteration of lemon yellow is with 
 pale chrome ; of course, sulphuretted hydrogen detects this 
 falsification by darkening or blackening the pigment. 
 Strontium chromate is distinguished from barium chromate 
 by its dissolving in boiling water to such an extent as to 
 yield a solution having a strong yellow colour. It may be 
 prepared in the same way as the chromate of barium. Zinc 
 chromate and calcium chromate are yellow pigments 01 
 inferior value. A mixture of zinc chromate with barium 
 chromate is sold as primrose yellow. 
 
 Gamboge : Gomme-gutte — Gummigutt. 
 
 Origin. — This gum-resin is produced by several species 
 of Garcinia. Siam gamboge comes from G. H anbury i 
 (Hook, f.) ; Ceylon gamboge from G. Morella (Desv.). 
 There are other species from which the same product is 
 obtained in various parts of India, as G. Cambogia (Desrouss.) 
 
GAMBOGE 
 
 153 
 
 and G. elliptica. The fine, deep-coloured gamboge, pro- 
 duced by the Burmese G. heterandra (Wall.), may prove to 
 be superior to Siam gamboge, but it has not yet become 
 an article of European trade. Gamboge is a mixture of a 
 gum soluble in water, and a resin which is soluble in alcohol, 
 chloroform, ether, etc. The pipe-gamboge of Siam, which 
 is as pure as any variety met with in commerce, contains 
 about 78 per cent, of resin and 18 of gum. The resin, 
 which is the true colouring-matter, may be easily obtained 
 pure by crushing pipe-gamboge into fine powder, mixing it 
 with a little water, and then shaking up the mixture with 
 ether; the ether dissolves the resin alone. From the ethereal 
 solution the colouring-resin is recoverable by evaporation ; 
 but it is better to add a little drying-oil and some copal- 
 varnish before driving off the ether by means of a very 
 gentle heat. The coloured, semi-fluid mass which then 
 remains may be preserved in bottles or tubes for use as an 
 oil-paint. The resin of gamboge has the properties of an 
 acid, and forms yellow, orange, or brown compounds, with 
 soda, lime, baryta, and other bases. Some of these com- 
 pounds might prove useful as paints. 
 
 Gamboge was used by the early Flemish oil-painters. In 
 the seventeenth century it was largely employed to give a 
 golden hue to the embossed leathers for which Amsterdam 
 was famous. 
 
 In water-colour painting gamboge is not trustworthy. It 
 is unaffected by sulphur compounds, but is darkened by 
 ammoniacal fumes, and slowly bleached by strong light. 
 Some samples prove, however, far less fugitive than others. 
 In two years' exposure to sunlight, one sample of cake- 
 gamboge lost more than half its original intensity ; while a 
 sample of moist gamboge, bought at the same time from 
 the same maker, retained nine-tenths. The same sample of 
 
4g£$$gg£c&£i 
 
 H 
 
 i54 
 
 INDIAN YELLOW 
 
 moist gamboge, after seven years, still showed seven degrees 
 out of the original ten of intensity. 
 
 As an oil-colour, gamboge affords a rich, transparent, 
 golden or amber hue; it has some claims to the con- 
 sideration of artists. To secure its permanence, admixture 
 with oil alone does not, however, suffice ; a resin such as 
 copal, or Strasburg turpentine, or wax, or paraffin, must be 
 used also. Some of Sir Joshua Reynolds' trials of gamboge 
 prove this, those with oil alone being a name only now ; 
 while those with resin, or wax, retain their original hue very 
 fairly, though they were spread upon the canvas in 1772. 
 It must, therefore, be remembered that reliance cannot be 
 placed upon the permanence of the ordinary gamboge oil- 
 paint as met with in commerce. 
 
 Gamboge, from its resinous nature, shows, when laid on 
 thickly as a water-colour, a rather shining surface. It appears 
 to have little or no chemical action on other pigments (with 
 the exception, perhaps, of white lead), although, if it be 
 mixed with anything which contains lime, or other alkaline 
 compounds, it becomes brownish, and darkens. Gamboge 
 forms beautifully clear and rich greens with Prussian blue or 
 indigo, but its place in water-colour painting may be advan- 
 tageously taken by aureolin, and even by Indian yellow. 
 When mixed with baryta yellow or cadmium yellow, the 
 permanency of gamboge is enhanced. 
 
 Indian Yellow : Piuri, Purree, Peori—Jaune Indien- 
 
 Indisch-zelb. 
 
 This remarkable pigment is obtained at Monghyr, a town 
 in Bengal, from the urine of cows which have been fed 
 upon mango-leaves. It generally occurs in the bazaars of 
 
INDIAN YELLOW 
 
 155 
 
 the Panjab in the form of large balls, having an offensive 
 urinous odour. 
 
 Indian yellow is an impure magnesium salt of euxanthic 
 acid. The essential part of it is a compound containing 
 4 '5 per cent, magnesia, 18*7 per cent, water, and 787 
 per cent, euxanthic anhydride ; but this substance is always 
 associated, even in the most carefully purified samples of 
 prepared Indian yellow, with various impurities both mineral 
 and organic. The pure magnesium euxanthate is repre- 
 sented by the formula C 19 H 10 MgO n ,5H 2 O. 
 
 For artistic purposes the crude imported Indian yellow 
 is thoroughly powdered, and then washed with boiling water, 
 until the liquid filtered from it is no longer coloured ; a 
 brown impurity, and much of the evil smell, is thus removed. 
 The colour of the washed product is enriched by leaving it 
 in contact for a day or two with a saturated solution of 
 sal-ammoniac, and then repeating the treatment with hot 
 water. 
 
 Thus purified, this pigment presents a translucent orange- 
 yellow colour of great depth and beauty. Ground in oil, 
 some specimens are practically unchanged, even after long 
 exposure to sunlight, any darkening they show being due 
 either to imperfect purification, or to the change of the 
 associated oil. Such change is reduced to a minimum if 
 poppy oil be substituted for linseed oil, or if the latter be 
 previously treated with manganese borate. On the other 
 hand, I have met with specimens of Indian yellow ground 
 in oil which, after five years' exposure, have lost nearly one- 
 third of their original depth, and have, at the same time, 
 become rather reddish-brown in hue. As a water-colour, 
 Indian yellow retains its hue unimpaired when exposed to 
 diffused daylight ; sunlight very slowly bleaches it, the hue 
 it acquires being somewhat brownish. The rate of altera- 
 
:;'■;; 
 
 .W:.,^ V?; ^ : .w,^'S;, : .',v, 
 
 mMmmssm & 
 
 ,,:,;,.,:,.: ||| ■,.,,, 
 
 156 
 
 INDIAN YELLOW 
 
 tion and of reduction in force caused by sunlight may be 
 approximately represented by these figures : 
 
 Original intensity 
 
 10 
 
 After 2 years ... 
 
 9 
 
 After 5 years ... 
 
 7 
 
 After 7 years ... 
 
 6 
 
 After 10 years 
 
 5 
 
 When this water-colour pigment is exposed to sunlight 
 in the presence of air maintained in a state of perfect 
 dryness it loses its colour much more rapidly than under 
 ordinary conditions. 
 
 As a general rule, Indian yellow suffers no change by 
 admixture with any pigment itself permanent, nor is it 
 affected by sulphur compounds. True Naples yellow, how- 
 ever, most of the chromates, and probably aureolin also, 
 tend to embrown it to some extent. 
 
 Indian yellow which has been adulterated with lead 
 chromate (chrome yellow) becomes dark-brown when 
 moistened with ammonium sulphide. 
 
 A fine yellow pigment may be prepared from the euxanthic 
 acid, which is the characteristic constituent of Indian yellow, 
 by throwing it down in combination with the two bases — 
 alumina and magnesia. The following directions may be 
 followed : Dissolve 1 part of pure euxanthic acid in just 
 sufficient dilute ammonia. Pour the solution into a liquid 
 prepared by dissolving 45 parts of potash-alum, 15 parts 
 Epsom salts, and 6 parts sal-ammoniac in 250 parts of 
 water. Now cautiously add dilute ammonia to the mixture, 
 stirring all the time, and avoiding any excess of ammonia. 
 The precipitated pigment is to be thoroughly washed, and 
 then pressed, dried, and ground. 
 
MARS YELLOW 
 
 iS7 
 
 Mars Yellow : Mars Orange — Artificial Ochre— Jaime de 
 Mars. 
 
 This pigment is a kind of yellow ochre prepared arti- 
 ficially. It may be made by precipitating a salt of iron 
 mixed with alum by means of caustic soda, or potash, or 
 lime. The salts of iron used are either green vitriol (ferrous 
 sulphate) or the ferric chloride. If green vitriol be cm- 
 ployed the precipitate formed gradually becomes yellow on 
 exposure to the air. Upon the proportion of alum mixed with 
 the iron salt depends the depth of the yellow colour in the 
 product, for the alumina precipitated with the iron hydrate 
 acts as a diluent of the colour. When lime is used as a 
 precipitant for the iron compound (if this be green vitriol 
 or ferric sulphate), calcium sulphate, that is, gypsum, comes 
 down along with the ferric hydrate and basic ferric sulphate, 
 and serves to lighten the colour. 
 
 By submitting the different varieties of Mars yellow to 
 various degrees of heat, with or without a little nitre, a 
 number of products of different hues are obtained, including 
 Mars orange, Mars red, Mars brown, and Mars violet. All 
 these preparations require very thorough washing to fit them 
 for use on the palette of the artist. 
 
 The Mars colours are permanent when carefully prepared 
 and thoroughly purified from soluble salts. They seem 
 sometimes to have a slightly injurious effect upon a few of 
 the best semi-permanent pigments of organic origin, such as 
 the madder colours. This action may be due to the ferric 
 hydrate in them combining with the colouring matter, and 
 displacing some of the alumina previously united with it. 
 In this direction it is probable that Mars yellow will be 
 more active than the deeper-coloured pigments produced by 
 calcining it at various temperatures. 
 
... , .... ; . ........ '■..,■..,':■.':.'.:..... 
 
 I 5 8 
 
 NAPLES YELLOW 
 
 Naples Yellow : Jaune de Naples — -Jaune iV Antinwine — 
 Neapel-gelb — Giallo di Naftoli. 
 
 Under this name three different substances are included. 
 The pigment generally sold in England as ' Naples yellow ' 
 is an excellent imitation made by mixing cadmium yellow or 
 deep cadmium with a white, preferably a zinc white. But a 
 true Naples yellow, which is a basic lead antimoniate, is 
 still procurable from some artists' colourmen.* This pre- 
 paration is sometimes made by heating together for two 
 hours a mixture of 1 part tartar emetic, 2 parts nitrate of 
 lead, and 5 parts common salt, all the ingredients being of 
 the purest quality, and the heat not exceeding that at which 
 common salt fuses. A more recent process, in which zinc 
 oxide is introduced among the materials which are heated 
 together, yields a paler but excellent product. A bright 
 pale variety of yellow ochre seems to have formerly gone 
 under the name of Naples yellow. 
 
 This antimonial yellow has been known from very early 
 times as an enamel colour. It has been found upon Baby- 
 lonian bricks at least 2,500 years old. Persian pottery as 
 early as the thirteenth century of our era is occasionally 
 decorated with antimonial yellow. 
 
 In oil the genuine and the imitative Naples yellows are 
 quite permanent, so far as light is concerned, but the 
 genuine kind is liable to be darkened, like other lead 
 compounds, by air containing sulphuretted hydrogen. In 
 water-colour painting genuine Naples yellow is quite in- 
 admissible, for it blackens rapidly, but irregularly, in the 
 presence of mere traces of sulphur compounds. This 
 
 * Roberson ; Edouard, of Paris 
 others. 
 
 Schonfcld, of Diisseldorf ; and 
 
NAPLES YELLOW 
 
 iS9 
 
 blackening, like that of lead white under similar conditions, 
 is much more marked in darkness than in light. 
 
 Naples yellow, in contact with metallic iron, tin, pewter, 
 zinc, and several other metals, is discoloured and blackened. 
 An ivory instead of a steel spatula, or palette knife, should 
 be used with this pigment. The darkening in question is 
 due in part to attrition, owing to the extreme hardness of 
 the particles of the lead antimoniate, however finely the 
 material may have been ground, and partly to the reducing 
 effect of the above-named metals upon this antimoniate. 
 Iron in the form of its oxide or hydrate (as in light red or 
 yellow ochre), or in complex combinations (such as Prussian 
 blue), does not exert any effect upon Naples yellow. A 
 statement to the contrary effect has crept into a large number 
 of technical manuals, but I have been unable to discover 
 the slightest experimental evidence in favour of such a view. 
 Naples yellow, however, is injured by and does injure some 
 of the organic pigments, such as the cochineal reds and the 
 numerous yellow lakes. But as Naples yellow cannot be 
 used as a water colour, and as the above-named organic 
 pigments ought to be entirely excluded from the palettes 
 of all artists, the action in question is of little importance. 
 Naples yellow acts upon indigo also. Indigo, however, is a 
 pigment, to which a very high degree of permanence cannot 
 be assigned ; there is, moreover, no reason why it should be 
 associated with Naples yellow, as other yellow pigments may 
 be safely used to modify its hue. 
 
 Another pigment also is sold as jaune d'antimoine. It is 
 a mixture of the oxychlorides of bismuth and lead with lead 
 antimoniate. When carefully prepared it yields a rich paint 
 of good body, but its use cannot be recommended to 
 artists. 
 
hwkKh 
 
 m§m 
 
 1 60 
 
 YELLOW LAKE 
 
 Yellow Lake: Broivn Pink — Citrine Lake — Yellow 
 Madder — Italian Pink — Quercitron Lake. 
 
 Origin. — The sources of yellow lake are numerous, but 
 the best kind is obtained from quercitron bark from Quercus 
 tinctoria, Qu. nigra, and Qu. citrina, three species of North 
 American oak. A hot- water decoction is made, and this 
 is precipitated by a solution of alum and dilute ammonia. 
 A richer yellow pigment is obtained by extracting the 
 powdered bark and alburnum with boiling dilute sulphuric 
 acid instead of with water. The original colouring matter 
 of the bark (quercitrin) is thus changed into a more stable 
 compound known as quercetin. The former substance is a 
 glucoside, the latter has the character of an acid ; both may 
 be converted into lakes by bringing them into contact with 
 precipitating or precipitated hydrate of alumina. Yellow 
 lake was formerly made from the fruits of various species of 
 buckthorn, known as Persian, Turkish, or Avignon berries. 
 The species yielding these fruits are Rhamnus infectorius, 
 R. oleoides, R. saxalilis, R. amygdalinus, R. catharticus. 
 The bark of R. frangula and of R. catharticus also yields a 
 yellow pigment. ' Stil de grain,' and several of the conti- 
 nental yellow lakes, are made from the above-named berry. 
 
 Italian pink, Dutch pink, and deep yellow madder are 
 names usually given to the richer yellow lakes of quercitron, 
 although some of these pigments are occasionally prepared 
 from Turkish or Avignon berries. 
 
 Beautiful and useful as many yellow lakes undoubtedly 
 are, they should be rigorously excluded from the artist's 
 palette. In oil most of them are very bad driers, as well as 
 fugitive : in water-colour they generally lose nine-tenths of 
 their colour within two years of exposure to sunlight : the 
 residual stain is ultimately of a bluish-grey. 
 
BROWN PINK 
 
 161 
 
 The following observations as to the behaviour of several 
 members of this group, on exposure for two years to sunlight, 
 apply to the colours as ground in oil, and as mixed with 
 flake-white in tint : 
 
 Name 
 Laque Robert — hell- 
 
 In Oil only 
 
 With Original 
 Flake-white Intensity =10 
 
 • 
 
 gelb - 
 Laque Robert — dun- 
 
 kel-gelb 
 Laque brun-jaune - 
 
 Lemon yellow - 
 
 Deep lemon 
 Salmon - 
 
 Pale straw 
 
 Stone 
 Pale rose 
 
 - 2 
 
 - 4 
 
 - 7 
 
 s 
 ■22 
 
 Laque brun-fonce - 
 Pale yellow madder - 
 
 Yellowish-grey 
 Pale orange 
 
 Smoke-grey 
 Pale buff 
 
 - 8 
 ■ 7 
 
 
 Deep yellow madder 
 
 Greyish salmon 
 
 Pale greyish pink 
 
 - 6) 
 
 *< 
 
 The same pigments used as glazing colours over flake- 
 white have faded to about the same extent, but their change 
 of hue is, in one or two cases, rather less marked. 
 
 The so-called brown pink is usually a deep quercitron 
 lake, although it was formerly made from the berries of one 
 of the kinds of buckthorn (Rhamnus) previously named. I 
 have never met with a specimen of it which would stand a 
 year's exposure to sunlight without suffering almost complete 
 change or loss of colour both in water and in oil. And it 
 further presents the awkward effect of becoming ultimately of 
 a cool bluish-grey hue, a change particularly unfortunate when 
 it has been freely used to represent foreground vegetation, 
 or the golden lights on the near foliage of trees. Yet I am 
 bound to confess that in Mr. W. Simpson's fifteen years' 
 trial of certain water-colour pigments, the brown-pink has 
 suffered comparatively little alteration. Had a portion of 
 the original cake-colour employed been preserved for ex- 
 amination it might have been possible to have discovered 
 the cause of this anomalous behaviour of the particular 
 specimen in question. 
 
 ir 
 
f^^M^^^^^J 
 
 162 
 
 CHROME YELLOW 
 
 Chrome Yellow 
 
 Chrome — Chromate of Lead — -Jaune de 
 Chrome — Chromgelb. 
 
 This pigment, when of a pure yellow hue, is the neutral 
 lead chromate. By associating it with an additional quantity 
 of lead oxide it may be obtained of various orange and 
 reddish orange hues. It may be made by the mutual action 
 of a soluble lead salt, such as the acetate or nitrate, and the 
 chromate or bichromate of potassium. Or white lead in 
 fine powder (2 kilos.) may be boiled with a solution of 
 bichromate of potassium (| kilo.) in water (10 litres). Alum 
 and baryta-white, or lead sulphate, are also employed in the 
 preparation of some of the paler chrome yellows. Lemon 
 chrome is a mixture of lead chromate and sulphate. Orange 
 chrome and chrome red are prepared from a mixture of lead 
 acetate (6f kilos.), litharge (5! kilos.), neutral potassium 
 chromate (6 kilos.), caustic potash being sometimes used in 
 addition. Chrome red may be obtained also by the direct 
 action of caustic soda in solution upon the yellow lead 
 chromate : its chemical formula is PbCr0 4 , PbO, or 
 Pb 2 Cr0 5 . 
 
 The chromates of lead are peculiarly liable to change, 
 and are quite unfitted for use in tempera or water-colour 
 painting. In oil, especially if protected by,varnish, or locked 
 up in a resinous vehicle, these pigments show a certain 
 measure of permanence, except when they are mingled with 
 paints of organic origin. In fact there are two causes which 
 militate against the integrity of the lead chromates. One 
 of these is the tendency which they possess towards reduc- 
 tion, that is, the loss of oxygen by their chromic constituent, 
 by which the green or lower oxide of chromium is formed. 
 This change is brought about by many kinds of organic 
 matter, notably by such animal or vegetable pigments as 
 
KINGS' YELLOW 163 
 
 are themselves prone to oxidation. The other cause of 
 deterioration is the presence of certain sulphur compounds 
 which act upon the lead chromates in the same way as they 
 act upon white lead, producing lead sulphide of a dark 
 brown, or a grey colour. 
 
 As the artist had better avoid the employment of these 
 pigments, further details concerning their characteristics 
 need not be given. 
 
 Vanadium Yellow. 
 
 It has been proposed to employ the beautiful golden- 
 bronze crystals of meta-vanadic acid as a pigment. They 
 possess, when finely ground, an intense colour, like that of 
 a very rich golden ochre, but less earthy, and more brilliant. 
 This pigment has remarkable covering power,* and works 
 admirably both as an oil and a water-colour. Although 
 the material is somewhat costly, the price for which it 
 could be prepared need not preclude its use. But, unfortu- 
 nately, this colour is not permanent. A few hours' expo- 
 sure to sunshine of a water-colour wash of vanadium yellow 
 suffices to change and deteriorate its hue in a marked 
 degree. 
 
 Kings' Yellow : Orpiment— Jaime Royal — Konigsgelb. 
 
 The yellow arsenious sulphide (As 2 S 3 ), though extremely 
 beautiful in hue, cannot be relied on as a pigment. Even 
 in oil or varnish its colour fades : Sir Joshua Reynolds' 
 experimental canvas shows some pale brown patches which 
 have once been kings' yellow, but which now have almost 
 entirely disappeared. Strange to say, in one of his trials, a 
 few quite visible crystals of orpiment are preserved. As it 
 cannot be imagined that he used this pigment in this ex- 
 ceedingly coarse form, it would seem that a molecular 
 
 11 — 2 
 
■SERBS 
 
 164 
 
 PURE ORANGE 
 
 aggregation of a part of the orpiment has taken place in 
 the lapse of years. If this change has not occurred, then 
 we may conclude that only the largest particles of the kings' 
 yellow have escaped alteration. Under any circumstances 
 the inadmissibility of kings' yellow to the palette of the 
 artist is obvious : moreover it cannot be safely mixed with 
 any pigment containing lead or copper. 
 
 Another compound of arsenic and sulphur (As 2 S 2 ) has 
 been employed as a pigment. It is of an orange-red hue 
 and is known as realgar. Not only is it extremely poison- 
 ous but it suffers change on exposure to light and acts 
 injuriously upon colours containing copper or lead. It was 
 used by the Romans : I identified a fragment of it amongst 
 the objects discovered at Silchester in the year 1896. 
 
 Pure Orange : Marigold — Alizarin Yelloiv — Alizarin 
 Orange. 
 
 Under the above names a pigment of great richness and 
 beauty has been recently introduced. It is a kind of lake, 
 and consists of a coal-tar colour known to chemists as /3-nitro- 
 alizarin thrown down upon an aluminous base. Nitro- 
 alizarin, as its name implies, is a derivative of alizarin, one 
 of the least changeable of all organic pigments, and the 
 chief tinctorial product of madder. There is no doubt 
 about the beautiful hue of this paint, a deep brownish gold : 
 the trials first made as to its permanence in oil promised 
 well, but on continuing the exposure to light of this pig- 
 ment ground in oil it became evident that it suffered con- 
 siderably. The deterioration was more marked when the 
 paint had been mixed with flake white, but even as a glazing 
 colour it is not safe. 
 
CHAPTER XV 
 
 RED PIGMENTS 
 
 Vermilion : Cinnabar — Vermilioti — Zinnober. 
 
 The mineral cinnabar, or mercuric sulphide, occurs in many 
 parts of Europe, and abundantly in China, and is extensively 
 worked in New Almaden in California ; it would be tedious 
 to recount the numerous localities in which it has been, or 
 is, found. Its colour in the mass varies from cochineal-red 
 and red-brown to lead-grey ; its powder is usually scarlet, or 
 red. Its hardness lies between that of gypsum and that of 
 calc-spar. It seldom contains even i part in ioo of im- 
 purities, but consists in ioo parts of very nearly 14 parts of 
 sulphur by weight, united with 86 of mercury, or 1 atom of 
 each element. The density of native vermilion is about 9. 
 Vermilion was formerly known as vermiculus, cinnabaris, 
 cenobrium, and minium ; the last name is now appropriated 
 to red lead. Vermilion and vermiculus are derived from 
 the Latin vermes, a name originally designating the 'kermes' 
 insect found on the ilex or evergreen oak, which is still used 
 for the preparation of a red dye. From kermes, in its turn, 
 the words crimson and carmine are derived. The name 
 cinnabar is supposed to be of Oriental origin (compare the 
 Persian zanjifraJi), and was used sometimes to designate 
 dragon's blood, a red resin. Theophrastus informs us that 
 two kinds of cinnabar were known to the Greeks. One of 
 
|a§mij|9| 
 
 im 
 
 1 66 
 
 VERMILION 
 
 these was undoubtedly real cinnabar (chiefly from Spain), 
 the other was red lead. Pliny's 'cinnabar' or 'minium' 
 was true vermilion, so was the ' minium ' of Vitruvius. 
 Theophilus calls it ' cenobrium,' Wyclif ' cynoper,' Hakluyt 
 1 cinaper,' and Ben Jonson ' cinoper.' 
 
 One of the most curious facts concerning vermilion is 
 that it is identical in the nature and proportion of its two 
 constituent elements with an artificial black substance, 
 1 ^Ethiop's mineral.' The red substance may be changed 
 into the black, and vice versa, and this without any loss or 
 gain, or any alteration of chemical composition, the change 
 being a physical or molecular one merely. The black sub- 
 stance is amorphous, the red crystalline. 
 
 The pigment vermilion may be made by simply grinding 
 selected pieces of native cinnabar, or it may be obtained 
 artificially by combining the two elements sulphur and 
 mercury. 
 
 All the methods of preparing vermilion artificially may 
 be grouped under two divisions. The first of these is the 
 dry way, the other the ivet way. In the former method 
 metallic mercury 42 parts, and sulphur 8 parts, are inti- 
 mately mixed and agitated together in revolving drums 
 until they have combined. The brownish-black powder 
 thus obtained is then submitted to sublimation in vertical 
 iron cylinders, surmounted by heads which are connected 
 with receivers. On sufficient heating, the mercuric sulphide 
 sublimes as cinnabar or vermilion, the best part condensing 
 in the retort-heads. The rest of the sublimed product 
 (which has travelled farther) contains free sulphur, and is of 
 inferior colour. The selected portions are next ground, 
 moistened with water, warmed with a little caustic potash 
 solution or nitric acid, and then thoroughly washed with 
 boiling water. In another dry process the mercury is 
 
VERMILION 
 
 167 
 
 gradually added to the proper proportion of melted sulphur 
 in an iron basin. When the combination (which is accom- 
 panied by a violent evolution of light and heat) is complete, 
 the fused blackish mass is poured out, broken into frag- 
 ments, heated until excess of sulphur has been driven off, 
 and then sublimed in the way already described. Some 
 makers add to the crude sulphide, previous to sublimation, 
 1 per cent, of antimony sulphide, with the object of improv- 
 ing the colour ; the product is afterwards ground, digested 
 with liver of sulphur, and then washed with hydrochloric 
 acid. 
 
 There are numberless processes for preparing vermilion 
 by the wet way. One of the best of these consists in 
 grinding, in the presence of water, 100 parts of mercury 
 with 38 parts of flowers of sulphur until these elements 
 have united. The black product is then triturated at 45 C. 
 for many hours with a solution of 25 parts of caustic potash 
 in 150 parts of water. When the product has attained its 
 maximum of redness and beauty, it is thrown into water, 
 and thoroughly washed by decantation. In a second 
 process mercury, sulphur, and potassium pentasulphide 
 are boiled together for three or four hours, and then the 
 mixture is kept at a temperature of 50 C. for several days. 
 Vermilion may also be prepared from the black sulphide 
 obtained by precipitating a mercuric salt with a soluble 
 sulphide, from ' white precipitate,' and from metallic mer- 
 cury itself, by warming any one of these substances with 
 a solution of an alkaline pentasulphide, and then purifying 
 the product by means of a potash-solution heated to 45 C. 
 It has also been found that vermilion is produced when a 
 mixture of mercurous chloride (calomel) and zinc sulphate 
 is heated to 45 — 50 C. with an excess of a solution of 
 sodium thiosulphate. 
 
i68 
 
 VERMILION 
 
 Except where carmine or realgar (red sulphide of arsenic) 
 is present, a very simple test suffices to ascertain whether 
 vermilion be pure or not. A small pinch should be heated 
 over a spirit-lamp on a fragment of hard porcelain ; no ap- 
 preciable residue will be found, unless red-lead, red iron 
 oxide, brickdust, or other non-volatile adulterants be present. 
 Carmine, which is sometimes added to scarlet vermilions to 
 approximate their hue to that of the crimson varieties such 
 as the Chinese, may be detected by laying a pinch of the 
 powdered pigment on a small pad of white blotting-paper, 
 and moistening the substance with a few drops of strong 
 ammonia-water ; a crimson stain will appear on the paper if 
 carmine or crimson-lake be present. The colour of a good 
 vermilion is not changed by moistening it with nitric acid. 
 The accidental impurities which impair the hue of vermilion 
 are free sulphur, and compounds of iron and lead ; that 
 prepared in the wet way often retains alkaline salts, owing 
 to imperfect washing. A spurious vermilion, called anti- 
 vermilion or antimony vermilion, is made by warming anti- 
 monious chloride with sodium thiosulphate. 
 
 Vermilion prepared from the mineral or native cinnabar 
 is probably less liable to change than the artificial products, 
 whether obtained by the dry way or the moist way ; but 
 ' moist way ' vermilions are certainly the most alterable. 
 And it may also be remarked that the more finely a vermilion 
 is ground, the less stable it is — at least, as a water-colour 
 paint. Thus it happens that, other things being equal, an 
 orange-vermilion is inferior in permanence to a scarlet, and 
 a scarlet-vermilion to one inclining to crimson. As an oil- 
 pigment, vermilion does not dry well, but suffers, especially 
 if it be locked up in copal or paraffin, no change by light 
 or impure air; ioo parts of the dry substance require less 
 than 20 parts of oil. Owing to its great density, vermilion 
 
VERMILION 
 
 169 
 
 tends to separate from the oil with which it has been ground. 
 This result may be obviated by the addition to the oil of 
 a little aluminium oleate or linoleate, or by the employment 
 of oxidized and thickened oil in which a small quantity of 
 ceresin has been dissolved by the aid of heat. In water- 
 colour painting most vermilions are found to be changed on 
 exposure, the solar rays gradually converting the red into the 
 black modification of mercuric sulphide, without, of course, 
 producing any chemical alteration. This change occurs 
 even in the absence of air and of moisture. Impure air, 
 per se, even if sulphuretted hydrogen be present, does not 
 discolour vermilion. 
 
 Anyone who has examined old illuminated manuscripts 
 must have noticed the apparent capriciousness with which 
 the ornaments, and especially the initial letters, painted with 
 vermilion, have been affected. I have more than once 
 observed that, while all the vermilion used in one part of 
 a missal or choral-book has remained red, a leaden hue has 
 spread irregularly over the rest of the work in places where 
 this pigment has been used. This may be due to the use 
 by the illuminator of a sample of vermilion adulterated with 
 minium or red lead, but sometimes to a change in the 
 technique, as a change in the style or handiwork is often 
 associated with the difference above described. In oil- 
 painting there are no permanent pigments, save the copper- 
 greens, with which vermilion may not be safely mixed. 
 Only when it contains impurities, such as free sulphur, does 
 it darken flake-white. 
 
 Vermilion prepared from native cinnabar is found per- 
 fectly preserved in the flesh-tints of Italian tempera-paintings 
 of the thirteenth and fourteenth and fifteenth centuries. It 
 has stood in the wall-paintings of Pompeii, where it often 
 seems to have been waxed. A comparatively recent but 
 
ifflijiip '"''" ''':'' :f|t^lf I 
 
 170 
 
 MADDER PIGMENTS 
 
 instructive instance of the permanence of vermilion in oil is 
 furnished by a portrait, dated 1758, in the National Portrait 
 Gallery. It represents the painter, Hogarth, with his palette 
 set before him. The second of the dabs of colour thereon 
 is vermilion, perfectly intact. In the same collection there 
 is a portrait by Marc Gheeraedts of Mary Sidney, Countess 
 of Pembroke, in which the vermilion has stood. This work 
 was painted in 1614. Scores of earlier and later examples 
 might be cited. 
 
 The variations in hue observable in different specimens 
 of vermilion are mainly due to the differing degrees of fine- 
 ness in which the pigment occurs. The coarsest grain cor- 
 responds with a crimson hue, and then we have every variety 
 of colour ranging from scarlet to reddish orange or orange. 
 The processes of regrinding and ' washing-over ' enable us 
 to obtain the kinds separately. And if we repeat these 
 operations often enough, we may ultimately convert the 
 whole of a crimson vermilion into the orange form. It was 
 formerly supposed that the latter material was a mere scum, 
 or impurity, or at least differed from the crimson kind in 
 composition. When any vermilion is mixed in tint with 
 white, an opposite effect to that of further grinding is pro- 
 duced. For, as the early writer Eraclius states : ' If you 
 mix white with vermiculus, carmine is made ' — that is, the 
 hue of the mixture becomes more rosy, and therefore further 
 removed from orange. 
 
 Madder : Pink Madder — Rose Madder — Madder Carmine 
 — Madder Red — Ruben? Madder — Madder Purple — 
 Madder Lake — Madder Brown — Carmin de Garance — 
 Laque de Garance — Krapp-lack. 
 
 Some authorities assert that madder was used in dyeing 
 long before its employment in painting. But there is some 
 
HPhBH 
 
 
 
 
 
 
 evidence. 
 
 derived from 
 
 MADDER 
 1 finds ' of pigments 
 
 and from 
 
 171 
 paint- 
 
 ings, that the ancient Greeks and Romans were acquainted 
 with a pink pigment derived from madder, while there are 
 good reasons for believing that such substances were widely 
 known in Europe as early as the thirteenth century. Even 
 in England, such a pigment is almost certainly referred to, 
 under the name 'sinopis,' in the middle of the fourteenth 
 century. Now Alcherius (close of fourteenth century) tells 
 us that ' sinopis is a colour redder than vermilion, and it is 
 made from varancia.' ' Varancia ' is clearly garance — that 
 is, madder — the same material being named ' warancia ' and 
 ' waranz ' in a British Museum manuscript (Sloane, No. 416) 
 which contains recipes of the fourteenth century. Besides 
 ' sinopis ' (strictly, a red earth), madder-lake was called, in 
 English account-rolls of the fourteenth century, ' sinopre ' 
 and ' cynople.' It is, however, difficult, if not impossible, 
 to ascertain the precise date at which pigments derived from 
 madder came into use in the various schools of painting in 
 Europe. For the nomenclature of pigments has always 
 been somewhat vague, while the evidence furnished by 
 existing pictures does not at present enable us to trace back 
 with absolute certainty the mediaeval use of madder paints 
 to an earlier time than the fifteenth century. Eraclius does 
 not mention madder, nor does Cennini, who lived at a 
 much later time. Mr. R. Hendrie, in his notes to ' Theo- 
 philus,' speaks of an English manuscript of the fourteenth 
 century in which directions are given for extracting the 
 colouring matter of 'madyr.' From these directions we 
 are, perhaps, justified in concluding that the preparation of 
 a kind of liquid paint was intended. 
 
 The European madder-plant, a native of Greece, belongs 
 to the tribe Galiese, of the order Rubiaceae ; it is the Ridna 
 tinctorum of Linnaeus. Several other species of this genus 
 
172 
 
 MADDER 
 
 are used or grown in India for the sake of the red dye they 
 afford. Among such species, Ritbia cordifolia (Linn.) and 
 R. sikkimensis (Kurz.) may be named, but the European 
 madder is also cultivated extensively in India. Much 
 madder was formerly grown in the Levant, in Holland, and 
 in the south of France ; but the manufacture by artificial 
 means from the anthracene of coal-tar of its two chief 
 colouring matters, alizarin and purpurin, has almost entirely 
 extinguished the cultivation of the madder-plant in Europe. 
 We shall have something to say presently concerning the 
 artificial products above named. 
 
 The root of madder contains a much larger proportion of 
 the colouring matters (or, it would be more correct to say, 
 colour-making substances) than the other parts of the plant. 
 They occur dissolved in the yellow cell-contents of the soft 
 tissue of the root. The finest madder was grown in the 
 ' Palud,' a chalky valley near Vaucluse. 
 
 The colouring matters obtained from madder exist in the 
 plant in the form of glucosides. These glucosides are re- 
 solved by the fermentation, brought about by a peculiar 
 ferment in the plant itself, and by many chemical agents, 
 such as mineral alkalies and acids, mainly into glucose on 
 the one hand, and on the other into the several colouring 
 principles. Of such colouring principles the glucosides in 
 madder yield at least three, of which the most important are 
 these two : 
 
 i. Alizarin, C 14 H 8 4 . 
 2. Purpurin, C 14 H 8 5 . 
 
 Both alizarin and purpurin are now manufactured arti- 
 ficially from anthracene. This compound, which occurs in 
 coal-tar, is a crystalline fluorescent hydrocarbon, C U H 10 . 
 By a series of processes this substance gives rise to alizarin 
 
MADDER LAKES 
 
 173 
 
 and purpurin, which are in all respects identical with these 
 colouring matters as derived from the madder plant itself. 
 The artificial alizarin of commerce contains several other 
 colouring matters, two of which are better known than the 
 others ; these are anthrapurpurin (C u H 8 5 ) and purpuro- 
 xanthin (C 14 H s 4 ). Purpuroxanthin is also present in the 
 natural pigments derived from madder, but it exists in small 
 proportion. Of all these compounds alizarin is the most 
 important and the best known, and yields lakes having 
 various hues of crimson, rose, purple, violet and marone, 
 according to its purity, its concentration, and the nature of 
 the base (alumina, aluminium phosphate, iron oxide, man- 
 ganese oxide, copper oxide, or lime with alumina) with 
 which it is associated. The purpurin and anthrapurpurin 
 resemble one another closely, and give pigments which are 
 generally characterized by more orange or red hues than 
 those obtained with alizarin. The rose and pink madders 
 and the madder carmines of commerce are generally so 
 manufactured as to include, for their colouring constituents, 
 much alizarin and very little purpurin. A few indications 
 of the ordinary methods of preparing these lakes may first 
 be given. 
 
 The material used is often that called 'madder flowers,' 
 which consists of the finely ground dried root after it has 
 been submitted to the action of dilute sulphuric acid and 
 washed. Four pounds of this madder are taken and 
 warmed for two or three hours on a steamer, with a solution 
 of 1 pound of pure alum in 1 gallon of water. The mix- 
 ture is placed in a filter-press, and the liquor obtained 
 (which must be perfectly clear) precipitated by the gradual 
 addition of a solution of sodium carbonate. The first 
 portions of madder lake which fall, being the best, should 
 be collected apart. All the precipitates should be thoroughly 
 
174 
 
 MADDER LAKES 
 
 washed with rain or distilled water till the wash-waters are 
 no longer troubled on the addition of barium chloride 
 solution ; they are then moulded into small cones, drops, 
 or discs, and carefully dried at a moderate temperature. 
 Another process for preparing madder lakes is a modifica- 
 tion of the above. Four pounds of madder-root in powder, 
 after having been fermented and then washed with a weak 
 solution of sodium sulphate, are boiled for fifteen minutes 
 with 4 gallons of a 10 per cent, solution of pure alum, the 
 whole is filtered, and at a temperature of 45 partially 
 neutralized with a solution in water of about 8 ounces of 
 pure sodium carbonate. The liquor is now brought nearly 
 to the boiling - point ; the madder lake which is then 
 deposited is to be thoroughly washed and then dried : it is 
 much denser than that produced by the preceding process. 
 In the actual manufacture of madder colours it is customary 
 to introduce a small quantity of a preparation known as 
 Turkey-red oil or sulphated castor oil. This is made into a 
 soap and added to the alkaline solution employed to pre- 
 cipitate the lake. 
 
 By the employment in various proportions of solutions of 
 alum and calcium chloride, by the substitution of sodium 
 phosphate for the carbonate, and by choosing various 
 qualities of madder root, a number of hues and tints of 
 rose and pink madder may be obtained when one or other 
 of the methods above described is adopted. The oxides of 
 iron, manganese and copper, when used in association with 
 more or less alumina as a base for receiving the various 
 colouring matters of madder, give other hues, including 
 madder-purple and madder brown. 
 
 But occasionally the pigments sold under these names 
 are mixtures. For instance, burnt sienna and copper ferro- 
 cyanide have been found in samples of madder brown ; the 
 
ALIZARIN AND PURPURIN 
 
 175 
 
 presence of copper in madder brown seems, however, to be 
 usual, but it arises from the employment of copper sulphate 
 in its preparation along with alum. 
 
 From alizarin and from purpurin (either natural or arti- 
 ficial) madder lakes may be readily prepared by dissolving 
 these substances in the smallest necessary quantity of an 
 alkali, such as ammonia or sodium carbonate, and then 
 adding a solution of a pure aluminium salt or some pure 
 freshly precipitated and thoroughly washed aluminium hy- 
 drate. Another and more recent process consists in dis- 
 solving the colouring matter in a solution of sodium alumi- 
 nate, and then precipitating the ' lake ' by adding dilute 
 sulphuric acid or, better, a solution of alum. 
 
 The best artificial alizarin of commerce occurs as a 
 yellowish powder, presenting the aspect of raw sienna. It 
 may, however, be obtained in yellow or orange red crystals, 
 either by repeated crystallization from a solvent or by 
 sublimation in vacuo. Its colour is always brighter than 
 that of purpurin, which in powder has about the hue of 
 Venetian red. But when solutions are made of these two 
 substances in alkalies, then it is seen that the colours are 
 reversed — alizarin yielding a crimson verging upon purple, 
 and purpurin a red verging upon crimson. Differences of 
 colour will be noticed in the lakes prepared with these two 
 bodies. The directions for preparing pigments from the 
 above-named bodies are practically identical with those 
 already given in outline, but the minute details of manipula- 
 tion can be learned only in actual practice. One peculiarity, 
 however, distinguishing purpurin from alizarin, may be here 
 noticed. It will be found that, while alizarin is practically 
 insoluble in cold saturated alum-water, and but slightly 
 soluble in the same liquid even when boiling, purpurin 
 dissolves to a marked extent in this solvent. From this 
 
mm ■' 
 
 5wM$$$^llf^ 
 
 176 
 
 MADDER LAKES 
 
 purpurin solution, which possesses a crimson colour and 
 exhibits a fine orange red fluorescence, alkalies throw down 
 a pure red-coloured lake. The following process gives a 
 red madder of excellent hue : Equal weights of pure alum 
 (absolutely free from iron and lime) and of the purest 
 artificial purpurin in powder are ground together, and then 
 washed with cold water until the washings are colourless ; 
 then the residue on the filter is boiled with a 5 per cent. 
 solution of pure alum, filtered while boiling, and immediately 
 neutralized with pure sodium carbonate solution (also boil- 
 ing) until red flocks appear. These are filtered off, and 
 constitute, when washed and dried, a fine pigment of a rich 
 red hue. By heating the mother liquor to 8o°, and adding 
 more sodium carbonate, a further and equally good product 
 is obtained. The purpurin residue, when again heated with 
 more alum-solution and precipitated as above directed, 
 yields a further quantity. The final residue, after several 
 such exhaustions, produces an impure madder lake, having 
 a brownish red hue. A very large number of commercial 
 preparations of alizarin and of other dye-stuffs closely allied 
 to it are now available for the preparation of the so-called 
 ' madder lakes.' Some of these preparations when dis- 
 solved and then precipitated on a suitable basis, yield pig- 
 ments of great richness and stability, others, especially 
 those which possess a yellow, orange, or red brown hue are 
 less permanent. 
 
 Although the madder colours are very much less affected 
 by light than are the pigments derived from cochineal, yet 
 it cannot be affirmed that any of them are absolutely per- 
 manent when continuously exposed. The following figures 
 show approximately the amount and nature of the change, 
 observed after certain intervals, in the case of several madder 
 pigments used as water-colours : 
 
MADDER LAKES 
 
 177 
 
 Name 
 of Pigment 
 
 
 
 Orig 
 
 Intensi 
 
 inal 
 ty = 
 
 O 
 
 Change of Hue 
 
 *Madder Carmine, 
 
 A 
 
 After 1 
 
 year, 
 
 IO ■ 
 
 Very slight. 
 
 i> )> 
 
 
 B 
 
 - ,, 
 
 I 
 
 ,, 
 
 8 
 
 Much more purplish. 
 
 !> )l 
 
 
 C 
 
 >> 
 
 5 
 
 > » 
 
 2 ■ 
 
 
 () )) 
 
 
 C 
 
 j j 
 
 7 
 
 > s 
 
 ■ 
 
 
 * 
 11 )) 
 
 
 F 
 
 )> 
 
 4 
 
 ,, 
 
 10 - 
 
 More purplish. 
 
 Madder Red - 
 
 
 - 
 
 > » 
 
 1 
 
 )) 
 
 6 • 
 
 Less red, more blue. 
 
 Rose Madder - 
 
 " 
 
 - 
 
 >> 
 
 I 
 
 ,, 
 
 8 
 
 Slightly more purplish. 
 
 ,. B 
 
 
 - 
 
 » » 
 
 2 
 
 ,, 
 
 3 ■ 
 
 
 ,, B 
 
 " 
 
 
 - ,, 
 
 5 
 
 M 
 
 1 ■ 
 
 Smoke grey. 
 
