Transcriber’s Notes:
Underscores “_” before and after a word or phrase indicate _italics_
in the original text.
Equal signs “=” before and after a word or phrase indicate =bold=
in the original text.
Small capitals have been converted to SOLID capitals.
Illustrations have been moved so they do not break up paragraphs.
Old or antiquated spellings have been preserved.
Typographical and punctuation errors have been silently corrected.
THE MANUFACTURE OF MINERAL AND LAKE PIGMENTS
THE MANUFACTURE OF
MINERAL AND LAKE PIGMENTS
CONTAINING DIRECTIONS FOR THE MANUFACTURE
OF ALL ARTIFICIAL ARTISTS’ AND PAINTERS’ COLOURS,
ENAMEL COLOURS, SOOT AND METALLIC PIGMENTS
A Text-Book For
Manufacturers, Merchants, Artists and Painters
BY
DR. JOSEF BERSCH
TRANSLATED FROM THE SECOND, REVISED EDITION
BY
ARTHUR C. WRIGHT, M.A. (OXON.), B. SC. (LOND.)
FORMERLY ASSISTANT LECTURER AND DEMONSTRATOR
IN CHEMISTRY AT THE YORKSHIRE COLLEGE, LEEDS
_WITH FORTY-THREE ILLUSTRATIONS IN THE TEXT_
LONDON
SCOTT, GREENWOOD & CO.
Publishers of the “Oil and Colourman’s Journal”
19 LUDGATE HILL, E.C.
1901
[_The sole right of publishing this work
in English rests with the above firm._]
PREFACE.
We know hardly another branch of chemical technology which has made
such remarkable advances of late as the manufacture of colours; a large
number of pigments have been recently discovered, distinguished by
beauty of shade and permanence. Chemists are continually endeavouring
to replace handsome and poisonous colours by others equally handsome
but non-poisonous.
In writing this work I have endeavoured to give it such a character
that it may be a text-book for the practical man, only those methods
have been given which certainly lead to a good result; in the case of
new pigments I have only described methods of preparation which I have
myself found to give good results.
Since it cannot be imagined that any one quite ignorant of chemistry
could successfully manufacture colours (colours being always made by
chemical processes which occasionally are rather complicated), I have,
therefore, presupposed a knowledge of the principles of chemistry. In
the short sketch of the chemical properties of the raw materials used
in making ordinary pigments, the principal properties of the materials
used by the colour maker are given.
In order to make this treatise useful to dealers in and consumers of
colours, the chapters dealing with the examination of pigments have
been so arranged that the nature or adulteration of a pigment can be
determined quickly and with certainty by any one.
Recipes, which originated at a time when empiricism ruled in chemistry,
have been omitted, since they would only detract from the clearness of
the matter.
As far as it is possible I have avoided the “recipe fetish,” and have
endeavoured to make clear to the reader the chemical processes to which
regard must be had in the manufacture of the different pigments. Since
the appearance of the first edition there have been many valuable
innovations in the mineral colour industry, to which regard has been
given in preparing this second edition in so far as they possess a
really practical value.
A critical examination of proposals and formulæ, which are found in
large numbers in the journals, has been avoided, since I wished to
keep for my book that character of a reliable text-book and book of
reference which was ascribed to it in the form of its first edition.
DR. JOSEF BERSCH.
TRANSLATOR’S PREFACE.
If excuse be needed for presenting a translation of Dr. Bersch’s book
at so long an interval after the publication of the original (1893),
it must be sought in the paucity of the English literature on the
subject. It is hoped that the practical nature of the work will make it
acceptable to the English reader.
The subject-matter of the original has been preserved in the
translation without alteration or addition, with the exception of an
unimportant change in the order of arrangement.
The metric system of weights and measures has been used throughout;
for the convenience of those who are not familiar with this system,
directions are given in an appendix for converting into English weights
and measures.
The section on paint grinding (Chapter LXIX.) is perhaps somewhat
incomplete; for a more detailed and modern account of this branch of
the subject the reader is referred to _Practical Paint Grinding_, by
Mr. J. Cruickshank Smith, B. Sc., shortly to be issued by the same
publishers.
A. C. WRIGHT.
HULL, _January, 1901_.
TABLE OF CONTENTS.