 „ B 
 
 
 
 ») 
 
 7 
 
 ,, 
 
 1 - 
 
 Grey. 
 
 „ F 
 
 - 
 
 - 
 
 >> 
 
 4 
 
 ,, 
 
 H ■ 
 
 Slightly more purplish. 
 
 Pink Madder - 
 
 
 
 >> 
 
 2 
 
 19 
 
 1 
 
 
 Purple Madder, 
 
 A 
 
 - 
 
 >j 
 
 1 
 
 ) > 
 
 7 ■ 
 
 Duller, less red, more blue 
 
 )) !! 
 
 C 
 
 - 
 
 - ,, 
 
 2 
 
 )> 
 
 6 • 
 
 More bluish. 
 
 1) )) 
 
 I) 
 
 
 >) 
 
 5 
 
 >> 
 
 7 ■ 
 
 
 )) )) 
 
 c 
 
 - 
 
 , > 
 
 7 
 
 »> 
 
 2 ■ 
 
 
 * 
 
 E 
 
 
 >! 
 
 7 
 
 >» 
 
 9 
 
 Somewhat puce. 
 
 Brown Madder, 
 
 A 
 
 - 
 
 )> 
 
 1 
 
 )» 
 
 9 ■ 
 
 Less red, more yellow. 
 
 !> )» 
 
 B 
 
 - 
 
 - ,, 
 
 2 
 
 >! 
 
 1 - 
 
 Grey. 
 
 )> )) 
 
 B 
 
 - 
 
 !) 
 
 5 
 
 >> 
 
 1 - 
 
 
 !> >> 
 
 1! 
 
 
 - ,, 
 
 7 
 
 if 
 
 - 
 
 Grey. 
 
 The letters A to F indicate different samples of the several 
 pigments, which were in all cases ' moist ' colours ; a parallel 
 but less complete series with ' cake ' colours gave practically 
 the same results. The four samples marked * are instances 
 of exceptional stability, and are of importance as showing 
 the possibility of obtaining some, at all events, of the madder 
 pigments in a satisfactory form. It is noticeable that the 
 paler (pink and rose) madders, which contain much water, 
 are generally more perishable than the concentrated madder 
 carmine ; the comparative trials having, of course, been 
 made with washes of nearly the same depth of tint. 
 
 A study of this table inclines one to think that the 
 genuineness and purity of some of these pigments are 
 
v":; : 
 
 I 7 8 
 
 MINERAL LAKE 
 
 doubtful, yet one specimen only (Madder Carmine C) was 
 not tested, in this case the material used was not available 
 for analysis, but I have no reason to doubt its authenticity. 
 
 Mineral Lake : Pink-Colour — Laque Min'erale. 
 
 Attempts have been made to obtain mineral pigments of 
 absolute permanence in order to acquire substitutes for the 
 reds and purples of vegetable origin. None of them equals 
 in intensity and splendour of colour the derivatives of 
 madder. One of the best of these substitutes is mineral 
 lake. This compound may be made in many ways. In 
 some receipts stannic oxide, chalk and a little potassium 
 chromate are directed to be heated together: in one process 
 the operations are begun by precipitating a solution of 
 neutral potassium chromate by means of a solution of 
 stannic chloride. The precipitate is collected on a filter 
 and thoroughly washed. Still moist, it is ground into a 
 paste with half its bulk of pure nitre and some stannic 
 oxide, and allowed to dry. The dry mixture is projected, 
 little by little, into some nitre heated to low redness in a 
 crucible. When the basic chromate of tin has settled, the 
 nitre, still fused, is poured off, and the residue washed 
 thoroughly with water. The product thus obtained requires 
 calcination for two hours at a high temperature in a luted 
 crucible, in order to develop its colour, which much resembles 
 that of almond-blossom, when the matter is finely ground. 
 It appears much richer in hue and less opaque when used 
 as an oil-colour. It constitutes an unalterable pigment. 
 
 Light Red: Burnt Ochre — Rouge Anglais — Brun Rouge. 
 
 Light red is, or ought to be, yellow ochre burnt — that is, 
 calcined. The different varieties of yellow ochre yield, as 
 might be expected, products having various hues and tints 
 
VENETIAN RED 
 
 179 
 
 of this rather pale and dull brownish or orange red. More- 
 over, these hues depend in some measure upon the tempera- 
 ture at which the calcination is effected. To prepare light 
 red, the selected yellow ochre is usually crushed and then 
 roasted on an iron plate heated to redness. When the 
 desired tint has been attained the material is thrown into 
 cold water, ground, and washed. Light red may also be 
 made by conducting the finely-divided yellow ochre sus- 
 pended in a current of air into a heated chamber or furnace. 
 Light red consists, then, of yellow ochre deprived of its 
 water of hydration by means of heat. It is necessary to 
 employ yellow ochre as free as possible from organic matter 
 and from lime if a bright-coloured product be desired. 
 
 Light red possesses a considerable degree of opacity. Its 
 hue may be defined as a scarlet, modified by a little yellow 
 and grey. It is perfectly permanent and without action 
 upon other pigments. 
 
 Light red boiled with hydrochloric acid will, if genuine, 
 yield a solution, which after filtration will give no precipitate, 
 but merely a slight cloudiness, on the addition of a few drops 
 of barium chloride solution. The terms 'rouge Anglais ' and 
 ' Brun rouge ' are not infrequently applied to artificially pre- 
 pared iron reds. 
 
 Venetian Red : Rouge — Crocus — Colcothar — Caput Mor- 
 tuum Vitrioli. 
 
 Originally Venetian red consisted of a native ferric oxide 
 or red hsematite, less purplish in its tints and washes than 
 Indian red. But of recent years the name appears to have 
 been transferred to a particular quality of artificial ferric 
 oxide, made by calcining green vitriol. When this salt is 
 heated in a crucible the upper portion of the product, which 
 has been less strongly heated than the lower, is of a brighter 
 
Hgfi 
 
 I $ ■ ; - 
 
 1 80 
 
 INDIAN RED 
 
 red than the remainder, and after washing and grinding is 
 sold as Venetian red. If moistened with a solution of nitre, 
 again heated, and then ground and washed, the red tint of 
 the product becomes somewhat brighter. 
 
 The hue of Venetian red is less brownish than that of 
 light red, and not at all purplish like that of Indian red. 
 
 Venetian red, whether artificial or natural, is a permanent 
 pigment which may be mixed with other permanent pigments 
 without fear of injuring them ; but it must be perfectly free 
 from soluble salts and from any trace of sulphates. The 
 presence of the latter may be detected by the test described 
 under ' Light Red ' and ' Indian Red.' But few commercial 
 samples will stand this test, however, and we consequently 
 find that many samples of Venetian red, owing to the pres- 
 ence therein of sulphates, exert an injurious action upon 
 some of the organic pigments used as water-colours — 
 notably, upon indigo. 
 
 A very fine native red ochre comes from Tuscany and 
 from Krasso in the Banat, Hungary. It is represented by 
 the formula 2Fe 2 3 , H 2 0, and goes under the mineralogical 
 name of turgite. Its hue is that of a fine Venetian red, 
 but it is probable that the fine native Indian reds and red 
 ochres sometimes consist of or contain this hydrated ferric 
 oxide, and are not really anhydrous. 
 
 Indian Red : Persian Red — Indian Red Ochre. 
 
 Indian red is a variety of red ochre, or red haematite, 
 containing about 95 per cent, of ferric oxide, and having a 
 slightly purplish hue. It varies somewhat in quality, and 
 often requires sifting through a fine silk sieve, followed by 
 washing over, in order to fit it for use as a pigment. Most 
 of the Indian red imported from India is a natural product, 
 but some has been prepared by calcination. Some so-called 
 
INDIAN RED 
 
 Indian red is imported from Ormuz in the Persian Gulf; 
 some is an English haematite from the Forest of Dean. 
 
 A recent recipe for making an artificial Indian red 
 directs that a mixture of 75 parts of green vitriol be taken 
 and dried at a moderate heat previous to mixing it with 
 18 parts of calcined magnesia and 7 parts of common salt, 
 all the ingredients being in fine powder. The mixture is 
 then ignited, preferably under reduced pressure, and the 
 residuum thoroughly washed with water. By the introduc- 
 tion into the original mixture of a little aluminium sulphate 
 the purple hue of the product may be enhanced ; indeed, it 
 is quite possible in this way to obtain the pigment known 
 as Mars violet. 
 
 Indian red, when genuine, is a perfectly permanent pig- 
 ment in all media, and is without action upon other colours. 
 It was extensively employed by the older masters of the 
 English Water- Colour School, in association with true 
 ultramarine, with Prussian blue, with indigo, or with indigo 
 and yellow ochre, to produce the lilac greys of stormy 
 clouds. The indigo in some of these greys having often 
 perished, the Indian red (and the yellow ochre where 
 employed) remains intact, giving a hot and frequently 
 foxy red to spaces which were originally cool in hue, and 
 comparatively neutral. This change has been incorrectly 
 attributed to an action exerted upon the indigo by the 
 Indian red. But as indigo disappears when used alone, or 
 when a thin wash of it on a sheet of gelatine is placed over, 
 but not in contact with, a wash of Indian red, the current 
 explanation of the phenomenon in question cannot be true. 
 Greys made with light red or Venetian red show similar 
 alterations of colour. Colcothar, or jewellers' rouge, the red 
 oxide of iron obtained as a residue when green vitriol (ferrous 
 sulphate) is calcined, has sometimes been called Indian red, 
 
r 
 
 ,...,. 
 
 182 
 
 RED OCHRE 
 
 and substituted for the native oxide. Those portions of the 
 above-named residue which have been more strongly heated 
 generally present something of the purplish red hue which 
 belongs to the true native Indian red. And this peculiar 
 hue may be imparted to ordinary rouge by moistening it 
 with a weak solution of potassium chlorate, drying, and then 
 calcining the mass once more. It generally contains basic 
 ferric sulphate, and then should be looked upon with 
 suspicion, for it may seriously damage the indigo and other 
 organic pigments with which it is associated. If a small 
 pinch of Indian red be boiled with hydrochloric acid, thrown 
 on a filter, and the nitrate tested with barium chloride 
 solution, the genuineness of the pigment will be proved by 
 the absence of any white precipitate of barium sulphate. 
 
 Red Ochre: Red Hcematite — Red Iron Ore — Scarlet Ochre 
 — Red Chalk — Ruddle — Bole — Sinoper — Sinopis — Ru- 
 hr ica — Miltos — Terra Rosa — Arrabida Red. 
 
 The pigments above-named are native ferric oxide (or 
 iron peroxide) associated with variable proportions of mineral 
 impurities such as clay, chalk, and silica. They differ from 
 the yellow and brown ochres described on page 126, by not 
 containing combined water, in other words, the iron to 
 which they owe their colour is ferric oxide, not ferric hydrate, 
 except in the case of turgite, named on page 180. They 
 occur in very many localities accompanying or even con- 
 stituting some of the most important iron ores. Their 
 colour varies with their physical state, and with their purity ; 
 some are iron grey, or even black, until they are finely 
 ground, when they assume a cherry-red hue. Cappadocia 
 yielded to the ancient Greeks some at least of their sinopis, 
 or red ochre, but they were familiar with the process of 
 calcining yellow ochre in order to redden its hue ; and they 
 
 
INDIAN LAKE 
 
 183 
 
 thus prepared the pigment to which the name ' light red ' is 
 now assigned. 
 
 An unusually bright red variety of hsematite from Cumber- 
 land gave me on analysis, in 100 parts, ferric oxide, 947 ; 
 alumina, 2*0; silica, 2'2, and moisture, i*i. But some 
 almost equally rich red ochres contain much less iron oxide, 
 a ' sinopis ' from Anatolia, analysed by Klaproth, having 
 been found to contain 21 per cent, only, and others, from 
 other localities, not above 40. The paler varieties of a 
 reddish brown or yellow brown hue often consist of mixtures 
 of haematite and yellow ochre. A very fine red ochre from 
 Tuscany, the Banat, Hungary, and from the Urals, contains 
 about 5 per cent, of water, and is considered to belong to a 
 distinct mineral species called turgite, as mentioned before 
 under the heading 'Venetian Red.' 
 
 When red chalk (from Hunstanton, Norfolk) is calcined 
 at a high temperature it loses its red colour, and becomes of 
 a dull olive green hue, a change due in this case to the 
 production of calcium ferrite, a compound of lime and ferric 
 oxide. 
 
 The terra rosa of Italy owes its pinkish red hue to ferric 
 oxide, but it is probably often, if not always, an artificial 
 product. 
 
 All the pigments described under the title ' red ochre ' 
 are permanent, and without action on other pigments. 
 
 For the substitution of artificially prepared ferric oxide, or 
 colcothar, for red ochre, and for the method of detecting it, 
 reference should be made to page 182, under ' Indian 
 red.' 
 
 Indian Lake : Lac Lake — Lack-Lack. 
 
 Lac is a resinous secretion produced by certain plants 
 when punctured by the larvae of the Coccus lacca, an East 
 
: : 
 
 
 INDIAN LAKE 
 
 Indian hemipterous insect. Amongst the trees which the 
 insect chiefly attacks are Butea frondosa, Ficus religiosa, 
 and F bengalensis, Schleichera trijuga, Shorea robusta, and 
 Zizyphus jujuba. The lac, though a secretion primarily 
 derived from the tree on which the insects feed, is yet 
 profoundly modified, particularly with respect to its colour, 
 during its passage through the animal's body. It varies in 
 colour with the species of tree, but always consists mainly of 
 three substances, namely, a resin, a colouring matter, and a 
 wax. The resin, which constitutes two-thirds of the sub- 
 stance, is obtained in the form known as ' seed-lac ' by 
 pounding in water the lac which has been removed by 
 pressing with a roller the encrusted twigs on a floor. The 
 water becomes red; from it, by evaporation, the crude 
 ' lac-dye ' is obtained. This is made into cakes, and dried. 
 
 The lac-dye of commerce contains nitrogenous and mineral 
 matters, as well as several dark-coloured impurities, and 
 some resin. In order to prepare a lake from it, it should be 
 first powdered, and then digested in spirits of turpentine, or 
 benzene. The purified residue is, when dry, extracted with 
 sodium carbonate solution : the liquor is afterwards filtered 
 and precipitated with alum solution. The precipitate thus 
 formed is washed and dried in the dark. 
 
 Indian lake was used by the Venetian and Flemish 
 painters of the sixteenth century, but it does not seem, so 
 far as one can gather from the notices of it in the work of 
 De Mayerne, and in the Secreet-Boeck, to have been often 
 obtained of good colour. It is even spoken of as a ' light 
 brown.' 
 
 Indian lake is inferior in beauty, and in variety of hues, to 
 the colours from madder ; it is also more affected by light. 
 But it is much less fugitive than crimson lake and the other 
 cochineal pigments. 
 
COCHINEAL LAKES 
 
 185 
 
 I do not know from direct experiment whether the com- 
 parative stability of the red colouring matter from kermes 
 when used as a dye for animal fibres belongs also to all the 
 lakes prepared from this substance : anyhow, kermes pigments 
 are, so far as I can learn, not met with in commerce at the 
 present time. 
 
 Carmine and the Cochineal Lakes : Carmin — Laque 
 Cramoisie, or Crimson Lake— Purple Lake, etc. 
 
 Cochineal consists of the dried wingless females of a 
 species of coccus (C. cacti) which feeds upon several kinds 
 of Oftiintia, or cactus. The best quality comes from Tene- 
 riffe, and contains about half its weight of colouring matter. 
 This colouring matter is a glucoside, to which the name of 
 carminic acid has been given. When this substance is 
 treated with weak sulphuric acid, it is resolved into a sugar 
 and another colouring matter called carmine red. 
 
 The carmine of commerce is prepared directly from 
 cochineal, and is the most concentrated and purest form of 
 any of the pigments derived from this source. The methods 
 of preparation differ, but in all the colouring matter is ex- 
 tracted from the insects by means of boiling water, with the 
 subsequent addition of small quantities of alum, or nitre, or 
 potassium oxalate, or cream of tartar ; occasionally a small 
 quantity of stannous chloride is employed also. The liquor, 
 after a repose of some days or even weeks, deposits a great 
 part of the colouring matter as a deep crimson-red powder, 
 which is then thrown on a filter, washed and dried in the 
 dark. However prepared, it contains fat, albuminoid matter, 
 mineral salts, and other impurities ; the finest varieties, how- 
 ever, dissolve perfectly in strong liquor ammonias. The 
 liquor, which has deposited the carmine, gives up the re- 
 mainder of its colouring matter to freshly-precipitated alu- 
 

 COCHINEAL LAKES 
 
 minium hydrates, or, after having been rendered alkaline by 
 potassium carbonate, to a solution of alum. Lakes are thus 
 formed. Lakes are also made by directly precipitating 
 cochineal extract with solutions of potassium carbonate and 
 alum. A purplish tinge is given to the product by a small 
 quantity of lime ; other hues, generally dull, are imparted by 
 the presence of iron, manganese, or copper in the solutions 
 employed. The cochineal lakes always contain a larger 
 quantity of water and of alumina (or other mineral basis) 
 than carmine, and are consequently weaker. Scarlet lake is 
 a mere mixture of crimson lake and vermilion. 
 
 Beautiful and rich as are the colours prepared from cochi- 
 neal, not one of them should ever find a place upon the 
 palette of the artist. They all become brownish, and ulti- 
 mately almost disappear after a short exposure to sunlight 
 or the more prolonged attack of strong diffused daylight. 
 In six hours of sunshine a strong wash of fine crimson lake 
 on Whatman paper lost 8 per cent, of its original intensity ; 
 this was on April 12. The loss during a second period of 
 six hours' exposure was much less, but after the lapse of 
 four months less than 5 per cent, of the original colour 
 remained. In the case of carmine, from one to two years 
 was required for the complete obliteration of every trace of 
 the original crimson from a deep wash of this pigment. All 
 the cochineal pigments become somewhat brownish during 
 the course of fading, but ultimately, when all the red has 
 disappeared, either a greenish grey or a faint sepia-like brown 
 is the sole residue. 
 
 The term ' lake ' belongs to all colouring-matters thrown 
 down upon such a basis as alumina ; but when purple, 
 crimson, or scarlet is prefixed to the word lake, cochineal 
 colours are always understood. So carmine used alone 
 refers to cochineal carmine, although it is a general term 
 
BURNT CARMINE 
 
 187 
 
 for a group of rich pigments, of which madder carmine and 
 indigo carmine are perfectly distinct examples, derived from 
 madder and indigo respectively. 
 
 It is not necessary to say more about the various cochi- 
 neal pigments, nor to point out their many falsifications, for 
 their value as artists' colours is very small. No artist who 
 cares for his work and hopes for its permanency should 
 employ them. 
 
 Burnt Carmine. 
 
 This preparation should rather be called 'roasted car- 
 mine.' It is obtained by carefully heating the carmine 
 made from cochineal. It possesses a beautiful hue, but is 
 quite as fugitive as the product which yields it. Two years' 
 exposure to sunlight completely destroyed a strong wash of 
 cake burnt carmine on paper. The moist pigment had lost 
 nine-tenths of its intensity at the end of the same period, 
 while the small residual proportion of the colour had suffered 
 no further change in depth at the end of a further lapse of 
 three years. Burnt carmine is rather less fugitive in oil 
 than in water colour. Experiments in the latter medium 
 gave, after exposure to sunlight, the following residual inten- 
 sities out of ten : 
 
 Moist, after two years 
 Cake, after two years 
 Moist, after five years 
 
 A sample of burnt carmine purchased of Messrs. Newman 
 about the year 18 15 was found (as might have been antici- 
 pated) to have retained its colour in the cake perfectly to 
 the present year ; but a wash of it on paper possessed no 
 greater nor less degree of permanency than a wash of the 
 same pigment prepared by the same makers in 1886. 
 
mam 
 
 :,:,:■:;■,' ; o:,; .,,'.,:■.: ,;■; ; < .■■■.^■■^•O'' a .-/.Ky 
 
 ill 
 
 188 
 
 RED LEAD 
 
 Red Lead: Minium — Saturnine — Mine Rouge, Mine 
 Orange — Mennige — Rosso Satumo. 
 
 This beautiful orange-red pigment approaches in com- 
 position a compound of two molecules of protoxide of lead 
 with one molecule of binoxide, and may be approximately 
 represented by the formula Pb 3 4 . The paler and more 
 orange-tinted varieties contain an excess of protoxide of 
 lead, often accompanied by a little carbonate. 
 
 This pigment is peculiarly liable to discoloration in the 
 presence of sulphuretted hydrogen : it acts energetically 
 upon some paints, on the cadmium yellows, for example. 
 It is quite inadmissible as a water-colour, and cannot be 
 considered as safe in oil. 
 
 Cobalt Red : Rose de Cobalt — Cobalt Violet. 
 
 This little-used pigment should consist of the oxides of 
 magnesium and cobalt. It is prepared at a high tempera- 
 ture and is quite permanent. One method of making this 
 pigment involves the use of magnesium carbonate or oxide, 
 which is made into a paste with a solution of pure cobalt 
 nitrate. This paste is then slowly dried, and ultimately 
 calcined in a crucible. Different preparations of this pig- 
 ment differ considerably in hue ; a purplish cast is some- 
 times due to the accidental presence of alumina. 
 
 Pigments consisting of cobalt arseniate are occasionally 
 called ' cobalt-red ;' the term ' Cobalt violet ' is usually and 
 may be more fitly applied to them. The hue they present 
 is rather bluer (or less red) than that of the flowers of the 
 common foxglove. Cobalt violet has been made from the 
 mineral known as erythrite, or cobalt-bloom, which has the 
 formula Co 3 As 2 8 , 8H 2 ; an artificial cobalt arseniate is 
 also made by oxidizing cobalt sulph-arsenide, which is first 
 
COBALT RED 
 
 189 
 
 reduced to powder and then roasted with twice its weight of 
 potassium carbonate. After further treatment, the final 
 product obtained by grinding and washing constitutes a 
 pigment of a rather coarse grain which does not work 
 smoothly as a water-colour, but has the advantage of 
 complete stability in all vehicles. A sample of this cobalt 
 violet of good quality was found to contain no water and to 
 suffer no change when heated to a red heat in the air ; along 
 with cobalt arseniate it contained some phosphate. 
 
$Mm>m!* 
 
 . : ■ S t 
 
 CHAPTER XVI 
 
 GREEN PIGMENTS 
 
 Terre Verte : Green Earth — Terre de Verone — Grilne 
 Erde — Terra Verde. 
 
 There are two rather indefinite minerals, probably not really 
 distinct, namely, glauconite and celadonite, which furnish 
 the raw material from which the artists' pigment, generally 
 known as terre verte, is prepared. The form, or variety, 
 celadonite is the rarer of the two : it is softer than glauco- 
 nite : both minerals are probably mixtures. Green earth of 
 very good quality is found at Bentonico, to the north of 
 Monte Baldo, near Verona, where it occurs in cavities in an 
 amygdaloid rock. The best samples possess a deep olive- 
 green colour ; inferior specimens are celandine or apple- 
 green. Green earth is obtained from a large number of 
 European and American localities, and varies much in 
 chemical composition. From its greenish hue it has been 
 assumed to consist chiefly of a ferrous silicate — that is, a 
 silicate of protoxide of iron, and in this way it is represented 
 in the older analyses. But more exact analyses have shown 
 that green earth contains but a small part of its iron in the 
 protoxide condition, and that it is mainly a ferric silicate. 
 A choice specimen of fine hue from Monte Baldo gave the 
 following results on analysis, the numbers representing parts 
 in one hundred : 
 
TERRE VERTE 
 
 191 
 
 Water, given off at ioo° C. - 4'i 
 Water, given off at a red heat 4*2 
 Ferric oxide (Fe 2 3 ) - - 2C3 
 Ferrous oxide (FeO) - - 2*6 
 Alumina - - - - 1*7 
 
 Lime - 
 
 Magnesia 
 Potash 
 Soda - 
 Silica - 
 
 1*1 
 
 5-6 
 6-4 
 2-3 
 
 Si'7 
 
 Green earth is thus allied to the hornblendes, differing 
 mainly in the partial replacement of soda by potash and in 
 the presence of water. Being itself an alteration-product, it 
 is not likely to be amenable to further change, particularly 
 as the iron in it is for the most part fully oxidized. 
 
 Terre verte occurs in ancient Roman wall-paintings (the 
 prepared pigment was found in the ruins of Pompeii), and 
 was largely employed by the early artists of Italy in their 
 works in tempera, fresco, and oil. But amongst the green 
 pigments found in ancient wall-paintings in Rome and 
 Pompeii there occurs also a substance of a richer and deeper 
 hue than that possessed by terre verte. It was made by 
 grinding into fine powder a kind of green jasper; it has 
 proved quite permanent. 
 
 Terre verte is prepared by carefully selecting the richest- 
 coloured and most uniform specimens of the mineral, grinding 
 them to fine powder, and washing the pulverized material 
 with rain-water ; it is then dried. Sometimes the selected 
 fragments are heated, and then quenched in very dilute 
 hydrochloric acid to remove ochre and other impurities ; the 
 undissolved portion is then ground, washed thoroughly, and 
 dried. Most samples of terre verte are found to be perfectly 
 stable both in water-colour and oil-painting. It is a semi- 
 opaque or translucent pigment, without much body in oil. 
 It has no action on, nor is it affected by, other permanent 
 pigments. When used in oil or tempera as a ground-colour 
 or in the under-painting, terre verte sometimes becomes more 
 conspicuous in the course of time, owing partly to the 
 
192 
 
 GREEN OXIDE OF CHROMIUM 
 
 deepening of its own hue and partly to the increased trans- 
 lucency of the pigments which have been laid over it. 
 Some samples of terre verte seem to be liable to become 
 slightly rusty when brought into contact with lime hydrate 
 in true fresco painting. This is probably due to the further 
 oxidation of some of the ferrous oxide they contain. 
 
 Terre verte is rarely adulterated. A pure sample is not 
 affected when drenched with liquor ammonias, becoming 
 neither more bluish (presence of copper compounds), nor 
 more brownish (presence of Prussian blue). But although 
 adulterated terre verte is rarely met with I have found that 
 a well-known firm of artists' colourmen sell, or have sold, a 
 mixture with green ultramarine under the name of terre 
 verte. Tubes of oil-colour of this sort have been submitted 
 to me for analysis. This substitution is unfair to the artist, 
 who has a right to obtain the material he demands. Green 
 ultramarine freed from oil gives sulphuretted hydrogen when 
 moistened with hydrochloric acid, which has no such action 
 on terte verte. 
 
 Green Oxide of Chromium : Chromium Sesquioxide — 
 True Chrome Green — Opaque Oxide of Chromium — Vert 
 de Chrome — Gricnes Chromoxyd. 
 
 The so-called native oxide of chromium, or chrome ochre, 
 is a mere greenish clay, containing not more than 10 per cent, 
 of chromium oxide. But another mineral (from Okhansk, 
 in Siberia) is of a deeper green, and sometimes contains 
 one-third of its weight of this oxide. We are not aware that 
 any attempt to employ these minerals as pigments has ever 
 been made. 
 
 The green oxide of chromium, Cr 2 3 , varies in hue, in 
 depth of colour, and in opacity according to the process of 
 its preparation. It may be made either in the ' dry ' way or 
 
GREEN OXIDE OF CHROMIUM 
 
 193 
 
 the ' wet ' way. Perhaps the finest quality is that produced 
 by heating mercurous chromate in a retort till the whole of 
 the mercury has been distilled off. This is an expensive 
 process, but the product is excellent in colour and body. 
 Ammonium bichromate gently heated, in small portions at a 
 time, yields a dull-coloured but a useful variety of this pig- 
 ment; but there is a similar, though more economical process, 
 yielding a better-coloured product. This consists in gently 
 heating together and then calcining a mixture of 3 parts of 
 neutral potassium chromate with 2 parts of ammonium 
 chloride. The mass is to be thoroughly washed with hot 
 water, dried, and again ignited. Two other processes for pre- 
 paring this pigment in the dry way may be commended. In 
 both of them potassium bichromate (free from iron) is used, 
 but in the one case sulphur, in the other starch, is employed, 
 in order to effect the reduction of the chromic salt to the 
 condition of sesquioxide. The sulphur method yields at 
 once a good pigment, which needs nothing but a thorough 
 washing, first with very dilute sulphuric acid and then with 
 water, followed by grinding, to fit it for use, but a second 
 calcination is required in the starch process. In order to 
 prepare oxide of chromium by the wet way, a solution of an 
 alkaline chromate or bichromate is to be reduced by sulphur 
 or other reducing agents, or a sesquisalt of chromium is 
 precipitated by ammonia or a fixed alkali. The hydrated 
 sesquioxide is thrown down ; after having been washed, this 
 substance is gently calcined. The hydrate itself, when air- 
 dried, constitutes one of the forms of ' transparent oxide of 
 chromium.' 
 
 The ordinary or opaque oxide of chromium usually occurs 
 in the form of a greyish-green powder of considerable body. 
 It is quite permanent under all conditions of exposure and 
 of commixture with other pigments, and is available in all 
 
 13 
 
 / ) 
 
nr 
 
 ■■ g i 
 
 194 
 
 VIRIDIAN 
 
 the processes of painting. Its tints with flake-white, and the 
 yellowish greens which it yields with aureolin, are peculiarly 
 valuable to the landscape-painter. 
 
 Green oxide of chromium is rather imitated than adul- 
 terated. This pigment when genuine is not altered in 
 colour either by ammonium sulphide or caustic potash. 
 But under the name of chrome-green mixtures of Prussian 
 blue and lead chromate are constantly sold. These pre- 
 parations generally contain some barium sulphate, often a 
 considerable quantity of gypsum, and, occasionally, alumina. 
 The term 'chrome-green ' cannot be justly applied to these 
 mixtures, which are greatly inferior in stability to the pig- 
 ments under discussion, and are all discoloured by lime 
 and alkalies. 
 
 Viridian: Emerald Oxide of Chromium — Vert Pannetier — 
 Vert de Guignet — Vert Emeraude — Matter's Green. 
 
 About the year 1838 Pannetier and Binet began to make 
 a beautiful chromium green by means of a secret method. 
 Many years afterwards M. Guignet discovered and patented 
 a process by which this admirable pigment could be manu- 
 factured. About 8 parts of crystallized boracic acid and 
 3 parts of potassium bichromate are thoroughly mixed and 
 calcined. The mass obtained is treated with cold water, 
 washed by decantation, ground wet, washed with hot water, 
 and carefully dried. The product is a hydrated chromium 
 sesquioxide, in which a variable amount of the boracic con- 
 stituent is often retained. Viridian is, however, essentially 
 a hydrated sesquioxide of chromium, having the formula 
 Cr 2 3 , 2H 2 0. In the preparation of this pigment it often 
 happens that sufficient care is not taken to wash it perfectly 
 free from all soluble salts. I have known the metal tubes 
 in which this moist water-colour has been kept to be cor- 
 
VIRIDIAN 
 
 195 
 
 roded by these salts and to fall to pieces in a few months. 
 The presence of such saline matter is easily detected by 
 mixing the moist or cake colour with water and noting if 
 coagulation or curdling takes place. 
 
 It would be difficult to exaggerate the value of this addi- 
 tion to the artist's palette. The colour of viridian is a very 
 deep bluish green of great purity and transparency. It 
 furnishes, with aureolin on the one hand and with ultra- 
 marine on the other, an immense number of beautiful hues, 
 adapted to represent the colours of vegetation and of water. 
 It is quite unaffected by sunlight and sulphuretted hydrogen, 
 and it has no action on other pigments. Moreover, it may 
 be safely used with all the different painting media, and 
 upon all kinds of painting-grounds. 
 
 Viridian is the name by which this pigment is perhaps 
 now best known in England. It is unfortunate that it 
 should be called ' Vert Emeraude ' in France, since it has 
 little in common with the poisonous emerald green of our 
 colourmen. This pigment is sometimes adulterated with 
 baryta yellow in order to modify its hue. This substance 
 may be readily detected by moistening the pigment with 
 dilute hydrochloric acid, when a yellow solution is obtained. 
 
 Arnaudon's chrome green is of a somewhat opaque green 
 hue, rather like that of Schweinfurt; it is a phosphate of 
 chromium. A similar product is Mathieu-Plessy's chrome 
 green; but under the name of 'chrome green,' 'green 
 cinnabar ' and ' griiner Zinnober,' spurious pigments are 
 constantly sold, the commonest of them consisting of mix- 
 tures of chrome yellow and Prussian blue. They are worth- 
 less in comparison with viridian. 
 
 
 13—2 
 
. ,: ,. I 
 
 ;. . ■ v., B ... 
 
 196 
 
 COBALT GREEN 
 
 Cobalt Green : Rtnmann's Green — Vert de Cobalt — Vert 
 de Zinc — Kobaltgriln. 
 
 It has long been known that the oxide or a salt of zinc, 
 moistened with a solution of cobalt nitrate, and then strongly 
 heated before the blow-pipe, gives a porous mass of a beauti- 
 ful green hue. This compound or mixture of the oxides of 
 zinc and cobalt may be prepared by : (1) Precipitating with 
 an alkaline carbonate a mixture of the nitrates of cobalt and 
 of zinc, and then strongly heating (after washing) the pre- 
 cipitate formed ; (2) Making a paste of zinc oxide and water, 
 and adding to it a solution of nitrate or sulphate of cobalt, 
 or of roseo-cobaltic chloride; the mass is then dried, calcined 
 at a dull red heat, thrown into water, ground, washed, and 
 dried. Method No. 2 gives a finely-coloured product, the 
 depth of hue being proportional to the percentage of cobalt 
 oxide. If the latter oxide amount to one-third of that of 
 zinc the colour is a very deep bluish green ; with no more 
 than one-sixth the colour is still rich. Some specimens do 
 not contain more than one-twentieth — sometimes even less 
 — of cobalt oxide, and yet they are far from pale. An excel- 
 lent deep sample contained 12 per cent, of cobalt oxide. 
 
 When properly prepared, cobalt green is a pigment of 
 great beauty and power.* The deeper tones of cobalt green 
 are almost transparent in oil. The pigment works well, is 
 quite permanent, and has no action on other pigments. 
 Cobalt green is, in fact, one of the too-rare pigments which 
 is at once chemically and artistically perfect ; such at least 
 is the conclusion I reached from my own trials, but Mr. 
 J. Scott Taylor tells me that cobalt green fades a good deal 
 when exposed to damp, although it stands light well. It 
 
 * The deep transparent cobalt green sold by Edouard, of Paris, is by 
 far the best I have examined. 
 
EMERALD GREEN 
 
 197 
 
 must be admitted, however, that it may be exactly imitated 
 by a mixture of viridian and artificial ultramarine with a 
 little zinc white. 
 
 Cobalt green is again coming into artistic use, as it is 
 equally adapted for all the methods of painting. It was 
 discredited for awhile by the inferiority of the product 
 obtained by Rinmann's original process (No. 1 above). It 
 ought not to be an expensive pigment. 
 
 Sometimes cobalt green is prepared by precipitating a 
 cobalt salt with an alkaline arseniate or phosphate, and then 
 heating the precipitate with zinc white. 
 
 Emerald Green 
 
 Cupric Aceto-Arsenite — Schweinfurt Green 
 — Vert Paul Veronese. 
 
 This pigment was discovered in 1814 during the course of 
 experiments made with the object of preparing an improved 
 Scheele's green. It may be prepared by half a dozen slightly 
 differing processes, but in all verdigris (or vinegar and blue 
 vitriol) and white arsenic are the two essential materials 
 employed. Generally verdigris is dissolved in acetic acid, 
 and added to a boiling aqueous solution of white arsenic : 
 on continued ebullition a deposit of emerald green occurs. 
 Sometimes copper sulphate, potassium arsenite, and acetic 
 acid are employed. Whatever the method, it is necessary 
 that the coloured product be washed with boiling water to 
 remove the last traces of soluble salts. 
 
 The hue of this pigment is a nearly normal green, slightly 
 verging upon bluish green ; it is brighter and more opaque 
 than Scheele's green, and, like it, is a deadly poison. It is 
 less attacked by sulphuretted hydrogen than Scheele's green, 
 but as a water-colour, does not long remain untarnished in 
 impure air. In oil it is practically permanent, both alone 
 and when used with the majority of permanent pigments. 
 

 198 
 
 SCHEELE'S GREEN 
 
 It is, however, quickly blackened by the cadmium yellows. 
 Emerald green cannot be relied upon as permanent in fresco 
 and tempera painting. Its use in wall papers and in the 
 decoration of all domestic furniture and fabrics is to be 
 deprecated, by reason of its poisonous character ; but is, 
 happily, at the present time, in great measure abandoned. 
 
 Emerald green, if pure, dissolves perfectly in boiling dilute 
 nitric or hydrochloric acid ; the solutions thus made should 
 yield no precipitate with a few drops of barium chloride 
 solution. An undissolved residue generally shows the pre- 
 sence of baryta white. 
 
 Emerald green may be distinguished from Scheele's green 
 by a simple experiment. If a small pinch of the dry powder 
 be warmed with a few drops of moderately strong sulphuric 
 acid (half oil of vitriol, half water), acid vapours, having the 
 smell of vinegar, will be given off only when true emerald 
 green is the subject of the experiment. 
 
 On the Continent, Vert Emeraude is the name given to 
 viridian, the emerald oxide of chromium. 
 
 Scheele's Green : Cupric Arsenite — Swedish Green — 
 Mitis Green — Scheele's Griin. 
 
 This pigment, discovered in 1778, is an arsenite of copper 
 with an excess of copper oxide. It is best prepared by 
 dissolving, in separate portions of hot water, white arsenic 
 and blue vitriol. The solutions are then mixed, and to the 
 mixture is added, in small successive portions, a solution of 
 potassium carbonate. These additions are stopped when 
 the precipitated pigment has attained its maximum of colour 
 intensity. In another process, a hot solution of potassium 
 arsenite is added to a hot solution of blue vitriol. This 
 pigment needs thorough washing with hot water, and must 
 be dried at a moderate temperature. 
 
MALACHITE 
 
 199 
 
 Scheele's green presents nearly the same characteristics as 
 emerald green, but is in every way inferior to that pigment. 
 It is eminently poisonous. It should not find a place on 
 the palette of the artist. 
 
 Vienna green, Mitis green, and Veronese green are names 
 which have been given to specially prepared varieties of 
 this cupric arsenite ; but there are very many other desig- 
 nations by which pigments of essentially the same composi- 
 tion are known. They are prepared by slightly modified 
 processes, and frequently contain such foreign matters as 
 chalk, heavy spar, or gypsum. 
 
 Malachite : Green Verditer — Green Bice — Mountain 
 Green — Green Carbonate of Copper — Vert de Montague 
 — Berggrun. 
 
 This green copper mineral was employed as a paint by 
 the ancients. It often accompanies the blue carbonate, 
 and occurs in many European, Asiatic, African, and 
 American localities. The mines at Ekaterinburg and 
 Nischne Tagilsk in Russia, and at Burra-Burra in South 
 Australia, furnish malachite of fine colour; it also occurs 
 abundantly in Namaqualand. Its variations in depth of 
 colour are due less to impurities than to differences in its 
 state of aggregation. Its specific gravity is about 4. Its 
 composition is that of a hydrate and carbonate of copper. 
 It may be represented by the formula CuC0 3 ,CuH 2 2 . It 
 contains, therefore, less of the copper carbonate than 
 azurite, or blue verditer. 
 
 Malachite requires no other treatment than careful grind- 
 ing to fit it for use as an artists' pigment. The raw material 
 must, however, be carefully selected, and all visible im- 
 purities, such as ochreous veins and deposits, and azurite, 
 
B 
 
 200 VERDIGRIS 
 
 completely removed. An artificial malachite has been 
 prepared, and is often substituted for the mineral ; but it is 
 inferior in colour and stability to the native form. 
 
 Malachite as an oil-paint has often proved to be perma- 
 nent, although it may seem to acquire a dull, brownish hue, 
 owing to the darkening and yellowing of the oil; some- 
 times, however, it becomes somewhat olive in colour. In 
 admixture with cadmium yellow it is liable to blacken. It 
 is so easily injured by impure air when unprotected by any 
 hydrofuge, that it is quite inadmissible as a water-colour. 
 In old tempera paintings it is sometimes found to have 
 stood well; but the sulphur from the egg-medium and from 
 the size has not infrequently browned it. 
 
 Malachite is sometimes adulterated with baryta white ; 
 sometimes a mixture of that pigment and an arsenical green 
 is substituted for it. The former falsification may be 
 detected by boiling the sample in hydrochloric acid, when 
 the malachite dissolves, leaving the baryta white as a sedi- 
 ment. To detect an arsenical green, a small portion of the 
 sample should be mixed with powdered charcoal, gently 
 warmed at first in a long narrow test-tube to drive off 
 moisture, and then strongly heated ; a dark sublimate of 
 metallic arsenic will form on the cooler part of the tube. 
 
 Verdigris: Basic Copper Acetate — Vert-de-Gris — Verdet 
 de Montpellier — Grilnspan. 
 
 This green copper pigment was called by the writers of 
 the fourteenth century ' viride Gnecum,' or, more simply, 
 'viride,' 'viride terrestre ' being used for green-earth — that 
 is, ' terre verte.' ' Vert-de-Grece ' — that is, verdigris — was 
 used by the ancient Romans as a pigment, and has been 
 detected in the wall-paintings of Pompeii. It occurs in 
 early Italian tempera pictures ; but it has frequently injured 
 
VERDIGRIS 
 
 the gesso-ground on which it has been laid, forming calcium 
 acetate with the calcium carbonate, and disintegrating the 
 surface. The blackness of the shaded parts in many 
 Venetian and Spanish pictures of the sixteenth and seven- 
 teenth centuries has been attributed to the changes which 
 this pigment suffers in oil. The medieval writers on the 
 practice of painting endeavoured to show how the peculiar 
 liability of verdigris to change could be obviated by locking 
 it up in some hydrofuge substance, such as a resin or balsam. 
 But the problem actually possesses little practical interest 
 to-day, though of real moment in the study of old pictures. 
 In the modern palette the place of verdigris is taken by 
 permanent greens derived from chromium and from cobalt : 
 concerning the safety of these we need not be anxious. 
 The large proportion of resinous matter employed by early 
 painters for the protection of verdigris from alteration, and 
 the success of this precautionary measure, may be seen in 
 the green drapery in several pictures by Van Eyck and 
 Mabuse in the National Gallery and at Hampton Court. 
 It should, however, be stated that the older processes for 
 preparing verdigris often yielded a product much more 
 alterable in the presence of damp than is the verdigris 
 which for a century or more has been made at Mont- 
 pellier. 
 
 Verdigris is commonly called in chemical language a 
 basic acetate of copper. In fact, it is a mixture of three such 
 acetates, its varying hues, ranging from green to greenish 
 blue, being dependent upon the relative proportions of these 
 acetates. The most blue basic acetate contains i molecule 
 of copper acetate, and i of copper hydrate, with 5 mole- 
 cules of water; the greenest has twice as much acetate. 
 Average verdigris contains in 100 parts about 29 parts of 
 anhydrous acetic acid, 43 of copper oxide, and 27 of water. 
 
'■>'".■■> ■•'■■■.■' v -.■:■ 
 
 "■■>.: ■ SSjtJ - : S & :' H ^^SSCiSSS 
 
 VERDIGRIS 
 
 It is nearly insoluble in cold water; but by continuous 
 washing, or by continuous exposure to moist air, is ulti- 
 mately decomposed. 
 
 The Montpellier process for making verdigris consists in 
 exposing thin strips of metallic copper to the vapours arising 
 from grape marc undergoing the acetic fermentation. The 
 operation is conducted in a moist, warm atmosphere ; finally, 
 the whole substance of the metallic copper is transformed 
 into verdigris. 
 
 An impure atmosphere containing sulphuretted hydrogen 
 blackens verdigris ; it is also affected by moisture and by 
 carbonic acid. As a water-colour, it is quite inadmissible ; 
 in oil, it stands pretty well if ' locked up ' in the way already 
 described. But it acts energetically upon several important 
 pigments, and is very poisonous. For these reasons its 
 employment in artistic painting ought to be abandoned. 
 
 Verdigris, if pure, dissolves perfectly in liquor ammonias, 
 any gypsum or barytes present as diluents or adulterants 
 remaining undissolved. If blue vitriol has been added to 
 verdigris, it also will dissolve in the ammonia; but this 
 falsification may be detected by acidifying the ammoniacal 
 solution with hydrochloric acid, and then adding solution of 
 barium chloride — a white precipitate of barium sulphate 
 indicates the presence of copper sulphate. 
 
 There are many composite green pigments sold by artists' 
 colourmen ; none is of real value. Green lake, a mixture 
 of quercitron lake and Prussian blue ; Hooker's green — 
 gamboge and Prussian blue ; olive green — Indian yellow, 
 umber and indigo ; and olive lake, a mixture of quercitron 
 lake, bone brown and ultramarine — all these belong to the 
 same category. 
 
CHAPTER XVII 
 
 BLUE PIGMENTS 
 
 Ultramarine : Lapis Lazuli Blau — Lasurstein Blau — 
 Outre?ner — Bleu d'Azur. 
 
 There are at least three mineral species, closely allied in 
 chemical composition, and generally presenting a more or 
 less marked blue colour, which contain as their essential 
 constituents the five elements, silicon, aluminium, sodium, 
 sulphur, and oxygen, and which owe their characteristic hue 
 to the sarnie compound. From one of these minerals, a 
 variety of 'hauyne/ often called 'lapis-lazuli,' the true or 
 native ultramarine is obtained. This stone occurs, of very 
 varying purity and colour, at Bucherei, Transbaikal, and in 
 many other Siberian localities ; at Ditro, in Transylvania ; 
 in the Andes of Ovalla, Rio Grande ; and in several regions 
 of Persia, Tibet, and China. It is the ' sapphire ' of ancient 
 authors. Small golden specks of iron-pyrites are frequently 
 irregularly scattered through its substance ; it is also very 
 frequently associated intimately with portions of the rocky 
 gangue, or matrix (limestone, syenite, granite, etc.), in which 
 it occurs. Very fine lapis-lazuli comes from Tibet. 
 
 To prepare a pigment from this mineral, selected pieces 
 of small size, as free as possible from pyrites or other impuri- 
 ties, are heated in a crucible and quenched (etonne) in cold 
 water, or very weak vinegar. The material, thus disin- 
 
Bd&fltfj 
 
 
 204 
 
 ULTRAMARINE 
 
 tegrated, is washed by decantation, and then dried and 
 carefully ground. The powder is then purified by elutria- 
 tion, or ' washing over,' the several wash-waters depositing 
 pigments of different depths of colour, and of different 
 degrees of fineness. Some manufacturers adopt an old 
 process, and make the powder into a soft mass with a little 
 rosin, linseed oil and beeswax, and knead, beat, or macerate 
 the lump under very weak potash, or soda-lye — the alkaline 
 water carries off or withdraws the greater part of the pig- 
 ment, and deposits it on standing. The richness of the blue 
 product obtained depends primarily upon the original quality 
 of the stone, but several grades are always procurable from 
 the same raw material by means of the above- described 
 processes, bluish grey and grey powders, known respec- 
 tively as ultramarine ash and mineral grey, being the last 
 and the least valuable products, while the deepest and 
 finest pigments are deposited from the earliest wash- 
 waters. 
 
 Optically, the superb blue of native ultramarine approaches 
 more closely than the blue of any other pigment to the pure 
 normal blue of the solar spectrum ; it shows very little violet 
 and in this respect is unlike most specimens of artificial 
 ultramarine. Ultramarine is somewhat harsh and granular 
 in texture, a characteristic which may be reduced by a small 
 admixture of Chinese white, but which becomes more 
 marked when it is used, as a light wash, or in conjunction 
 with transparent pigments, in water-colour painting. It 
 more nearly approaches transparency when used in oil, and 
 is then of excellent working quality. 
 
 It is generally considered that ultramarine withstands the 
 action of light, moisture and sulphuretted hydrogen perfectly, 
 and that it neither affects nor is affected by any other pig- 
 ments. I have, however, been informed by an English 
 
ULTRAMARINE 
 
 205 
 
 landscape painter in oil, who has largely employed native 
 ultramarine in the skies of his pictures, that he has lost faith 
 in its inalterability. But the question arises, ' Was the pig- 
 ment used always authentic ?' It dries well in oil. It is 
 decolourized at once by a hot solution of alum, and 
 ultimately even by a saturated cold solution, which, how- 
 ever, bleaches very quickly all but the most stable varieties 
 of the artificial pigment. All mineral acids, save carbonic, 
 and all the common organic acids, such as acetic, oxalic 
 and citric, discharge the colour of native ultramarine. It 
 is only by a combination of several tests in the hands of 
 a skilled chemist that the discrimination of genuine from 
 spurious ultramarine may be with certainty accomplished. 
 
 It may, however, be mentioned here that when a current 
 of hydrogen gas is passed over true ultramarine heated in a 
 glass tube the powder retains its colour wholly or partially 
 for an hour or more, while the best artificial pigment similarly 
 treated becomes grey or greenish grey. 
 
 In the works — both in fresco and tempera, and in oil — 
 of many of the old masters, and in a large number of 
 illuminated manuscripts, the permanence of true ultramarine 
 may be seen. If in some cases it has acquired a greenish 
 or dull hue in oil-painting, such change is due to the yellow- 
 ing of the oil and varnish, and not to any deterioration of 
 the pigment. 
 
 The price of genuine ultramarine is very high. This 
 is due less to the scarcity of the original lapis-lazuli from 
 which it is derived, than to the small yield and to the 
 elaborate and tedious operation by means of which the pig- 
 ment is prepared. But when every allowance is made on 
 account of the troublesome and lengthy process of manufac- 
 ture, the cost of ultramarine is unwarrantably excessive. 
 
^^l^j^j^j^^JSS^^is^s^^^^S^^^i 
 
 206 ARTIFICIAL ULTRAMARINE 
 
 Artificial Ultramarine : New Blue— French Blue — 
 Permanent Blue — Gmelin's Blue — Guimefs Blue. 
 
 In the year 18 14 a blue coloration, subsequently proved 
 to be due to ultramarine, was noticed in the soda (black-ash) 
 furnaces of St. Gobain. About fourteen years afterwards a 
 method of making the same blue substance at will was 
 discovered by Christian Gmelin, and by Guimet ; this 
 method was founded in part upon chemical analyses of 
 natural ultramarine, and in part upon a study of the condi- 
 tions under which the above-named blue coloration 
 occurred. By successive improvements in its manufacture 
 artificial ultramarine is now produced at a cost of no more 
 than a few pence per pound. It is chiefly made in Germany 
 and in France. 
 
 The raw materials employed in the preparation of ultra- 
 marine are kaolin, or China-clay, silica, sodium sulphate, 
 sodium carbonate, sulphur, charcoal and rosin. Some 
 makers omit the sodium sulphate, others the rosin, while 
 calcined alum is occasionally substituted for the kaolin. 
 These materials are heated together in closed crucibles in a 
 furnace, and slowly cooled. A greenish porous cake is the 
 product : this is powdered and gently roasted, after the 
 addition of a little sulphur, for some hours. The material 
 is again powdered, and then washed and dried : further 
 calcination is sometimes required to develop the proper 
 blue colour. 
 
 In preparing artificial ultramarine for use as an artists' 
 pigment it must be very finely ground, and very thoroughly 
 washed with water free from lime. The grinding not only 
 improves the colour, but renders working with the paint less 
 difficult to manage ; the washing removes soluble sulphates 
 and certain sulphur-compounds, which are liable to discolour 
 
ARTIFICIAL ULTRAMARINE 
 
 207 
 
 some of the pigments (those containing lead or copper) with 
 which the ultramarine may be associated in a picture. 
 
 The hue of artificial ultramarine is commonly of a less 
 pure quality than that of the natural pigment, verging some- 
 what towards a purple. But its range of hue is considerable, 
 from a greenish-blue to a decided violet. The greenish-blue 
 and blue varieties are not affected in hue by admixture with 
 zinc white, but the varieties which incline towards violet 
 become remarkably enfeebled in richness of colour by this 
 admixture, such weakening being out of all proportion with 
 the dilution of tint which would be expected to ensue from 
 this addition of white. However, other white substances do 
 not produce this curious result. 
 
 Weak acetic acid, and a saturated cold solution of alum, 
 which are without immediate action upon natural ultra- 
 marine, generally change the hue, and always ultimately 
 decolourize the artificial product. Those kinds which have 
 a somewhat violet tinge resist the destructive action of the 
 above reagents longer than the pure blue and greenish-blue 
 varieties. Neither sulphuretted hydrogen, nor caustic lime 
 or other alkaline substance, affects the colour of artificial 
 ultramarine. 
 
 Although the colour of ultramarine is certainly due to a 
 substance containing sulphur, the precise chemical composi- 
 tion of this blue substance has not yet been determined. 
 Some chemists are of opinion that it is a compound of 
 aluminium, sodium, sulphur, and oxygen ; others regard it 
 as a sulphide of aluminium. There is little doubt, however, 
 that it contains sulphur in two conditions. Some curious 
 derivatives of blue ultramarine, of various colours, have 
 been obtained, in which it is believed that the sodium of 
 the original compound has been replaced by other metals ; 
 such is the yellow • silver-ultramarine,' prepared by keeping 
 
ee r rag . asg ./'■'■■'■.'" ■ ,. E sags >•■..-■■.■ | a gsg 
 
 208 
 
 ARTIFICIAL ULTRAMARINE 
 
 blue ultramarine in a solution of silver nitrate. These 
 bodies are, however, useless as pigments. The function of 
 the silica in ultramarine is not known, although it forms 
 from 30 to 45 per cent, of the total weight of all the 
 varieties, and although it has been found by experience 
 that ultramarines rich in silica resist the action of alum 
 better than those which are poor in this constituent : these 
 silicious ultramarines are sometimes sold under the name 
 of ' Oriental Blue.' 
 
 Artificial ultramarine, when properly prepared, is perma- 
 nent both in water and oils. When thin washes on paper 
 appear to lose strength as they dry, or soon afterwards, 
 the change is due to the chemical action of the alum, or 
 other aluminium compound, present in the size of the 
 paper. If an ultramarine should discolour emerald green, 
 chrome yellow, Naples yellow (true), or flake white, it pro- 
 bably contains free sulphur, or has been insufficiently 
 washed. 
 
 In order to test the purity of ultramarine, an easy plan, 
 useful so far as it goes, is this : Boil a small quantity of the 
 sample with distilled water in a wide test-tube for five 
 minutes. Pour the liquid on to a wetted Swedish filter- 
 paper fitted in a funnel. Divide the clear filtrate which 
 runs through into 2 parts — to one add a few drops of basic 
 acetate of lead ; to the other a few drops of barium chloride 
 solution. No darkening should occur in the first case, nor 
 any white cloudiness in the second. Besides the white 
 adulterants, gypsum and heavy spar, both chessylite and 
 Prussian blue have been found in artificial ultramarine. If 
 chessylite be present, its presence may be detected by 
 warming the sample with ammonia solution, when a blue 
 solution will be obtained. Ultramarine containing Prussian 
 blue acquires a brown hue when warmed with caustic soda 
 
ARTIFICIAL ULTRAMARINE 
 
 209 
 
 solution, while it does not completely lose its blue colour 
 when treated with dilute hydrochloric or sulphuric acid. 
 
 When an acid (such as hydrochloric or oxalic) acts upon 
 ultramarine, it disengages both sulphur and sulphuretted 
 hydrogen ; a good deal of silica is also, in most cases, 
 then separated in a gelatinous form. The sulphur separated 
 as such may amount to as much as 10 per cent, of the 
 weight of the pigment taken, or it may be less than a half 
 per cent. The sulphur disengaged as sulphuretted hydrogen 
 through the action of an acid varies between a half per cent, 
 and 6 per cent. As these variations have no relation to the 
 depth of colour in the several samples, it is evident that a 
 great proportion of this sulphur does not form an essential 
 part of the blue pigment itself. Other things being equal, 
 it is well to select samples of ultramarine which contain as 
 little as possible of sulphur in any state. 
 
 The ultramarines known as ' Guimet's ' and ' Heumann's' 
 are of fine quality. Large quantities of this pigment are 
 manufactured in Germany and France, smaller amounts in 
 Belgium and England. The green, violet, lilac, purple and 1 
 red ultramarines of commerce are permanent pigments of ' 
 some artistic value. They are or may be produced in the 
 manufacture of the blue variety, the green being its pre- 
 cursor and the others being formed by further heating of 
 the blue kind. The final product is a greyish white body. 
 
 There are two easily applied tests which, taken together, 
 enable one to estimate the relative values of a set of 
 samples of ultramarine in powder. These tests have dis- 
 tinct objects in view. In one, resistance to alteration is 
 determined — in the other, the colouring power. The 
 quantity operated on is only 5 centigrams, so the best plan 
 is to begin by weighing out, with the aid of a sensitive 
 balance, two portions of '05 gram a-piece from each sample. 
 
 14 
 

 I 
 
 210 COBALT BLUE 
 
 One of each of these portions is thoroughly mixed, by 
 means of an ivory spatula, on highly glazed white paper, 
 with 2 grams of pure kaolin : the tints of the several kinds 
 are then compared. For the other test we require a 
 number of small precipitating glasses or large test-tubes, 
 and a supply of a saturated solution of potash alum in 
 distilled water. The five centigrams of each sample of 
 ultramarine are put into the duly labelled glasses and a 
 measured quantity (say 50 cubic centimetres) of the alum 
 solution is poured on with constant stirring. The change 
 or loss of colour is duly noted at intervals of time, some 
 samples opposing a resistance of days to the destructive 
 influence of the alum, while others are injured by a contact 
 of a few hours, or, in some extreme cases, of a few minutes. 
 It is scarcely necessary to add that the contents of each 
 test-glass should be thoroughly stirred at regular intervals. 
 To avoid this necessity, and at the same time to improve 
 the accuracy of the results, a slight modification of the 
 method may be introduced. Ten grams of the purest agar- 
 agar are dissolved by the aid of heat in a litre of the 
 alum solution. Just before this liquid has become a jelly 
 by cooling, a measured portion is poured upon the neces- 
 sary quantity of ultramarine : the mixture after thorough 
 agitation is allowed to set, so that the pigment remains 
 suspended throughout the mass; any changes of colour 
 can be easily recognised. 
 
 Cobalt : Cobalt Blue — Bleu de Th'enard — Kobaltblau. 
 
 Excluding smalt, which owes its colour to a cobalt 
 silicate, there are at least three pigments which go under 
 the name of 'cobalt' or 'cobalt blue.' The best known 
 of these is a combination of alumina and cobalt oxide ; then 
 comes Leithner's or Thenard's blue, a cobalt phosphate; on 
 
COBALT BLUE 
 
 an aluminous base ; lastly, there is an aluminous cobalt 
 arseniate very much like the phosphate. 
 
 The original and simplest form of cobalt blue, or 
 Wenzel's blue, may be made by calcining strongly an inti- 
 mate mixture of aluminium hydrate and cobalt oxide. A 
 better way consists in moistening freshly-precipitated 
 aluminium hydrate with a solution of cobalt nitrate, drying 
 and then strongly igniting the mass. It may likewise be 
 prepared by precipitating a solution of sodium aluminate 
 by means of cobalt chloride solution. Thenard's blue may 
 be prepared by mixing about 8 parts of aluminium hydrate 
 with i part of cobalt phosphate, both in the moist condition, 
 then drying and strongly calcining the mixture ; cobalt 
 arseniate may replace the phosphate. Another variety of 
 Thenard's blue is obtained by adding sodium phosphate 
 solution to a solution of alum containing a little cobalt 
 sulphate. In all the above methods, the complete freedom 
 of the materials used from iron and nickel is essential to 
 the purity and beauty of the blue pigment formed. 
 
 The cobalt blues work well in all media. They are un- 
 affected by light, moisture, and oxygen. The best samples 
 of them are practically permanent even in impure air, but 
 ammonium sulphide tends to discolour them. If they 
 appear changed in hue in any oil-paintings, the yellowing of 
 the admixed or overlying oil or varnish must be regarded as 
 the cause. Cobalt blues may be used in fresco-painting ; 
 they are unaffected by commixture with other pigments. 
 Cobalt blues do not lose their colour when boiled with 
 alum solution, nor when treated with moderately strong 
 acids. 
 
 Cobalt blue as an oil-colour is usually ground with about 
 three-fourths its weight of linseed or poppy oil. 
 
 Cobalt blue examined optically is found to reflect much 
 
 14 — 2 
 
........ gasaggaga jm 
 
 1 "■■':"'■ ■.■"..-,■ -...,. 
 
 HHHHr 
 
 212 CCERULEUM 
 
 green and violet light as well as blue. Viewed by candle 
 or gas light it acquires a very marked purplish hue. 
 
 The introduction of cobalt blue to the palette of the 
 artist may be said to have created a revolution in the 
 style of painting, especially obvious in water-colour land- 
 scapes. 
 
 Cceruleum : Cerulium — Cerulean Blue — Coelinblau — 
 Bleu Celeste. 
 
 When oxide of tin is moistened with cobalt nitrate solution 
 and strongly heated, a greenish blue mass is obtained, 
 which, after powdering and washing, constitutes one of the 
 varieties of the pigment known as cceruleum. There are 
 other ways of preparing this substance. One of these con- 
 sists in precipitating potassium stannate with cobalt chloride, 
 collecting and washing the precipitate, and then mixing it 
 with some pure silica and heating it. A good specimen of 
 cceruleum contained in ioo parts : 497 tin binoxide, 18*6 
 cobalt oxide, and 317 silica. Some samples contain cal- 
 cium sulphate, or lead sulphate, in place of the silica ; they 
 are of inferior quality. 
 
 Cceruleum is a permanent pigment of a rather greenish- 
 blue colour, without any tendency to the violet cast, so 
 noticeable with other cobalt blues (page 210), when viewed 
 by gas or candle light. It suffers little, if any, change by 
 exposure to light or impure air, or by commixture with other 
 pigments. It is a sub-opaque, rather earthy pigment, with 
 a moderate tingeing power. Although some painters find 
 it useful, cceruleum may be imitated so nearly by a mixture 
 of ultramarine, viridian, and white that its presence on the 
 palette can easily be dispensed with. 
 
PRUSSIAN BLUE 
 
 2I 3 
 
 Prussian Blue : TurnbulPs Blue — Antwerp Blue — Berlin 
 Blue — Prussiate of Iron — Chinese Blue — Saxon Blue — 
 Bleu de Berlin — Pariser-blau. 
 
 There are at least three different though closely allied 
 chemical compounds included under the above names, not 
 to mention those varieties of this pigment which contain 
 added or extraneous substances, such as alumina, plaster-of- 
 Paris, or zinc-white. The three typical and distinct com- 
 pounds are : 
 
 I. Soluble Prussian Blue. — This is made by pouring a 
 solution of ferric chloride or ferric nitrate into an excess of 
 potassium ferrocyanide solution (yellow prussiate of potash), 
 or by pouring ferrous sulphate solution into excess of potas- 
 sium ferricyanide solution. The blue precipitate formed is 
 washed with distilled water until the wash-water begins to 
 acquire a blue tint. The composition of the pigment 
 thus prepared is, when dry, represented by the formula 
 K 2 Fe 2 (CN) 12 Fe 2 . It contains potassium, and is, in reality, 
 a double ferrocyanide — a ' potassio-ferric ferrocyanide.' It 
 is less stable than either of the other kinds of Prussian blue, 
 while its solubility in water causes it to stain the paper on 
 which it is spread in water-colour painting. It should in- 
 variably be rejected by artists, although it must be owned 
 that it works very smoothly both in water and in oil. It 
 may always be distinguished from the superior kinds of 
 Prussian blue by very simple tests. One of these consists 
 in roasting a small portion of the dry powdered pigment in 
 a porcelain bason or iron tray, allowing the brown residue 
 to cool, and then throwing it into a little pure water. Then 
 place the mixture on a wetted filter contained in a funnel, 
 and see whether the clear filtrate is alkaline by dipping a 
 piece of yellow turmeric paper into it ; if the yellow tint of 
 
JfB$g&^&& 
 
 WgsgB&f | ' /«3isN$$ 
 
 214 
 
 TURN BULL'S BLUE 
 
 this paper is reddened, then the Prussian blue belongs to 
 this section. Another test is applied by simply washing 
 some of the powdered blue with warm distilled water on a 
 Swedish filter — the filtrate becomes blue. 
 
 II. Insoluble Prussian Blue may be prepared by boiling 
 No. I. (the soluble kind) with a solution of ferric chloride, 
 by mixing solutions of ferrocyanic acid and ferric chloride, 
 by pouring potassium ferrocyanide solution into an excess 
 of a solution of ferric chloride, or of ferric nitrate, and heat- 
 ing the mixture for some time, or by precipitating a watery 
 solution of Blue No. I. with an excess of either of the 
 above-named iron salts. It may also be obtained by oxidiz- 
 ing Turnbull's blue (No. III.) with chlorine water or nitric 
 acid. The chemical composition of this pigment is very 
 complex, the simplest empirical formula for it being 
 Fe 7 (CN) ]8 : it will be seen that it contains no potassium. 
 It always contains some combined water, which cannot be 
 driven off by heat without decomposition of the salt. This 
 blue is more permanent than No. I. 
 
 III. Turnbull's Blue. — The chief constituent of the original 
 Turnbull's blue (more properly, Gmelin's blue) closely re- 
 sembles ordinary soluble Prussian blue, and, like it, contains 
 potassium. But the potassium may be removed from it by 
 stannous chloride solution, a substance being produced 
 having the empirical formula Fe 5 (CN) 12 , but containing 
 some water. Or the same body may be made by precipi- 
 tating a solution of ferricyanic acid with a solution of ferrous 
 sulphate or ferrous chloride. This blue is of good colour, 
 but is more difficult to obtain pure than No. II., the other 
 insoluble Prussian blue. Exposed to light, all the forms of 
 Turnbull's blue, pure and impure, have a more decided 
 tendency to become greenish or to fade than No. II. 
 
 The ordinary commercial Prussian blue is a mixture, in 
 
PRUSSIAN BLUE 
 
 = >5 
 
 varying proportions, of the three blues above described. It 
 is made by adding green vitriol (ferrous sulphate) solution to 
 a solution of yellow prussiate of potash (potassium ferrocya- 
 nide). The precipitate formed (which varies in colour from 
 a light to a deep blue, according to the amount of ferric salt 
 present in the green vitriol) is then oxidized by means of 
 dilute nitric acid or of a solution of bleaching powder. 
 After having been washed, the substance is treated with 
 hydrochloric acid, and is then again washed with water. 
 
 All the above blues are of a very deep blue colour in 
 powder or in the lump, but when pressed or rubbed they 
 all show a coppery lustre. The only one fit for artists' use 
 is the insoluble variety (No. II.), the others being less stable 
 or having other defects. The insoluble form is, moreover, 
 the only one which yields, when roasted, a perfectly satis- 
 factory ' Prussian brown.' 
 
 Prussian blue is a transparent colour of great force and 
 richness, and works well in oil as well as in water. In thin 
 washes or layers it has a slightly greenish hue. Its colour 
 is changed by lime and by the weakest alkalies, so that it 
 cannot be employed in fresco or on newly-plastered walls. 
 Long-continued exposure to strong light weakens and alters 
 the colour of Prussian blue, but the insoluble varieties are 
 less affected than the soluble. When this fading of the pig- 
 ment in water-colour washes has taken place, a brief sojourn 
 in darkness generally suffices to restore the hue almost to its 
 original depth and quality. This strange phenomenon, 
 which awaits explanation, has been long familiar to artists' 
 colourmen. The influence of moisture in determining the 
 fading of Prussian blue under solar exposure is seen in three 
 comparative trials with water-colour washes on paper. In 
 a sealed tube with ordinary air the intensity was reduced 
 from io° to i°, and the colour became sea-green in thirteen 
 
i 
 
 m&m 
 
 : . He -.' SKSrextiE His 
 
 216 
 
 CYAN IN E 
 
 months ; after four years a part of the same wash retained 
 its full depth when the slip was exposed in air kept dry ; 
 another portion was reduced to 8-5° by four years' exposure 
 in an ordinary frame. A sample of Prussian blue (as 
 ordinarily made) in oil, after five years' exposure, had 
 become somewhat greenish, with a loss of about one-tenth 
 of its depth. These changes were more obvious in the 
 pure transparent pigment than in its tint with flake-white. 
 A second specimen, from another maker, similarly exposed, 
 was rather less affected, both as to loss of colour and as 
 to change of hue. 
 
 Prussian blue was discovered in 1704 by a colour-maker 
 of Berlin, Diesbach by name. When, as is sometimes the 
 case, this pigment is found in water-colour paintings of the 
 seventeenth century, it is scarcely necessary to state that 
 its presence betrays the brush of the restorer or the forger. 
 
 Antwerp blue is a sort of Prussian blue lake, the pigment 
 consisting of a colourless base dyed with Prussian blue. 
 According to one method of preparation, a solution of 
 1 part of green vitriol and 2 parts of zinc sulphate in 40 parts 
 of water is precipitated by adding to it a solution of 4 parts 
 of potassium ferrocyanide in 40 parts of water. The blue 
 colour of the precipitate deepens as it is washed. Alumina 
 is sometimes used as the base upon which the blue pigment 
 is thrown. Antwerp blue is less transparent and less intense 
 in colour than Prussian blue ; it has about the same degree 
 of stability. 
 
 Cyanine : Leitctts Blue. 
 
 A mixture of Prussian blue and cobalt blue has been sold 
 under the name of cyanine. It would seem from some 
 recent experiments made with this mixed pigment that it is 
 fairly permanent, even in water-colour painting. It is, of 
 
INDIGO 
 
 217 
 
 course, not adapted for use in fresco, as the Prussian blue 
 in it is at once turned into rust by the lime of the intonaco. 
 Mixed pigments cannot, however, be recommended, as it is 
 in nearly all cases better for the artist himself to associate 
 together those paints which he wishes to mingle. This plan 
 gives him the opportunity of ascertaining the purity and 
 quality of the several components of his mixtures. In the 
 case of cyanine, it appears that the more permanent consti- 
 tuent, the cobalt, partially protects the Prussian blue from 
 change — a result which is still better seen when a separate 
 wash of cobalt is laid over a wash of Prussian blue. In this 
 case the light which has penetrated through the cobalt par- 
 ticles would seem to have been deprived of those rays which 
 effect the decomposition of the Prussian blue beneath. 
 Such a phenomenon is not unusual, and has been observed 
 in the case of several pairs of pigments having very closely- 
 allied hues. 
 
 Indigo. 
 
 Indigo has been used either as a pigment or a dye from 
 very early times in India and in Egypt. It is referred to 
 under the name of indicum by Pliny ; later on the Byzantine 
 writers called it azorium Romanum. ' Indigo bagadel ' — 
 that is, indigo of Bagdad — is named as early as 1228 in the 
 Marseilles tariffs ; in the early English accounts relating to 
 painting works (1274) it is called ' indebas.' In the four- 
 teenth century it was designated as 'ind,' 'inde,' and 'ynde.' 
 ' Endego ' and ' indico ' were used in the sixteenth and 
 seventeenth centuries. It was first largely imported from 
 India into Europe in the seventeenth century by the Dutch. 
 
 A large number of different plants yield true indigo. 
 This pigment was once obtained in considerable quantity 
 from a crucifer, Isatis tinctoria, the dyers' weed or woad, 
 
:■■■■■■■■ 
 
 WM$| > | S8$ Wf &k£$|9 WgM- \ M |1^|H ' ^ 
 
 218 
 
 INDIGO 
 
 the ' pastel ' of the French ; but the chief source is now 
 Indigofera tinctoria, a leguminous shrub, probably of Indian, 
 or at least Asiatic, origin. 
 
 Indigo (C 16 H 10 N 2 O 2 ) does not exist ready-formed in the 
 plants which yield it, but occurs in the form of a colourless 
 compound, or glucoside, which, by combining with water, 
 splits up into a sugar and indigo. It is prepared from the 
 freshly-cut plants, or from the dried foliage, by maceration 
 in water and fermentation, followed by boiling (sometimes 
 lime-water is first added) ; the dark precipitate which forms 
 is thrown on to cloth-strainers, and finally pressed and dried. 
 The mineral impurities which commercial indigo contains 
 are derived partly from the plant itself, partly from the water 
 used in preparing it, and partly from the lime-water above 
 mentioned; moreover, it is sometimes adulterated. Indigo 
 is easily oxidized by a very large number of substances rich 
 in oxygen, yielding a yellow product called isatine; it is 
 converted into a colourless body (C 1G H 12 N 2 2 ) by many 
 reducing agents. 
 
 Indeed, several of the processes of purifying indigo 
 depend upon the reduction of the blue colouring sub- 
 stance, or ' indigotin,' into ' white indigo,' and the subse- 
 quent precipitation of the blue matter by exposure to the 
 oxygen of the air. Green vitriol is the commonest reducing 
 agent, and is used in association with lime. The purified 
 indigo prepared by this process, though of fair colour, does 
 not, however, work so well as a paint as the best Bengal 
 indigo treated successively with acid, alkali, acid, and 
 alcohol. Indigotin, if quite pure, has a somewhat purplish 
 cast in thick water-colour washes ; this hue is observable 
 with this substance whether obtained by sublimation or by 
 Fritzche's process with grape-sugar, caustic soda, and 
 alcohol. 
 
INDIGO 
 
 219 
 
 The impurities in commercial indigo constitute from 20 
 up to 70 or 80 per cent, of its total weight — the average is 
 about 50. They consist mainly of mineral matter, indigo 
 red, indigo brown, and nitrogenous compounds. Much of 
 the mineral matter may be removed by digestion in hydro- 
 chloric acid, followed by treatment with boiling water. 
 Sodium hydrate solution dissolves the indigo brown, while 
 strong alcohol takes away the indigo red, which amounts to 
 nearly 4 parts in 100 of the original indigo. After treatment 
 with these three solvents, the residual purified indigo is of 
 an intense and very beautiful hue. Java indigo is generally 
 of very good quality, that from Bengal comes next, and then 
 the indigo from Oudh, Kurpah, and Madras. Japanese 
 indigo is generally poor. 
 
 Indigo frequently receives no purifying treatment previous 
 to its being ground into a fine powder suitable for admixture 
 with oil or with gum and the other media of water-colours. 
 The necessity of choosing the purest and finest samples of 
 the commercial dye-stuff is of course evident, but it is better 
 in every case to adopt the processes of purification named 
 in the preceding paragraph. No sample of purified indigo 
 should leave, after being burnt, more than 3 per cent, of 
 ash. 
 
 This rich and transparent blue is, unfortunately, gradually 
 oxidized and browned when exposed to light. In thin 
 washes of water-colour it disappears rapidly in the sun's rays, 
 much more slowly when submitted to diffused daylight. 
 The following figures approximately represent the reduction 
 in force of a sample of indigo as a moist water-colour when 
 exposed to sunlight : 
 
 Original intensity ... 10 
 
 After two years ... 1 
 
 After ten years ... ... ... o 
 
sm 
 
 . : ^y' : '~ 
 
 ■■,:; < v 
 
 WSSSSSSBt 
 
 INDIGO 
 
 Other trials with other samples gave in some cases less un- 
 favourable results. 
 
 Indigo in cake is sometimes less affected by sunlight than 
 the moist preparations. As an oil-colour, indigo loses from 
 one-third to one-half of its intensity when exposed to sun- 
 light for five years, its hue being at the same time altered, 
 in different specimens, either to a greyish or a greenish blue ; 
 the change is more conspicuous when the indigo has been 
 mixed in tint with flake or other white. Locked up in copal 
 or amber varnish it is more slowly changed. The fading is 
 due to oxidation. 
 
 Indigo may be replaced advantageously by ultramarine 
 mixed with a trace of viridian, or by a good Prussian blue, 
 either being associated with a little ivory-black. 
 
 Several pigments, such as aureolin, true Naples yellow, 
 and all the chromates, have a very marked effect upon 
 indigo. 
 
 In order to ascertain whether the fading of indigo as a 
 water-colour, on exposure to sunshine, was increased by the 
 presence of alum in the paper, a series of comparative ex- 
 periments were made. A pale tint of indigo was spread 
 upon (i) paper free from alum ; (2) paper washed with alum 
 solution ; (3) paper containing a trace of alum ; (4) paper 
 which had been washed with weak ammonia-water after 
 having received an alum-size. After six months' (April to 
 September inclusive) exposure to sunlight, all the four speci- 
 mens showed complete extinction of the blue pigment, the 
 disappearance of the colour from No. 2 having, however, 
 been a trifle more rapid than in the other cases. Honey 
 and glycerin, owing to their hygroscopic character, appear 
 to hasten the fading, so does water vapour; for a dried slip of 
 indigo-washed paper sealed up in a glass tube loses its colour 
 less quickly than one in its ordinary moist condition, when 
 
INDIGO 
 
 both are exposed side by side to sunshine. A tightly-framed 
 water-colour drawing presents, of course, a close analogy to 
 the second or more unfavourable set of conditions. When 
 a medium tint of indigo on paper was exposed for four years 
 to sunlight in a tube containing air kept dry by a water- 
 absorbing agent, its original depth of colour was perfectly 
 preserved. An identical experiment in an ordinary glazed 
 frame resulted in a reduction of tone from io° to i°, while 
 the residual hue was a greenish grey. 
 
 The effect, if any, of the several iron reds, such as light 
 red, Venetian red, and Indian red, in accelerating the 
 fading of indigo in sunshine has been tested in many ways. 
 Provided the three red pigments above-named be free from 
 soluble salts, and especially from sulphates, they are equally 
 innocuous ; the indigo disappears with or without them at 
 the same rate. In one instance only a wash of Venetian 
 red with indigo lost its indigo completely three weeks before 
 the destruction of the blue in the parallel experiments was 
 complete, which was the case in six months. It is impos- 
 sible to assert that this result was not due to a smaller 
 amount of indigo having been present in this particular 
 case, but I believe it to have been due to this sample of 
 Venetian red having been a spurious one prepared from 
 colcothar. 
 
 In comparing under the same conditions the relative 
 stability, when exposed to light, of different indigoes, it 
 appears that ' Bengal refined ' is superior to the best ' raw 
 Bengal,' and even to the indigotins obtained by the green 
 vitriol and glucose processes. 
 
 The superiority, when exposed to light, of refined indigo 
 — that is, of indigo which has been purified by the treatment 
 with acid and the other solvents already named — although 
 observed in recent experiments, seems to have been ascer- 
 
P^^^^^W^m^^^WfPWm 
 
 INDIGO 
 
 tained in the time of De Mayerne. One of the authorities 
 (Elias Feltz, of Constance) quoted by De Mayerne affirms 
 that this pigment may be rendered safe by steeping it in 
 vinegar and exposing it to the sun for several days ; the 
 vinegar is then to be poured off, and the paste when dry 
 ground in oil. Another plan recommended (in a note, 
 dated 1642) by Feltz consists in grinding the indigo with a 
 little calcined alum ; this plan is, however, objectionable 
 for several reasons. The treatment of the indigo with the 
 solvents previously named, which are adapted to remove its 
 natural impurities, is the only legitimate plan. It is scarcely 
 necessary to add that there is abundant evidence to prove 
 that in De Mayerne's day indigo was generally regarded as 
 an unstable colour. Under all circumstances no indigo 
 should be employed in painting unless it be completely free 
 from acids. 
 
 Although it is not possible to ascertain the exact richness 
 of commercial indigoes by any tests save those in use by 
 professional chemists, yet it is easy to learn a good deal 
 about any particular sample by means of a few simple ex- 
 periments. A good sample should appear homogeneous, 
 and should float on water. Dried at 100° C, it should not 
 lose more than 6 parts per 100 of moisture. When rubbed 
 with a hard smooth substance it should show a coppery 
 lustre. One hundred grains when burnt should not leave 
 more than 10 grains of grey ash. It should dissolve per- 
 fectly in four times its weight of fuming sulphuric acid. 
 Starch, gypsum, clay, chalk, steatite, and Prussian blue are 
 amongst the adulterants of indigo. 
 
 Indigo dissolved in four times its weight of fuming oil of 
 vitriol (kept cool) forms a liquid from which, after slight 
 dilution and filtration through asbestos cloth, potassium car- 
 bonate precipitates a fine blue compound, which has been 
 
SMALT 
 
 223 
 
 used in water-colour painting under the name of indigo 
 carmine. It is not a safe pigment. 
 
 It is probable that the artificial indigo, now being made 
 on a large scale in Germany, may yield excellent pigments 
 for the use of artists. At present this synthetic product 
 does not appear to have been the subject of adequate trials 
 as a paint. 
 
 In examining old water-colour drawings, it will often be 
 found that the parts protected by the mount or frame show 
 the indigo used in compounding the greys of clouds and the 
 greens of vegetation perfectly intact, while it has completely 
 left the exposed parts. In many cases where indigo is sup- 
 posed to have withstood long exposure to light, it will be 
 found that the blue used has been Prussian blue, modified 
 by admixture with other pigments. But in many old 
 pictures and drawings it will be found that the unnatural 
 bluish hue of the foliage represented is due to the complete 
 loss of rapidly evanescent yellows, rather than to the entire 
 stability of the indigo with which the greens have been 
 compounded. Nor must it be forgotten that indigo was not 
 the only blue in such mixed greens, blue carbonate of copper 
 and even lapis-lazuli having been extensively employed at 
 that time. The latter pigment is perfectly permanent except 
 in the presence of acids and alum. 
 
 Smalt : Royal Blue — Dumonfs Blue — Zaffre — Bleu de 
 Smalte — Snialte. 
 
 Glass and vitreous mixtures containing cobalt, and of a 
 rich blue colour, have been known for ages, although copper, 
 not cobalt, was the colouring principle of most of the antique 
 materials of this class. The smalt now made is a very deep- 
 blue glass (appearing black in the lump), consisting essenti- 
 ally of cobalt and potassium silicate. It generally contains, 
 

 HH 
 
 flam 
 
 224 
 
 CHESSYLITE 
 
 in 100 parts, silica, 65 to 71 ; potash, 16 to 21 ; and cobalt 
 oxide, 6 to 7 parts : a little alumina is always present. In 
 the inferior varieties the oxides of iron and nickel always 
 occur. 
 
 In order to prepare a pigment from the dark cobalt glass, 
 it is fused, and then poured into cold water. After the 
 disintegration thus effected, the glass is ground into a 
 moderately fine powder, and submitted to the process called 
 elutriation, or washing-over. The finest particles, which 
 take longest to settle from the wash-waters, are the palest in 
 colour ; the larger particles, though of richer hue, are very 
 difficult to use as a paint. 
 
 Smalt is rarely employed now as an artists' pigment, 
 cobalt blue and artificial ultramarine having been very 
 advantageously substituted for it. For not only is it a 
 difficult pigment with which to work, in both water and oil, 
 but it is gradually altered by moisture and by the carbonic 
 acid of the air, becoming paler and greyer ; moreover, the 
 finer the state of division in which it exists, the more rapid 
 is the change. It will be found that even spring or dis- 
 tilled water is competent to start the decomposition of 
 smalt. For if a little of this pigment be placed on a piece 
 of yellow turmeric-paper, and moistened with clean water, 
 there will soon be formed a red stain beneath the smalt — 
 proof of the liberation of some of the alkaline constituent 
 (potash) of this blue glass. 
 
 Chessylite : Blue Verdiier — Bice — Mountain Blue — 
 Azurite — Cendres Bleues — Bergblau. 
 
 This copper mineral differs from malachite in containing 
 less hydrate, or more carbonate of the metal, its composition 
 being represented by the formula 2CuC0 3 , CuH 2 2 . Its 
 best-known locality is Chessy, near Lyon, in France, but 
 
MANGANESE VIOLET 
 
 225 
 
 very fine specimens are found at Wallaroo and Burra-Burra, 
 in South Australia, and in the district of Perm, Siberia. 
 
 This blue pigment has been prepared artificially, but the 
 natural substance is far less liable to change on exposure to 
 impure air. The introduction of cobalt blue, and more 
 particularly of artificial ultramarine, has practically caused 
 the disuse of blue verditer. 
 
 Under the name of Bleu Lumiere a beautiful turquoise- 
 coloured paint has been introduced to artists. It consists 
 mainly of an artificial copper hydrate. It becomes greenish 
 by exposure to sunlight or a very moderate degree of heat. 
 Like all similar compounds of copper it proves to be un- 
 trustworthy. 
 
 Many old pictures, especially those in tempera, afford 
 evidence of blue verditer having become green. With the 
 extensive range of more permanent blues at the command 
 of the modern artist, there is no need to retain this pigment 
 on the palette. 
 
 Manganese Violet : Mineral Violet — Permanent Violet — 
 Number gerviolett. 
 
 This pigment is rarely met with on the palette of the 
 artist ; it is, however, quite permanent and has a truer violet 
 hue than cobalt violet, which is redder as well as brighter. 
 Its preparation is somewhat tedious. It is made by means 
 of manganous chloride and phosphoric acid, solutions of 
 these compounds being mixed together, evaporated to 
 dryness, and then the residual mass fused. The fused mass 
 is broken up and boiled with a solution of ammonium car- 
 bonate. The turbid liquor is allowed to settle, and then the 
 clear portion is decanted or filtered off and evaporated to 
 dryness, and the residue fused. By grinding the fused mass 
 and boiling it with water a fine precipitate of ' manganese 
 
 15 
 
■||BHB HBBBHHHiB W BHW B H HH HHBI 
 
 226 
 
 MANGANESE VIOLET 
 
 violet ' separates : it is removed by filtration and thoroughly 
 washed and dried. It appears to be essentially manganous 
 metaphosphate, although by no means pure. 
 
 Two other violet or purple pigments of a permanent 
 character have been already described. One of these is 
 violet cobalt (page 189), the other violet ultramarine 
 (page 209). 
 
CHAPTER XVIII 
 
 BROWN PIGMENTS 
 
 Raw Umber: Levant Umber — Terr e d' Ombre- 
 Umbra — Terra Ombra. 
 
 Umbraun — 
 
 This earth is found in several localities ; the best variety 
 has come for some time past from Cyprus. A considerable 
 number of Cypriote specimens, of several nuances, some 
 excellent, were shown in the Colonial and Indian Exhibition 
 of 1886. It differs chemically from the yellow and brown 
 ochres in several particulars, notably in the presence of a 
 considerable quantity of one of the higher oxides of manga- 
 nese (Mn 3 4 , or Mn0 2 ), and in the small proportion of 
 water which it contains. Samples from English localities 
 are poor in iron ; one Derbyshire specimen gave Mr. G. H. 
 Hurst no less than 30 per cent, of barium sulphate. A 
 recent analysis of my own, made with a choice sample from 
 Cyprus, showed the following percentages : 
 
 Water, lost at 100° C - 
 
 4-8 
 
 Magnesia - 
 
 • 0-5 
 
 Water, lost at a red heat* - 
 
 8-8 
 
 Alumina 
 
 - 2*1 
 
 Iron oxide (Fe 2 O a ) 
 
 48-5 
 
 Phosphorus pentoxide - 
 
 - 0-9 
 
 Manganese dioxide (Mn0 2 ) 
 
 19/0 
 
 Silica - 
 
 " 137 
 
 Lime 
 
 1 "4 
 
 Carbon dioxide, etc. - 
 
 - 0-3 
 
 This sample had the peculiar greenish hue so much prized 
 
 * Includes a little organic or bituminous matter. 
 
 15—2 
 
PMM 
 
 
 MM 
 
 228 
 
 RAW UMBER 
 
 by artists. It should be stated that a part of the manganese 
 probably existed as Mn 3 4 . 
 
 Before being used as a paint, this brown mineral is finely 
 ground, washed with water, and then dried at ioo° C, or 
 at a slightly higher temperature. When, by a stronger heat, 
 the whole of its water has been expelled, the umber acquires 
 a reddish hue, and is then the pigment known as burnt 
 umber. This change of colour is due to the passage of the 
 brown ferric hydrate into the red ferric oxide, and to an 
 increase in the proportion of the red-brown manganese oxide 
 present. 
 
 Raw umber in powder, after having been purified, soon 
 acquires a very slight reddish hue on exposure to light and 
 air; it is a good plan to place the undried, finely-ground 
 mineral on trays in the sunshine before completing its 
 desiccation and mixing it with oil or other medium. 
 
 Raw umber is permanent when used with each or any 
 of the painting media : the slight yellowish or dull aspect 
 which it acquires in oil may be traced to the augmented 
 tra.nslucency of the paint, and to the yellowing of the 
 associated oil. Umber is without action on other pigments. 
 A very few samples of umber, used as a water-colour, have 
 been observed to fade slightly after from five to ten years' 
 exposure to sunlight. But this deterioration is due to the 
 presence of traces of brown peaty acids, or ' humus ' sub- 
 stances, which occasionally occur in the umbers from certain 
 localities. 
 
 Raw umber possesses a semi-opaque, citrine-brown colour; 
 it works and dries well in oil. Associated with transparent 
 blues, it yields soft, quiet green hues ; it is invaluable both 
 in figure and landscape painting. As a priming or first 
 painting-ground, it is apt, like most dark pigments, to 
 become more conspicuous in time, owing chiefly to the 
 
RA W SIENNA 
 
 229 
 
 translucency which the superimposed painting gradually 
 acquires. 
 
 Raw umber is not subject to adulteration, but a ferru- 
 ginous brown coal has been occasionally substituted for the 
 true mineral. The great variation in quality shown by the 
 umbers of commerce is due, in great part, to the difficulty of 
 securing, even from the same mine, continuous supplies of 
 the same excellence. 
 
 Burnt Umber. 
 
 It has before been pointed out that raw umber, from 
 which burnt umber is prepared by calcination, is not an 
 ordinary ochre, but owes its colour in great measure to the 
 presence of a considerable amount of some compound of 
 manganese. The exact constitution of raw umber is not, 
 however, known, although the slight change in hue which 
 occurs when it is roasted negatives the idea that it contains 
 any considerable proportion of the ordinary ferric hydrates. 
 If these were present in notable proportions, roasting would 
 certainly redden raw umber much more than is actually the 
 case. 
 
 Burnt umber differs in quality and hue from the raw earth 
 mainly in being more translucent, and of a warmer brown. 
 Although some Continental authorities affirm that this pig- 
 ment darkens and becomes purplish in course of time, I 
 cannot regard it as otherwise than perfectly permanent, and 
 as exerting no action on stable pigments. 
 
 Raw Sienna : Terre de Sienne- 
 Siena. 
 
 -Siena-erde — Terra di 
 
 This earth, which is found chiefly in Tuscany and the 
 Hartz, is a particularly rich variety of yellow ochre, and 
 contains a large proportion of a ferric hydrate. Mr. G. H. 
 
ffl&ffl 
 
 m8m 
 
 m sm sm 
 
 230 
 
 RA W SIENNA 
 
 Hurst (' Chem. News,' vol. lix., p. 172) gives three analyses 
 of raw sienna. In these the range in the percentages of 
 the more important constituents is as follows : 
 
 Hygroscopic water 
 Combined water* . 
 Manganese dioxide 
 Iron oxide (Fe 2 3 ) 
 Silica 
 
 8*2 to 17*5 
 
 9'° » I2 '4 
 o-6 „ 1*5 
 
 45'8 ,, 597 
 5'° » 17 "4 
 
 Raw sienna is prepared for use by crushing, sifting to 
 remove sand, grinding and washing in the same way as in 
 the case of yellow ochre. It should be noted that when 
 lumps of fresh raw sienna are first broken and exposed to 
 the air, their surfaces acquire a slight olive-green nuance. 
 In order to avoid any disadvantage which might arise from 
 such an alteration taking place subsequently, it is a good 
 plan to expose the crushed earth to the air and light previous 
 to its final preparation as a pigment. Before grinding it in 
 oil, it should be cautiously dried at 6o° C. to remove the 
 greater part of the accidental or hygroscopic moisture. 
 
 Raw sienna is somewhat deeper in tint and of a warmer 
 and browner hue than yellow ochre. Owing to a trace of 
 organic or peaty matter which it contains, raw sienna is 
 liable to become rather less brown and more yellow by long- 
 continued exposure to strong light. It is without action on 
 other pigments, and is available for water-colour, oil, fresco, 
 and tempera painting. A given weight of raw sienna 
 requires a larger proportion of oil than any other pigment ; 
 the finished oil-paint contains only 30 per cent, of pigment 
 
 Raw sienna is not subject to adulteration, but it is well to 
 be certain that the pigment has been well washed. 
 
 Includes traces of organic matter. 
 
CALEDONIAN BROWN 
 
 231 
 
 Burnt Sienna. 
 
 The roasting or calcination of raw sienna produces a very 
 great change in its hue as well as in the depth of its colour. 
 The ferric hydrate of the raw earth becomes wholly con- 
 verted into ferric oxide, this change being accompanied by 
 a great increase in the translucency and depth of the colour. 
 
 When small fragments (or the coarse powder) of raw 
 sienna are calcined, it will be noticed that the change of 
 hue which occurs is not quite uniform, some points being 
 of a brighter and redder brown than others. A very fine 
 powder, thoroughly stirred during roasting, shows this pecu- 
 liarity in a much less marked degree. 
 
 Burnt sienna possesses a very beautiful, warm, reddish- 
 brown hue, which cannot be exactly imitated in translucency 
 and depth by mixtures of other pigments. It is permanent, 
 without action on other pigments, and not liable to adul- 
 teration. It is available for use in every method of painting. 
 Some fine and permanent foliage-greens may be made by 
 associating viridian with burnt sienna. 
 
 Caledonian Brown. 
 
 This brown, although a natural earth, presents very much 
 the appearance of burnt sienna. It contains a small quan- 
 tity of combined moisture. It consists mainly of the brown 
 hydrates and oxides of manganese and iron. When cal- 
 cined it loses its ruddy hue and becomes almost black — a 
 black with a slight brownish hue. 
 
 Caledonian brown, whether raw or burnt, is a permanent 
 and innocuous pigment, which is well adapted for oil and 
 tempera painting. It is said that the original source of this 
 pigment is exhausted, and that an imitative mixture of burnt 
 
H^^^^^^H^^^^^^HH 
 
 232 
 
 VANDYKE BROWN 
 
 sienna and bituminous Vandyke brown is sold in lieu of 
 Caledonian brown. 
 
 Vandyke Brown. 
 
 Three brown pigments pass in commerce under the name 
 of Vandyke brown. The first is made by calcining certain 
 very ferruginous earths or brown ochres ; the second is 
 nothing more than a dark-brown variety of colcothar ; the 
 third is a kind of brown earth containing, along with some 
 iron oxide and hydrate, a good deal of organic substance in 
 the form of humus or bituminous matter. The first and 
 second kinds are permanent and innocuous, but the third 
 kind will not resist the prolonged action of light, becoming 
 paler and redder in the course of time. The discrepancies 
 in the published statements as to the permanence of this 
 pigment are thus readily explained ; it is to be regretted 
 that most of the samples of Vandyke brown now met with 
 in England belong to the third kind, and therefore fade 
 quickly in water-colour, more slowly in oil. This sort may 
 be recognised by the dark sublimate which it yields when 
 its powder is heated in a test-tube, as well as by the change 
 in colour and great loss of weight which it then shows. 
 We shall designate this less satisfactory variety in the Tables 
 of Permanent and Fugitive Pigments in the present volume 
 as Vandyke brown B. , the other kinds being called Vandyke 
 brown A. It is unfortunate that the colour-value of the 
 perishable variety is incomparably greater than that of the 
 inalterable sort. 
 
 Cologne or Cullen earth, and Cassel brown or Cassel earth, 
 are soft, impure varieties of brown coal or lignite. They 
 vary in fixity, some of them being even more easily bleached 
 by light than Vandyke brown B. ; these should not find a 
 place on the palette of the artist. When slightly roasted, a 
 
CAPPAGH BROWN 
 
 233 
 
 part of the brown organic matter in these earths is charred 
 or carbonized, and the substance becomes darker, duller, 
 and decidedly less alterable by exposure. Some of the so- 
 called Cologne earth now sold is merely Vandyke brown B., 
 slightly changed by gentle roasting ; it is then rather less 
 alterable. We have met with some specimens of Cassel 
 earth which proved practically permanent in oil, but even 
 these faded quite distinctly when exposed to strong light 
 after having been mixed with flake-white. 
 
 Cappagh Brown: Euchrome — Mineral Brown. 
 
 This earth was found on the estate of Lord Audley, in the 
 Cappagh Mine, which was opened in the year 18 14, and is 
 situated about ten miles west of the town of Skibbereen, in 
 the county of Cork. In composition and general characters 
 it resembles raw umber, but has a more reddish hue. It 
 contains ferric hydrate and ferric oxide, with a considerable 
 amount of one of the oxides or hydrates of manganese. It 
 gives off a good deal of water when heated to ioo° C, and 
 acquires a rich reddish-brown colour, not unlike that of 
 burnt sienna, and almost identical with that of Caledonian 
 brown. The specimens examined contained mere traces of 
 organic matter, so that it cannot be regarded as a kind of 
 bog-earth or peat, although it is, of course, possible that there 
 may be another mineral found in the same locality which 
 might be correctly so designated. The following analysis 
 represents the composition in 100 parts of a characteristic 
 specimen of this pigment : 
 
 Water, lost at ioo° C. - 187 
 
 Water, lost at a red heat - 11 '6 
 Iron oxide (Fe 2 3 ) - - 34*4 
 Manganese dioxide (Mn0 2 ) 27 "2 
 
 Alumina - - - - 2 "6 
 
 Lime - - - - - I 'I 
 
 Silica 4'6 
 
 Phosphorus pentoxide (F 2 5 ) 0'4 
 
■HHHHHHHHH^B^^^m^^^^^^n 
 
 234 
 
 BISTRE 
 
 It is probable that a part of the manganese really exists 
 in the form of the red oxide (Mn 3 4 ), and a part of the iron 
 as ferrous oxide (FeO). I have, however, calculated both 
 these metals into their higher oxides. In this way it 
 happens that the added percentages exceed 100, even when 
 the traces of magnesia and potash present in Cappagh 
 brown are not included in the total. The large quantity of 
 water present in this mineral in a loosely-attached form 
 (hygroscopic), amounting to nearly one-fifth of the weight of 
 the pigment, indicates the desirability of cautiously drying 
 the substance previous to grinding it in oil. A temperature 
 of 6o° C. should not be exceeded. 
 
 Cappagh brown works well in oil, particularly if it be dried 
 at a heat below that of boiling water before it be ground in 
 oil. It is an innocuous pigment, but its permanence has 
 scarcely been sufficiently tested. A rub of Cappagh brown 
 in oil, exposed to strong sunlight for one month, lost a little 
 of its yellow, assuming a somewhat ruddier hue ; the change, 
 however, was very slight, and did not appear to have 
 increased after continued exposure for five months more. 
 
 Bistre : Bister — Brauner Lack — Russbraun. 
 
 Bistre is prepared from the tarry soot of certain woods, 
 especially from that of beech-wood, by the following process : 
 The soot is finely ground and sifted, and then the powder is 
 digested with successive portions of hot water until the latter 
 no longer acquires a brown or yellow tint ; the residue is 
 then ground with suitable quantities of gum-water and 
 glycerin, and preserved in the moist state. To form cake- 
 bistre the glycerin is omitted, but more gum is employed. 
 Bistre is not used as an oil-colour. 
 
 The tarry matter in bistre is its element of weakness. By 
 exposure to strong light this tarry matter oxidizes, and the 
 
ASPHALTUM 
 
 235 
 
 residual pigment becomes cooler in hue and paler. Pro- 
 fessor Ogden Rood, experimenting with a weak water-colour 
 wash of bistre, found that it lost 19 parts of its original 
 intensity of 25 by an exposure of three and a half months 
 to the summer sun. I have not found so considerable a 
 change to occur with the samples of bistre which I have 
 tried ; but this pigment varies much in composition, being 
 obtained from the soot of different woods as well as from 
 that of peat. The most fugitive preparations are those 
 made from samples of soot containing the highest propor- 
 tions of tarry matters. 
 
 Asphaltum : Bitumen — Mineral Pitch — Antwerp Brown — 
 Mu mmy — Asphalt-bra un. 
 
 Asphalt, asphaltum, or mineral pitch, has long been used 
 as a pigment. The best known is that from the Dead Sea 
 (Lacus asphaltites). Other abundant sources of this car- 
 bonaceous mineral occur in Trinidad ; Caxitambo and Be- 
 rengela, in Peru ; Val de Travers, Neufchatel ; Avlona, in 
 Albania, etc. 
 
 Asphalt is rather a mixture of minerals than a single 
 mineral ; it is, moreover, very variable in the nature, char- 
 acter, and proportion of its constituents. Essentially it 
 consists of a number of liquid, semi-solid and solid, colour- 
 less hydrocarbons (related to the paraffins), associated with 
 certain ill-understood dark-brown or black substances, which 
 constitute the useful part of the raw material. The best 
 varieties for artistic use are those which contain the smallest 
 proportion of the above-described hydrocarbons, for to the 
 presence of these the treacherous character of asphalt as a 
 pigment is due. On this account the hardest, most earthy 
 and most brittle kinds should be chosen, and the crushed 
 samples should always be submitted to a temperature of at 
 
gBR ^ffi 
 
 236 
 
 ASPHALT UM 
 
 least 250 C. before being ground in oil or turpentine. The 
 operation of roasting native asphalt — keeping it over a slow 
 fire ' till it will boil no more and becomes nearly a cinder ' 
 — was recommended by Williams in his ' Essay on the 
 Mechanic of Oil-Colours ' (1787), and furnishes a perfectly 
 satisfactory and safe product. 
 
 If carefully-selected asphalt be submitted to either of the 
 processes named above, and then be moistened with spirits 
 of turpentine, and ground in drying-oil (prepared with borate 
 of manganese), a paint is obtained which neither cracks nor 
 moves on the canvas like the unpurified material. Its fixity 
 is further insured by mixing it with a little copal varnish, 
 and more particularly by associating it with a denser pig- 
 ment, such as umber or flake-white. It is superior to the 
 imitative asphalts made from coal-tar, now largely sold in 
 lieu of the original and genuine product. The disadvan- 
 tages attending the use of these coal-tar browns and of 
 ordinary asphalt are two-fold. Not only are they treacherous 
 on account of their easy fusibility, but they are liable to 
 stain contiguous pigments by reason of their solubility in 
 oil or varnish. When used successfully by the older artists 
 they were always introduced sparingly, or were largely com- 
 mingled with more solid paints. 
 
 ' Mummy,' as a pigment, is inferior to prepared, but 
 superior to raw, asphalt, inasmuch as it has been submitted 
 to a considerable degree of heat, and has thereby lost some 
 of its volatile hydrocarbons. Moreover, it is usual to grind 
 up the bones and other parts of the mummy together, so 
 that the resulting powder has more solidity and is less fusible 
 than the asphalt alone would be. A London colourman 
 informs me that one Egyptian mummy furnishes sufficient 
 material to satisfy the demands of his customers for twenty 
 years. It is perhaps scarcely necessary to add that some 
 
PRUSSIAN BROWN 
 
 237 
 
 samples of the pigment sold as ' mummy ' are spurious. 
 Mummy was certainly used as an oil-paint at least as early 
 as the close of the sixteenth century. 
 
 Asphalt, after having been heated to drive off the hydro- 
 carbons previously alluded to, cedes to ammonia a consider- 
 able quantity of a dark-brown colouring-matter, which in 
 this way may be made available for water-colour painting. 
 The ammoniacal solution is either evaporated slowly, to the 
 consistence of a thick syrup, after the addition of a little 
 gum and glycerin, or it is precipitated with acetic acid, and 
 the precipitate (after washing) is mixed with gum and 
 glycerin, and then partially dried until it has acquired a 
 suitable degree of consistency. But the water-colour paint 
 thus made is not permanent. 
 
 Merimee's process for preparing asphalt for use as an oil- 
 colour cannot be recommended. He introduces shellac, 
 white wax, and Venice turpentine into the mixture, as well 
 as a large proportion of boiled linseed-oil. This preparation 
 constitutes a very treacherous pigment. 
 
 Prussian Brown. 
 
 This pigment, as usually met with in commerce, contains 
 a considerable quantity of a soluble salt of potash, and is 
 not fitted for the use of artists. But this impurity need not 
 be present, as it may be removed by a thorough washing of 
 the powdered colour with boiling water. A still better plan 
 is to prepare Prussian brown from one of those varieties of 
 Prussian blue which contain no potassium. It is made by 
 throwing small pieces (the size of hazel-nuts) of Prussian 
 blue upon a plate of iron maintained at a red heat. Each 
 fragment burns like tinder, and if care be taken to employ 
 the right heat for the proper time, will show a mixed hue, 
 partly yellowish brown, partly reddish brown, and partly 
 
BBSf ; - M^Hi^H|l M SBBH 
 
 238 
 
 PRUSSIAN BROWN 
 
 black. The product, still hot, is thrown into water, ground, 
 washed, and dried. Prussian brown thus made has a rich 
 colour of considerable translucency and good drying 
 character. In hue it is warmer than asphalt. It is quite 
 permanent. 
 
Indian Ink 
 
 CHAPTER XIX 
 
 BLACK PIGMENTS 
 
 Chinese Ink— Japanese Ink — Encre de CImie 
 — Chinesische Tusche. 
 
 This ink has been prepared in China for at least 2,000 
 years. It consists essentially of a very fine lamp-black, 
 associated with gelatin, and scented with musk, camphor, 
 cloves, or rose-water. The lamp-black employed is derived 
 from the imperfect combustion of oil or of pine-wood. The 
 oils chiefly used are those of Sesamum indiciim, Cannabis 
 sativa, and Dryandria cordata ; but in some factories rape- 
 oil, bean-oil, or the oil of Gleditschia sinensis is employed. 
 According to the treatise of Chen-ki-suen, which was written 
 a.d. 1398, these oils are burnt in small earthenware lamps 
 in the presence of a limited supply of moist air. The 
 smoke is collected in earthenware conical covers ; from 
 these the condensed soot is removed at short intervals, care 
 being taken to preserve those portions only which are free 
 from tarry products. The soot is finally sifted, and reduced 
 to an extremely fine powder. Lac-resin, rock-oil, as well 
 as many kinds of wood, have been employed for the pre- 
 paration of this carbonaceous basis of China ink in different 
 parts of the empire, and at different times. It would appear 
 that from all of these combustibles, if due care be taken, 
 an excellent product may be obtained. The next step in 
 
■•■ 
 
 wBBffiBBfflB&BBSSBmBBBBSM 
 
 240 
 
 INDIAN INK 
 
 the manufacture consists in the incorporation of the soot, 
 prepared as above described, with the necessary amount of 
 size. The size employed should be made from a mixture 
 of clean fish-glue and parchment-size ; this is thoroughly 
 mixed, while warm, with the fine soot. The paste thus 
 formed is made into balls, which are heated for some time 
 at the temperature of boiling water, and then fashioned 
 roughly into sticks. These are subjected to repeated blows 
 — some hundreds, at least — from a hammer; they are re- 
 heated occasionally during this operation, in order to 
 prevent them from becoming hard. The perfume, consisting 
 of musk and camphor, mixed with a little rose-water, is 
 incorporated with the mass. The material, after further 
 pounding and beating, may then be pressed into the wooden 
 moulds which are to give it its final form. A tedious process 
 of drying follows next, the sticks of ink being finally packed 
 in the ash of rice-straw frequently renewed. After the 
 removal of adhering ash, the sticks are cleaned, gilt or 
 otherwise ornamented, and polished with an oily brush. 
 
 If the soot used in the manufacture of this ink be con- 
 taminated with tarry or empyreumatic matters, it yields a 
 brownish-black product ; the purer and the finer the state 
 of division of the carbon, the more intense is the black, 
 and the more neutral are the greys which it yields on dilu- 
 tion with water, or by admixture with opaque white pig- 
 ments. 
 
 There are many qualities of this ink made in China. 
 The best kinds are hard and homogeneous ; they show a 
 lustrous black fracture, and, when rubbed with water, do 
 not give rise to the separation of any curdy particles. Those 
 having, in tint with water, a bluish or violent tinge are the 
 most esteemed; the pure black come next, and the brownish 
 or yellowish black last. 
 
INDIAN INK 
 
 241 
 
 A stick of Indian ink should be rubbed on the palette, 
 in straight lines, backwards and forwards. A very con- 
 venient ink-slab for this purpose forms part of the fittings 
 of the Japanese writing-case or box, called 'suzuri-bako.' 
 It consists of an oblong block of dark slate, in which a 
 sloping cavity has been hollowed out. The slight ' tooth/ 
 or roughness of the surface, greatly helps the rubbing-down 
 of the ink. A strong wash of this ink, on sized paper, 
 should not be affected, when once dry, by having water 
 brushed freely over it. Bluish-black and pure black Indian 
 ink is permanent under prolonged exposure to sunlight or 
 impure air ; but the brownish varieties become paler, less 
 brown, more neutral, by the action of light. Like most 
 carbonaceous matters, Indian ink occasionally tends to 
 absorb to a small extent some of the organic pigments 
 which may be brought into contact with it in the process of 
 colouring a drawing. 
 
 Indian ink is available for tempera-painting, but cannot 
 be used with oil. 
 
 Indian ink has been imitated with fair success in France. 
 The chief difficulty in preparing it seems to lie in the pre- 
 paration of a suitable gelatinous medium with which to mix 
 the purified lamp-black. A size prepared from washed fish- 
 glue (by partial precipitation with tannin, and subsequent 
 solution of the precipitate in more size) affords a good 
 binding material. The size, in true Chinese ink, forms a 
 very large part of the total weight, varying from one-fourth 
 to over one-third ; but the European imitations rarely con- 
 tain as much. Japanese ink is generally inferior to Chinese. 
 
 Chinese amateurs sometimes form collections of rare and 
 old kinds of Chinese ink, occasionally giving for sticks bear- 
 ing the marks of renowned makers not less than their weight 
 in gold. Such specimens are prized for their rarity, not 
 
 16 
 
'■■■■■■.■ ■'■■■■■■.■■ 
 
 .,■'■-,' lag ' .>;•;. 
 
 242 
 
 LAMP-BLACK 
 
 
 on account of any special merits as pigments which they 
 may possess ; and a Chinese ink collector regards it as an 
 unpardonable offence to moisten any of his specimens with 
 a view to testing their quality. 
 
 Lamp-Black : Noir de Lampe — Noir de Fumee — Noir de 
 Houille — Russ — Lamftenschwartz. 
 
 When resins, resinous woods, fatty oils and fats, paraffin 
 and paraffin oil, or coal-tar oils, are burnt with an insufficient 
 supply of air, a considerable part of the carbon they contain 
 may be deposited in the form of soot. This soot is not, 
 however, pure carbon, but retains variable proportions of 
 the tarry products of imperfect combustion or destructive 
 distillation ; these impart to lamp-black a more or less 
 pronounced warm brownish hue, except in the cases in 
 which it has been prepared by processes specially devised 
 to intercept the tarry and oily products in question. Some- 
 times small furnaces, sometimes large lamps with long wicks 
 are employed in its manufacture, the soot given off being 
 collected in two or more receivers ; the soot first deposited 
 contains the larger part of the impurities. This point may 
 be illustrated by the simple experiment of depressing a white 
 porcelain plate into the flame of a candle ; the nearer the 
 plate to the wick, the browner will be the soot deposited. 
 
 Lamp-black carefully made is an unalterable pigment ; 
 but its employment for pictorial purposes has frequently 
 been objected to by writers on artistic practice as tending 
 to heaviness and opacity in the shadows. With the excep- 
 tion of a few pigments of organic origin, which in water- 
 colour painting have a tendency to cede some of their 
 colouring matter to any kind of carbonaceous black, lamp- 
 black exerts no injurious influence upon any pigments which 
 are stable when used alone. 
 
CHARCOAL-BLACK 
 
 243 
 
 Numerous carbonaceous substances have been used as 
 black or brown-black pigments. Amongst these anthracite 
 and common bituminous coal may be named. Van Mander 
 and De Mayerne both mention forge or pit coal. Black 
 shales and black slates have long been employed in the 
 preparation of dark grey pigments. These minerals owe 
 their colour in part to carbon or compounds of carbon, 
 in part to very finely divided iron pyrites. They are 
 permanent. 
 
 Charcoal -Black : Blue- Black — Vine-Black — Frankfort- 
 Black — Noir de Vigne — Rebenschwartz. 
 
 When non-resinous woods and woody tissues are strongly 
 heated in crucibles or other almost completely-closed vessels, 
 the residue contains the greater part of the carbon of the 
 original material, and preserves its form. As the charcoals 
 thus made contain some soluble mineral matter, particularly 
 potash salts, they should be coarsely ground and thoroughly 
 washed with hot water previous to their being finally con- 
 verted into paints. They are also hygroscopic, and there- 
 fore need to be dried before being ground in oil. 
 
 Amongst the best materials for producing these charcoal 
 or vegetable blacks may be named the hard shells or stones 
 of plums, almonds, and similar fruits ; coco-nut shell broken 
 into small pieces ; cork cuttings, and the twigs of beech and 
 shoots of vine. Coco-nut yields the densest, most velvet- 
 like black ; vine-shoots a less solid black, having a bluish 
 hue. Washed wine-lees yield a rich black — Frankfort- 
 black. 
 
 When charcoal has been prepared at a sufficiently high 
 temperature, and then has been thoroughly washed, there is 
 no question as to its permanence as a pigment in all media. 
 But if it retains tarry matters, or has been imperfectly 
 
 16 — 2 
 
sekkkhi 
 
 '.■■■■■ - ■-.>■■■'.■ i 
 
 244 
 
 IVORY BLACK 
 
 carbonized, then it may become greyer or less brown (when 
 used in thin washes) after long exposure to light. This 
 change is due to the oxidation of the tarry matters, or of 
 the brown substances which are intermediate in composition 
 between the original vegetable materials and the carbon, 
 which is the final product of their torrefaction out of con- 
 tact with the air. And one peculiar property, possessed in 
 varying degrees by charcoal of every kind, must not be lost 
 sight of. Charcoal withdraws the majority of organic colouring 
 matters from suspension, and even from solution in water. 
 A pale tint of rose-madder in water, if a pinch of coco-nut 
 or vine-black be added, becomes rapidly decolourized, the 
 pigment being completely absorbed, although not really 
 destroyed. Animal charcoal (bone-black, ivory-black) exerts 
 a still more energetic action of this character ; but lamp- 
 black is less powerful. 
 
 It is to be regretted that the beautiful bluish blacks, 
 derived from such materials as the shoots of the vine and 
 beech, are frequently fraudulently imitated by mixtures of 
 lamp-black and indigo. The purple vapours of indigotin, 
 given off when such a mixture is heated in a test-tube, betray 
 the adulteration at once. 
 
 Ivory Black : Noir d'lvoire — Elfenbeinschwartz. 
 
 Waste ivory, in the form of turnings, shavings, and saw- 
 dust, if charred in closed vessels, leaves a black residue, 
 which, however, consists essentially of bone-earth (calcium 
 carbonato-phosphate), stained by the presence of a few per 
 cents, of carbon. On exposure to the air, ivory black 
 absorbs, not only the gases of the atmosphere, but also a 
 very considerable proportion of moisture. On this account 
 ivory black, just previous to its being ground in oil, should 
 always be thoroughly dried. As this substance has a strong 
 
GRAPHITE 
 
 245 
 
 decolourizing power when placed in contact with moist 
 organic pigments, it is better adapted for use in oil painting 
 than with water colours. This decolourizing property 
 belongs also to the animal blacks obtained by charring 
 horn and bone shavings — products which are frequently 
 substituted for genuine ivory black. Sir Charles Eastlake 
 tells us that in a collection of specimens of water-colour tints 
 inserted in the Mayerne manuscript the ' hartshorn ' black, 
 made from cornu cervinum, remains very intense. 
 
 Ivory and bone black are perfectly permanent black pig- 
 ments ; the latter is quite free from the bluish tinge which 
 characterizes most of the vegetable charcoals. Both are 
 better adapted for oil than for water-colour painting, for 
 which vine black is preferable. 
 
 Black Lead : Plumbago — Graphite. 
 
 The material of which so-called black-lead pencils are 
 made is essentially nothing but one of the three forms in 
 which the element carbon occurs ; diamond is another ; 
 lamp black may be taken as a good representative of the 
 third form. Graphite is the most appropriate name for the 
 mineral commonly known as black lead, but which in reality 
 contains no lead, and is in no way related to that metal. 
 Graphite was found of good quality at Borrowdale in Cum- 
 berland, a locality which has been stated, probably errone- 
 ously, to be now exhausted ; but excellent supplies of this 
 mineral come from the Albert Mine, Siberia, Mount Alibert 
 in the Ural, Ceylon, and many other places. Graphite, how- 
 ever, is never found in a state of perfect purity, always 
 leaving, when burnt, some incombustible matter or ash. 
 
 In order to prepare graphite for use as a pigment, the 
 purest pieces should be selected ; these should be at first 
 broken into small fragments in order that obviously con- 
 
^^^■■^^^^^^^^^^^H 
 
 m 
 
 246 
 
 SEPIA 
 
 taminated bits may be rejected before the material is ground. 
 Inferior qualities of graphite may be purified by being 
 coarsely ground, and then heated with strong hydrochloric 
 acid to remove iron and alumina. After washing, the thus- 
 far purified material should be placed in a leaden or platinum 
 vessel and gently warmed with a solution of hydrofluoric 
 acid to remove silica. The graphite, after this treatment, is 
 to be washed with abundance of water, and ground to a very 
 fine powder, which is then ready for admixture with gum 
 water or, after drying, with oil. The addition of a little 
 china clay during the grinding of graphite in oil tends to 
 produce a more manageable paint. 
 
 Graphite has a very dark-grey colour, and forms pure 
 tints of grey with white pigments. It is equally well 
 adapted for use in water-colour, oil, fresco, and tempera 
 painting. It is absolutely permanent, and without action on 
 other pigments. 
 
 Graphite is sometimes adulterated with charcoal or lamp- 
 black. When a very thin layer of the suspected pigment 
 is spread on a piece of platinum foil and strongly heated 
 over a lamp, the lamp black will burn away, leaving the 
 true graphite unaltered. If a change of hue or tint occurs, 
 this is a sign of the presence of the above-named adul- 
 terant. 
 
 Sepia. 
 
 The dark-brown colouring-matter from the ink-bag of 
 Sepia officinalis^ Loligo tunicata, and other species of cuttle- 
 fish common in the Mediterranean and Adriatic, has not 
 been thoroughly investigated from a chemical point of view. 
 The pure pigment, which constitutes four-fifths of the weight 
 of the dried ink-bags as they occur in commerce, partakes 
 of the character of a weak organic acid, and is soluble in 
 
SEPIA 
 
 247 
 
 alkalies and precipitated by acids. In preparing the sub- 
 stance for artists' use, it is commonly first removed from the 
 sacs containing it, dissolved in soda or ammonia solution, 
 and then, after straining the solution, thrown down by 
 neutralizing the alkali with hydrochloric acid ; the precipitate 
 is then washed by decantation, and dried. Sometimes the 
 filtered ammoniacal solution is used directly as a liquid ink. 
 The chief impurities of the natural sepia are salts of lime 
 and magnesia, which may be partly removed by washing the 
 dried and crushed sepia first with dilute hydrochloric acid 
 and then with water, previous to dissolving it. 
 
 Sepia is of a redder or warmer brown hue than bistre, but 
 it is not so reddish as Vandyke brown. Of these three pig- 
 ments, there is no question that sepia is the least alterable. 
 It is not, however, permanent when exposed to sunshine, 
 although in darkness or in diffused daylight it suffers no 
 appreciable change either in depth or quality. It might, 
 indeed, have been supposed that sepia would prove unalter- 
 able, from the consideration of the observed fact of the pig- 
 ment from the ink-bags of fossil cuttle-fish showing now, 
 when used as a water colour, the same hue and the same 
 chemical characters as recent sepia from the Mediterranean 
 cuttle-fish of to-day. But it must be recollected that this 
 fossil pigment has been excluded completely from the 
 adverse influence of light, and in great measure from that 
 of air, during the long ages which have elapsed since it was 
 embedded in rock. And it is light which, in the case of 
 the majority of organic pigments, is the determining cause 
 of the changes brought about by the combined presence of 
 moisture and atmospheric oxygen. 
 
 Sepia is not employed as an oil colour. 
 
 There are several grey pigments which, being compounded 
 of other paints already described, need hardly be mentioned 
 
2 4 8 
 
 SEPIA 
 
 here. Amongst these are neutral tint and Payne's grey 
 which in water-colour are still prepared by commingling 
 indigo, crimson lake and ivory black, but which have been 
 replaced in oil by artificial ultramarine, ochre and ivory black 
 — an entirely trustworthy mixture. Slate grey, prepared 
 from a rather soft and very darkly-coloured slate, is a satis- 
 factory pigment both in artistic quality and in stability. 
 
CHAPTER XX 
 
 CLASSIFICATION OF PIGMENTS 
 
 The painter naturally classes pigments according to their 
 colour, or more exactly according to what are called the 
 constants of colour, namely — hue, brightness and purity. 
 He also takes into account transparency and opacity, 
 although these terms are conventional and comparative only, 
 since no pigment is perfectly transparent, none perfectly 
 opaque. Another basis of classification, and a very im- 
 portant one, that of stability, will be considered in the next 
 chapter; at present we are concerned with none of these 
 methods of grouping pigments, but with others founded 
 either upon their origin, or their physical characters, or their 
 chemical composition. 
 
 Pigments are often classified into two groups, the mineral, 
 and the organic. It is necessary to divide these groups 
 further, in some such wav as this : 
 
 Mineral Pigments. 
 
 Organic Pigments. 
 
 /Natural : as ochre, terre verte, ultramarine. 
 (-Artificial : as aureolin, viridian, cobalt blue. 
 
 (Animal : as Indian yellow, carmine, sepia. 
 Vegetable : as gamboge, sap green, indigo. 
 Artificial : as Prussian blue, verdigris. 
 
 Such a classification brings into prominence one marked 
 distinction between the two groups, for, in accordance with 
 one's expectation, the mineral pigments are, as a rule, 
 

 aaaaaaa 
 
 :■.•:.".' 
 
 250 
 
 CLASSIFICATION OF PIGMENTS 
 
 characterized by a much higher degree of permanence than 
 those of organic origin. [The chemist looks upon all com- 
 pounds containing carbon, save the carbonates, as organic ; 
 but at the same time the distinction between organic and 
 inorganic, or organic and mineral, is nothing more than a 
 convenient convention.] 
 
 Other bases of classification are afforded by physical or 
 mechanical characters. Pigments may be fixed or volatile, 
 soluble or insoluble, crystalline or amorphous. There are 
 difficulties in carrying out these schemes of classification, 
 and it will be found that distinctions of physical character 
 are utilized to the best purpose when connected with such 
 a chemical classification as is offered below. 
 
 The simplest chemical classification is this : 
 
 Elements ; as graphite, lamp-black, gold. 
 Compounds ; as aureolin, viridian, vermilion. 
 Mixtures ; as yellow ochre, brown pink, rose madder. 
 
 After considerable expansion and some rearrangement, 
 the differences just indicated afford a reasonable basis for a 
 chemical classification which will prove of real service in 
 judging of the degrees of stability, and of the possible inter- 
 action of pigments.* The mixed and even indefinite char- 
 
 * In a pamphlet by M. Paul de Lapparent there is an ingeniously 
 constructed diagram giving, at one view, a list of pigments which, in 
 the judgment of the author, react upon one another. If we omit from 
 the list red lead, we shall be able to cancel nearly one-third of the 
 black marks assigned to mixtures of two pigments ; but we shall still 
 include two conspicuous offenders, namely, pale cadmium and Prussian 
 blue. Pale cadmium is stated to be incompatible with Indian red, 
 Venetian red, burnt sienna, the native earths, ivory black, Prussian 
 blue, and cobalt violet ; while Prussian blue is marked as affecting, or 
 as affected by, Venetian red, burnt sienna, deep cadmium, orange 
 cadmium, pale cadmium, aurora yellow, the native earths, ivory black, 
 
CLASSIFICATION OF PIGMENTS 
 
 251 
 
 acter of many pigments, and the chemical solitariness of 
 others, preclude the formation of groups having equal rank 
 and precise group-characters : thus the proposed chemical 
 classification, though convenient, has no pretension to com- 
 pleteness. I suggest the following nine groups : 
 
 Group I. — Elements. 
 
 Ivory black 
 
 
 Silver. 
 
 Charcoal black 
 
 
 Gold. 
 
 Lamp black 
 
 -Contain carbon. 
 
 Platinum. 
 
 Indian ink 
 
 
 Aluminium. 
 
 Graphite 
 
 
 
 
 Group II. 
 
 — Oxides. 
 
 X. Zinc white - 
 
 - ZnO. 
 
 Coeruleum - CoO,?zSn0 2 . 
 
 Green oxide 
 chromium 
 
 }cr a O :i . 
 
 Red lead - Pb s 4 . 
 Venetian red-v 
 
 Burnt umber 
 
 /Oxides of Fe 
 I and Mn. 
 
 Lieht red 
 
 7*7 , hChiefly Fe„0 3 . 
 
 Indian red ' * a 
 
 Cobalt green 
 
 - CoO,«ZnO. 
 
 Burnt sienna 
 
 Cobalt red - 
 
 - CoO.wMgO. 
 
 
 Cobalt blue - 
 
 - CoO,mA1 2 3 . 
 
 
 
 Group III.- 
 
 -Sulphides. 
 
 Cadmium yellov 
 
 v CdS. 
 
 Ultramarine \ _, . _. 
 
 Artificial ultramarine 1 , , _. ' 
 . r Al.Na, 
 Green ultramarine , _ 
 
 r> j n ■ and S - 
 Red ultramarine J 
 
 King's yellow 
 
 - AS2O3. 
 
 Realgar - - 
 
 " AS2O2. 
 
 Vermilion 
 
 - HgS. 
 
 white lead, zinc white, and viridian. On the other hand, M. de 
 Lapparent allows that vine black is an entirely innocuous and per- 
 manent pigment. My experience is not in general agreement with the 
 judgments of M. de Lapparent as embodied in the diagram under con- 
 sideration. For instance, I do not find that aureolin reacts with white 
 lead or with ultramarine, nor can I admit that Prussian blue deserves 
 the bad character assigned to it. Possibly the purity of the particular 
 pigments with which our author dealt was not assured in all cases. 
 Might there not have been free sulphur in his pale cadmium and free 
 acid in his Prussian blue ? 
 
W^s^^'Ss^j^lfm^^^^^M 
 
 252 CLASSIFICATION OF PIGMENTS 
 
 Group IV. — Hydrates. 
 
 Yellow ochre - Fe 2 3 ,raH 2 0. 
 
 -r, . ("Oxides and hy- 
 Raw sienna 1 ' 
 „ , < drates of re 
 Raw umber , , , 
 I and Mn. 
 
 Emerald oxide) _, _ TT _ 
 . , . J-Cr 2 3 ,2H 2 0. 
 ol chromium J 
 
 Mountain blue- CuII 2 2 . 
 
 Group V. — Carbonates. 
 
 Flake white - 2PbC0 3 , PbH 2 2 . 
 
 Blue verditer - CuC0 31 CuII 2 2 . 
 
 Whitening - CaC0 3 . 
 
 Green verditer 2CuC0 3 ,CuH 2 2 . 
 
 Group VI.— Silicates. 
 
 „ f Silicate of Fe, K, 1 „ ( Silicate of Co 
 Terre verte 1 .. Smalt \ , „ 
 \ Mg. 1 \ and K. 
 
 Group VII.— Chromates. 
 
 Baryta yellow - BaCr0 4 . 1 Chrome red - Pb 2 Cr0 5 . 
 
 Strontia yellow SrCr0 4 . 
 
 Zinc chromate ZnCr0 4 . 
 
 Chrome yellow PbCr0 4 . 
 
 
 Group VIII.— Various Inorganic Salts. 
 
 Baryta white BaS0 4 . 
 Lead sulphate PbS0 4 . 
 
 „ , . , f Contains Cu. 
 Schweinfurt green \ . _ 
 ^ As, O. 
 
 Aureolin - - K 6 Co 2 i2N0 2 . 
 Naples yellow Contains Pb, Sb, 0. 
 
 ^ f Chromium 
 Tungsten green \ 
 
 & s 1 tungstate 
 
 
 , T . . L ,-Manganese 
 Manganese violet & , 
 
 xt-- i_ • , l1 metaphos- 
 = Nurnberg violet | 
 
 8 [ phate 
 
 Group IX.— Organic Compounds. 
 
 Indian yellow. 
 
 Brown madder. 
 
 Yellow lake, 
 
 Scarlet alizarin. 
 
 Gamboge. 
 
 Crimson alizarin. 
 
 Pure orange. 
 
 Carmine. 
 
 Rose madder. 
 
 Crimson lake. 
 
 Madder carmine. 
 
 Scarlet lake. 
 
 Rubens madder. 
 
 Purple lake. 
 
 Madder red. Sap green. 
 
 Purple madder. 
 
 Verdigris. 
 
SULPHIDES 
 
 253 
 
 Group IX. — Organic Compounds — continued. 
 
 Emerald green. 
 Indigo. 
 Prussian blue. 
 
 Antwerp blue. 
 
 Bitumen. 
 
 Bistre. 
 
 Sepia. 
 
 Vandyke brown, B. 
 
 One of the chief lessons to be learnt from this classifica- 
 tion is this, that the members of each class, as a general 
 rule, exert no action upon one another. This is explained 
 easily. The oxides of Group II., having already taken up 
 the full complement of oxygen which they can acquire 
 under ordinary conditions, are not likely to be oxidized by 
 admixture with other oxides of similar character. In the 
 same manner the sulphides of Group III. neither give 
 sulphur to, nor receive it from the other sulphides, for all 
 but one of them have been produced in the presence of 
 excess of sulphur. The following characteristics of each 
 group may prove useful in the study of their chief members : 
 
 Group I. : Elements. — All the black pigments in ordi- 
 nary use consist of or contain the element carbon, and are 
 not subject to change : graphite is a form of carbon and is 
 unalterable and inert. Gold, if nearly free from alloy, is 
 not liable to chemical change, but silver readily tarnishes 
 by combining with sulphur ; drawings in silver-point are 
 frequently found to have altered in hue from this cause. 
 The best metal-point for fine drawing is pure platinum. 
 
 Group II. : Oxides. — These have generally been pre- 
 pared at a high temperature, and are not easily amenable to 
 chemical or physical change : they are, moreover, not liable 
 to affect other pigments, being practically inert. 
 
 Group III. : Sulphides. — Some of these may give up 
 sulphur to the metallic bases of other pigments. Thus 
 cadmium yellow blackens emerald green, producing copper 
 sulphide. One of these pigments, vermilion, is prone to a 
 

 
 •./-,:-..•. 
 
 254 
 
 VARIOUS INORGANIC SALTS 
 
 molecular change, whereby the red crystalline form passes, 
 without chemical alteration, into the black amorphous 
 variety. The members of this group sometimes contain 
 free sulphur, or injurious sulphur compounds. 
 
 Group IV. : Hydrates. — The water present in these 
 compounds exists in two states, essential and hygroscopic. 
 Sometimes a part of the former may be lost, and a change of 
 hue occur in consequence, but the alteration is rare, save in 
 the pigments which owe their colour to the presence of copper 
 hydrate. In the case of raw umber, the water present acts 
 rather in aiding the oxygen of the air, under the influence 
 of sunlight, to oxidize some of the peaty or bituminous 
 matter sometimes present in this pigment. 
 
 Group V. : Carbonates. — Three out of the four car- 
 bonates included in this group are liable to suffer change 
 on account of the metal they contain (lead or copper) com- 
 bining with sulphur, and so forming a brown or black 
 sulphide. 
 
 Group VI. : Silicates. — These are generally inert bodies 
 little prone to suffer or cause change. Some of the ochreous 
 earths contain silicates of iron, manganese, and alumina, as 
 well as the hydrates of the two former metals, and so might 
 be placed in this group. 
 
 Group VII. : Chromates. — This group consists of com- 
 pounds rich in oxygen. When in contact with some of the 
 more alterable organic pigments belonging to Group VIII. 
 the chromates occasionally lose oxygen. On this account 
 they show a tendency to acquire a greenish or greyish hue, 
 the result of the reduction of the red oxide of chromium to 
 the green oxide. This change is accompanied by a corre- 
 sponding injury to the colour of the organic pigment which 
 has been involved in the reaction. 
 
 Group VIII. : Various Inorganic Salts. — A number 
 of miscellaneous compounds having no chemical relation- 
 
CLASSIFICATION OF PIGMENTS 
 
 255 
 
 ship have been thrown into this group. One, a sulphate, is 
 insoluble and inalterable ; another, potassium cobalti-nitrite, 
 is generally inert, but, owing to its nitrous constituent, acts 
 injuriously upon some organic pigments, notably on indigo. 
 The members of the group which contain lead or copper 
 may darken in the presence of sulphuretted hydrogen and 
 of some other sulphur compounds. 
 
 Group IX. : Organic Compounds. — This group in- 
 cludes many more pigments than any other : not one of its 
 members possesses the permanency belonging to the majority 
 of the mineral pigments, while some are so fugitive that they 
 may even be used for producing a photographic picture by 
 being exposed to sunlight under a negative. This fading is 
 generally due to the combined action of water and oxygen : 
 in oily and resinous media it is lessened, retarded, or even 
 prevented by the hydrofuge character of these vehicles. 
 
 It should be noted that members of each group, though 
 presenting one or more characters in common, often exhibit 
 certain chemical and physical differences of deportment. 
 Here is a list of the chief changes which they are capable of 
 suffering; with illustrative examples : 
 
 Molecular rearrangement 
 
 Subsidence ... 
 
 Volatilization 
 
 Solution 
 
 Fusion 
 
 Oxidation ... 
 
 Reduction ... 
 
 Sulphuration 
 
 Vermilion ; cadmium sul- 
 phide. 
 Smalt. 
 
 Kings' yellow. 
 Strontia yellow ; aureolin. 
 Asphalt. 
 
 Carmine ; Vandyke brown. 
 Naples yellow ; chromates. 
 White lead ; emerald green. 
 
 The effect of pulverization upon pigments may be men- 
 tioned in this connection. Generally, the more finely an 
 alterable pigment is ground, the more susceptible does it 
 
4 -\i\''X'k!%y 
 
 j m j 
 
 256 
 
 CLASSIFICATION OF PIGMENTS 
 
 become to chemical injury : its colour becomes at the same 
 time paler, and may even change in hue as well as in tone. 
 Continued grinding, beyond the degree necessary to develop 
 the proper colour, improves some pigments, but injures others. 
 
 In the chemical classification of pigments which has been 
 sketched in the present chapter there comes out in rather 
 striking relief one point to which no allusion has yet been 
 made. It is indeed a point which touches the chemist 
 rather than the artist, and yet it seems to merit a passing 
 reference in this place. I refer to the number of gaps in 
 the table — to the number of elements and of classes of salts 
 which have no place therein. The scientist will not, indeed, 
 expect to find amongst these 9 groups any substances 
 possessed, to a marked degree, of the property of solubility 
 in water, for he will recognize the unfitness of such bodies 
 for use as paints. But he will probably observe, with some 
 surprise, that there are no compounds of fluorine, chlorine, 
 bromine, or iodine in our lists, but two sulphates, only one 
 substance containing tungsten, and not one containing 
 nickel, uranium, molybdenum, or vanadium. Coloured in- 
 soluble compounds indeed exist of all these elements ; 
 several of such compounds have been proposed and even 
 employed as pigments, but instability or injurious action 
 upon other pigments has banished these candidates from 
 the palette of the artist. 
 
 No mention has been made in the present chapter or in 
 the seven preceding chapters of certain new and beautiful 
 pigments employed in this country or on the Continent. 
 Experiments with many of these pigments have been made, 
 but the results have tended to shew that those colours which 
 might have become welcome additions to the palette of the 
 artist have been lacking in that most important property, 
 namely, assured stability. 
 
CHAPTER XXI 
 
 TABLES OF PERMANENT, FUGITIVE, AND ALTERABLE 
 PIGMENTS 
 
 By several different methods, data may be obtained which 
 enable us to classify pigments — roughly, it is true — in accord- 
 ance with their varying degrees of stability. Such data are 
 derived partly from the known chemical and physical con- 
 stitution of the various substances ; partly from a study of 
 old paintings and drawings in which they have been used ; 
 and partly from special experimental tests of permanency 
 to which they have been subjected. Selections from these 
 data are given in Chapters XX., XXIV., and XXVI., of the 
 present work ; but much additional information has been 
 furnished by other trials, conducted by the author and other 
 experimenters, for which space could not be found in this 
 volume. Tables constructed from such data must not be 
 regarded as affording exact values, but merely approxima- 
 tions. From some minute and often obscure cause differ- 
 ences of deportment, under exposure to hostile influences, 
 will occasionally be observed in the case of two specimens 
 of the same pigment having the same hue. And, further, 
 the grouping of pigments into a small number of classes is a 
 conventional and convenient arrangement which cannot 
 accurately represent the numerous degrees of stability or 
 instability which characterize the several pigments under 
 
 !7 
 
eBbbK'-c V MMBW KM •GraSSm 
 
 258 
 
 TABLES OF PIGMENTS 
 
 discussion. For when we leave the practically unalterable 
 mineral pigments, we have to deal with a number of prepara- 
 tions which fall by irregular and often barely recognisable 
 steps from the almost permanent to the hopelessly fugitive. 
 One example of this difficulty in classification must suffice : 
 aureolin is almost worthy of a place in Class I., Indian 
 yellow scarcely deserves inclusion in Class II. The action 
 of mixed pigments upon one another, though not as frequent 
 as it is supposed to be, creates another difficulty in our 
 classification, so also does the medium employed in painting, 
 which may either protect an alterable pigment from change 
 or aid in its destruction. In fact, each method of painting, 
 if really distinct, requires a special classification of the 
 pigments to be employed in carrying it out. 
 
 In the annexed classification, a limit of three orders of 
 stability has been adopted, the first class including the 
 truly permanent pigments ; the second class those which, 
 though liable to a variable measure of change, may yet 
 generally be allowed ; and the third class those which should 
 be definitely excluded from the palette : 
 
 CLASSIFIED TABLE OF PIGMENTS FOR OIL-PAINTING 
 
 Class I 
 
 Class II 
 White 
 
 Class III 
 
 Baryta white. 
 Zinc white. 
 -; Flake white. 
 
 Yellow 
 
 
 Yellow ochre. 
 Raw sienna. 
 ~? Naples yellow. 
 ,; Cadmium yellow. 
 Cadmium orange. 
 
 Aureolin. 
 Baryta yellow. 
 Indian yellow. 
 Strontia yellow. 
 Chrome yellow. 
 
 Kings' yellow. 
 Yellow madder. 
 Brown pink ; yellow 
 
 lake. 
 Gamboge. 
 Zinc chromate. 
 
 \- <k» 
 
 
 
 
 C< * * }i*^~4e£fi m 
 
TABLES OF PIGMENTS 
 
 2 59 
 
 -f 
 
 Class I 
 
 Class II 
 Red 
 
 Class III 
 
 Vermilion. 
 
 Madder carmine. 
 
 Crimson lake. 
 
 Indian red. 
 
 Rubens' madder. 
 
 Carmine and burnt 
 
 Light red. 
 
 Rose madder. 
 
 carmine. 
 
 Venetian red. 
 
 Madder red. 
 
 Indian lake. 
 
 Red ochre. 
 
 Purple madder. 
 Violet 
 
 Scarlet lake. 
 Purple lake. 
 
 Cobalt violet. 
 
 Mars violet. 
 
 Violet carmine. 
 
 Manganese violet. 
 
 Green 
 
 
 Emerald oxide of 
 
 Emerald green. 
 
 Verdigris. 
 
 chromium. 
 
 Terre verte. 
 
 Sap green. 
 
 Green oxide of chro- 
 
 Malachite. 
 
 ' Green vermilion. 
 
 mium. 
 
 Madder green. 
 
 etc. 
 
 Cobalt green. 
 
 
 
 Green ultramarine. 
 
 Blue 
 
 
 Ultramarine. 
 
 Smalt. 
 
 Indigo. 
 
 Artificial ultramarine. 
 
 Prussian blue. 
 
 Blue verditer. 
 
 Cobalt. 
 
 Antwerp blue. 
 
 Blue ochre. 
 
 Cceruleum. 
 
 Brown and Black 
 
 
 Burnt sienna. 
 
 Madder brown. 
 
 Vandyke brown B 
 
 Raw and burnt umber. 
 
 Cologne earth. 
 
 {bittiminous). 
 
 Cappagh brown. 
 
 Bitumen. 
 
 
 Verona brown. 
 
 Vandyke brown A. 
 
 
 Prussian brown. 
 
 {earthy). 
 
 
 Ivory-black. 
 
 
 
 Charcoal-black. 
 
 
 
 Lamp-black. 
 
 
 
 Graphite. 
 
 
 
 Kc. 
 
 
 17 — 2 
 
26o 
 
 TABLES OF PIGMENTS 
 
 II 
 
 In order to adapt the foregoing classified table to water- 
 colours, some changes and additions must be made. Flake 
 white, Naples yellow (true), cadmium (pale), and vermilion 
 (artificial), must be removed from the Class (I.) of permanent 
 pigments and placed in Class III., to which also must be 
 relegated several pigments from Class II., namely, chrome 
 yellow, malachite, and madder brown. Of course, it should 
 be clearly understood that no pigment belonging to Class III. 
 should be employed in artistic painting. One satisfactory 
 addition, and one only, can be made to Class I. in the table. 
 Indian ink is a pigment available for water-colour painting, 
 and when it is free from a brownish hue may be safely used. 
 Bistre and sepia are likewise used only as water-colours, but 
 they are both fugitive, and must be placed in Class III. 
 Almost the same modifications of the table are required in 
 the case of tempera-painting as in water-colour painting. 
 With fresco-painting the exclusion of many more pigments 
 is an absolute necessity, as they are completely ruined by 
 caustic lime. Not only are all the chromates inadmissible, 
 as well as all the pigments which cannot be trusted as water- 
 colours, but likewise Prussian blue and Antwerp blue, while 
 the madder colours are much altered in hue when used in 
 this process. In stereochromy the number of available pig- 
 ments is still further reduced. 
 
 It may not be uninstructive if we cite in this place the 
 classification of pigments as used in oil which M. Decaux 
 has published. The order followed by this experimenter is 
 that of stability ; the figures prefixed to the names of the 
 individual pigments indicate the degree of permanence, 
 i marking out the materials which are quite unchangeable, 
 while 45 is the most fugitive of all : 
 
TABLES OF PIGMENTS 
 
 261 
 
 DECAUX'S TABLE OF PIGMENTS FOR OIL-PAINTING 
 
 Class I 
 
 I. 
 
 Zinc white. 
 
 1. 
 
 Green oxide of chro- 
 
 4- 
 
 Cobalt green. 
 
 I. 
 
 Flake white. 
 
 
 mium. 
 
 5- 
 
 Mars yellow. 
 
 I. 
 
 Yellow ochre. 
 
 1. 
 
 Ivory black. 
 
 6. 
 
 Mars orange. 
 
 I. 
 
 Naples yellow. 
 
 1. 
 
 Terre verte. 
 
 7- 
 
 Burnt umber. 
 
 I. 
 
 Cadmium (deep). 
 
 1. 
 
 Green ultramarine. 
 
 8. 
 
 Viridian. 
 
 I. 
 
 Raw sienna. 
 
 I. 
 
 Cobalt blue. 
 
 9- 
 
 Indian red. 
 
 I. 
 
 Red ochre. 
 
 1. 
 
 Artif. ultramarine. 
 
 10. 
 
 Mars violet. 
 
 I. 
 
 Mars red. 
 
 I. 
 
 Ivory black. 
 
 11. 
 
 Indian yellow. 
 
 I. 
 
 Venetian red. 
 
 2. 
 
 Mars brown. 
 
 12. 
 
 Emerald green 
 
 I. 
 
 Burnt Italian earth, 
 
 3- 
 
 Burnt sienna. 
 Class II 
 
 
 
 13. Malachite green. 17. Prussian blue. 26. Madder ' r< 
 
 14. Scheele's green. 18 to 23. Various madder doree.' 
 
 15. Raw umber. lakes. 27. Brown madder. 
 
 16. 
 
 Vandyke brown. 
 
 24. 
 
 Madder carmine. 
 Class III 
 
 29. 
 
 Cassel earth. 
 
 3°- 
 
 Pale chrome. 
 
 35- 
 
 Asphalt. 
 
 43- 
 
 Yellow lake. 
 
 3i- 
 
 Zinc chromate. 
 
 36. 
 
 Brown pink. 
 
 44. 
 
 Carmine. 
 
 32. 
 
 Pale cadmium. 
 
 38. 
 
 Vermilion. 
 
 45- 
 
 Crimson lake 
 
 33- 
 
 Orange chrome. 
 
 42. 
 
 Burnt carmine. 
 
 
 
 On comparing this classified list with that previously 
 given a general accordance will be perceived, the low 
 position given to raw umber and to vermilion, as well as 
 the very high place assigned to Indian yellow and to terre 
 verte, constituting the chief exceptions. 
 
 In closing this chapter it may be useful to state that the 
 pigments to which a place in our Class I. has been assigned 
 have stood the very severe test of long exposure to direct 
 sunlight. On a subsequent page it will be shown that this 
 method of determining the stability of pigments is not in 
 
262 
 
 TABLES OF PIGMENTS 
 
 all cases a fair one, because changes brought about by such 
 exposure may not occur at all when the temperature does 
 not rise beyond a particular point, and when the radiant 
 energy of light and actinism does not exceed a moderate 
 measure of intensity. So far then as exposure to light is 
 concerned, it may happen that some of the pigments in 
 Class II. really deserve a higher position than that assigned 
 to them in our table. In this connection we may give 
 some of the conclusions which Messrs. Winsor and Newton 
 have published as to the stability of oil colours when ex- 
 posed, not to sunshine, but to a strong north light. It will 
 be noticed that the class of permanent pigments has been 
 greatly enlarged as the result of the milder ordeal through 
 which the materials have passed : 
 
 Zinc white. 
 Aureolin. 
 Cadmium yellow. 
 Yellow ochre. 
 Raw sienna. 
 Baryta yellow. 
 Mars yellow. 
 Vermilion. 
 Venetian red. 
 Light red. 
 Indian red. 
 Alizarin lakes. 
 Crimson madder. 
 
 Class I. — Permanent 
 
 Madder carmine. 
 Pink madder. 
 Rose madder. 
 Purple madder. 
 Brown madder. 
 Rubens' madder. 
 Scarlet lake (new). 
 Burnt lake (madder). 
 Cobalt green. 
 Oxide of chromium. 
 Viridian. 
 Cerulean blue. 
 Cobalt blue. 
 
 Ultramarine. 
 Manganese violet. 
 Cobalt violet. 
 Prussian brown. 
 Caledonian brown. 
 Cappagh brown. 
 Burnt umber. 
 Burnt sienna. 
 Vandyke brown. 
 Bone brown. 
 Black lead. 
 Blue black. 
 Ivory black. 
 
 Class II. — Moderately Permanent 
 
 Flake white. 
 Chrome yellow. 
 Naples yellow (imi- 
 tative). 
 Kings' yellow. 
 
 Indian yellow. 
 Green cinnabar. 
 Emerald green. 
 Malachite. 
 Rose doree. 
 
 Leitch's blue. 
 Prussian blue. 
 Antwerp blue. 
 Asphaltum. 
 Brown pink. 
 
TABLES OF PIGMENTS 
 Class III. — Fugitive 
 
 263 
 
 Citron yellow 
 
 (ZnCrOJ. 
 Yellow lake. 
 Gamboge. 
 Primrose yellow. 
 Carmine. 
 
 Burnt carmine. 
 Crimson lake. 
 Indian lake. 
 Purple lake. 
 Violet carmine. 
 
 Green lake. 
 Sap green. 
 Verdigris. 
 Indigo. 
 Italian pink. 
 
CHAPTER XXII 
 
 SELECTED AND RESTRICTED PALETTES 
 
 It is by no means easy to construct a palette which shall be 
 at once artistically and scientifically perfect. For it is im- 
 possible to exclude every pigment which is susceptible of 
 change, and it is unwise to include every pigment for which 
 the fancies and partialities of particular painters desire to 
 find a place. An artist discovers how to obtain a required hue 
 by means of a special pigment, and is naturally reluctant to 
 learn by tedious experimenting whether it cannot be secured 
 by means of a more complex commingling of the ordinary 
 paints. And although some great masters have done mar- 
 vellous things with five, four, or even three pigments only, 
 there is no sound argument which can be urged in favour 
 of so severe a restriction. If much mixing of paints be bad, 
 then a reasonable enlargement of the palette will render 
 such mixing unnecessary. And the artist wants something 
 more than a mere match in hue ; he knows that there is a 
 peculiar quality of colour to be sought as well. He can 
 make a transparent pigment opaque, but the reverse opera- 
 tion is impracticable. Scumbling of one opaque colour thinly 
 over another which is also opaque very imperfectly attains the 
 effect of translucency. So the artist demands, in addition 
 to a chromatic series of opaque pigments, a second series 
 possessed of transparency, or, at least, of translucency. 
 
SELECTED PALETTES 
 
 265 
 
 Thus he adds to his cadmium yellow, aureolin ; to his ver- 
 milion, madder carmine ; to his emerald green, viridian ; to 
 his coeruleum or cobalt, ultramarine. And, moreover, he 
 has to take account of the peculiar and often unexpected 
 ^effects produced by the lightening of the tone of a pigment 
 by commixture with white, and by the darkening due to the 
 addition of black. Two nearly identical translucent reds 
 may yield with white two different hues, one verging on 
 salmon, the other on rose. Charcoal-black yields with 
 aureolin or Indian yellow a series of greens quite distinct 
 from those obtained by mixing these yellow pigments with 
 ivory-black. So the artist in making his first choice from 
 the whole number of trustworthy pigments at his command, 
 will proceed towards his final selection by two stages. He 
 first retains those pigments which commend themselves to 
 his judgment for their own chromatic qualities when un- 
 mixed ; he then proceeds to test the characteristics of 
 the remainder by trying the tints which they severally 
 produce with white, the shades they yield with black, and 
 the mixed hues to which they give rise by commixture with 
 one another in twos and threes. To this set of experiments 
 he adds another, in which these pigments are mixed, after 
 the same manner, with those belonging to the first series. 
 As the result of these trials the artist will be enabled to 
 exclude several paints which would merely serve to encumber 
 his palette. 
 
 Before deciding finally as to the elements which shall be 
 retained for our fundamental palette, it will be instructive 
 to study the selections of pigments which from time to time 
 have been employed by artists of recent times and of the 
 present day. The obvious weakness of many of such 
 palettes lies in their inclusion of a few treacherous pigments, 
 such as asphaltum, and of a few evanescent pigments, such 
 
BKKflHH 
 
 266 
 
 SELECTED PALETTES 
 
 as carmine, crimson lake, and the bituminous variety of 
 Vandyke brown. Nevertheless, in making our selection of 
 pigments from the classified list previously given, we may 
 obtain many useful hints from the palettes employed by 
 artists with whose works we are familiar. It is particularly 
 interesting to observe how extremely restricted were the sets 
 of pigments used by several painters who are distinguished 
 for the refinement and for the rich variety of hues shown in 
 their works. In the following paragraphs the names of all 
 decidedly fugitive and alterable pigments are printed in 
 italics. 
 
 Sir Joshua Reynolds, although too fond of varying his 
 practice by the introduction of many dangerous compounds, 
 and by the use, in the same picture, of incompatible media 
 and methods, executed many works between the years 1770 
 and 1775 w,tn one or other of these five restricted palettes, 
 containing from four to eight pigments : 
 
 i. Flake white. Yellow ochre. 
 
 ii. Flake white. 
 iii. Flake white. 
 
 iv. Flake white, 
 v. Flake white. 
 
 Yellow ochre. 
 Orpiment. 
 
 Yellow ochre. 
 Naples yellow. 
 
 Asphaltum. 
 
 Naples yellow. 
 
 Lake. 
 
 Lake. 
 Carmine. 
 
 Carmine. 
 Vermilion. 
 
 Vermilion. 
 
 Lake. 
 
 Minium. 
 
 Ultramarine. Black. 
 
 Ultramarine. 
 
 Ultramarine. 
 
 Blue. 
 Asphaltum. 
 
 Black. 
 Blue black. 
 
 Black. 
 
 Paul Delaroche and H. Vernet employed these eleven 
 pigments : 
 
 Flake white. 
 
 Yellow ochre. 
 Naples yellow. 
 Raw sienna. 
 
 Vermilion. Artificial ultra- 
 Lake. marine. 
 Bran rouge. 
 Burnt sienna. 
 
 Blue black. 
 Ivory black 
 
 W. Etty, 
 
 R.A., used 
 
 1 2 pigments : 
 
 
 Flake white. 
 
 Naples yellow. 
 Yellow ochre. 
 
 Vermilion. Tcrre verte. 
 Light red. Blue verditer. 
 Indian red. 
 Lake. 
 
 Raw umber. 
 Burnt umber. 
 Black. 
 
SELECTED PALETTES 
 
 267 
 
 Samuel Palmer employed in oil 
 pigments, twenty-eight in all : 
 
 painting the following 
 
 Flake white. 
 
 Naples yellow. 
 Yellow ochre. 
 Raw sienna. 
 Cadmium 1, 2, ; 
 Aureolin. 
 
 Field's vermilion. 
 Vermilion. 
 Light red. 
 Venetian red. 
 Indian red. 
 Madder carmine. 
 Pink madder. 
 Rose madder. 
 
 Ultramarine. 
 Ultramarine 
 
 ash. 
 Cobalt. 
 Antwerp blue. 
 Terre verte. 
 Green oxide 
 
 chromium. 
 Emerald green. 
 
 Vine black. 
 Ivory black. 
 Brown madder. 
 Raw umber. 
 Burnt sienna. 
 
 Thomas Wright, of Derby, employed fourteen pigments, 
 and, it is to be presumed, flake-white also : 
 
 Naples yellow. 
 
 Vermilion. 
 
 Carmine. 
 
 Terraccum blue. 
 
 Ivory 
 
 Brown fiink. 
 
 Burnt ochre. 
 
 Lake. 
 
 Ultramarine. 
 
 black. 
 
 
 Indian red. 
 
 Burnt lake. 
 
 Prussian blue. 
 
 
 
 Light red. 
 
 
 Lake azure (?). 
 
 
 From the Portfolio of 1875-6 we obtain the particulars 
 given below concerning the pigments used by several well- 
 known artists : the palettes quoted have been chosen as 
 representative of different types. 
 
 P. H. Calderon, R.A., employed fifteen pigments : 
 
 Vermilion. Cobalt blue. 
 
 Venetian red. Antwerp blue. 
 Pink madder. 
 
 Flake white. Naples yellow. 
 Yellow ochre. 
 Cadmium yellow. 
 Raw sienna. 
 Mars yellow. 
 
 W. C. T. Dobson, R.A., ten pigments : 
 
 Flake white. Yellow ochre. Vermilion. Cobalt blue. 
 
 Yellow ochre. 
 Raw sienna. 
 
 Vermilion. 
 Rose madder. 
 Ptirple lake. 
 
 Burnt sienna. 
 Raw umber. 
 Vandyke brown. 
 Ivory black. 
 
 Raw umber. 
 Vandyke brozvn. 
 Ivory black. 
 
 The following are water-colour palettes : 
 Alfred W. Hunt, seventeen pigments, and in addition 
 Chinese white : 
 
 Lemon yellow. Vermilion. 
 
 Gamboge. Light red. 
 
 Yellow ochre. Indian red. 
 
 Raw sienna. Madder lake. 
 
 Terre verte. 
 
 Cobalt. 
 Ultramarine. 
 Ultramarine ash. 
 Smalt. 
 
 Sir John Gilbert, R.A., fifteen pigments 
 
 Chinese white. 
 
 Yellow ochre. 
 Raw sienna. 
 
 Vermilion. 
 Light red. 
 Venetian red. 
 Indian lake. 
 
 Cobalt. 
 
 Artificial ultra- 
 marine. 
 Indigo. 
 Prussian blue. 
 Antwerp blue. 
 
 Madder brown. 
 Raw umber. 
 Burnt sienna. 
 Burnt umber. 
 
 Burnt sienna. 
 Vandyke brozvn. 
 Ivory black. 
 
268 
 
 SELECTED PALETTES 
 
 The selection of a good set of permanent or fairly per- 
 manent pigments must depend to some extent upon the 
 idiosyncrasy of the artist, upon his training and methods of 
 work, upon the class of subjects with which he deals. As a 
 good general working set for oils, the following selection is 
 offered. It is arranged in two sections, the second including 
 what may be called ' supplementary ' pigments : 
 
 Vermilion. 
 Madder car- 
 mine. 
 Light red. 
 
 Viridian. 
 
 Artificial ul- 
 tramarine. 
 
 Raw umber. 
 Cappagh brown 
 Ivory black. 
 
 Purple madder. 
 Madder brown. 
 Cobalt violet. 
 
 Green oxide 
 chromium. 
 
 Terre verte. 
 
 Cobalt green, 
 light. 
 
 Cobalt. 
 Prussian blue 
 
 (insol.). 
 Burnt sienna. 
 
 q ■ i I Flake white. 
 
 , , ' I Cadmiumyellow. 
 includes U ureolin / 
 12 pigments. [ YMoyf Qchre 
 
 ('Raw sienna. 
 Section II. J Naples yellow, 
 includes 1 Bar V ta y ellow - 
 12 pigments. I 
 
 Emerald green is excluded since it cannot be safely asso- 
 ciated with cadmium yellow, but there is no reason why 
 several other pigments should not be added in Section II., 
 beyond the desirability of limiting the number of paints to 
 those really required. Garance doree, Rubens' madder, 
 deep cobalt-green, burnt umber, Verona brown, vine black, 
 and graphite might be added to the list. On the other 
 hand, further restrictions become by practice possible. One 
 does not know what white, vermilion, yellow, and vine or 
 charcoal black can do until one has purposely debarred 
 one's self from the employment of any other coloured pig- 
 ments. Here are two such restricted palettes : 
 
 i. Flake-white, yellow ochre, light red, cobalt, ivory-black. 
 
 2. Flake-white, cadmium yellow, vermilion, ultramarine, 
 ivory-black. 
 
 A third restricted palette, containing ten pigments instead 
 of five, is thus constituted : 
 
 3. Flake-white, yellow ochre, cadmium yellow, aureolin, 
 vermilion, madder carmine, ultramarine, viridian, Cappagh 
 brown, ivory-black. 
 
RESTRICTED PALETTES 
 
 269 
 
 It is scarcely necessary to say that the capacity of No. 1 for 
 representing the range of natural hues is extremely limited ; 
 indeed, it is fitted only for ' dead colouring,' and for the 
 ' first painting.' With No. 3, however, we can imitate with a 
 near approach to exactness all the pigments excluded from 
 this palette, and we may therefore regard it as practically 
 complete. Some of the hues obtained by the mixtures which 
 it is necessary to employ for this purpose will be a little 
 less luminous than the originals, since these hues will have 
 been produced by the increased absorption of certain ele- 
 ments of the incident white light — they are consequently 
 duller, or have more grey in them. This palette, No. 3, is 
 nearly the same as one devised by the late Mr. P. G. Hamer- 
 ton (Fort/olio, 1876, p. 132), which was constituted of flake- 
 white, pale cadmium, yellow ochre, vermilion, rose madder, 
 artificial ultramarine, emerald oxide of chromium, Vandyke 
 brown, black. I have added one pigment, aureolin, and 
 have substituted for pale cadmium, full cadmium yellow; 
 for rose madder, the more stable madder carmine ; and for 
 Vandyke brown, Cappagh brown. Mr. Hamerton tested the 
 range of his restricted palette by imitating with its consti- 
 tuents many of the excluded pigments. I give some of his 
 results, as modified by my own experiments with my palette 
 No. 3. 
 
 Naples Yelloiv. — Imitated by flake-white, with cadmium 
 yellow and a trace of yellow ochre : exact. 
 
 Lemon Yellow. — Flake-white, cadmium yellow, with a 
 trace of viridian : less brilliant than the original. 
 
 Cadmium Orange. — Cadmium yellow, with vermilion : 
 less brilliant. 
 
 Light Red, — Vermilion, yellow ochre, Cappagh brown. 
 
 Venetian Red. — Vermilion, yellow ochre, madder carmine, 
 a little Cappagh brown : exact. 
 
270 
 
 RESTRICTED PALETTES 
 
 Indian Red. — Vermilion, trace of yellow ochre, madder 
 carmine, ivory black : a good match, but less translucent. 
 
 Cobalt Blue. — Artificial ultramarine, flake-white, a little 
 viridian : less translucent ; does not match cobalt blue by 
 artificial light. 
 
 Prussian Blue. — Ultramarine, black, a trace of viridian : 
 lacks the translucency and depth of the original. 
 
 Raw Sienna. — Yellow ochre, aureolin, Cappagh brown. 
 
 Burnt Sienna. — Madder carmine and Cappagh brown, 
 with a trace of vermilion : less translucent. 
 
 Emerald Green. — White, cadmium yellow, viridian, arti- 
 ficial ultramarine : not so brilliant as the original. 
 
 Malachite. — White, cadmium yellow, yellow ochre, viridian, 
 ultramarine. 
 
 Terre Verte. — White, aureolin, viridian, ivory-black. 
 
 Cobalt Green. — Ultramarine, viridian, trace of flake-white. 
 
 Indigo. — Ultramarine, with black and trace of viridian : 
 very close. 
 
 Vandyke Brown. — Cappagh brown, with much madder 
 carmine and a little ivory-black. 
 
 It is needless to multiply further our illustrations of the 
 resources at the command of the painter who limits himself 
 to our restricted palette of ten pigments (No. 3, page 268), 
 as experimental trials of its capacity are easily made. 
 
 So far thus as regards selected and restricted palettes of 
 oil colours. Some modifications must be made in our list 
 in order to devise corresponding palettes of useful and en- 
 during water colours. In the more extended list (page 268), 
 zinc-white must replace flake-white, while vermilion, purple 
 madder, brown madder, and cobalt violet must be discarded. 
 In the limited palette (No. 3), the changes to be made 
 comprise the substitution of zinc-white ( = Chinese white) 
 for flake-white, the replacement of vermilion by one of the 
 
RESTRICTED PALETTES 
 
 271 
 
 brightest native varieties of iron reds (the mineral turgite is 
 perhaps the best kind), Cappagh brown by Mars brown, 
 and of ivory-black by Indian ink. The two palettes (A. 
 and B.) will then finally resume the following forms : 
 
 7 
 
 (A.) I Zinc white. Light red. 
 
 Section I. J Cadmium yellow. Indian red. 
 
 includes j Aureolin. Madder car- 
 13 pigments. V. Yellow ochre. mine. 
 
 Section II. ("Raw sienna. 
 
 includes "j 
 5 pigments. * 
 
 Red ochre. 
 
 Viridian. Raw umber. 
 
 Artificial ultra- Burnt sienna. 
 
 marine. Indian ink. 
 Cobalt. 
 
 Prussian blue Mars brown, 
 
 (insol.). Ivory black. 
 
 Chinese 
 
 Yellow ochre. 
 
 Red ochre. 
 
 Ultramarine. 
 
 Mars brown. 
 
 white. 
 
 Cadmium yellow. 
 Aureolin. 
 
 Madder car- 
 mine. 
 
 Viridian. 
 
 Indian ink. 
 
 Doubtless artists will especially miss from this palette six 
 pigments, namely, gamboge, vermilion, rose madder, brown 
 madder, Vandyke brown, and indigo. But after the over- 
 whelming evidence adduced in Chapter XXVI. as to the 
 want of permanence shown by these water-colour paints, 
 one feels compelled to exclude them. Our second and 
 more restricted palette (B.) is thus composed : 
 
 (B.) 
 
 Although it is obvious that with these limited palettes it 
 is impossible to produce exact imitations of every excluded 
 pigment, yet there are two considerations which must not 
 be forgotten in estimating the influence of this defect on 
 artistic painting. Foremost may be placed the fact that 
 pigments are rarely employed wholly unmodified by admix- 
 ture with others ; then it must be noted that the differences 
 between our imitations and the original pigments which 
 they are intended to replace are rather those of lessened 
 brightness, translucency, and depth than those of hue. 
 
jBjBSrBSStyiWDMicmf 
 
 PART IV 
 
 METHODS AND RESULTS 
 
 Chapter XXIII.— Painting Methods. Chapter XXIV.— Study of Old 
 Paintings and Drawings. Chapter XXV. — Conservation of Pictures. 
 Chapter XXVI. —Trials of Pigments. 
 
CHAPTER XXIII 
 
 PAINTING-METHODS 
 
 As the grounds, vehicles, and pigments employed in painting 
 have been already described in Parts I., II., and III. of this 
 volume, it will not be necessary to do more in the present 
 chapter than give a summary or general view of the chemistry 
 of each method of employing these materials. 
 
 These methods are six in number, and may be thus de- 
 fined : 
 
 Methods Vehicles , C ! ia % e . s . 
 
 during Fixing 
 
 i. Tempera - • Egg-yolk emulsion ; solution o. gelatin ) ( Desiccation or 
 
 or albumen j ( coagulation. 
 
 2. Fresco - - Lime-water, in both buon' fresco and 
 
 fresco secco - - - - Carbonation. 
 
 3. Stereochromy Aqueous solutions of alkaline silicates - Formation of in- 
 
 soluble silicates. 
 
 4. Oil - Painting ) . f Oxidation,. 
 
 and Spirit ■ J- Oil, and solutions of resin, wax, paraffin J Kesimncation, 
 
 Fresco Evaporation, 
 
 J ... V. Solidification. 
 
 5. Water-Colour Aqueous solutions of gum, glycerin, 
 
 honey Desiccation. 
 
 6. Pastel, ^ 
 
 Charcoal. k „ - T 
 
 Plumbago, f None None - 
 
 Silver-point J 
 
 i. Tempera-painting, or painting in distemper, is generally 
 assumed to include two, if not three, methods of procedure, 
 in which different vehicles or media are employed. These 
 vehicles all contain a nitrogenous constituent ; but in one of 
 them — and that the most important — oil or fat is present in 
 addition. Tempera-grounds must be rigid, tenacious, and 
 
 18—2 
 
276 
 
 TEMPERA -PA INT IN G 
 
 ~L- 
 
 firm ; they need not be dry, but if organic pigments are to 
 be used, they should not contain caustic lime. Thus, a sur- 
 face of plaster made with slaked lime and sand must have 
 been so long exposed to the air as to have absorbed the 
 amount of carbonic acid necessary to convert the hydrate of 
 lime present into ' mild lime ' — that is, the carbonate. To 
 detect the existence of caustic lime in such a painting-ground 
 recourse may be had to test-papers. Three kinds are avail- 
 able for this purpose. Thus, yellow turmeric-paper, first 
 wetted and laid upon the surface of the plaster, should show 
 no change of colour ; if it become reddish, the presence of 
 caustic lime is indicated. Under the same circumstances 
 red litmus-paper turns blue or purple, while phenolphthalein- 
 paper acquires a crimson hue. If these tests show the 
 absence of caustic lime, the painting may be commenced, 
 otherwise the surface must be carbonated by syringing it or 
 washing it with water charged with carbonic acid gas. These 
 precautions are, of course, unnecessary in cases where the 
 painting-ground has been prepared with plaster of Paris or 
 other neutral compositions of which caustic lime is not a com- 
 ponent. Before commencing work the painting ground must 
 be slightly and uniformly moistened with distilled water, and 
 then coated with weak size. The pigments to be employed 
 are those recommended for use as water-colours ; they are 
 thoroughly mixed with the medium to be employed, namely, 
 egg-yolk emulsion, or size, or prepared white of egg. These 
 media serve not only to bind the pigments to the ground, 
 but also the coloured particles to one another. To render 
 the egg-yolk more tractable, its alkaline reaction should be 
 exactly neutralized by the cautious addition of a very few 
 drops of white vinegar — fig-tree sap or white wine were 
 sometimes formerly employed for the same purpose. Some 
 artists content themselves with diluting the egg-yolks with a 
 
FRESCO-PAINTING 
 
 277 
 
 little water, others add a small proportion of white of egg, 
 previously shaken with a little water and filtered. To keep 1 
 the egg-emulsion sweet, a lump of camphor or a few cloves 1 
 may be put into it. Size and also white of egg have been , 
 employed in tempera-painting. The white of egg needs dilu- 
 tion with water, thorough shaking, and then filtering through 
 muslin. When egg-yolk is used in this method of painting, 
 the oil in it gradually hardens, while the albuminoid matters 
 which accompany it become partly insoluble and coagulated. 
 As the amount of oil in egg-yolk is twice as great (31 per 
 cent.) as the albuminoid matters (15 per cent.), this vehicle 
 presents considerable resemblance to those employed in oil- 
 painting, the albuminoid matters corresponding in a measure 
 to the resins often used in the latter method. This vehicle 
 does not act so effectually as oil and varnish in ' locking up ' 
 pigments, and so the protection against change which it 
 affords is less. Moreover, instances have been observed in 
 which the sulphur present in the albuminoids of egg-yolk 
 has acted injuriously upon some of the pigments of the 
 picture ; but by excluding, as we now do, all paints contain- 
 ing lead and copper from the tempera-palette, accidents of > 
 this kind are prevented. A finished tempera-picture was 
 often — one might almost say generally — rubbed with a cloth 
 and then varnished, the varnish being often made by dis-\ 
 solving sandarac in oil. The tone of the colours was thus 
 warmed, while further protection was at the same time 
 afforded against moisture and impure air. 
 
 2. In fresco-painting — both buon' fresco and fresco secco 
 — the ground must not only be wet, but caustic. In true 
 fresco the pigments are applied to the last and freshly-spread 
 coat of plaster before it has had time to absorb more than a 
 trace of carbonic acid from the air ; the painting-ground is 
 in fact saturated with an aqueous solution of hydrate of 
 
 
I 
 
 
 278 
 
 FRESCO-PAINTING 
 
 lime, while there remains a large reserve of this compound 
 in an undissolved condition. When on such a surface a 
 layer of pigment mixed with water is placed, as that water 
 evaporates the lime-water in the ground diffuses into the 
 paint, soaks it through and through, and gradually takes up 
 carbonic acid from the air, thus producing carbonate of 
 lime, which acts as the binding material in this method. 
 As there still exists an ample reserve of hydrate of lime in 
 the ground, wetting the painted surface with pure water will 
 cause more of this hydrate to enter into solution, and so the 
 liquid present in the plaster will be reinforced with a fresh 
 supply of the binding material. Ultimately the ground and 
 the pigment become incorporated and harden together. If 
 more binding material be required, it may be introduced by 
 means of lime-water itself, or even by baryta-water, which 
 contains twenty times as much hydrate of baryta as the 
 strongest lime-water contains of hydrate of lime; these 
 liquids or hydrate of lime may also be mixed with the pig- 
 ments used. Although the chief binding material in fresco- 
 painting is this carbonate of lime, yet with some plasters 
 and with some pigments another substance is produced. 
 This is silicate of lime, produced by the action of caustic- 
 lime in solution upon the soluble silica of the plaster or of 
 the pigments. Some sands, infusorial earths, and ochreous 
 pigments contain such soluble silica, but it is certainly not 
 present in every case. Silicate of lime as a binding material 
 is more permanent than the carbonate. 
 
 In fresco secco the plaster is allowed to harden, and, 
 in some measure, to dry, and the operation of painting 
 may be continued at leisure. The ground immediately 
 before beginning work is moistened with lime or baryta- 
 water, and the pigments are mixed with one or other of these 
 liquids, or with a little slaked lime. This modified process 
 
FRESCO-PAINTING 
 
 279 
 
 is far easier of execution than true fresco ; but the fixation 
 of the pigments, though resulting from the same cause, is 
 less complete. 
 
 In the treatises of Cennini and other later writers the 
 expression ' painting in secco ' is generally employed to 
 designate any process of tempera-painting, but the fresco 
 secco described in the preceding paragraph was practised 
 before and during the thirteenth century as the precursor 
 of buon' fresco, and is briefly mentioned in Theophilus 
 (' Schedula,' Book I., chapter xv.). 
 
 The protection afforded to the pigments by the binding 
 material in fresco-painting is not generally very efficient. 
 In the case of a dry wall, free from soluble saline matter, 
 and exposed to a pure atmosphere, it may remain good 
 for centuries. But in air contaminated with the products 
 of the combustion of coal and gas, and with tarry and 
 sooty impurities, a fresco picture soon perishes. The bind- 
 ing carbonate of lime is converted into the sulphate, break- 
 ing up the paint, and becoming itself disintegrated in the 
 process of change. Through the same cause, and through 
 the production of sulphate of magnesia from the carbonate 
 of magnesia in the plaster, even the layer of paint itself 
 may scale off, while the lodgment of dirt and soot upon the 
 surface obscures such colours as still remain in their place. 
 And fresco-paintings often show scaling-off, by reason of 
 the interposition of a film of carbonate of lime between the 
 coats of paint — a film formed during the completion of the 
 picture. 
 
 True fresco did not come into use in mediaeval times 
 until the close of the fourteenth century. About the year 
 1390, Pietro d'Orvieto painted some subjects from Genesis 
 in the Campo Santo at Pisa. In 1503, Pinturicchio, at Siena, 
 began some works in fresco, which he finished in tempera 
 
28o 
 
 STEREOCHROMY 
 
 with lakes and other pigments injured by lime. This mixed 
 method was much used in Italy to a late period, as it 
 enabled a greater richness of effect to be attained. For the 
 palette of the painter in true fresco is severely restricted in 
 certain directions, very few colours of organic origin with- 
 standing the decomposing action of lime. It is a good 
 plan to test each pigment intended to be employed in this 
 method : The pure pigment is thinly painted over a slab of 
 plaster of Paris, and then half of it moistened with lime- or 
 baryta-water. No change of hue, only a lightening of the 
 tone, should be observed, after drying, in the treated portion. 
 Prussian blue may be named amongst the pigments most 
 quickly and seriously altered by lime ; it becomes a mere 
 stain of rust. As lime in the caustic state acts strongly 
 upon wood, it is necessary to employ palettes of zinc or 
 glazed earthenware ; bone or ivory palette-knives are prefer- 
 able to those of steel. 
 
 3. In stereochromy, or water-glass painting, a process intro- 
 duced more than fifty years ago, the fixative employed is an 
 alkaline silicate dissolved in water. From time to time 
 different experimenters have improved the painting grounds, 
 the preparation of the pigments, and the mode of applying 
 the fixing liquid; but the main chemical actions involved in 
 this method of painting are identical in all the modifications 
 which have been introduced The constituents and pre- 
 paration of painting-grounds adapted for this process have 
 been discussed in Chapter II. The pigments should be 
 treated, as recommended by Kuhlmann, with some of the 
 fixing liquid, and then reground ; in some cases they 
 require the addition of oxide of zinc, powdered marble, 
 powdered glass, carbonate of baryta, soluble silica, hydrate 
 of alumina, etc., in order that their natural inaptitude for 
 equal fixation by the alkaline silicate should be remedied. 
 
OIL-PAINTING 
 
 281 
 
 Opinions differ as to the desirability of treating the painting- 
 ground with some of the water-glass solution before laying 
 on the colours ; but it is essential that if a solution of this 
 silicate be used at this stage, it should be very dilute. The 
 finished painting is sprayed with a warm dilute solution of 
 potash water-glass or potash-soda water-glass, to which has 
 been added liquor ammonias. The surface is shortly after- 
 wards washed repeatedly with hot distilled water; and, if 
 necessary, the application of the water-glass solution, and 
 the subsequent washing, are repeated. The final result of 
 these operations is to bind the particles of pigment to one 
 another, and to the ground, by means of an insoluble double 
 silicate. This silicate, formed partly out of some of the 
 constituents of the ground, of the pigments, and of the 
 water-glass, mainly consists of silica, lime, and potash ; it 
 often contains zinc, magnesia, and alumina. The soluble 
 salts removed by washing the painting with water are the 
 carbonates of potash and ammonia ; when, however, soda 
 is present in the water-glass, carbonate of soda has been 
 formed, and is removed at the same time. The pigments 
 employed in stereochromy are more limited in number even 
 than those available in fresco-painting, and consist chiefly of 
 natural oxides and earths, the artificial oxides and hydrates 
 of chromium and iron, cobalt green, ultramarine, cobalt 
 blue, and ivory-black. 
 
 4. Oil-Painting and Spirit- Fresco. — The essential charac- 
 teristic of these methods is to be found in the use of a 
 binding material which is in itself insoluble in water. The 
 painting-ground employed should be dry, and free from 
 alkali and from soluble salts. If it be primed canvas or 
 panel, it is a good plan to cleanse it with oxgall and water, 
 or with a very weak solution of carbonate of ammonia, 
 before commencing work. A discoloured lead-priming 
 
282 
 
 OIL-PAINTING 
 
 should be restored to its original brightness by laying a 
 sheet of white blotting-paper upon it, and then just satu- 
 rating this paper with a solution of peroxide of hydrogen. 
 The moist surface is now exposed to a moderate degree of 
 heat — as by holding it in front of a fire — which greatly 
 quickens the activity of the peroxide. When the paper has 
 become dry, it may be removed, and the bleaching of the 
 tarnished ground will be found to have been effected, the 
 brown sulphide of lead having been oxidized into the white 
 sulphate. In order to learn whether a plaster-ground or 
 a wall is sufficiently dry to be safely painted upon in oil or 
 spirit-fresco, the gelatin-test may be employed. A small 
 oblong piece of coloured sheet-gelatin is held firmly and 
 closely against the plaster or wall, by means of a stick 
 applied at the centre. If hygroscopic equilibrium have 
 been established between the wall and the air, the gelatin 
 will remain fiat ; if the wall be moister than the air, the 
 sheet will curl outwards, the inner surface becoming highly 
 convex. Slate and several other suitable painting-grounds 
 may be dried and further prepared for work in oil or spirit- 
 fresco by heating them gradually in a water-oven up to the 
 temperature of boiling water, and then rubbing them with 
 a piece of hard paraffin-wax. The slate is again heated in 
 the water-oven, withdrawn, and then at once rubbed with a 
 dry, warm cloth, so as to remove all excess of paraffin-wax. 
 Other methods of treating stone, etc., for the reception of 
 oil-colours have been previously given. A very convenient 
 means of neutralizing the residual alkalinity of a lime-plaster 
 ground intended for oil or spirit-fresco painting is afforded 
 by linoleic acid.* This liquid fatty acid is an article of 
 commerce, moderate in price, and easily obtainable. A 
 
 * By linoleic acid is here meant the mixture of fatty acids obtainable 
 from raw linseed oil. 
 
OIL-PAINTING 
 
 283 
 
 wide-mouth tin of it is placed in a vessel of boiling water ; 
 when the linoleic acid is hot, it is paid on to the surface of 
 the plaster with a wide brush, any excess being removed by 
 wiping the ground with a cloth. Solid stearic acid may be 
 melted and used in the same way, but its effect is inferior. 
 
 The vehicles employed in this method of painting are not 
 miscible with water — are, in fact, hydrofuge materials repel- 
 lent of moisture. If an absorbent ground or other porous 
 material be soaked with water, and then covered with oil, 
 as the water evaporates the oil penetrates, and at last com- 
 pletely takes its place. But, on the other hand, the reverse 
 process cannot be carried out, since the water outside will 
 not displace the oil inside. These vehicles are either oils or 
 else solid substances in solution — solids which, though in- 
 soluble in water, may be dissolved with more or less ease in 
 one or other of a long series of liquid solvents (Chapters V., 
 VI., XI. and XII.). The changes experienced by these 
 vehicles and their constituents during the painting process 
 may be thus summarized : 
 
 (a) The oils used absorb oxygen from the air, increasing 
 in weight thereby to the extent of 10 or n per cent. — such 
 increase in weight being accompanied by a considerable in- 
 crease in bulk. This latter change is clearly shown when a 
 layer of a drying oil, spread upon glass, is allowed to dry ; 
 it then becomes rippled or wrinkled from expansion ; such 
 expansion, owing to the viscosity of the oil, takes place 
 mainly in a direction perpendicular to that of the surface of 
 the glass. 
 
 (b) The above-described absorption of oxygen by the oil 
 employed in painting results in the formation of a substance 
 or mixture of substances called linoxifie. Now this product 
 is not only solid instead of liquid, but it is much less soluble 
 in the usual solvents of oils than is the oil from which it has 
 
284 
 
 OIL-PAINTING 
 
 been formed. But there are circumstances, not yet ac- 
 curately denned, in which linoxine itself occasionally suffers 
 a peculiar change, finally becoming brown in colour, tacky 
 in consistence, and soluble even in spirits of wine. This 
 degradation of linoxine is, however, of very rare occurrence 
 in the ordinary practice of oil-painting. A singular circum- 
 stance connected with the transformation of ' linolein ' into 
 ' linoxine ' has been noticed ; this change is accompanied by 
 the formation of hydrogen peroxide, a compound which is 
 also produced during the oxidation of the terpenes. The 
 continuous production of the peroxide may be recognised 
 on the surface of an oil-painting long after it has been 
 completed by the blue colour which it develops in starch- 
 paste containing potassium iodide. 
 
 (c) The resins present in varnishes and media contract 
 for some time after the major part of their volatile solvent 
 has escaped by evaporation, and thus leave a residue which 
 becomes fissured. In a properly-proportioned medium this 
 contraction should be balanced, or rather more than 
 balanced, by the expansion of the oil present. Hence the 
 desirability of associating a varnish (or a resin dissolved 
 in a volatile solvent) with a drying oil, in this method of 
 painting. 
 
 (d) Waxes and solid paraffins, when once deposited from 
 a solution by the escape of the solvent, neither expand nor 
 contract by desiccation or oxidation, but only through 
 changes of temperature. 
 
 (e) Most of the liquid solvents simply evaporate, leaving 
 no fixed residue due to their previous presence. But oil 
 of turpentine (spirits or essence of turpentine) generally 
 behaves differently. Some kinds of oil of turpentine differ 
 from the majority in this particular, but the remainder suffer 
 two simultaneous changes. A portion evaporates ; another 
 

 BM W 
 
 OIL-PAINTING 
 
 285 
 
 portion absorbs oxygen from the air, becoming converted 
 into a sticky, yellow, and resinous substance, which remains 
 behind. The resin thus formed is a very objectionable con- 
 stituent in the structure of a picture, and its production 
 should be avoided either by employing a variety of turpen- 
 tine not subject to easy resinification, or by using a freshly- 
 distilled turpentine which has been secluded from the air, 
 and in which a few lumps of freshly-burnt lime have been 
 placed, to remove water and such resinous matters as may 
 be produced. 
 
 An important precaution to be observed in the ' conduct ' 
 of a painting during its progress is based upon the two 
 actions just referred to, namely, the oxidation of the oil 
 during its hardening, and the escape of volatile solvents. 
 The latter action takes place more easily than the former, 
 and so if a picture is to be carried on rapidly to completion, 
 the earlier and lower paintings should contain less oil than 
 those nearer the surface, into which more oil and less resin 
 (copal or amber), dissolved in some volatile solvent, should 
 be introduced. If the reverse order be followed, the highly 
 oleaginous layers below, having had no sufficient opportunity 
 for oxidizing, drying, and hardening, will be rent by the 
 strong and quickly drying resinous layers above them. 
 
 The harder resins, paraffin-wax, wax, and oil, possess in 
 varying degrees the power of ' locking-up ' the pigments with 
 which they are mingled, in such a way that these become 
 much less liable to act upon one another, and to suffer 
 injury from external agencies. In a measure they repel and 
 exclude moisture and oxygen — two of the chief agents of 
 chemical change. But the value of these ' locking-up ' 
 materials has been exaggerated : they often prove quite 
 ineffectual in preventing the oxidation or other change 
 suffered by non-permanent pigments and the inter-action 
 
286 
 
 OIL-PAINTING 
 
 of pigments. For instance, the oil which surrounds each 
 particle of cadmium yellow and emerald green, in a mixture 
 of these two oil-paints, is not capable of preventing the 
 formation of the black sulphide of copper. And Dr. A. P. 
 Laurie has found that when a layer of linseed-oil is inter- 
 posed between these oil-colours separately spread, it is the 
 emerald green which appears to travel towards the cadmium 
 yellow — perhaps owing to its solubility in the medium. 
 In consequence, the production of spots of black sulphide 
 of copper occurs chiefly, if not entirely, on that side of the 
 oil-layer which is in contact with the cadmium yellow. To 
 Dr. Laurie we are also indebted for a very ingenious 
 method of comparing the locking-up function of various 
 oils and resins. Dr. Laurie prepared some anhydrous 
 sulphate of copper which is white, but acquires a blue 
 colour when exposed to moisture. He ground this white 
 sulphate with various media, painted glass slides with the 
 mixtures, dried them in a desiccator, and then exposed 
 them to moist air. A solution of amber in turpentine 
 proved superior, in its power of resisting the access of 
 moisture, to boiled linseed-oil, oil-copal varnish, amber 
 dissolved in oil, resin or mastic dissolved in turpentine. 
 Another set of trials, in which the test substance was 
 ground in linseed-oil, allowed to harden in a desiccator and 
 then coated with different varnishes, indicated a temporary 
 superiority on the part of mastic in turpentine, and of oil- 
 copal varnish over amber or copal in turpentine. The 
 inferiority of the latter solutions may be due to the rupture 
 in continuity of the resinous films which they leave on 
 evaporation. (See Journal of Chemical Industry, June, 
 1890.) But it must not be forgotten that many an old oil- 
 picture furnishes distinct evidence of the value of resinous 
 matters (such as Strasburg and Venice turpentine) in locking 
 
OIL-PAINTING 
 
 287 
 
 . t/w* 
 
 up such changeable and destructive pigments as verdigris 
 and orpiment. The slow and laborious execution of such 
 paintings constituted an important element in the success 
 achieved, for each layer dried and hardened before the next 
 was applied. 
 
 It should be noted that different oil-paints contain very 
 different percentages of oil. This fact should be taken into 
 account, so far as possible, in adjusting the amount of 
 resinous matter to be introduced during the course of work 
 upon an oil-picture. A table giving approximately the 
 quantities of oil required in grinding 100 parts of various 
 dry pigments as oil-paints will be found on page 53. 
 Further information concerning such pigments is given in 
 Chapters XIII. to XIX. 
 
 In completing an oil-picture, the three operations of 
 ' glazing,' ' oiling out,' and ' varnishing ' remain to be con- 
 sidered. As to glazing and oiling out, it should be stated 
 that drying oil, with a little copal or amber varnish, should 
 alone be employed — mastic varnish should never be added 
 to the oil. Of course oil-paints are used in admixture with 
 oil and copal for glazing purposes. If mastic be introduced, 
 a risk is incurred of its partial removal during any cleaning 
 operation to which the picture may be afterwards subjected. 
 The question of the kind of varnish to be finally applied to 
 an oil-picture has been much discussed. Our choice lies 
 between a strong irremovable varnish, and a weak one 
 capable of being abraded by friction, or of being dissolved 
 by the application of a suitable solvent, which will not touch 
 the true painting beneath. Mastic dissolved in turpentine 
 fulfils the latter conditions ; copal or amber dissolved in oil 
 and thinned with turpentine, and mixed with a little oil, 
 constitutes a strong, hard, irremovable protection to the sur- 
 face, and becomes a part of the picture itself. Under no 
 
288 
 
 SPIRIT-FRESCO PAINTING 
 
 circumstances should any varnish be applied to the painting 
 until the latter has become thoroughly hard and dry ; the 
 danger of tearing the layers of paint by such application will 
 then have been reduced to a minimum. A further advan- 
 tage of delay in varnishing a picture accrues through the 
 increasing insolubility with age of the oxidized oil present 
 therein, the pigments associated therewith becoming less 
 liable to removal by any treatment to which the work may 
 afterwards be submitted. 
 
 The chemistry ot Gambier-Parry's spirit-fresco method, 
 and of the process in which paraffin-wax and copal varnish 
 are employed as the vehicle, is essentially the same as that 
 of oil painting. The wax or paraffin- wax is introduced 
 merely to secure a matt surface. Pictures executed in these 
 methods are, of course, never varnished. The method of 
 spirit-fresco was devised by the late Mr. Gambier-Parry with 
 the object of obtaining such effects in mural paintings as 
 are realized in true fresco, but with greater ease in working, 
 and greater permanence under adverse atmospheric condi- 
 tions. He desired to exclude linseed or other fixed drying 
 oils completely from the medium and other materials em- 
 ployed. With this end in view, he directed that the pig- 
 ments used should be ground up, not with oil, but with the 
 medium itself. He was apparently unaware that the copal 
 varnish, which enters largely into the composition of his 
 vehicle, contains a greater proportion of oil than of any other 
 ingredient (see Chapter XII.). So, after all, the medium 
 used in spirit-fresco differs from that generally employed in 
 oil-painting rather in the proportions than in the nature of 
 its ingredients. Thus in working with it we shall find that 
 its binding character is obtained as a result of the same two 
 changes which cause the fixing and solidification of an oil 
 painting, namely, the oxidation of the oil, and the desicca- 
 
WATER-COLOUR PAINTING 
 
 2S9 
 
 tion of the resin. The wax present suffers no chemical 
 alteration at first, but merely solidifies, although after the 
 lapse of years it is liable to produce a kind of exudation or 
 bloom ; indeed, in the course of years the wax may wholly 
 disappear. It should be added that the painting-ground 
 for this method of working is first prepared with the medium 
 diluted with oil of turpentine (see Chapter II.). 
 
 The method of painting with the paraffin-copal medium 
 involves the same chemical and physical changes as those 
 which occur in the use of the spirit-fresco vehicle, and is 
 carried out in the same manner. Colours stiffly ground in 
 oil may be used or in a mixture of the medium with oil : dry 
 colours ground in the medium generally are to be preferred. 
 The medium may be diluted to any desired consistency with 
 spirits of turpentine or with oil of spike, but no dilution 
 further than that required to secure perfect freedom in the 
 manipulation and use of the paints is desirable, while it is 
 important to remember that the use of abundance of medium 
 is necessary to bind the particles of pigments firmly together. 
 Artists have sometimes found that a picture painted in 
 spirit-fresco will cede colour to a cloth used in rubbing its 
 surface. This result is due either to excessive use of a 
 diluent in working with this medium, or to a deficiency of 
 oil in the copal-varnish used. I have never known a friable 
 surface to be formed where the colours employed had been 
 ground in oil instead of in the medium, or where a little 
 extra oil had been added to the latter. 
 
 5. Water-colour Painting. — The usual binding material in 
 this method is gum ; glycerin and honey are also employed 
 to some extent. Raw honey should never be used, but only 
 one of the sugars it contains, known to chemists as laevulose 
 (Chapter VIII.). Great care must be taken not to introduce 
 any unnecessary excess of either glycerin or laevulose, as 
 
 19 
 
 1) 
 
EKK 
 
 I 
 
 290 
 
 WATER-COLOUR PAINTING 
 
 
 these materials attract moisture from the air, and we know 
 that moisture is one of the most potent agents in causing 
 injury to works in water-colour. Glycerin and laevulose are, 
 however, useful, when employed in moderation, for preserv- 
 ing the pigments in working condition, and in counteracting 
 the tendency of gum to crack. The media used in water- 
 colour painting, consisting wholly of aqueous solutions, 
 afford very slight protection to the pigments used. In the 
 presence of the moisture of the ground (paper often contains 
 naturally 10 per cent, of water) and of the air, water-colour 
 pigments have abundant opportunities, not only of acting 
 " upon one another, wherever from their chemical constitution 
 such action is possible, but also of being acted upon by 
 external agents. Thus it comes to pass that several pig- 
 ments (vermilion, for instance, and emerald green) useful 
 in oil-painting cannot be safely used as water-colours. 
 Again, there are a few pigments (such as strontia yellow) 
 which are soluble in water, and which consequently may 
 gradually sink into the paper, and so partially disappear from 
 the surface. 
 
 Assuming the paper-ground to be of linen-pulp, and free 
 from ' filling,' from bleaching substances, from antichlors, and 
 from fragments of iron, it will still contain about 5 per cent 
 of size. When in preparation for painting it is moistened 
 with water, this size swells, and on the subsequent application 
 of washes of pigments, enters partially into mechanical 
 union with them, so that the various coloured materials ap- 
 plied to the surface become associated with the size rather 
 than with the paper-fibres. One paint, Indian ink, itself 
 contains size, and for this reason when washes of it are laid 
 upon paper previously damped, their incorporation with the 
 size of the latter is so intimate that their removal is imprac- 
 ticable. The size in a water-colour drawing becomes in 
 
PA STEL-PA INTING 
 
 291 
 
 time partly coagulated and insoluble ; the gum merely dries. 
 Instances are known where the size has in some degree 
 ultimately perished. 
 
 6. Pastel, Charcoal, Plumbago, Silver-point. — The com- 
 mon characteristic of all the processes which form our 
 sixth group is the absence of any vehicle or binding material. 
 The usual ground on which drawings in the above-named 
 substances are executed is paper (Chapter I.) ; but as the 
 hold of coloured chalks and of charcoal is very precarious, 
 the paper is generally mounted on some comparatively rigid 
 backing, such as millboard, cardboard, copper, or panel. If 
 a chalk or charcoal drawing be carried out on paper which 
 has first received a wash of gum-water or of dextrin-solution, 
 it is easy to effect a partial fixation of the powdery pigment 
 by subsequently steaming the finished work, although it is 
 usual to employ a fixing solution in the form of very fine 
 spray to the finished drawing. For pastel work a specially 
 prepared paper is now generally employed. This has a 
 surface of finely-powdered pumice, which affords an efficient 
 tooth, and helps in securing the coloured chalks or clays. 
 This result is further aided by the plan of working in and 
 mingling the pigments by means of rubbing with the fingers 
 and the palm of the artist's hand. Pastel-paper is often 
 made of inferior pulp, and lacks strength. It should be less 
 sized than paper intended for water-colours. Pastel colours 
 are generally made with a basis of purified chalk or pipe- 
 clay mingled with the usual pigments in powder, a slight 
 degree of cohesion being secured by making up the crayons 
 with starch-paste or gum-tragacanth. In plumbago (lead- 
 pencil) and silver-point work the mechanical adhesion of the 
 coloured particles is naturally less imperfect, a portion of 
 the plumbago or silver becoming, in fact, incorporated with 
 the fibres of the paper-ground. This is particularly the case 
 
 19 — 2 
 
 '-4 
 

 292 
 
 SILVER-POINT DRAWING 
 
 
 with silver-point, in which method the ground receives a 
 particular preliminary preparation. One of the best materials 
 for this purpose is Chinese white (oxide of zinc). An even 
 wash of this pigment in the form of ' moist ' water-colour is 
 first spread over the paper. As a silver-point drawing is 
 often heightened with touches of Chinese white, it is desir- 
 able to bring these into prominence by tinting the ground. 
 For this purpose a small quantity of some permanent pigment 
 is mixed with the wash of Chinese white. Yellow ochre, 
 raw umber, green oxide of chromium, Mars violet, ultra- 
 marine with a little ivory-black, may be used. The ' tooth ' 
 of surface which increases the attrition of the silver-point is, 
 however, furnished by the presence of the Chinese white. 
 It should be added that the silver used should be free from 
 any alloy of copper, which hardens the metal, but may 
 advantageously contain a few per cents, of metallic lead ; 
 an alloy of 2 parts of lead with 1 part of tin was sometimes 
 used instead of silver. The silver in silver-point drawings 
 is liable to become brown from the sulphur compounds in 
 impure air. The blackening of the high lights in old silver- 
 point drawings is due to the tarnishing of the lead white 
 employed ; it may be got rid of by keeping the drawing for 
 some time in an atmosphere of moist ozone, or by a careful 
 treatment with a solution of hydrogen peroxide in ether. 
 
 A pointed pencil of pure gold is occasionally used instead 
 of one of silver or graphite. It produces on a prepared 
 paper surface the same grey line, and is theoretically a perfect 
 material for drawing purposes. But, strange to relate, gold- 
 point drawings have been observed to suffer change, becom- 
 ing nearly invisible, not by reason of any chemical action 
 on the metal, but in consequence of a rearrangement of the 
 metallic particles whereby their grey hue disappears and the 
 original yellow lustre of the gold is resumed. Drawings in 
 
PASTEL-PAINTING 
 
 293 
 
 platinum-point are not susceptible of this change. The 
 platinum employed must be pure, otherwise this metal is 
 too hard for comfortable manipulation. 
 
 Pastel or coloured chalk drawings frequently show a 
 higher degree of preservation, so far as certain hues are 
 concerned, than contemporary works executed in oil. One 
 can easily account for the pure and fresh air of old pastel 
 drawings, knowing that they have been carefully mounted 
 and framed, and that there has been no oil or resin to 
 yellow and darken the pigments. But how can the remark- 
 able state of preservation in which the ' carnations ' are 
 found in so many examples be explained ? Has the 
 intimate commixture of chalk or of clay with crimson lake 
 preserved the latter from the destructive action brought 
 about by light ? If there have been such a preservative 
 action, has it been physical rather than chemical ? Answers 
 to such questions must be reserved until the chemistry of 
 coloured pastels has been thoroughly studied. It should, 
 however, be recollected that the white basis of coloured 
 pastels is not always the same. In the eighteenth century 
 it seems to have been invariably purified chalk, that is, 
 ' whitening ' or ' whiting,' which is essentially calcium 
 carbonate. But, on examining lately a well-known make 
 of French pastels, a considerable percentage of calcium 
 sulphate was recognised, in addition to chalk. Further 
 experiments seem to show that the colouring matter used is 
 first ground up with a mixture of chalk and plaster of Paris, 
 and that, in consequence, the subsequent addition of water 
 causes the whole to set into a mass of just sufficient tenacity 
 to hold together, though very soft and fragile. In this way 
 the use of starch-water as a binding material is obviated. 
 In other pastels pipe-clay or china-clay has been employed 
 as the basis for the colouring matter. 
 
 r 
 
I 
 
 CHAPTER XXIV 
 
 THE STUDY OF OLD PAINTINGS AND DRAWINGS 
 
 The study of old pictures, with the view of discovering the 
 causes of the physical and chemical changes which have 
 taken place in them, is fraught with interest. The material 
 on which they are executed, the medium employed, the pig- 
 ments which can be identified, and the varnish which has 
 been applied to the surface, all these matters demand atten- 
 tion. The dates of the various works examined, the coun- 
 tries in which they have been produced, the conditions 
 under which they have been preserved, and the treatment 
 to which they have been subjected, constitute elements in 
 the investigation which, whenever possible, should be kept 
 in view. But the adequate treatment of this extensive sub- 
 ject requires not a brief chapter, but a whole volume. And 
 then our materials, though in some directions most abun- 
 dant, are in great measure inaccessible. We must confine 
 our attention to such specimens as are shown in our public 
 galleries. Even then we find ourselves hampered by the 
 impossibility of making the thorough investigation which is 
 desirable, and by the too frequent absence of certain im- 
 portant data. In the present chapter we limit ourselves to 
 some general remarks, and to a few brief observations upon 
 a certain number of pictures in the National Gallery, the 
 National Portrait Gallery, and the Victoria and Albert 
 
CHANGES IN PICTURES 
 
 295 
 
 Museum ; and our selection will be confined to paintings 
 in oil, tempera, and water-colour, as the available works in 
 fresco in England are too few and too fragmentary to 
 furnish the information for which we are seeking. 
 
 It will hardly be necessary, with respect to changes in 
 painting-grounds, to do more than refer the reader to what 
 has been already said on this subject in Part I. of the 
 present work. The causes of the decay of panels and of 
 the convexity which their painted surface shows in so many 
 cases have been already discussed. The disruption of the 
 ground and of the superposed layer of paint consequent 
 upon this convexity needs no further explanation. The 
 staining of the white priming which has been laid on certain 
 kinds of wood has been traced to dark-coloured exudations 
 of soluble organic matters. The grain of some kinds of 
 wood, notably of oak in pictures of the Dutch and Flemish 
 schools, often becomes painfully conspicuous in course of 
 time, and gives to the surface-cracks a peculiar character. 
 The microscopic structure of certain woods and the peculiar 
 distribution of their histological constituents serve to explain 
 these appearances. The causes of the decay and cracking 
 of gesso-grounds in which size has been used, and the 
 injurious mechanical and chemical alterations which paper 
 and primed canvas may exhibit, have been already touched 
 upon. The other conspicuous changes which may be ob- 
 served in old pictures are connected with the medium, the 
 pigments, or the varnish. All these matters have been 
 referred to in Parts II. and III., yet there are three points 
 on which further discussion may not be out of place. I 
 refer to the number and character of the pigments used in 
 early works, to the manipulation of the paint, and to the 
 employment of white lead. Now, the pigments to which the 
 earlier painters were restricted were not only few in number, 
 
296 
 
 OLD PAINTINGS 
 
 but were mainly of mineral origin. At the first glance one 
 sees that the Italian artists of the thirteenth century, and of 
 the first half of the fourteenth, worked almost exclusively in 
 natural inorganic pigments, two of which stand out in their 
 works in startling prominence, namely, vermilion and ultra- 
 marine ; and their pigments were nearly all opaque or semi- 
 opaque. The absence of any pure and brilliant yellow, 
 opaque or transparent, from their pictures is another notice- 
 able characteristic. In the works of Jan van Eyck and 
 Rogier van der Weyden, and in those of many of the Italian 
 painters of the fifteenth century, the range of colours is more 
 extensive. Pigments which could not be used in tempera 
 or size, or which were semi-opaque when employed with 
 these vehicles, gave great richness and variety to their works 
 in oil. This tendency to press into the service of pictorial 
 art other coloured materials besides those of mineral origin, 
 namely, animal and vegetable pigments in considerable 
 variety, became more marked as time went on. And during 
 the nineteenth century the progress of synthetical chemistry 
 placed at the disposal of the picture-maker a long series of 
 pigments — good, bad, and indifferent, — so that the chances 
 of introducing dangerous and fugitive colours have been 
 enormously increased. It is to this increase in the number 
 of pigments, and to their greatly extended range of compo- 
 sition, rather than to their mode of preparation, that one 
 should attribute in great part the frequent deterioration of 
 modern paintings. 
 
 But the second point to which reference has been made 
 is concerned with the mode of laying on colours. The 
 exquisitely minute and careful manipulation of Jan van Eyck, 
 of Fra Giovanni Angelioo, of Hans Memlinc, of Gerard Dou, 
 of Gerard Terborch, and of many another old master, could 
 not have been hurried. It was solid but smooth; the paints 
 
ACTION OF WHITE LEAD 
 
 297 
 
 hardened gradually into one organic whole. And we could 
 name several oil-painters of the eighteenth century, and even 
 of the present day, whose work is executed in the same safe 
 manner, and which, were it not for the occasional intro- 
 duction of dubious materials, would be sure to remain sound 
 for hundreds of years, provided, of course, that the painting- 
 ground be satisfactory. But this careful mode of painting 
 does not suit the temperament, nor is it capable of expressing 
 the ideas of many artists. The thick impasto and loaded 
 colour, the effective brush-work, the juicy pencil, and the 
 dashing haste of several painters often prove to be elements 
 of danger. 
 
 The third point, concerning which a few remarks seem 
 advisable, is connected with the use of flake-white. There 
 are many old oil-paintings in which the only perfectly- 
 preserved parts of the work are those in which flake-white 
 has been used with considerable freedom. Here the con- 
 tinuity of the layer of pigment is intact, elsewhere there are 
 cracks and roughnesses and scalings-off. To what cause is 
 the preservation of the high lights and of the paler flesh-tints 
 attributable ? The association of hardness and cohesiveness 
 which these parts show is traceable to the white lead. This 
 pigment was formerly always prepared in such a way as to 
 contain a considerable quantity of lead hydrate. The par- 
 ticles of this hydrate do not lie, as it were, side by side with 
 those of the chief constituent (the lead carbonate), but are 
 so united with the latter as to form one complex compound. 
 This compound acts upon the linseed or other drying oil 
 with which it is ground, forming a substance of great hard- 
 ness and durability. 
 
 This substance seems to be formed in part out of the 
 free fatty acids of the linseed-oil, in part out of the glycerides 
 present therein. It combines in an unusual degree tough- 
 
298 
 
 ACTION OF WHITE LEAD 
 
 ness and hardness ; and it is to the production of this lead- 
 soap that I attribute the preservation of the continuity of 
 surfaces of the white, and of the pale tints into which white 
 lead enters, in many an old picture. No other pigment in 
 common use is capable of ' saponifying ' the admixed oil to 
 anything like the extent that characterizes white lead. Now 
 there are modern preparations of white lead made chiefly by 
 precipitation or the 'wet way,' which produces a pigment 
 containing little or no lead hydrate. Some writers on pig- 
 ments advocate the use of these newer products. ' Why,' 
 say they, ' should you carefully exclude from your pictures 
 oils, and varnishes, and siccatives which contain lead in the 
 form of a lead-soap, and then introduce the very same sub- 
 stance in your white lead ground in oil ?' Many years ago 
 I tried to answer such a question as this by means of 
 experiment. I was actuated by a desire, based on theoreti- 
 cal considerations, of preventing altogether the formation of 
 lead-soaps. I tried comparative experiments with zinc oxide, 
 pure lead carbonate, and the Dutch-made lead hydrato- 
 carbonate, or ordinary flake-white. The two lead pigments 
 (with which alone we are now concerned) were washed 
 thoroughly with distilled water and dried before being 
 ground in linseed oil. The oil-paints thus prepared were 
 spread in duplicate series upon glass, paper, and primed 
 canvas ; one set was kept in a dark box, the other was ex- 
 posed to strong light. So decided was the superiority of 
 the ordinary flake-white over the pure carbonate, when both 
 series of specimens were examined after the lapse of various 
 intervals of time, that I was reluctantly compelled to abandon 
 my recommendation of the latter. Ease in working, solidity 
 of body, and rapidity of drying, were not the only points of 
 superiority ; for the films of paint, after having been kept a 
 year, showed differences in hardness and in smoothness of 
 
I^mj 
 
 ILLUMINATED MANUSCRIPTS 
 
 299 
 
 surface which were all in favour of the hydrated carbonate. 
 No discolouration was observed in the specimens exposed 
 to light, except in the case of the pair upon paper ; the 
 absorbent ground had withdrawn some of the protecting oil, 
 and both specimens had equally darkened. In darkness all 
 the specimens had become of a somewhat greyish yellow, 
 the discolouration being about equal in all the pairs, the 
 pair spread on paper having, as in the previous case, become 
 darker than the others. The late Mr. G. W. Wigner tried 
 a somewhat similar series of experiments, and came to the 
 same conclusions. I should add that these deductions were 
 corroborated by the results of other trials, in which numerous 
 permanent coloured pigments mixed in pale tints with these 
 two lead whites were treated in the same way. If, however, 
 we feel bound to recommend the ordinary flake-white instead 
 of pure lead carbonate, that recommendation does not pre- 
 vent us from excluding lead-containing oils from our pictures, 
 seeing that we possess perfect substitutes for them, and that 
 there is no reason for thus multiplying the causes of possible 
 change. 
 
 Before commenting on some of the lessons to be drawn 
 from individual pictures, it may be desirable to make a few 
 observations on some of the changes frequently observable 
 in old illuminated manuscripts and choral books. The 
 tarnishing of lead and copper pigments laid on without any 
 protection but that of gum is very frequently seen. The 
 darkening of vermilion is apparently capricious,* but is 
 really explicable in part by the substitution of red lead for 
 vermilion, and in part by the molecular change which the 
 latter pigment is known to suffer, and which has been 
 already described. Ultramarine always stands out absolutely 
 
 * An initial letter in vermilion, painted in the fifteenth century, and 
 perfectly unchanged, became black by one year's exposure to sunshine. 
 
\J2^ 
 
 300 
 
 OLD PAINTINGS 
 
 intact ; sometimes it acquires extraordinary prominence by 
 reason of every other pigment on a page having altered. 
 The red cochineal and kermes lakes have either gone or 
 become paler and brownish. Sometimes fruits painted in 
 vermilion have been shaded or dotted with a crimson lake, 
 but the latter has disappeared, leaving nothing but a slight 
 gummy appearance upon the scarlet ground. Blue flowers 
 painted in smalt and veined with indigo show scarcely 
 a trace of the latter pigment. Verdigris, which is partly 
 soluble in water, has run and discoloured the vellum, and at 
 the same time has acquired a brownish hue. Sap-green, 
 from buckthorn berries, has faded greatly. Lilien-griin (of 
 the seventeenth century), from the flowers oi Iris germanica, 
 has disappeared. 
 
 We now cite a few pictures, out of a large number which 
 have been studied for the purpose of observing the present 
 state of the materials which have been used in their pro- 
 duction. We begin with some works in the National 
 Gallery, Trafalgar Square. 
 
 Margaritone da Arezzo (12 16-1293). No. 564. In the 
 very limited palette of this early painter in tempera we note 
 that the vermilion, a yellow earth, lamp-black and a puce 
 colour are well preserved ; the last-named pigment may be 
 a form of iron oxide, and corresponds in hue to the artificially 
 prepared oxide called 'Mars violet.' 
 
 Gaddi, School of (late fourteenth century). No. 579A. 
 The crimson on the robes of two of the three figures which 
 occupy these panels seems to be derived from madder, and 
 is well preserved. 
 
 Jan van Eyck (1390 ?-i44o). No. 186. The green robe 
 in this famous picture shows distinct cracks, which differ in 
 character and are larger in size than any others in the work. 
 The flesh-tints are perfectly preserved as to texture. I 
 
■^i_5>OK_ 
 
 OLD PAINTINGS 
 
 301 
 
 suspect that verdigris has formed a constituent of the green 
 paint employed. 
 
 Fra Giovanni Angelico (1387-1455). No. 663. The 
 translucent reds and purples in this work have faded some- 
 what j the green, which appears to be malachite — ' green 
 bice ' — has stood. On the whole this exquisite work in 
 tempera is remarkably well preserved. 
 
 Rogier van derWeyden (1400 ?- 1464). No. 664. Painted 
 on linen which had received a very thin priming ; the pre- 
 servation of this work, which has never been varnished, is 
 remarkably good except in two particulars— the red pigment 
 used for the sleeves, linings of robes, etc., having faded, and 
 the white paint on the dress of the Virgin having partially 
 scaled off. From certain peculiarities in the touch, and 
 from the minutely wrought details of the landscape, I con- 
 clude that the medium used could scarcely have been the 
 usual egg-yolk tempera, but was rather a thin size. 
 
 Bennozzo Gozzoli (1420-1498). No. 591. Thevermilion 
 in this tempera picture is preserved in startling brilliancy ; 
 the translucent reds have become rather faded and em- 
 browned. 
 
 Melozzo da Forli (1438-1494). No. 755. It is probable 
 that verdigris was employed in painting the green carpet in 
 this work. If so, the cracks in this part of the picture 
 (more conspicuous here than in other parts) would be due 
 to the corrosive action of this dangerous pigment. 
 
 Tuscan School (end of fifteenth century). No. 781. 
 The lining of the cloak of Tobias in this picture seems to 
 have been painted with verdigris ; it is now very dark, in 
 parts nearly black, although the pigment used has evidently 
 been mingled with much protective resin, as its thickness 
 is excessive when compared with that of other parts of the 
 work. 
 
P^ 
 
 302 
 
 OLD PAINTINGS 
 
 Gregorio Schiavone (fl. 1470). No. 630. The madder 
 and vermilion in the robe of one of the figures in this 
 tempera picture are well preserved. This is also the case 
 in another work by the same artist in the author's pos- 
 session. 
 
 Gheeraert David (1460-1523.) No. 1,045. The fine 
 crimson glazings of madder-lake in this oil picture are in 
 perfect preservation. The same remark may be made con- 
 cerning another picture (No. 1,432) by the same artist. 
 
 Michelangelo Buonarotti (1475-1564). No. 790. This 
 unfinished tempera picture affords an instance of the 
 stability of vermilion mixed with red-lead (in the robe of 
 one of the figures), of terre verte and of madder-lake. The 
 last-named pigment is also to be noted in the well-preserved 
 hatchings and stipplings on the robes of two of the angels 
 in No. 809. 
 
 Ridolfo del Ghirlandaio (1483-1561). No. 1,143. This 
 oil picture, originally painted on wood but transferred to 
 canvas, has been repaired and repainted in several places. 
 But the red glazings, apparently madder-lake, and the green 
 colour, seemingly verdigris on malachite, are, if original, 
 well preserved. The preservation of verdigris when glazed 
 on malachite is not unusual ; the two pigments are closely 
 related chemically, and are not likely to react upon or 
 injuriously affect each other. 
 
 In the National Gallery there are ten portraits in wax- 
 pigments from the Hawara Cemetery in the Fayum, Egypt. 
 There is a rich purple paint in several of these works, a 
 purple which one might perhaps be inclined to identify with 
 Tyrian purple from Purpura capillus and other molluscs, 
 but which the examination of certain specimens of ancient 
 pigments leads one to conclude to be a madder derivative. 
 Anyhow, it has lasted, apparently unchanged, for some 
 
OLD PAINTINGS 
 
 3°3 
 
 seventeen centuries. But it must be remembered that 
 these remarkable paintings (Nos. 1,260-1,265, and 1,267- 
 1,270) have been preserved in darkness since they were 
 executed by Greek or Grasco-Roman artists in the second 
 century a.d. The other pigments in these paintings are 
 yellow, red and brown ochre, charcoal black, a blue made 
 from cupreous glass, a green from malachite, and perhaps 
 verdigris also. An orange-red pigment may be either red 
 lead or realgar. The pigments, incorporated with wax, were 
 laid on, in a fused condition, upon a distemper priming. 
 
 It happens that some information as to the pigments 
 actually employed by a Greek or Grseco-Roman artist of the 
 second century is furnished by six specimens found in one 
 of the Hawara graves by Mr. W. M. Flinders Petrie. These 
 pigments were : white, mainly gypsum ; yellow ochre having, 
 however, almost the precise hue of true antimony yellow ; 
 red lead ; dark red due to ferric oxide ; pink, probably 
 derived from madder ; and a blue cupreous glass. 
 
 As to British pictures in the National Gallery, we can 
 afford space for a few words only. The works of Sir Joshua 
 Reynolds generally show the fading of the crimson lake 
 (from cochineal) in the flesh tints, the vermilion and mineral 
 yellows alone remaining. The picture of the 'Infant Samuel ' 
 may be cited as an example of the large and wide cracks 
 caused by the free use of bitumen (in the dark background). 
 Two paintings by J. M. W. Turner may be particularly 
 mentioned. In No. 560, ' Chichester,' the bright lake-reds 
 in the sky have become reduced to brown stains — anything 
 but luminous. In No. 534, the 'Approach to Venice,' we 
 notice how, in a group of small clouds near the top of the 
 picture, where vermilion and lake have been introduced, 
 the vermilion remains, but the lake is now a pale yellowish 
 brown. 
 
3°4 
 
 OLD PAINTINGS 
 
 The good condition of the great majority of the pictures 
 in the National Gallery of British Art at Millbank is worthy 
 of note. In this category may be placed the works of 
 Mr. G. F. Watts, R.A., and a number of other paintings 
 out of which I select a very few for special mention. 'The 
 Death of Chatterton,' by Mr. Henry Wallis (No. 1,575), 
 painted in 1856, was retouched subsequently, so far as the 
 breeches of the dead poet are concerned, the crimson lake 
 originally employed having practically perished. No. 1,685, 
 ' Christ Washing St. Peter's Feet,' by Ford Madox Brown, 
 was completed half a century ago. It shows, so far as one 
 can judge, no signs of deterioration. Of ' The Annuncia- 
 tion,' by D. G. Rossetti (No. 1,210), painted in 1849, tne 
 same observation may be made. Anyone familiar with 
 Lord Leighton's practice and with his extreme care in the 
 choice of permanent pigments, would not expect to see any 
 change in No. 1,574, ' The Bath of Psyche,' a work, more- 
 over, which was finished so recently as 1890. To the critic 
 of pigments, paintings of flowers afford much information, 
 partly because they are generally pitched in a very high 
 key, and partly because the living flowers themselves are 
 generally available for comparison with their representations 
 in paint. Two of the pictures by George Lance (Nos. 443 
 and 1,184) betray the free use made by this accomplished 
 artist of such fugitive pigments as carmine, crimson lake, 
 gamboge and yellow lake. 
 
 We may now pass on to some instructive examples pre- 
 served in the National Portrait Gallery : 
 
 Marc Gheeraedts (1 561-1635). No. 64. In this por- 
 trait, painted probably in 16 14, while the vermilion has 
 stood, the translucent reds appear to have faded and changed. 
 The white sleeves of the dress are ornamented with small 
 sprigs, which are now brown, and were probably originally 
 
OLD PAINTINGS 
 
 305 
 
 painted in some vegetable yellow. The reddish pattern of 
 conventional foliage on the cloak now clashes with the 
 colour of the chair, the curtain, and the table ; the hues of 
 all or some of these parts must have altered. 
 
 Sir Peter Lely (1617-1680). No. 509. A well-preserved 
 picture in most respects, but it is probable that crimson-lake 
 has been used for the satin dress, which is now a pinkish 
 grey, and clashes with the flesh tints. This work was pro- 
 bably painted about 1669. 
 
 William Hogarth (1697-1764). No. 289. This por- 
 trait of Hogarth, painted in 1758 by himself, affords some 
 information as to the pigments he employed. He holds in 
 his left hand a mahogany palette ' set ' with eight colours. 
 The first of these is white lead, and remains unchanged ; 
 so also is the second, vermilion ; the third is a pale warm 
 brown, precisely the hue of faded crimson lake ; the fourth 
 is now nearly black and undeterminable ; the fifth is yellow 
 ochre, slightly embrowned ; the sixth is a pale yellow, well 
 preserved — much like true Naples yellow ; the seventh is a 
 grey-blue, probably much changed ; and the eighth and last 
 a fair lavender blue colour. The seventh pigment may have 
 been indigo, and the last blue verditer. The cap on the 
 artist's head has certainly faded in colour ; probably it was 
 painted with lake. 
 
 William Hoare, R.A. (1 706-1 792). No. 112. This por- 
 trait of Alexander Pope, in coloured crayons on grey paper, 
 shows the blues apparently intact. 
 
 Thomas Phillips, R.A. (1770-1845). No. 269. This 
 portrait of Faraday, painted in 1842, shows a large number 
 of cracks, many of them wide. Where flake-white has been 
 introduced somewhat freely, as in the face and hands, the 
 shirt and collar, and the galvanic battery on the table, the 
 paint has not lost its continuity. 
 
306 
 
 WATER-COLOUR DRAWINGS 
 
 John Partridge (i 789-1872). No. 342. 'Meeting of the 
 Royal Fine Arts Commission.' This picture was painted in 
 1846. Almost every part of it is very badly cracked through 
 the use of bitumen, and perhaps also of much megilp. 
 Even the shaded portions of the faces have not escaped, 
 although the high lights have been preserved where the pro- 
 portion of white lead present has been large. 
 
 Many instructive illustrations of the degrees of stability 
 shown by pigments are furnished by examples in the Wallace 
 Collection at Hertford House. 
 
 Philippe de Champaigne (1602-1674). No. 119. This 
 picture is remarkable not only for the perfection of its 
 technique, but for the extraordinary state of conservation of 
 all the pigments, which cover a wide range of colours, and 
 include a transparent amber-yellow and a rose. 
 
 Sir Joshua Reynolds (1 723-1 792). No. 47. Here the 
 fatal asphaltum asserts itself, the background resembling a 
 dissected map. 
 
 J. L. E. Meissonier (1815-1891). No. 291. Generally 
 the works of this careful painter are well preserved, but in 
 this small example there are to be seen a few thin long 
 cracks, which seem to have arisen in consequence of the 
 premature application of varnish to the picture before the 
 oil-paint was hard. 
 
 In Sir John Soane's Museum the two fine series of oil- 
 paintings by W. Hogarth (1697-1764) will repay careful 
 study from the point of view now being considered. 
 
 The remaining works to which attention is now called 
 are a few of the water-colour drawings shown in the Victoria 
 and Albert Museum. 
 
 William Daniell, R.A. (1769-1837). In one of the water- 
 colours by this artist the blue and green elements have dis- 
 appeared, save just in one little bit of smalt blue in a sailor's 
 
WATER-COLOUR DRAWINGS 
 
 307 
 
 clothes. In another drawing the sky is now a mere dirty 
 laboured stain. 
 
 William Green (1761-1823). No. 685. An iron red has 
 here become too prominent. 
 
 Samuel Howitt (1765-1822). No. 3,019, 1876. Ap- 
 parently well preserved, but, on further scrutiny, it seems 
 that the ultramarine in the shaded parts of some of the 
 rocks and trees stands out more prominently than it could 
 have done originally. 
 
 Anne Frances Byrne (1775-1837). No. 1,358, 1874. In 
 this fruit and flower piece the indigo in the sky has gone, 
 while the yellow pigments and the red lakes have suffered 
 greatly ; the roses are blanched, and the purple grapes have 
 lost their crimson element. 
 
 John James Chalon, R.A. (1 778-1854). No. 570. The 
 'River Scene in Devonshire,' painted in 1808, shows the 
 shaded parts of the clouds pink, from the loss of indigo. 
 The hills are now too pale for the trees dotted upon them, 
 through the fading of sap-green and gamboge, which have 
 been used in painting the grass. The shadows under the 
 ripples of the water have greatly altered, from the change 
 of indigo and other pigments ; they now show dirty stains 
 and elaborate brushwork. 
 
 No. 54, 1887, ' At Hampstead Heath,' by the same artist, 
 is, on the other hand, a well-preserved drawing, which has 
 been more recently acquired by the museum. The blues 
 are particularly good, although the vegetable yellows may 
 perhaps have faded somewhat in spite of the care which has 
 been taken with the drawing. 
 
 JohnCristall(i767-i82i). No. 142, 1890. This recently- 
 acquired drawing seems to have kept its hues well, and 
 affords a good example of the style of colouring of the 
 period and school to which it belongs. 
 
 20 — 2 
 
3 o8 
 
 WATER-COLOUR DRAWINGS 
 
 Jacob Xavery (painted in 1757). No. 15, 1872. This 
 has faded woefully. The sickly peaches and spectral grapes 
 proclaim the evanescence of crimson lake, gamboge, and 
 indigo. 
 
 Mary Moser, R.A. (1744-1819). No. 160, 1881. Very 
 little is left of the original colour here; the 'roses and other 
 flowers ' are a complete wreck. 
 
 Francis Danby, A.R.A. (1 793-1861). No. 480. The 
 Prussian blue in the sky unchanged, but the pigments which 
 once modified its hue have fled. 
 
 John Varley (1778-1842). No. 381. Hot iron reds show 
 themselves in great force in clouds and elsewhere — even in 
 the river; the modifying organic pigments with which they 
 were mixed have nearly disappeared. 
 
 George Cattermole( 1 800-1 868). No. 503. The crimson 
 lake seems to have faded from the face in this drawing. In 
 No. 507, painted in 1850, we have a good illustration of the 
 warm brownish hues produced by the change of crimson 
 lake. 
 
 Samuel Prout (1783-1852). Nos. 1,473, l86 9. and 3>°5 6 > 
 1876, afford examples of the stability of true ultramarine. 
 The skies in both these drawings are now quite out of har- 
 mony with the architectural features, some of the pigments 
 in which must have faded. These drawings should be com- 
 pared with others by the same artist which hang beside 
 them, and in which the blues of the skies, as well as some 
 of the pigments in other parts, have faded. Here it may be 
 convenient to remark upon the startling prominence of the 
 skies, and sometimes of the blue distances, in many water- 
 colour drawings. The first glance on entering a room in 
 which such works are gathered reveals the permanence of 
 ultramarine and cobalt blue, the latter pigment being, of 
 course, of comparatively recent introduction. But the want 
 
WATER-COLOUR DRAWINGS 
 
 3°9 
 
 of harmony in such drawings furnishes evidence at the same 
 time of the decay of many other pigments — of liquorice and 
 tobacco-juice, of yellow lake and brown pink, of indigo and 
 rose pink. 
 
 William Henry Hunt (1 790-1864). No. 1,031, 1873. 
 Some of the ruddy hue from the cheeks of the boy appears 
 to have gone. In 1,525, 1869, some of the pink in the 
 apple-blossom has faded ; the primrose-flowers are greener 
 and less yellow than they once were, probably from a 
 change in lemon yellow. The hawthorn-blossom in 1,470, 
 1869, has lost the faint rosy blush that was once visible in 
 some of the flowers. 
 
 The above examples, selected almost at random, must 
 suffice. But I may point to a different kind of injury, from 
 which water-colour drawings sometimes suffer, by citing the 
 case of W. Delamotte's 'View of Christ Church, Oxford.' 
 This seems to have been pasted on wood, and to have 
 been stained in consequence ; at least, it appears likely 
 that the brown spots in the sky may be traced to the 
 mount. 
 
 A work by T. Barker (No. 134, 1878) and the 'Dieppe' 
 of J. S. Cotman (No. 3,013, 1876) furnish additional 
 examples of the same kind of damage. 
 
CHAPTER XXV 
 
 CONSERVATION OF PICTURES AND DRAWINGS 
 
 It is generally conceded that a finished oil painting is best 
 kept in such a position that it is exposed to daylight of just 
 sufficient intensity for it to be well seen, the direct beams 
 of the sun being excluded. In darkness, or even in ap- 
 proximate darkness, the lead-whites may tarnish, and the 
 oil and resins darken. Even with the most moderate illumi- 
 nation, however, the more fugitive pigments, such as the 
 cochineal and quercitron lakes, will in no long time alter 
 and fade to such a serious extent as to destroy the ' keeping' 
 of the work. But there is really no need to introduce these 
 evanescent pigments, for every nuance the artist can desire 
 may be produced with paints having a sufficient if not 
 perfect degree of permanence. The question of artificial 
 lighting here comes in. Against oil lamps, properly con- 
 structed and managed so as to avoid the production of 
 smoke and soot, nothing can be urged ; the same opinion 
 may be given in reference to the use of electric incande- 
 scent lamps. The introduction of electric arc lamps seems 
 less safe, even when the illumination they afford is reduced 
 to the necessary minimum, for the light they emit is richer 
 in those rays which, as a general rule, are peculiarly effective 
 in bringing about chemical changes in the less stable pig- 
 ments. But the light by which pictures are to be seen is 
 
CONSERVATION OF PICTURES 
 
 3ii 
 
 but one of the conditions out of several which have to be 
 considered in their conservation, though perhaps the most 
 important. The mode of securing a picture in its frame is 
 not an altogether trivial matter. In the majority of cases 
 the expansion and contraction with variations of moisture 
 and temperature, of panel and canvas, do not correspond 
 accurately with the similar changes of the frame. In con- 
 sequence, too great rigidity in the system of fixing adopted 
 should be avoided. Duly adjusted springs or blocks of 
 indiarubber (not vulcanized), secured in the rebate, afford 
 convenient means of obtaining the necessary freedom of 
 movement, while preventing the jar caused by accidental 
 concussions. An equable temperature is another important 
 condition ; on no account should currents of hot or of cold 
 air impinge directly upon the front or back of a painting. 
 Moreover, this is not a mere question of temperature, for 
 such currents of air may bring in particles of dust and other 
 impurities, while their hygroscopic condition is sure to vary. 
 This question of moisture is of some moment. For if 
 freshly-warmed air, which is pretty sure to be comparatively 
 dry air, is allowed to come in contact with panels or can- 
 vases, it will withdraw from them some of their necessary 
 hygroscopic moisture, and thus cause capricious and hurtful 
 changes of size. Such changes, often repeated, cannot but 
 result in the production of cracks and fissures in the oil 
 paintings subjected to these varying conditions. The hygro- 
 scopic balance between picture and air can be maintained 
 only by a due supply of moisture to the warmed air before 
 the latter comes in contact with the painting ; the warmer 
 the air the more moisture must be added to it. The same 
 reasoning applies to the entrance of cold air, but in this case? 
 care must be taken that it is sufficiently dry not to deposit 
 water upon the picture. For the purpose of regulating 
 
312 
 
 CONSERVATION OF PICTURES 
 
 the hygroscopic condition of the atmosphere in a picture- 
 gallery, the introduction of a dew point thermometer is 
 advisable. And there is another contrivance by means of 
 which the presence of the right proportion of moisture in 
 the air may be recognised. A strip of drawing-paper, 
 another of primed canvas, and another of mahogany, all 
 three being in a normal hygroscopic state, are to be separ- 
 ately balanced by means of counterpoises. When the air 
 gets too dry, the strips will rise, owing to their loss of water ; 
 when excess of moisture is present, they will sink. So long 
 as the equilibrium of the beams to the ends of which they 
 are attached remains practically true, the air may be regarded 
 as in a satisfactory hygroscopic condition. Three pairs of 
 ordinary apothecaries' scales (or spring-balances) suffice for 
 the construction of this apparatus, which should be protected 
 by a glass case to which the air has free access. This 
 question of the due amount of moisture in the air — neither 
 in excess nor in defect — has scarcely received the attention 
 it deserves. But it will be allowed on all hands that few 
 conditions are more trying to pictures in oil or water-colour 
 than those caused by currents of hot, dry air rising directly 
 below them during the day, succeeded by currents of cold, 
 moist air descending upon them down the surfaces of the 
 walls at night. 
 
 The covering of an oil picture with glass, whatever objec- 
 tions may be urged against it from an artistic point of view, 
 certainly secures the protection of its surface from the solid 
 and liquid and, to some extent, from the gaseous impurities 
 in the air. But the backs of pictures, especially of those 
 painted on canvas, are often forgotten, yet excess of moisture 
 and deleterious vapours and gases often enter from behind, 
 and seriously discolour the painting-ground, and even the 
 paint itself. Mention has previously been made of methods 
 
FRAMING AND MOUNTING OF PICTURES 
 
 313 
 
 by which this cause of injury may be prevented by means 
 of a double canvas, or a layer of white lead in powder mixed 
 with starch-water, applied to the back of the original canvas; 
 American leather cloth, or even parchment-paper, affixed to 
 the frame behind is nearly as effective. 
 
 A few words only are requisite as to the mounting and 
 framing of water-colour paintings. On no account must the 
 back of the paper on which a drawing is executed come into 
 contact with any kind of wood, or even with an inferior sort 
 of paper or mounting-cardboard. Injurious substances in 
 the latter may travel forwards into the painting-ground, and 
 affect the pigments, while wood may cause stains. Iron 
 brads produce rust-spots. Flour-paste is not a sound 
 material for mounting drawings ; far better is an antiseptic 
 size, which may also be used for fixing to the back of the 
 frame the sheet of paper which is there placed to exclude 
 dust. If we could secure a water-colour drawing from dust, 
 and yet allow of the escape of any water set free in the form 
 of vapour when the drawing gets, from whatever cause, 
 somewhat warmer than usual, we should have affected an 
 improvement upon the ordinary plan of framing. In this, 
 the moisture liberated from the paper and mount cannot 
 escape, but condenses upon the glass when it cools, only to 
 be reabsorbed by that surface of the paper which carries the 
 pigments, where it favours chemical and physical changes, 
 until the hygroscopic equilibrium of the whole system — 
 frame, mount, lining, paper, etc. — is once more re-established. 
 I have used with advantage grey linen in lieu of brown 
 paper at the back of frames, and, by means of a few strips 
 of thick drawing-paper, have established an air-communica- 
 tion between the space in front of the drawing and that at 
 the back. Thus the ventilation of the system is arranged 
 for, yet dust is excluded. To hermetically seal a framed 
 
3H 
 
 PRESERVATION OF DRAWINGS 
 
 drawing, to the entire exclusion of all moisture and all air, 
 is not possible. That under such conditions nearly every 
 pigment would be unalterable has been long known. We 
 should add to these observations upon the conservation of 
 works in water-colour that they should certainly be kept in 
 a rather drier atmosphere than that recommended for oil 
 paintings. 
 
 The plan of preserving the water-colour drawings of 
 Turner, devised by the late John Ruskin, may be mentioned 
 fitly here. It was described in a letter to the editor of the 
 Times (October 28, 1856). The recommendation is to 
 enclose each work in a light wooden frame, under a glass, 
 the interior surface of which is prevented from coming in 
 contact with the drawing by means of a raised mount. A 
 number of such frames (five to fifteen) are kept together in 
 cases, which can be carried or wheeled to any part of the 
 room where the drawings are to be studied. Each frame 
 slides vertically into grooves in the case. Professor Ruskin's 
 reasons include the following : ' A large number of the 
 drawings are executed with body colour, the bloom of which 
 any friction or handling would in a short period destroy.' 
 This argument, it will be seen, is directed against the keep- 
 ing of such works, in their unframed state, in portfolios. 
 Another reason given by Mr. Ruskin is that in the case of 
 these drawings ' their delicate tones of colour would be 
 destroyed by continuous exposure to the light, or to smoke 
 and dust.' He fortifies his position in reference to such 
 exposure in a letter to the Literary Gazette (November 13th, 
 1858), in which he says that ' the officers of both the Louvre 
 and of the British Museum refuse to expose their best 
 drawings or missal-pages to light, in consequence of ascer- 
 tained damage received by such drawings as have been 
 already exposed ; and among the works of Turner I am 
 
PRESERVATION OF DRAWINGS 
 
 315 
 
 prepared to name an example in which, the frame having 
 protected a portion, while the rest was exposed, the covered 
 portion is still rich and lovely in colour, while the exposed 
 spaces are reduced in some parts nearly to white paper, and 
 the colour in general to a dull brown.' ' That water-colours 
 are not injured by darkness is also sufficiently proved by 
 the exquisite preservation of missal paintings, when the 
 books containing them have been but little used. Observe, 
 then, you have simply this question to put to the public : 
 " Will you have your Turner drawings to look at when you 
 are at leisure, in a comfortable room, under such conditions 
 as will preserve them to you for ever, or will you make an 
 amusing exhibition of them (if amusing, which I doubt) for 
 children and nursery-maids ; dry your wet clothes by them 
 and shake off the dust from your feet upon them for a score 
 or two of years, and then send them to the wastepaper 
 merchant?" ' Mr. Ruskin in another letter to the Times, 
 which appeared on October 21, 1859, wrote thus : ' I take 
 no share in the responsibility of lighting the pictures either 
 of Reynolds or Turner with gas ; on the contrary, my ex- 
 perience would lead me to apprehend serious injury to those 
 pictures from such a measure ; and it is with profound 
 regret that I have heard of its adoption.' Although consider- 
 able weight is rightly given to the opinions of Mr. Ruskin 
 above quoted, it must not be forgotten that all paintings of the 
 modern school are not to be classed with those of Turner 
 and Reynolds in respect to susceptibility to the injurious 
 action of the products of the burning of gas and of con- 
 tinuous exposure to moderate light. When, therefore, Mr. 
 Ruskin wrote (in the Daily Telegraph, July 5, 1876): 'I 
 do not think it necessary to repeat my former statements 
 respecting the injurious power of light on certain pigments 
 rapidly, and on all eventually,' I find myself compelled to 
 
316 
 
 LIGHTING OF PICTURE-GALLERIES 
 
 reject so sweeping an assertion. That light injures all 
 pigments eventually cannot for one moment be conceded. 
 And if we could but succeed in so modifying the light that 
 illuminates our pictures as to remove from it certain par- 
 ticularly active beams, we might considerably augment the 
 list of permanent pigments. Experiments on a small scale 
 prove that several fluorescent substances, such as a solution 
 of quinine sulphate, while intercepting dangerous rays, do 
 not sensibly modify the colour of the light, and yet lessen 
 its chemical activity. In the first edition (published 1890) 
 of the present handbook, I wrote : ' Possibly a transparent 
 screen of this character will some day be used for our picture- 
 galleries.' Since then an arrangement of coloured glass — 
 peacock blue and yellow — has been devised by Sir W. 
 Abney and introduced into one of the galleries of the 
 Victoria and Albert Museum, with the object of preventing 
 the entrance through the skylight of a great part of the 
 injurious rays. It is instructive to note how much differ- 
 ence exists between different specimens of apparently 
 colourless glass in their absorptive power for the so-called 
 chemical rays. These differences may be tested by framing 
 a strip of paper washed with carmine and covering it cross- 
 wise with the samples of glass to be valued, adding for 
 comparison a plate of rock-crystal. Under the last-named 
 material the fading is nearly as rapid as it is where the pig- 
 ment is without any cover. It may be safely affirmed that 
 miniatures should be protected by glass, not by rock-crystal. 
 Further experiments on the selection of protective glasses 
 and the construction of transparent screens are needed. A 
 partial discussion of this subject will be found in the next 
 chapter, and to this I would refer my readers. 
 
 The question of the lighting of a gallery or room where 
 pictures are to be displayed has been touched upon already 
 
AIR IN PICTURE-GALLERIES 
 
 317 
 
 at the beginning of the present chapter. We would now 
 add that actual skylights are not without drawbacks. One 
 of these, especially in the case of water-colours, is the 
 presence in large proportion in the light from the zenith of 
 those rays which act most energetically upon pigments. A 
 few observations as to gas cannot be excluded. Gas, before 
 and after burning, is bad for pictures. The evil effects of 
 an occasional escape of unburnt gas are less to be dreaded 
 than those caused by the products of gaseous combustion. 
 These products are sulphuric acid, sulphurous acid, carbonic 
 acid, and the moisture which is formed at the same time. 
 Thence results a hot, moist atmosphere laden with these 
 corrosive compounds. The water-vapour condenses into 
 the liquid form and dissolves a part of the acids named 
 above ; the drops which trickle down are very injurious to 
 paper, wood, canvas and pigments. In any case, all the 
 products of the combustion of gas should be removed from 
 the room as they are formed. For even when there may 
 be no visible condensation of liquid, the vapours formed are 
 often absorbed as such by paper, canvas, etc., and do in 
 that form their destructive work. An illustration of this 
 fact is furnished by an analysis of the leather back of an old 
 calf-bound volume. Owing to its absorption of the products 
 of the burning of gas this back had decayed and fallen off, 
 and was found to contain over 6 per cent, of free sulphuric 
 acid. 
 
 With respect to the building itself in which pictures are 
 to be kept, our aim should be to secure as far as possible 
 pure air, an equable and agreeable but moderate tempera- 
 ture, and freedom from dust and dirt. Solidity of construc- 
 tion, a continuous damp-proof course, a certain degree of 
 elevation above the ground-level, and double walls enclosing 
 an air-space, are desirable as conducing to uniformity of 
 
3i8 
 
 AIR IN PICTURE-GALLERIES 
 
 temperature, and preventing the condensation of moisture 
 upon the interior of the rooms. Due provision should be 
 made for excluding from the galleries themselves the dust 
 and dirt which may be brought in by visitors. And it 
 cannot be too strongly urged that the supply of fresh air 
 should not, as it were, accompany the visitors, but be 
 brought in from an independent source. The place of 
 in-take of such supply should not be gratings near to, or on 
 the level of the ground, in out-of-the-way and dirty corners, 
 the certain depositories of uncertain rubbish. From such 
 sources air laden with organic and inorganic impurities can 
 alone come. The question of the exclusion of fog and city- 
 smoke may be mentioned here. Some kind of air-filter is 
 useful. It is astonishing how effectively the solid and liquid 
 particles suspended in a yellow fog may be strained off and 
 intercepted by passing the air through a layer of loosely 
 packed carded cotton — this air-filter of course requires 
 occasional renewal. Moist white lead, that is, white lead in 
 powder reduced to a paste by admixture with water, will 
 absorb the sulphuretted hydrogen as well as the sulphuric 
 and sulphurous acid present in town air. And if the walls 
 of the galleries are coated with a distemper paint containing 
 white lead, this absorption of impurities goes on continually. 
 For these impurities are more readily absorbed by an un- 
 protected and properly-prepared distemper than by the pig- 
 ments in the pictures. To secure this result the distemper 
 should be made, not with size, but with starch-water, just 
 sufficiently strong to bind the particles together and to the 
 wall. For further particulars as to these and other arrange- 
 ments for the conservation of pictures, especially in public 
 galleries, the reader is referred to a paper on the subject in 
 the Portfolio for 1882, pp. 106-108. 
 
 The conservation of pictures naturally leads us on to their 
 
RESTORATION OF PICTURES 
 
 319 
 
 restoration. Picture-restoration, like some other kinds of 
 restoration, often involves injury, often renewal. It is 
 frequently difficult, sometimes impossible, to re-establish the 
 pristine state of the work. The operations involved should 
 never be undertaken by the inexperienced amateur. And 
 picture-restorers themselves are too often artists who have 
 mistaken their profession, or who have been imperfectly 
 trained. Many possess no power or appreciation of accurate 
 draughtsmanship. Look, for illustrations, at those crucial 
 parts, the hands and feet, in ' restored ' pictures. Nor 
 have they that exquisite sense of quality in colour and of 
 delicate hues which will enable them to fill up properly 
 actual gaps in a painted surface. Then the pigments they 
 use are too often unsafe, and their vehicles unsatisfactory ; 
 so both soon alter. At the same time, the skill of some 
 restorers in the matter of mechanical repairs — parquetting, 
 transferring, relining, etc. — cannot be too highly extolled. 
 
 Several manuals of directions for restoring pictures have 
 been given to the world ; they are of very unequal value. 
 Some of these tell you nothing, for they are intended merely 
 to advertise the skill of the writers. Others advocate a 
 treatment which may be called heroic, giving you solvents, 
 not only for the discoloured varnish, but for glazings and 
 paints. In reality, no directions can replace experience and 
 skill. The late Max von Pettenkofer's method is one of the 
 best known, but it is very rarely applicable with safety and 
 success. The object of this method is the renewal of the 
 transparency and continuity of the varnish by a process of 
 re-solution in situ. With this intention, the picture is 
 exposed in a closed shallow box to the action of the vapour 
 evolved from moderately strong spirits of wine. This vapour 
 dissolves the mastic on the surface of the picture, forming 
 once more a spirit-mastic varnish. This, on exposure to 
 
320 
 
 RESTORATION OF PICTURES 
 
 the air, hardens, and leaves a shining coat of resin. But 
 this resin, being necessarily discoloured and sinking into the 
 cracks of the paint, makes them more prominent, while 
 there is great danger of its being unequally distributed over 
 the surface of the work. 
 
 When the varnish of an old picture is practically intact, 
 but the surface is begrimed with soot and dirt, it should not 
 be cleansed by the direct application of water, much less by 
 the use of a solution of soap ; but a loaf of household 
 bread, not more than a day old, should be taken, and its 
 crumb broken up into a tin canister furnished with a lid ; 
 it is important that no pieces of crust, and no fragments of 
 crumb which have become hard by drying, should be intro- 
 duced. Then the crumbs should be shaken out, in portions 
 at a time, from the canister on to the varnished surface, and 
 rolled gently thereon by means of the fingers. By repeating 
 this operation until fresh crumbs no longer become dis- 
 coloured, it is often possible to improve the appearance of a 
 picture very greatly. In any case, it affords a useful pre- 
 liminary to the removal of the old varnish where such a 
 further step is imperatively required. Such removal is 
 effected by the mechanical process of chafing. A single 
 tear of pure mastic resin is ground or crushed to fine 
 powder, and placed upon some unimportant part of the 
 surface of the picture; but the operation may be begun 
 without the aid of the mastic-powder. A gentle rotatory 
 movement of the ends of the fingers soon reduces the old 
 varnish-layer to powder, which is then removed by means 
 of a soft badger-hair brush, or other suitable means. The 
 work should be performed in a good light, and great care 
 must be taken not to injure any tender glazings belonging 
 to the painting itself. To ascertain whether the removal of 
 the varnish has been carried far enough, the parts treated 
 
REMOVAL OF VARNISH 
 
 3 2 < 
 
 may be moistened with distilled water applied on a plug of 
 carded cotton. When the operation is complete, and the 
 surface is quite dry, a new coat of mastic-varnish may be 
 applied, if possible in an artificially dried atmosphere. 
 Sometimes a little dragon's blood, or other warm-coloured 
 resin, is added to the mastic-varnish, in order to prevent the 
 cold and raw look which a picture which has lost its old 
 toned varnish frequently presents. An oil-painting in which 
 no megilp has been used, and which has received, a year 
 after completion, a thin layer of drying-oil containing a little 
 copal-varnish, and then, after the lapse of a twelvemonth, its 
 final coat of mastic-varnish, cannot be injured by the chafing 
 process just described. And, even under less favourable 
 conditions, it is the only method which can be recommended 
 for general adoption. But it has its risks, and is not easily 
 applicable in the case of pictures where the texture of a 
 coarse canvas, or the grain of a panel, is conspicuously 
 evident on the surface. To these remarks on the chafing 
 process, we may add that it is sometimes advisable to re- 
 varnish a picture with fresh mastic before commencing to 
 remove the old ; a day or two afterwards both layers may 
 be removed together. 
 
 The removal of old varnish by the use of solvents is a 
 hazardous, though easy, operation. The liquid usually 
 employed for this purpose is spirits of wine, of about 6o° 
 overproof, diluted with one-fourth of its bulk of distilled 
 water. It is applied by means of plugs of carded cotton, 
 the action of the solvent being arrested, when necessary, by 
 instantly moistening the spot with spirits of turpentine on 
 another plug, or, in some cases, with linseed-oil. But when 
 mastic megilp has been used as the painting-medium, it 
 also, as well as the pigments associated with it, may be 
 removed by treatment with these solvents. And it must be 
 
322 
 
 RESTORATION OF PICTURES 
 
 remembered that some artists introduce layers or touches of 
 water-colours in their oil-pictures ; these are almost certain 
 to be affected by spirits of wine. Sometimes further injury 
 to them may be arrested by the application of linseed-oil. 
 Whenever a solvent is used in cleaning a picture, the cotton 
 tufts employed should be examined carefully from time to 
 time, in order to see that no actual pigment has coloured 
 them — that they are stained by nothing but the brown 
 varnish. Other solvents besides those named are sometimes 
 used in cleaning pictures, particularly where hard or oily 
 varnishes have to be removed. Such solvents are acetone, 
 fusel-oil, benzene, chloroform, and solutions of caustic 
 alkalies. Great risk of injury attends their employment — 
 indeed, the application of any kind of solvent is fraught 
 with danger, and should never be attempted by the in- 
 experienced. 
 
 The usual plan of filling up actual gaps in the priming 
 or gesso-grounds of old pictures is by means of plaster of 
 Paris. When this has set, its surface is levelled by gentle 
 attrition with a cork and dry whitening, or cuttle-fish. Great 
 care is needed in order to prevent the pigments surrounding 
 the place from being abraded. I have found asbestos-putty 
 to be an excellent substitute for plaster in many cases ; its 
 surface is made smooth and level by means of a painting 
 palette-knife. But it cannot be tinted with water, or tempera- 
 colours, in order to make it match the hues of the neigh- 
 bouring parts of the picture ; oil-colours must be used. In 
 any necessary replacements of lost colours in old oil-paint- 
 ings, it has been recommended to use not oil-colours, but 
 water-colours, as these can always be distinguished from the 
 old work, and, if necessary, removed ; this can be done 
 on ' stoppings ' of whitening and size, as well as on those 
 of plaster. Tempera-pictures should, I think, be repaired 
 
RESTORATION OF PICTURES 
 
 323 
 
 with dry pigments mixed with egg-yolk, as in this case, 
 when the final varnish is applied, a general harmony of 
 effect is produced. If water-colours are introduced in 
 repairing an oil-painting, the coat of varnish subsequently 
 added is sure to deepen and darken them, unless this 
 change has been allowed for during the progress of the 
 work, by no means an easy thing to manage. When in any 
 kind of repainting oil-paints are used, they should be mixed 
 stiffly with a very little copal-varnish and spirits of turpentine, 
 and should be rather lighter and less yellow in tone than 
 the colours they are intended to match, since darkening and 
 yellowing in some degree, however slight, are sure to occur 
 subsequently. 
 
 The cleansing and restoration of paintings executed in 
 fresco require special care. Additions to supply colour 
 which has scaled off are best made in tempera. When a 
 fresco has become grimy by exposure to the smoky air of a 
 city, methylated spirits of wine, applied freely on tufts of 
 carded cotton, removes the tarry and sooty impurities which 
 a previous careful brushing of the painted surface has failed 
 to dislodge. Attempts to clear the clouded portions of an 
 injured fresco by means of distilled water or aerated distilled 
 water are usually attended with but slight success. The 
 films which obscure the surface in such cases sometimes 
 consist of sulphate of lime, produced from the carbonate of 
 lime present by the action of the sulphuric acid occurring 
 in the atmosphere of places where gas and coal are burnt. 
 In getting rid of this somewhat opaque film by means of 
 water, portions of the pigment are commonly removed. 
 When a fresco has been dusted and then cleansed with 
 spirits of wine it should be allowed to dry thoroughly, and 
 then be treated with the paraffin-copal medium (described 
 on p. 22) ; this medium must, however, be largely diluted 
 
324 
 
 RESTORATION OF PICTURES 
 
 with spirits of turpentine, or, preferably, with pure toluene, 
 before applying it to the fresco. By this treatment the dead 
 or matt surface of the painting is preserved, the obscuring 
 films are rendered translucent, and the picture may, when 
 cleansing is again required, be safely sponged with pure 
 water or weak spirits of wine. 
 
CHAPTER XXVI 
 
 TRIALS OF PIGMENTS 
 
 The testing of pigments for genuineness and for purity has 
 been discussed incidentally in Chapters XIII. to XIX. of 
 the present volume. Though genuineness and purity* have 
 often an important bearing upon the question of permanence, 
 this last quality must be ascertained by independent experi- 
 ments of another order. The study of old paintings often 
 furnishes us with results of some value, the results of unin- 
 tentional testings. But for the purpose of securing com- 
 plete and wholly trustworthy information, we must know 
 precisely all the materials and all the conditions of our 
 trials. Not only must the painting grounds, the mediums, 
 and the pigments, be chemically examined, but we must be 
 in a position to state the character of the atmosphere in 
 which they have been exposed, and the nature and amount 
 of the solar or other radiations to which they have been 
 subjected. In the great majority of these trials accurate 
 
 * The chromatic values of pigments — their approach in hue, etc., to 
 recognised standards of excellence — are not here taken into account. 
 Such data may be obtained by the use of Lovibond's Tintometer when 
 once the chromatic elements of a pigment in terms of the degrees of the 
 standard glasses employed in this instrument have been determined. 
 But really exact determinations of this kind require complex scientific 
 apparatus, which cannot be profitably used except by an expert mani- 
 pulator. 
 
326 
 
 TRIALS OF PIGMENTS 
 
 data as to materials and conditions are wholly wanting ; 
 even the South Kensington report affords us no information 
 as to the composition of the pigments employed, nothing 
 more than their commercial names, so that we have to take 
 on trust their genuineness and purity. However, in this 
 same most important series, quite unusual, if not unprece- 
 dented, care was taken in order to determine the conditions, 
 physical and chemical, under which the pigments were 
 tested. In my own experiments, carried on between 1856 
 and 1879, i n somewhat desultory fashion, and extended 
 and improved since 1880, the influence of purity of sample, 
 of the presence of moisture and of oxygen, and of the nature 
 of the ' light,' has not been neglected ; the full details of the 
 methods adopted, and of the results obtained, could not be 
 appropriately introduced into an elementary manual. Men- 
 tion will be made of the chief conclusions reached in the 
 present chapter ; there are also numerous references to them 
 in Chapters XIII. to XXII. 
 
 In many early treatises on painting we find observations 
 as to the degrees of stability possessed by various pigments, 
 along with suggestions as to methods of treatment by which 
 in certain cases greater permanency may be attained. To 
 some of these observations and suggestions reference has 
 been made in those chapters of the present volume which 
 deal with pigments ; many of the remainder are now with- 
 out practical importance, referring as they do to pigments 
 which have been rightly discarded. 
 
 It is only of recent years that trials of pigments have 
 been made with any approach to exactness. But in the 
 majority of cases no information has been secured concern- 
 ing the purity and genuineness of the pigments with which 
 the experiments have been made. I have not been able to 
 find a single chemical analysis of any one of the pigments 
 
TRIALS OF PIGMENTS 
 
 327 
 
 tested. The chromatic analysis of the light they severally 
 reflect has, however, been recorded in the case of the water- 
 colour paints examined by Dr. Russell and Sir W. Abney, 
 who have likewise furnished some particulars as to the 
 intensity of the solar radiations to which the pigments were 
 subjected. 
 
 More than a century ago Sir Joshua Reynolds tested, in 
 a rough way, the stability of some of the paints he employed. 
 Two causes detract from the value of his results. In the 
 first place, the information furnished concerning the nature 
 of many of the pigments he tried is too imperfect to be of 
 any use ; secondly, we are not acquainted with the condi- 
 tions under which his specimens have been kept during the 
 whole period since they left his hands. Two of his trial 
 canvases are preserved in the Royal Academy. Although 
 the darkening and embrowning of the surface are general, 
 and though the names of the pigments employed are often 
 undecipherable or meaningless, yet something useful re- 
 mains. From the experiments made in 1772 we may gather 
 the following facts : The proper hues of several pigments 
 remain in a measure— orpiment, or king's yellow in crystals; 
 yellow lake, with wax and drying oil ; gamboge, with lake 
 and Venice turpentine ; gamboge, with (Venice) turpentine § 
 prepared gamboge, with wax ; and verditer, with varnish.' 
 On the other hand, gamboge with oil, lake with oil, and 
 many other pigments of organic origin, when unmixed with 
 wax or varnish, are names only, or, at the most, brown dis- 
 colourations. 
 
 M. J. Blockz, in his ' Peinture a l'Huile,' gives the 
 results of a number of experiments made by M. J. Dyck- 
 man. He condemns, for various reasons, not only asphalt, 
 but also terre verte, cobalt green, emerald green, raw sienna, 
 raw umber, ivory brown, and all burnt madders. Cassel 
 
328 
 
 MR. ANDREWS EXPERIMENTS 
 
 earth was slightly changed ; brown ochre, burnt sienna, Mars 
 brown, ivory black, and vine black, proved to be permanent. 
 His lists of incompatible pigments are somewhat unneces- 
 sarily extended, not being justified, in all particulars, by 
 further and more careful experiments. 
 
 The experiments of Mr. F. W. Andrew, formerly of the 
 Victoria and Albert Museum, have been carried on since 
 1876, but have been confined to water-colours, both moist 
 and cake. His chief results will be found recorded along 
 with my own, in Part III., in the paragraphs devoted to the 
 consideration of the several pigments. His water-colour 
 washes, generally spread on Whatman paper, or Whatman 
 board, were exposed for periods varying from twenty-eight 
 to eighty-two months, in a south window, to all the sunshine 
 available ; half of each wash was doubled back, and so far 
 excluded from light. In some cases a third part of the 
 coloured slip was exposed to the air and light without the 
 protection of glass. The chief paints which were unaffected, 
 at all events, so far as some specimens were concerned, by 
 the exposure, are included in the following list : Yellow 
 ochre, raw sienna, deep cadmium, Mars red, light red, 
 Indian red, oxide of chromium, Leitch's blue, cobalt, 
 artificial ultramarine, Prussian blue, raw umber, burnt 
 umber. Naples yellow (true) became blackish in darkness, 
 but was unaltered in light, while orange chrome showed 
 dark patches. Further details must be given as to the 
 pigments which were affected. In the tabular statements 
 appended a selection from the results afforded by eleven sets 
 of experiments is recorded, the letters C and M prefixed to 
 the entries respectively denoting the employment of cake 
 or moist colours. The numerical values representing the 
 residual hues are rough approximations only, but in some 
 instances they were determined by means of comparisons 
 
TRIALS OF WATER-COLOURS 
 
 3 2 9 
 
 with standard coloured liquids, contained in glass cylinders 
 graduated into ten equal parts. The tintometer of Mr. 
 J. W. Lovibond, of Salisbury, may be employed with ad- 
 vantage in these estimations. 
 
 CHANGES IN WATER-COLOURS 
 
 Name of 
 Pigment 
 M. Aureolin - - 
 M. Aureolin - - 
 
 Months of 
 Exposure 
 
 - - 28 - 
 
 - - 62 - 
 
 Residual DeptJ 
 {Original = 10) 
 
 - - 10 - - 
 
 - - 10 
 
 Residual Flue, 
 and Remarks 
 Verges on orange 
 [yellow 
 
 M. Aureolin - - 
 
 - - 82 - 
 
 - - 9 
 
 
 C. Gamboge - - 
 
 - - 28 - 
 
 - - 4 
 
 
 M. Gamboge • - 
 M. Gamboge - - 
 
 - - 28 - 
 
 - - 82 - 
 
 - - 9 
 
 - - 7 
 
 
 M. Yellow lake - 
 
 - - 62 - 
 
 - - 2 - - 
 
 Yellowish grey. 
 
 M. Yellow lake - 
 
 - - 82 - 
 
 - - 
 
 
 C. Yellow madder 
 
 - - 28 - 
 
 - - 1 
 
 
 M. Yellow madder 
 
 - - 28 - 
 
 ■ - 3 - - 
 
 Pinkish grey. 
 
 M. Yellow madder 
 
 - - 62 - 
 
 - - i 
 
 
 C. Indian yellow - 
 
 - - 28 - 
 
 - - 8,9 
 
 
 M. Indian yellow - 
 
 - - 28 - 
 
 - " 9 
 
 
 M. Indian yellow - 
 M. Indian yellow - 
 
 - - 60 - 
 
 - - 82 - 
 
 - - 7 
 
 - - 6 
 
 
 M. Pale cadmium - 
 
 - - 82 - 
 
 - . 1 . . 
 
 Pale buff. 
 
 M. Vermilion - - 
 
 - - 62 - 
 
 . . _ . . 
 
 Blackish. 
 
 M. Vermilion - - 
 
 - - 82 - 
 
 . . — . . 
 
 Black. 
 
 M. Carmine - - 
 
 - - 28 - 
 
 - - - - 
 
 Pale grey. 
 
 M. Crimson lake - 
 
 - - 28 - 
 
 - - - - 
 
 Greenish grey. 
 
 M. Burnt carmine - 
 
 - - 28 - 
 
 - - 1 - - 
 
 » 
 
 C. Pink madder - 
 
 - - 28 - 
 
 - - 1 
 
 
 M. Rose madder - 
 
 - - 28 - 
 
 - " 3 
 
 
 M. Rose madder - 
 M. Rose madder - 
 
 - - 62 - 
 
 - - 82 - 
 
 . . 1 . . 
 
 Pinkish grey, 
 i) 
 
 M. Madder carmine 
 
 - - 62 - 
 
 - - 2 
 
 
 M. Madder carmine 
 
 - - 82 - 
 
 ■ - 
 
 
 M. Purple madder 
 
 - - 28 - 
 
 - - 4 - - 
 
 A pale wash. 
 
 M. Purple madder 
 
 - - 62 - 
 
 - - 7 
 
 
 M. Purple madder 
 
 ■ - 82 - 
 
 - - 2 
 
 
33° 
 
 MADDER VERSUS COCHINEAL 
 
 Name of 
 Pigment 
 
 C. Brown madder 
 M. Brown madder 
 M. Brown madder 
 
 C. Indigo - - - 
 M. Indigo - - • 
 M. Raw umber 
 M. Vandyke brown 
 M. Vandyke brown 
 M. Bone brown 
 
 Months of 
 Exposure 
 
 - 28 - 
 
 - 28 - 
 
 - 82 - 
 
 - 28 - 
 
 - 62 - 
 
 - 60 - 
 
 - 28 - 
 
 - 60 - 
 
 - 62 - 
 
 Residual Depth 
 (Original = 10) 
 
 - - 1 
 
 - - 1 
 
 - - o 
 
 - - 5 
 
 - - 1 
 
 - - 9 
 • ■ 7 
 
 - - 1 
 
 Residual Hue, 
 and Remarks 
 Warm grey. 
 
 Greenish grey. 
 Rather yellower. 
 
 The pigments containing lead, such as the ordinary 
 chromes, and those having a copper basis, like emerald 
 green, had altered capriciously, losing part of their original 
 colour, and becoming tarnished or embrowned in patches. 
 Brown pink faded like the yellow lakes, but acquired a bluish- 
 grey residual hue. 
 
 The testing of the madder colours is so important that I 
 introduce here a few additional experiments selected from 
 my own note-books. The washes of the moist-colour 
 paints were, as far as possible, of the same depth of tone, 
 and they were all exposed together in a glazed frame to one 
 year's sunshine : 
 
 Name of 
 
 Pigment 
 Rose madder - 
 Madder carmine 
 Madder carmine 
 
 Madder red - - 
 Turple madder - 
 Brown madder - 
 
 Residual Depth 
 (Original =10) 
 
 Change of Hue, etc. 
 
 Slightly more purplish. 
 
 Almost unchanged. 
 
 Much more purplish. This sample 
 
 was from another source. 
 Less red, more purplish. 
 Duller, less red, more blue. 
 Less red, more yellow-brown. 
 
 In contrast to the above results with madder carmine, the 
 following experiment with the ordinary carmine (prepared 
 from cochineal) is instructive. On a sheet of Whatman 
 paper, a space of 10 inches in length by 4 inches in width 
 
PROFESSOR ROOD'S EXPERIMENTS 
 
 33i 
 
 was covered with a uniform wash of the moist paint, having 
 a depth of tint about equal to that of the petals of the old 
 China rose. This coloured strip was then subjected to 
 summer sunshine in such a way that successive single inches 
 of its length received the light (during the same hours of 
 similarly bright days) for periods of 2, 4, 8, 12, 20, 26, 30, 
 40, and 100 hours, one single inch at one end being, how- 
 ever, protected completely from all access of light. The 
 exposure of 100 hours sufficed to bleach the last breadth 
 completely, but had the rate of fading been in a simple 
 arithmetical progression, a much shorter exposure would 
 have sufficed. In fact, the bleaching action was far more 
 energetic during the first period of 2 hours than during the 
 second, about 20 per cent, of the original colour having 
 been destroyed during these two first hours, while during 
 the second equal period the loss of depth did not exceed 
 one-tenth of this amount. Moreover, it was noticed that 
 the change of hue consequent upon the first exposure was 
 different in kind to that which occurred subsequently. 
 
 Professor O. N. Rood's Experiments. — In his ' Modern 
 Chromatics,' pages 90 and 91, Professor Rood gives the re- 
 sults of a few trials which he made as to the effect on washes 
 of water-colours laid on ordinary drawing-paper of three and 
 a half months' exposure to summer sunlight. 
 
 These pigments were unaffected : 
 
 Cadmium yellow, yellow ochre, Roman ochre. 
 
 Indian red, light red, Jaune de Mars. 
 
 Terre verte. 
 
 Cobalt, French blue, smalt. 
 
 Burnt umber, burnt sienna. 
 
 The following pigments were all affected. The sequence 
 represents the amount of alteration, the list commencing 
 with those colours which suffered but little change : 
 
w 
 
 PROFESSOR HARTLEY'S EXPERIMENTS 
 
 Name 
 0/ Pigment 
 
 1. Chrome yellow 
 
 2. Red lead - - 
 
 3. Naples yellow 
 
 4. Raw sienna • 
 
 5. Vermilion 
 
 6. Aureolin - - 
 
 7. Indian yellow 
 
 8. Antwerp blue 
 
 9. Emerald green 
 10. Rose madder 
 
 n. Sepia - - - 
 
 12. Prussian blue 
 
 Nature 
 of Change 
 
 Slightly greenish. 
 
 Less orange. 
 
 Slightly greenish 
 brown. 
 
 Fades, yellower. 
 
 Darkens, brownish. 
 
 Fades slightly. 
 
 Fades slightly. 
 
 Fades slightly. 
 
 Fades slightly. 
 
 Fades slightly, pur- 
 plish. 
 
 Fades slightly. 
 
 Fades somewhat. 
 
 Name 
 of Pigment 
 
 13. Hooker's green - 
 
 14. Gamboge - - - 
 
 15. Bistre - - - - 
 
 16. Brown madder • 
 
 17. Neutral tint - - 
 
 18. Vandyke brown 
 
 19. Indigo- - - - 
 
 20. Brown pink - - 
 
 21. Violet carmine 
 
 22. Yellow lake - - 
 
 23. Crimson lake - 
 
 24. Carmine - - - 
 
 Nature 
 ofCfiange 
 
 More bluish. 
 
 Fades, greyish. 
 
 Fades, greyish. 
 
 Fades. 
 
 Fades. 
 
 Fades, greyer. 
 
 Fades. 
 
 Fades greatly. 
 
 Fades greatly, 
 
 brownish. 
 Fades greatly, 
 
 brownish. 
 Fades out. 
 Fades out. 
 
 Professor Rood adds that rose madder, brown madder, 
 and purple madder were all a little affected by an exposure 
 to sunshine for seventy hours, and that pale washes were 
 completely obliterated by a much shorter exposure to sun- 
 shine in the case of carmine, dragon's blood, yellow lake, 
 gall-stone, brown pink, Italian pink, and violet carmine. 
 
 Professor W. N. Hartley's Experiments. — On September 
 4, 1886, Professor Hartley read, before the British Associa- 
 tion at Birmingham, a paper on 'The Fading of Water 
 Colours.' His trials as to the effect on pigments of a com- 
 paratively brief exposure to intermittent sunshine in pure air 
 may be thus summarized. Washes on the best drawing- 
 paper were the subject of the experiments : 
 
 Gamboge. — Pale washes were completely bleached in 
 three days ; in a week strong washes were much lightened 
 in colour, and rendered dull, even three hours' exposure 
 producing a very visible effect. 
 
 Crimson lake. — Six hours' exposure to sunlight and air 
 almost bleaches pale washes, while three days or eighteen to 
 twenty-four hours of intermittent sunshine cause dark crim- 
 son tones to become very much lighter, the hue of the pig- 
 ment being altered. 
 
 Light red, Indian red, and vermilion were unaffected. 
 
 Olive green and brown pink were rendered lighter in 
 

 PROFESSOR HARTLEY'S EXPERIMENTS 
 
 333 
 
 colour by six hours' exposure, the former pigment becoming 
 bluish and the latter brownish in hue. 
 
 Indigo, cobalt, and artificial ultramarine were unaffected. 
 
 Brown madder became rather lighter after eight days' or 
 forty-eight hours' exposure. 
 
 Bistre faded with great rapidity, a light wash appearing 
 much paler after six hours. 
 
 Sepia. — A pale wash became colder in hue, but not very 
 perceptibly paler. 
 
 In a second series of experiments, sectors of paper discs, 
 washed with various pigments, were enclosed between glass- 
 plates, the edges of which were fastened with gummed paper. 
 Under these circumstances, crimson lake and bistre were 
 found to have been considerably altered by five hours' ex- 
 posure—somewhat more so, indeed, than was the case when 
 these pigments were freely exposed to the air. 
 
 All the results above noted are in practical accord with 
 those obtained by other observers. The exposure to inter- 
 mittent sunshine ' for six hours a day during fourteen days,' 
 does not produce a sensible effect upon vermilion and indigo. 
 Had Professor Hartley extended his observations a few 
 weeks longer, his conclusions as to these pigments must 
 have agreed with those which we have given, and therefore 
 with the unanimous verdict of all other scientific observers. 
 His statement that 'indigo is permanent' (Brit. Assoc. 
 Report, 1886, p. 581) must, therefore, be modified into, 
 ' indigo appears to have suffered no change after fourteen 
 days' exposure to intermittent sunshine.' A similar alteration 
 is demanded with regard to the stability of vermilion. 
 
 Professor Hartley's experiments with water-colour washes 
 on paper enclosed between glasses require a few words of 
 comment. He is clearly and rightly dissatisfied with this 
 method of trial. A supply of atmospheric oxygen, and of 
 
334 
 
 PROFESSOR HARTLEY'S EXPERIMENTS 
 
 hygroscopic moisture, amply sufficient for large chemical 
 alteration and oxidation of the enclosed pigments, was cer- 
 tainly present. And the glasses did accelerate the action, 
 not because of ' the very slight tint of the plate-glass,' but in 
 spite of it. This acceleration of change is mainly caused by 
 the continued presence of moisture in the confined space 
 between the two glasses — it cannot escape as it freely, and 
 to a very great extent, does escape, when a piece of tinted 
 paper is exposed to sunshine in free air. I showed, indeed, 
 in my lectures at the Royal Academy, so long ago as 1880, 
 that the fading of many fugitive pigments is greatly lessened, 
 when not altogether prevented, by enclosing the paper 
 washed with them in a glass tube, the air of which is kept 
 dry by means of some strongly hygroscopic substance. 
 When both moisture and air are excluded (using a sealed 
 vacuum tube), the suspension of fading and alteration of 
 hue is still more marked and general. 
 
 It should be added here that Professor Hartley found 
 that cadmium yellow and Indian yellow are bleached by 
 peroxide of hydrogen, and changed into a muddy yellow by 
 sulphurous acid. This reagent bleaches artificial ultra- 
 marine and dulls vermilion. He attributes the partial or 
 complete destruction of the blue component of the hues in 
 certain old drawings, which have been long exposed to air 
 and light, to the presence of acids or acid substances in the 
 air, in the paper, or in the red ferruginous pigments with 
 which the blue colouring substances in question have been 
 associated. These blue pigments could have been nothing 
 other than Prussian blue, indigo, or natural ultramarine. I 
 have ascertained, by direct experiments on old drawings, 
 that the latter was but rarely employed for mixed tints, but 
 it is quite probable that the reds prepared from colcothar, 
 with which it may have been occasionally mingled, would 
 
MR. W. SIMPSON'S EXPERIMENTS 
 
 335 
 
 sometimes contain enough acid salts (certain ferric sul- 
 phates) to destroy its colour. The products of the burning 
 of gas and of coal would also be rich enough in sulphuric 
 acid to produce the same effect. I am unable to endorse 
 Professor Hartley's statement that the best drawing-papers 
 contain free sulphuric acid. 
 
 Mr. W. Simpson's Experiments. — Some washes of water- 
 colour, of thirty-one different kinds, were made upon cards 
 by the late Mr. W. Simpson. He so cut the cards as to 
 divide each coloured strip in half ; one section was preserved 
 in darkness, the other was exposed in an eastern aspect on 
 the shutter of a house in London for fifteen years, but the 
 sun did not shine upon the specimens after ten o'clock in 
 the morning. As they were not tightly framed, the cards 
 became a good deal discoloured by the absorption of noxious 
 vapours and dirt. The results were : 
 
 Name 
 
 Nature 
 
 Name 
 
 Nature 
 
 of Pigment 
 
 of Change 
 
 of Pigment 
 
 of Change 
 
 Yellow ochre - - 
 
 None. 
 
 Madder lake - - 
 
 More purplish. 
 
 Indian yellow - - 
 
 Faded consider- 
 
 Purple madder - - 
 
 Hue altered. 
 
 
 ably. 
 
 *Brown madder - - 
 
 Loss of redness. 
 
 Lemon yellow - - 
 
 None perceptible. 
 
 Emerald green - - 
 
 Slight. 
 
 ' Newman's perma- 
 
 
 Cyanine blue - - 
 
 Apparently none. 
 
 nent yellow ' - - 
 
 None. 
 
 ^Prussian blue - - 
 
 None. 
 
 Cadmium yellow - 
 
 Perhaps browner. 
 
 French blue - - - 
 
 Faded very slightly 
 
 Chrome yellow - • 
 
 Faded consider- 
 
 Cobalt 
 
 None. 
 
 
 ably. 
 
 Ultramarine - - - 
 
 None. 
 
 Brown pink - - - 
 
 Faded. 
 
 Indigo, rather deep 
 
 Very pale grey. 
 
 Vermilion - - - 
 
 None. 
 
 Burnt sienna - - 
 
 None. 
 
 Light red - - - 
 
 None. 
 
 *Vandyke brown 
 
 None. 
 
 Indian red - - - 
 
 None. 
 
 
 Faded very slightly 
 
 Crimson lake - - 
 
 Gone. 
 
 
 None. 
 
 Carmine - - • - 
 
 Gone. 
 
 
 
 It will be noted that the above results are for the most 
 part in agreement with those recorded by other experi- 
 menters ; the chief exceptions are marked with a star. 
 Vermilion is usually blackened, but it is possible that the 
 sample employed in these experiments was the less change- 
 able native form or cinnabar. The Vandyke brown, too, 
 
336 
 
 TRIALS OF PIGMENTS 
 
 was probably the earthy rather than the bituminous variety ; 
 the slightness of the change recorded for madder brown and 
 sepia, and the absence of any alteration on the part of bistre, 
 are less easy of explanation. The madder pigments seem 
 to have stood more than usually well, but they often exhibit 
 large differences of stability. Nor must it be forgotten, in 
 assigning values to the above results, that this trial of fifteen 
 years' exposure was not of the severest kind. Although, on 
 the one hand, there was the imperfect exclusion of an in- 
 jurious London atmosphere, on the other hand, the energy 
 of the solar radiation was much reduced by the prevalent 
 condition of the smoky air, while the intermittent and capri- 
 cious sunshine of the Metropolis never fell on the trial cards 
 after ten a.m. 
 
 The late Mr. R. H. Soden-Smith kindly placed at my 
 disposal a large number of specimens of old water-colour 
 cakes and of powder colours intended for oil-painting. One 
 set consists now of eleven cakes or fragments of cakes (in 
 their original box) bought about the year 1815 of Newman, 
 in Soho Square. This set is peculiarly interesting as the 
 colours, which all bear the name of the maker and his 
 device, represent those used by many of the best English 
 water-colour painters during the first quarter of the present 
 century. The cakes are : Indian yellow, raw sienna, raw 
 umber, burnt sienna, burnt umber, vermilion, carmine, 
 burnt carmine, pink madder, ultramarine, indigo ; neutral 
 tint and sepia are missing. On comparing the hues of the 
 first nine of these paints and of the indigo with the hues of 
 the corresponding cake-colours as sold by the same house 
 in 1886, no appreciable differences were detected save in 
 the case of the raw umber. Here the pigment of 18 15 
 showed a more beautiful nuance than that of 1886. On 
 making comparative tests of the stability, under exposure 
 
■•'"■•■■ 
 
 SOUTH KENSINGTON REPORT 
 
 337 
 
 to sunshine, of the two sets of pigments, the results were 
 found to be practically identical. One cannot, therefore, 
 claim for the water-colour paints in use seventy-five years 
 ago a degree of permanence greater than that possessed by 
 their representatives of to-day. 
 
 By far the most important series of trials of water-colour 
 paints yet published is that to be found in the report by 
 Dr. Russell and Captain (now Sir W.) Abney to the Science 
 and Art Department (1888). The reporters endeavoured 
 to give precision to their experiments and their conclusions 
 by a careful comparison of the effective radiation from 
 different sources of light. The first part of their report 
 contains a very useful discussion of the relative values of 
 direct sunlight, light from clouds, and from an overcast or 
 clear sky, and light from artificial sources. Several cognate 
 subjects are also discussed therein, such as the number of 
 years of exposure which pigments would require, if in the 
 picture-galleries of South Kensington, in order that they 
 might suffer the same changes as those caused by three or 
 twenty-two months' exposure in a southern aspect outside 
 the Museum. Part II. of the report contains the results of 
 twelve sets of experiments with various pigments. In all 
 the series the same paper (Whatman's) was used. In the 
 paragraph relating to this subject there is, however, one 
 curious error, and one obscure statement (page 27). It is 
 quite impossible that the paper used — its weight per ream is 
 not given — could have contained so little as ' nearly 1 grain ' 
 of sizing matter per square foot; 10 grains is a more 
 probable quantity. The next following sentences do not 
 state the condition of the papers which absorbed from a 
 moist atmosphere from 12*07 to 12*46 per cent, 'of their 
 weight of water.' Were they dried previously, and, if so, at 
 what temperature ? We ought to have been told within 
 
338 
 
 SOUTH KENSINGTON REPORT 
 
 what limits the percentage of water in these papers varied 
 during the course of the trials : I have pointed out for 
 many years past the importance of this hygroscopic moisture 
 in paper in reference to the fading of pigments. Eight tints 
 of each pigment were applied to strips of paper 8 inches 
 long by 2 inches wide ; they were exposed in tubes 
 open at both ends, but having the upper extremity curved 
 downwards so as to exclude wet and dirt. Of course, 
 exposure on a wall facing nearly south constituted a very 
 severe test, yet the circulation of air in the tubes was more 
 advantageous to the pigments than would have been the 
 steamy heat of a closed vessel, or even of an ordinary paper- 
 backed picture-frame. But on the other hand, this arrange- 
 ment allowed the free access to the pigments of any noxious 
 gases, such as sulphurous and sulphuric acids, and sulphur- 
 etted hydrogen, which might have been at any time present 
 in the atmosphere. The general results of this first series 
 of trials are gathered in the following table, the exposure in 
 all cases lasting from May, 1886, until March, 1888. The 
 pigments are arranged in the order of instability, the most 
 fugitive being placed first : 
 
 *Carmine. 
 *Crimson lake. 
 *Purple madder. 
 *Scarlet lake. 
 * Payne's grey. 
 *Naples yellow. 
 *01ive green. 
 *Indigo. 
 
 *Brown madder. 
 *Gamboge. 
 *Vandykc brown. 
 *Brown pink. 
 *Indian yellow. 
 
 Cadmium yellow. 
 
 Leitch's blue. 
 *Violet carmine. 
 *Purple carmine. 
 *Sepia. 
 
 Aureolin. 
 
 Rose madder. 
 
 Permanent blue. 
 
 Antwerp blue. 
 
 Madder lake. 
 
 Vermilion. 
 
 Emerald green. 
 
 Burnt umber. 
 
 Yellow ochre. 
 Chrome yellow. 
 Lemon yellow. 
 Raw sienna. 
 Indian red. 
 Venetian red. 
 Burnt sienna. 
 Terre verte. 
 Chromium oxide. 
 Prussian blue. 
 Cobalt. 
 French blue. 
 Ultramarine ash. 
 
SOUTH KENSINGTON REPORT 
 
 339 
 
 The pigments marked with an asterisk were found to have 
 distinctly altered either in depth or hue by a much shorter 
 exposure, from May to August 14, 1886. 
 
 In a second series of trials the tinted papers were dried, 
 and then introduced into the tubes, which had been pre- 
 viously heated ; the specimens were then sealed up hermeti- 
 cally ; as no moisture-absorbing material was enclosed with 
 the papers, traces of water must have been present. My 
 own much earlier results were abundantly confirmed by 
 those obtained in this series, for the number of pigments 
 which proved to be permanent under these conditions was 
 double that of the first series. Brown madder and Prussian 
 blue, were, however, acted upon in this second series. Dr. 
 Russell and Sir W. Abney make the remark that of the 
 eight colours which remained unchanged in dry air, but 
 were acted on in ordinary air, all, with the single exception 
 of madder lake, are mineral colours. But this is not correct, 
 for the pigments named are — madder lake, olive green, 
 Payne's grey, sepia, Naples yellow, cadmium yellow, emerald 
 green, and burnt umber, and of these the first four are either 
 wholly or partly of organic origin, while the seventh contains 
 an acetate. 
 
 In the next series of experiments, the pigments were ex- 
 posed in the presence of moisture-laden air. Very few 
 colours withstood this test — none of organic origin ; both 
 Prussian blue and Antwerp blue were entirely destroyed. 
 
 An atmosphere of moist hydrogen gas was employed in 
 the fourth series. Under these conditions carmine, crimson 
 lake, madder lake, brown madder, olive green, indigo, 
 Payne's grey, sepia, and Vandyke brown, suffered no 
 change. 
 
 When, as in the fifth series, both moisture and oxygen 
 were excluded, scarcely any even of the most fugitive pig- 
 
 22 — 2 
 
340 
 
 SOUTH KENSINGTON REPORT 
 
 ments were affected. Vermilion, however, as in all the 
 other experiments, became black. We know that the reason 
 for the change is physical, not chemical. 
 
 In the sixth series it was proved that the addition of ox- 
 gall had no beneficial effect in lessening the change of hue 
 and tone in fugitive pigments. 
 
 The remaining series, save the twelfth and last, were 
 devised in order to learn what influence upon the stability 
 of pigments might be exerted by admixture with Chinese 
 white, by exposure to the light of the electric arc, by heat 
 without light, by heat and light together, and by exposure 
 to the light transmitted through coloured glasses. Amongst 
 the results recorded, we may note the decided changes in 
 several pigments caused by admixture with Chinese white, 
 and by heating the prepared paper slips in sealed tubes for 
 seven hours a day for three weeks, all light being excluded. 
 In a twelfth series of trials, the pigments were exposed in a 
 picture-frame under glass in such conditions, and to such an 
 amount of light, as might be taken to represent the ordinary 
 circumstances in which pictures are kept. The frame was 
 exposed from August 6, 1886, until May 6, 1888, to very 
 bright light, but not to sunshine. Gamboge, indigo, Naples 
 yellow, brown pink, carmine, and Vandyke brown, had 
 faded in varying degrees. Some remarks on these results 
 will be found further on in the present chapter ; they are of 
 extreme importance, considering the large use that has been 
 made of these pigments by our water-colourists, and the 
 mild treatment to which they were subjected during the 
 short period of twenty-one months. 
 
 For the results obtained with mixtures of pigments under 
 varied conditions of exposure, we must refer our readers to 
 the report itself. It may, however, be remarked that, in the 
 great majority of cases, the changes of tone and hue which 
 
SOUTH KENSINGTON REPORT 
 
 341 
 
 occurred were such as might have been predicted from the 
 known degrees of stability of the several constituents of the 
 mixtures. Here, as elsewhere in the report, we find frequent 
 mention of the strange, but long known, recovery in dark- 
 ness of its colour by Prussian blue which has been bleached 
 by sunlight. 
 
 In the fourth appendix to this report is an instructive list 
 of the pigments employed by some of the most distinguished 
 artists using water-colours. Forty-six painters replied to the 
 invitation of the Science and Art Department ; from their 
 answers we learn that a large proportion of them include in 
 their palettes many pigments which must be unhesitatingly 
 condemned on account of their want of stability. Thus no 
 less than 17 out of the 46 artists who responded to the 
 appeal employ three of the most fugitive pigments in the 
 series — namely, gamboge, brown madder, and indigo. Con- 
 verted into percentages, we may say that 37 out of 100 
 painters in water-colours use these three untrustworthy 
 pigments, besides others which are worse, and others which 
 are little better ; of course, they employ also certain colours 
 as to the stability of which there is no question. The 
 following tabular statement gives the proportion of artists, 
 per 100, who use the eleven perishable pigments named 
 below : 
 
 Gamboge - - 
 Indian yellow - 
 Vermilion - - 
 Carmine - - 
 Crimson lake - 
 Purple madder 
 Brown madder 
 Brown pink - 
 Vandyke brown 
 Sepia - - - 
 Indigo - - - 
 
 70 
 24 
 70 
 8 
 22 
 28 
 
 74 
 11 
 
 74 
 65 
 52 
 
 Faded to JA 
 Faded to 6. 
 Gone black. 
 Gone. 
 Gone. 
 Faded to 8. 
 Faded to 3. 
 Faded to 7. 
 Gone. 
 Faded to 8. 
 Faded to 8. 
 
 1 represents the 
 lightest tint, 8 the 
 darkest. The washes 
 of pigment were fully 
 exposed for twenty- 
 two mouths. 
 
342 
 
 SOUTH KENSINGTON REPORT 
 
 We call these pigments perishable with good reason. 
 For, according to the report under review, all of them were 
 found to have faded, materially and conspicuously, after 
 twenty-two months' full exposure in a south aspect, while 
 three of them had entirely disappeared, and another (ver- 
 milion) had become black. But this is not all. For under 
 a less severe trial (p. 45) — namely, exposure for the same 
 time, not to direct sunlight, but to a very bright light from 
 a window, ' under conditions approximating to those to 
 which pictures are usually subjected ' — six out of the eleven 
 pigments had faded, though in varying degrees. With these 
 figures and results before us, it is impossible to resist the 
 conclusion that a life of 100 years is too much to allow 
 to many of the water-colour drawings of the present day. 
 What shall we say, then, as to the stability of the works of 
 the earlier masters of the English water-colour school? 
 How much care in the exclusion of ' the more fugitive 
 colours ' was taken by the water-colourists of 1780 to 1850? 
 Could it be honestly said of any large number of such 
 works, in which gamboge, brown pink, crimson lake, sap- 
 green, indigo, and sepia, were generally employed without 
 stint, ' that about a century of exposure would have to be 
 given to water-colour drawings in galleries lighted as are 
 those at South Kensington before any marked deterioration 
 would be visible in them ' ?* (Report, p. 46.) 
 
 * In the preceding brief resume of certain parts of the South Ken- 
 sington Report no reference has been made to an argument, developed 
 in §§ x. to xv., in which it is contended that ' if a certain tint be exposed 
 to an intensity of radiation which we will call. 100, and which bleaches 
 it in, say, 1 hour, then, if a similar tint be exposed to an intensity I, it 
 will require 100 hours' exposure to it to effect the same bleaching.' The 
 universal applicability of this conclusion cannot be conceded by those 
 who are familiar with numerous instances in which no chemical or 
 physical change occurs when certain substances are exposed continuously 
 
TRIALS OF WATER-COLOUR PAINTS 
 
 343 
 
 Dr. Russell and Sir William Abney add, indeed, the 
 proviso, ' If painted with any but the more fugitive colours.' 
 But this condition cannot be said to have been fulfilled by 
 the works in question ; for in the great majority of them, 
 most of the six fugitive pigments which we have just named 
 were freely employed. And it is these very pigments which 
 have been proved by the reporters themselves to suffer 
 1 marked deterioration ' by an exposure of twenty-one 
 months only to strong daylight without direct sunshine. 
 Moreover, it must not be forgotten that the fading of a 
 single important pigment in a water-colour drawing is 
 ruinous to the whole effect, destroying the balance of the 
 chromatic scheme of the artist more effectually than a slight, 
 but equal, degradation of all the hues. 
 
 An instructive set of trials of water-colour paints was 
 commenced in May, 1894, and continued for four years by 
 a sub-committee of the Burlington Fine Arts Club. The 
 results of these experiments have been embodied in three 
 reports. Winsor and Newton's moist water-colours were 
 used, flat washes on Whatman's ' not hot pressed ' paper of 
 the year 1888 being exposed to light in the windows of the 
 billiard-room of the club. One of the sets so exposed was 
 in an ordinary glazed frame, another set was enclosed in 
 hermetically sealed glass tubes containing ordinary air ; 
 while a third set was contained in similar tubes, but the 
 atmosphere present was maintained in a dry state by means 
 of a reservoir of burnt lime which absorbed all or almost 
 all traces of water in the pigments, the paper, and the 
 mount. The final comparisons were made with parallel sets 
 
 for long periods to a particular temperature, yet, when they are heated 
 but a degree or two higher, instantly alter, decompose, or react, as the 
 case may be. 
 
344 
 
 TRIALS OF WATER-COLOUR PAINTS 
 
 which had been kept in absolute darkness. We give here, 
 in tabular form, the condition of the paints at the end of 
 the fourth year of exposure ; reference must be made to the 
 original reports for information as to the results of six 
 months' and of thirteen months' exposure to sunshine. 
 
 Results of Exposure for Four Years, from May 25, 1894, 
 to May 25, 1898 
 
 (Original depth = 10) 
 
 Set in Dry Air Set in Moist Aii 
 No change. 
 Faded to 1. 
 Gone. 
 
 Pigment 
 Aureolin - - 
 Gamboge 
 Indian yellow 
 Cadmium yellow Deeper orange. 
 Vermilion 
 Crimson lake 
 Rose madder 
 
 Indian red - - 
 Madder carmine 
 
 Greyish. 
 Faded to o - 5. 
 Faded to 8-5. 
 
 No change. 
 Faded to 9. 
 
 Madder brown - Faded to 9. 
 
 Madder purple - 
 Prussian blue 
 French blue - 
 Indigo - - - 
 
 Vandyke brown 
 
 Sepia - - - ■ 
 Indigo with In- 
 dian red - - 
 
 Faded to 8. 
 No change. 
 No change. 
 No change. 
 
 Faded to 2, 
 
 yellow. 
 Faded to 8. 
 
 No change. 
 
 less 
 
 Faded to 9. 
 
 Faded to 1. 
 
 Faded to 1. 
 
 No change. 
 
 Greyish. 
 
 Gone. 
 
 Faded to 8 "o and 
 purplish. 
 
 No change. 
 
 Darker, more 
 purplish. 
 
 Faded to 6, pur- 
 ple gone. 
 
 Faded to 4. 
 
 Faded to 1. 
 
 No change. 
 
 Faded to 1, 
 greenish grey 
 
 Faded to 1. 
 
 Faded to 1. 
 
 Set in Frame 
 
 No change. 
 
 Faded to 1. 
 
 Faded to 1. 
 
 No change. 
 
 Greyish. 
 
 Gone. 
 
 Faded to 8'5 and 
 purplish. 
 
 No change. 
 
 Darker, more 
 purplish. 
 
 Faded to 8, purple 
 gone. 
 
 Faded to 5. 
 
 Faded to 8-5. 
 
 No change. 
 
 Faded to I, green- 
 ish grey. 
 
 Faded to 1. 
 
 Faded to 4. 
 
 Indigo gone. Indigo gone. 
 
 The most striking results of these trials was the complete 
 stability of Prussian Blue and of Indigo when exposed in 
 air kept dry. The further remark may be made that moist 
 air, that is, ordinary air containing moisture and confined 
 
EXPERIMENTS WITH OIL PAINTS 
 
 345 
 
 ini a sealed tube, inflicts more injury upon alterable pigments 
 than ordinary air enclosed in a frame which does admit of 
 some amount of ventilation occurring. There is no difficulty 
 iru so constructing a frame as to introduce a water-absorbing 
 substance which may be renewed from time to time. Thus 
 we shall be able to employ with confidence in water-colour 
 painting madder brown, madder purple, Prussian blue, 
 indigo and sepia — five pigments which under ordinary 
 conditions of exposure to sunshine suffer serious changes. 
 But no method has yet been devised by means of which we 
 may safely use gamboge, Indian yellow, vermilion, crimson 
 lake and Vandyke brown, although it must be stated that 
 instances have been recorded in which vermilion as a water- 
 colour has stood very severe exposure-tests, especially when 
 size and gum have been mixed with it. 
 
 Amongst the series of trials of oil-paints made by the 
 author of this handbook, one set first arranged in 1880 may 
 be described here. Chance's colourless plate-glass was 
 employed as the painting-ground, so as to avoid all interfer- 
 ence with the pigments from the surface on which they were 
 spread ; glass presents the further advantage of permitting 
 a complete examination of the back of each specimen, and 
 of changes in its translucency, opacity, or texture. Each 
 glass measured 8 inches by 6 ; the complete series was pre- 
 pared in duplicate — one for preservation in darkness, the 
 other for exposure to all the light that could be secured 
 (in Kew) during five years in a window facing nearly south- 
 west. The majority of the paints tried were obtained from 
 four firms (Messrs. Winsor and Newton, Messrs. Roberson 
 and Co., M. Edouard of Paris, and Schoenfeld of Diissel- 
 dorf). Specimens of each pigment were reserved for further 
 examination and analysis. Some of the chief results obtained 
 are given in the annexed table ; a few remarks on the changes 
 
346 
 
 TRIALS OF OIL-PAINTS 
 
 observed in some of the pigments which had been mixed 
 with flake white are added : 
 
 Pigment 
 
 Years of 
 
 Exposure 
 
 Residual 
 
 Depth 
 
 {Original— 10) 
 
 Change of Hue y 
 and Remarks 
 
 Yellow ochre - - - 5 
 
 Aureolin - - - - 5 
 
 Indian yellow - - - 5 
 
 Naples yellow (true) - 5 
 
 Pale yellow madder - 2 
 
 Deep yellow madder 2 
 
 Laque brun jaune - 2 
 
 Laque brun fonce - 2 
 
 Laque Robert, No. 5 2 
 
 Laque Robert, No. 6 2 
 
 Scarlet lake - - - 5 
 
 Crimson lake - - - 5 
 
 Madder red - - - 2 
 
 Madder carmine - - 5 
 
 Madder brown - - 2 
 
 Prussian blue - - - 5 
 
 Indigo 5 
 
 Artificial ultramarine 5 
 
 10 
 9 
 
 10 
 7 
 
 7 
 1 
 
 10 
 
 9'5 
 
 9 
 
 8-5 
 
 8 
 10 
 
 Browner; more translucent. 
 
 None. 
 
 Slightly brownish. 
 
 None. 
 
 Greyish salmon when mixed 
 
 with flake white. 
 Dirty pink when mixed with 
 
 flake white. 
 Lost much yellow. 
 Lost much yellow. 
 Warm grey when mixed 
 
 with flake white. 
 Warm grey when mixed 
 
 with flake white. 
 Dull pinkish red. 
 Almost gone. 
 None. 
 None. 
 
 Rather duller. 
 Slightly greener. 
 Slightly greener. 
 None. 
 
 A series of trials of seventeen madder colours in oil was 
 carried out in 1893. These were all prepared by Lefranc 
 of Paris. The samples were spread on thin lantern glass 
 4 in. x 4 in., and when dry each glass was cut in half. One 
 half was exposed to sunshine from March 26 until 
 October 26, the other half of each specimen being kept in 
 darkness. At the end of the seven months the halves of 
 each sample were rejoined and carefully mounted, and thus 
 an instructive set of slides obtained. The results are given 
 
TRIALS OF OIL-PAINTS 
 
 347 
 
 in the following table, in which I have grouped together 
 those varieties of ' laque de garance ' which resembled one 
 another in their degree of stability : 
 
 Name 
 Laque de garance fonce 
 
 ,, ,, rose intense 
 
 ,, ,, brun rouge 
 
 ,, ,, rouge brun 
 
 Laque de garance rose 
 
 ,, ,, rose dore 
 
 ,, ,, brun pourpre - 
 
 Laque de garance pourpre - 
 
 ,, ,, pourpre concentre 
 
 Carmin de garance 
 Laque de garance brun de madder 
 brun 
 
 brun fonce 
 jaune capucine 
 brunjaune 
 nuance bitume 
 
 -Little or no change. 
 
 -Slight change. 
 
 -Marked change. 
 
 Lost from 40 to 80 per 
 cent, of their original 
 depth. 
 
 In the fourth or least stable group, comprising the varieties 
 of madder brown, it was noticeable that the yellow con- 
 stituent of the colour was most affected by exposure, the 
 brun fonce and the nuance bitume losing all their characteristic 
 beauty of hue and becoming of a dull, poor, rusty tint and 
 not retaining over 20 per cent, of their original depth. Even 
 in Group II. the golden hue of the rose doree was the 
 only chromatic element of this madder paint which had 
 been lost to an appreciable extent during the six months' 
 exposure. 
 
 Experiments as to the degree of stability possessed by 
 many other oil-paints have been made ; the results will be 
 found for the most part incorporated with the accounts given 
 of the several pigments in Part III. One remark may 
 
348 
 
 TRIALS OF OIL-PAINTS 
 
 perhaps be usefully introduced in this place with reference 
 to the differences observable in the quality and behaviour of 
 pigments bearing the same name but obtained from different 
 artists' colourmen. It is a good plan to place side by side 
 on three trial-plates several ' makes ' of the same paint and 
 to keep one set in darkness, and to expose a second set to 
 sunshine and a third set to strong diffused daylight. It will 
 sometimes be found that the fascinating colour-quality which 
 at the first glance recommends one sample is not preserved 
 after exposure, although the reverse experience is not un- 
 common. It must not be forgotten that although the com- 
 position and constituents of the vast majority of pigments, 
 both natural and artificial, are known, yet there are differ- 
 ences in the methods of preparation which, in some cases at 
 least, are kept secret, and which result not in differences of 
 nuance only, but in differences of stability also. 
 
INDEX 
 
 
 Abney, Sir W., 316, 337 
 Acetic acid, 72, 77 
 Acetone, 93 
 Albumen, 72 
 Alcohol, 93 
 Alizarin crimson, 175 
 
 ,, lakes, 176 
 
 ,, orange, 164 
 
 ,, yellow, 164 
 Alterable pigments, 250, 258 
 Alum in paper, 10, 12 
 Alumina, linoleate, 54 
 
 ,, hydrate, 173, 280 
 
 ,, oleate, 54 
 Amber, 56 
 
 ,, oil of, 102 
 
 ,, varnish, 118 
 Amyl alcohol, 95 
 Andrew, Mr. F. W., 328 
 Anime, 60 
 Arabic acid, 79 
 Arnold paper, 9 
 Arrabida red, 182 
 Arsenic, sulphide of, 163 
 Asbestos, 21 
 Asphaltum, 235 
 
 Aureolin, 148 
 Aurora yellow, 142 
 
 Barium hydroxide, 89 
 
 „ chromate, 151 
 
 „ sulphate, 136 
 Baryta-water, 88 
 
 „ white, 136 
 
 „ yellow, 151 
 Bassorin, 80 
 Beeswax, 66 
 Bell's medium, 1 21 
 Benzene, 94 
 Bistre, 234 
 Bitumen, 235 
 Black lead, 245 
 Black pigments, 239 
 Bleu lumiere, 225 
 Blockz, Mr. J., 327 
 Blue black, 243 
 „ pigments, 203 
 „ verditer, 224 
 Borate of lime, 11 1 
 
 „ manganese, 46, 1 10 
 „ zinc, in 
 Brown madder, 174, 177 
 
350 INDEX 
 
 Brown pigments, 227 
 
 Chloroform, 93 
 
 ,, pink, 161 
 
 Chromates, 151, 162, 252, 254 
 
 Burlington Club trials, 343 
 
 Chrome green, 194, 195 
 
 Burnt carmine, 187 
 
 „ yellow, 162 
 
 „ sienna, 231 
 
 Chromium oxide, 192 
 
 „ umber, 229 
 
 Cineol, 106 
 
 
 Cinnabar, 165, 168 
 
 Cadmium, pale, 143, 145 
 
 Citral, 106 
 
 „ red, 144 
 
 Coagulation of albumen, 72 
 
 „ yellow, 142 
 
 Cobalt blue, 210 
 
 Calcium, carbonate, 18, 276 
 
 ,, green, 196 
 
 „ hydrate, 18, 87 
 
 ,, violet, 188 
 
 „ hydroxide, 18, 87 
 
 ,, yellow, 148 
 
 „ oxide, 18 
 
 Cobaltinitrites, 148 
 
 „ silicate, 19 
 
 Cceruleum, 212 
 
 „ sulphate, 22, 24 
 
 Collodion, 35 
 
 Caledonian brown, 231 
 
 Conservation of pictures, 310 
 
 Camphor, 103 
 
 Copal, Angola, 60 
 
 Canada balsam, 66 
 
 ,, Benguela, 64 
 
 Canvas, 32 
 
 i 
 
 oil of, 1 02 
 
 „ preservation of, 34 
 
 j 
 
 oil varnish, 117 
 
 „ priming of, 32 
 
 > 
 
 pebble, 59 
 
 ,, Willesden, 35 
 
 > 
 
 Sierra Leone, 59 
 
 Cappagh brown, 233 
 
 > 
 
 spirit varnish, 115 
 
 Carbon bisulphide, 92 
 
 , 
 
 West Indian, 61 
 
 Carbonate of copper, 199, 224 
 
 > 
 
 Zanzibar, 60 
 
 „ lead, 127 
 
 Copals, comparison of, 64 
 
 „ lime, 18 
 
 Cotton paper, 11 
 
 Carbonates, 252, 254 
 
 Cowdi resin, 61 
 
 Carmine, 185, 330 
 
 Cremnitz white, 130 
 
 Cassel brown, 232 
 
 Crimson lake, 185 
 
 Cellulose, 11 
 
 Cyanine, 216 
 
 Ceresin, 69 
 
 Cymene, 107 
 
 Cerulean blue, cerulium, 212 
 
 
 Chafing varnish, 320 
 
 
 Charcoal black, 243 
 
 Dammar, 61 
 
 Chessylite, 224 
 
 Dextrin, 82 
 
 Chinese ink, 239 
 
 Dextrose, 82 
 
 „ white, 134 
 
 Diluents, 90 
 
INDEX 
 
 351 
 
 Dipentene, 96 
 Dryers, 108 
 
 Eggs, 72 
 
 Elements, 251, 253 
 Elemi, 62 
 Emerald green, 197 
 
 ,, oxide of chromium, 194 
 Emulsions, 74 
 Epichlorhydrin, 95 
 Esparto, 11 
 Ether, 92 
 Eucalyptol, 106 
 Eucalyptus, oils of, 106 
 
 Ferrocyanides, 213 
 Flake white, 127 
 
 ,, action of, 131 
 
 Freeman's white, 133 
 Fresco grounds, 19 
 
 ,, method, 277 
 
 ,, secco, 21, 278 
 Fugitive pigments, 258, 261, 263 
 
 Gambier-Parry's medium, 106, 122 
 
 Gamboge, 152 
 
 Gelatin, 75 
 
 Geraniol, 91 
 
 Glass, protective, 316 
 
 Glue, 75 
 
 Glycerides, 39 
 
 Glycerin, 83 
 
 Graphite, 245 
 
 Green chrome, 192, 194 
 
 „ madder, 259 
 
 ,, oxide of chromium, 192 
 
 „ ultramarine, 207 
 
 ,, verditer, 199 
 Gum arabic, 78 
 
 Gum, British, 82 
 
 „ Senegal, 79 
 
 ,, tragacanth, 80 
 Gypsum, 21 
 
 Hartley, Prof. W. N., 332 
 Hodgkinson paper, 9 
 Hydrate of alumina, 173, 280 
 Hydrates of iron, 180 
 Hydrocarbons, 68, 94 
 Hydrogen peroxide, 16, 32, 132 
 Hydroxides, 87, 252 
 
 Illuminated manuscripts, 205 
 Indian ink, 239 
 
 „ lake, 183 
 
 „ red, 180 
 
 „ yellow, 154 
 Indigo, 217 
 
 Infusorial earth, 23, 278 
 Ink, Indian, 239 
 Intonaco, 20, 22 
 Iron, compounds of, 138, 178 
 Ivory, 16 
 Ivory black, 244 
 
 Kauri, 61 
 
 Kieselguhr, 16, 23, 278 
 
 Kings' yellow, 163 
 
 Lsevulose, 82 
 Lamp-black, 242 
 Lapis-lazuli, 203 
 Laurie, Dr. A. P., 286 
 Lavender, oil of, 105 
 Lead antimoniate, 1 58 
 
 ,, dryers, 108 
 
 „ oxychloride, 134 
 
 „ red, 188 
 
352 
 
 INDEX 
 
 Lead, sugar of, 108 
 i, sulphate, 133 
 „ white, 127, 297 
 Lecithin in egg-yolk, 74 
 Leitch's blue, 216 
 Lefranc's madders, 346 
 Lemon, oil of, 106 
 ,, yellow, 151 
 Light, action of, 261, 310, 316, 342 
 
 „ red, 178 
 Lime, burnt, 18 
 
 „ carbonate, 18, 88 
 „ hydrate, 18, 87 
 „ mild, 18, 24 
 „ putty, 19, 
 ,, slaked, 18 
 ,, sulphate, 22 
 „ water, 87 
 Limonene, 101 
 Linen fibre, 11 
 Linolein, 44 
 Linoxine, 45, 283 
 Linseed, 41 
 
 „ oil, 41 
 Linseed-oil, siccative, 46 
 „ testing, 48 
 
 „ white, 41 
 
 Litmus, 13 
 Lovibond's tintometer, 325, 329 
 
 Madder brown, 174, 177 
 „ lakes, 173 
 „ rose, 177 
 Malachite, 199 
 Manganese, borate, 46, no 
 ,, dryers, 109 
 
 „ oil, 47 
 
 „ violet, 225 
 
 Manuscripts, illuminated, 299 
 
 Marouflage, 25 
 Mars violet, 157 
 
 „ yellow, 142, 157 
 Mastic, 63 
 
 ,, varnish, 113 
 Mediums, 120 
 Megilp, 121 
 Mineral lake, 176 
 
 „ violet, 225 
 Mixed varnishes, 112 
 Mummy, 236 
 
 Naples yellow, 158 
 National Gallery, 300 
 
 ,, ,, British Art, 304 
 
 National Portrait Gallery, 304 
 Newman's colours, 336 
 Nut oil, 50 
 
 Ochre, chrome in, 142 
 ,, red, 182 
 ,, yellow, 139 
 Oil, action of, on paints, 51 
 
 ,, eucalyptus, 106 
 
 ,, extraction of, 40 
 
 ,, in egg-yolk, 74 
 
 ,, in paints, 53 
 
 ,, lemon, 106 
 
 ,, linseed, 41 
 
 ,, manganese, 46 
 
 ,, nut, 50 
 
 ,, orange, 106 
 
 ,. painting, 281 
 
 ,, poppy, 50 
 
 ,, rosemary, 107 
 
 ,, siccative, 46 
 
 ,, turpentine, 96 
 
 ,, varnishes, 112 
 Oils, essential, 105 
 
INDEX 
 
 353 
 
 Oils, fixed, 39 
 
 ,, drying, 40 
 Old pictures, 294 
 Orange, oil of, 107 
 Organic compounds, 252, 255 
 Orpiment, 163 
 O.W. paper, 9 
 Oxides, 251, 253 
 
 Painters' materials, 1 
 Painting methods, 275 
 Panel, 27 
 
 ,, preparation of, 29 
 Paper, 8 
 
 ,, alum in, 10, 12 
 
 ,, analyses of, 9 
 
 ,, ash of, 10 
 
 ,, cotton, 11 
 
 ,, fibre in, 7, 11 
 
 ,, linen, 11 
 
 ,, size in, 10, 15 
 
 ,, testing, 12 
 
 ,, water in, 9 
 
 ,, wood-pulp, 11 
 Paraffin, 67 
 
 ,, -copal medium, 122 
 Pastel method, 291, 293 
 Payne's grey, 248 
 
 Permanent pigments, 258, 261, 262 
 Petroleum spirit, 103 
 Piuri, 154 
 Plaster, 17 
 
 Platinum-point, 135, 293 
 Poppy oil, 50 
 Primrose yellow, 152 
 Prussian blue, 213 
 
 „ brown, 215, 237 
 Purpurin, 172 
 
 Raw sienna, 229 
 ,, umber, 227 
 Realgar, 164 
 Red lead, 188 
 ,, ochre, 182 
 ,, pigments, 165 
 Resin, 55 
 
 ,, amber, 56 
 
 ,, anime, 60 
 
 ,, copal, 59 
 
 ,, cowdi, 61 
 
 ,, dammar, 61 
 
 ,, mastic, 63 
 
 ,, sandarac, 62 
 Restoration of pictures, 319 
 Restricted palettes, 266, 268, 271 
 Reynolds, Sir J., 163, 327 
 Roberson's medium, 121 
 Rood, Professor O. N., 235, 331 
 Rose madder, 173, 177 
 Rosemary, oil of, 107 
 Rosin, 97 
 
 Royal Exchange Paintings, 24 
 Russell, Dr. W. J., 337 
 
 Sandarac, 62 
 
 ,, varnish, 115 
 Scheele's green, 198 
 Schweinfurt green, 197 
 Selected palettes, 265 
 Sepia, 246 
 Sienna, burnt, 231 
 
 ,, raw, 229 
 Silicates, 252, 254 
 
 ,, alkaline, 85, 280 
 Silver-point method, 291 
 Simpson, Mr. W., 335 
 Size, 10, 15, 32 ^4, 
 Slate, 25 
 
 2 3 
 
354 
 
 INDEX 
 
 Slate-grey, 248 
 
 Smalt, 223 
 
 Solvents, 91 
 
 South Kensington Museum, 306 
 )> >) Report, 337 
 
 Spike, oil of, 105 
 
 Spirit-fresco grounds, 23 
 ,, medium, 122 
 
 ,, method, 281, 288 
 
 Starch, 81 
 
 Stereochromy, 22, 280 
 
 Stone, 26 
 
 Straw in paper, II, 13 
 
 Strasburg turpentine, 65 
 
 Sulphides, 251, 253 
 
 Sylvestrene, 96, 101 
 
 Taylor, Mr. J. Scott, viii, 196 
 Tempera-grounds, 21 
 ,, method, 275 
 Terpenes, 97 
 Terre verte, 190 
 
 ,, ,, adulterated, 192 
 Testing-paper, 12 
 
 ,, pigments, 130, 142, et seg 
 Toluene, 95 
 TurnbulFs blue, 214 
 Turpentine, oil of, 96 
 
 ,, Strasburg, 65 
 
 ,, Venice, 65 
 
 Turpentines and balsams, 64 
 
 Ultramarine, 203 
 
 ,, artificial, 206 
 
 ,, ash, 204 
 
 ,, green, 209 
 
 ,, lilac, 209 
 
 ,, red, 209 
 
 ,, testing, 208 
 
 Ultramarine, violet, 209 
 Umber, 227 
 
 Vanadium yellow, 163 
 Varnish, amber, 116 
 
 ,, copal, 115 
 
 ,, mastic, 113 
 
 ,, sandarac, 115 
 Varnishes, 112 
 Vellum, 16 
 Venetian red, 179 
 Venice turpentine, 65 
 Verdigris, 200 
 Verditer, 199, 224 
 Vermilion, 165 
 
 „ tested, 168 
 
 Victoria and Albert Museum, 306 
 Vine black, 243 
 Violet cobalt, 188 
 Viridian, 194 
 Viscose, 13 
 
 Wallace Collection, 306 
 Water, 90 
 
 lime, 87 
 baryta, 88 
 in drawings, 313 
 in paper, 9 
 in resins, 56 
 Water-colour method, 289 
 Water-glass, 85 
 Wax, bees', 66 
 ,, Brazilian, 67 
 ,, ceresin, 69 
 
 ,, Chinese and Japanese, 67 
 ,, painting, 67, 302 
 ,, paraffin, 67 
 Whatman paper, 9 
 White lead, 127 
 

 INDEX 
 
 355 
 
 White lead, action on oil, 52, 131 
 ,, ,, adulteration of, 129 
 ,, ,, defects of, 128, 131 
 ,, ,, impurities in, 128 
 
 White of egg, 72 
 
 White pigments, 127 
 
 Willesden canvas, 35 
 
 Wood, 27 
 „ pulp, 11 
 ,, spirit, 93 
 
 Yellow, cobalt, 148 
 
 Yellow, kings', 163 
 ,, lake, 160 
 ,, madder, 161 
 ,, ochre, 139 
 ,, pigments, 138 
 
 Yolk of egg, 74 
 
 Zinc borate, 1 1 1 
 „ chromate, 152 
 ,, sulphate, III 
 „ sulphide, 136, 137 
 ,, white, 134 
 
 THE END 
 
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