PAGE
CHAPTER I. INTRODUCTION 1
CHAPTER II. THE PHYSICO-CHEMICAL BEHAVIOUR OF PIGMENTS 8
CHAPTER III. RAW MATERIALS EMPLOYED IN THE MANUFACTURE
OF PIGMENTS 14
CHAPTER IV. ASSISTANT MATERIALS 16
Water—Chlorine—Ammonia—The Hydrometer—Sal Ammoniac or
Ammonium Chloride—Ammonium Sulphide.
Acids.—Hydrochloric Acid—Sulphuretted Hydrogen
—Sulphuric Acid: Oil of Vitriol, Nordhausen
Sulphuric Acid—Nitric Acid—_Aqua Regia_
—Carbon—Carbonic Acid Gas.
Organic Acids.—Acetic Acid—Oxalic Acid—Tartaric Acid.
CHAPTER V. METALLIC COMPOUNDS 32
Alkalis.—Potassium Compounds—Potassium Carbonate
—Potassium Hydroxide—Potassium Nitrate—Potassium
Bitartrate—Potassium Bichromate—Potassium Sodium
Chromate—Chrome Alum—Potassium Ferrocyanide
—Potassium Ferricyanide—Sodium Salts—Sodium
Carbonate—Sodium Hydroxide—Sodium Thiosulphate
—Sodium Chloride—Salts of the Alkaline Earth Metals.
Calcium Compounds.—Calcium Oxide—Calcium Hydroxide
—Calcium Carbonate—Calcium Sulphate—Calcium Phosphate
—Magnesium Carbonate—Barium Compounds—Barium Chloride.
Aluminium Compounds—Aluminium Sulphate.
The Alums.—Potassium Aluminium Alum—Roman Alum—Soda
Alum—Ammonia Alum—Alumina and Hydrate of Alumina.
Compounds of the Heavy Metals.—Zinc Compounds—Cadmium
Compounds—Iron Compounds—Ferrous Sulphate—Ferrous
Chloride—Manganese Compounds—Nickel Compounds—Cobalt
Compounds—Chromium Compounds—Molybdenum, Tungsten and
Vanadium Compounds—Antimony Compounds—Bismuth Compounds
—Tin Compounds—Arsenic Compounds—Lead Compounds
—Lead Sulphate—Lead Nitrate—Lead Acetate—Basic Lead
Acetate—Lead Chloride—Copper Compounds—Copper Sulphate
—Copper Nitrate—Copper Acetate—Mercury Compounds
—Mercurous Nitrate—Mercuric Nitrate—Mercurous Chloride
—Mercuric Chloride—Silver Compounds—Gold Compounds.
CHAPTER VI. THE MANUFACTURE OF MINERAL PIGMENTS 71
White Mineral Pigments—White Lead.
CHAPTER VII. THE MANUFACTURE OF WHITE LEAD 77
Manufacture of White Lead from Metallic Lead.—Dutch
Process: Casting the Lead into Sheets—Building
up the Stacks—Removal and Grinding of the White
Lead—White Lead Mills—Hard White Lead—Soft White
Lead.—German Process.—French Process: Preparation
of the Solution of Basic Lead Acetate—Preparation
of the Carbonic Acid and Precipitation of the White
Lead—Manufacture of White Lead by Means of Natural
Carbonic Acid.—English Process.—Other Methods.
—Oxychloride White Lead: Lead Sulphite—Lewis
& Bartlett’s White Lead Pigment.—White Lead
-Antimony Pigments: Lead Antimonite—Lead Antimonate.
CHAPTER VIII. ENAMEL WHITE 116
Lithopone.
CHAPTER IX. WASHING APPARATUS 120
Filter Presses.
CHAPTER X. ZINC WHITE 126
Griffith’s Zinc White—Tungsten White—White Antimony
Pigments: Antimony Trioxide—Antimony Oxychloride
—Bismuth White—Tin White—Manganese White
—Magnesia White or Mineral White—Annaline.
CHAPTER XI. YELLOW MINERAL PIGMENTS 133
CHAPTER XII. CHROME YELLOWS 134
Lead Chrome Yellow—Preparation of the Lead Solution
—Precipitation of the Chrome Yellow
—The Pale Chrome Yellows.
CHAPTER XIII. LEAD OXIDE PIGMENTS 143
Red Lead, Minium.
CHAPTER XIV. OTHER YELLOW PIGMENTS 148
Cassel Yellow—Montpellier Yellow—Turner’s Yellow
or English Yellow—Naples Yellow—Antimony Yellow
—Calcium Chrome Yellow—Barium Yellow, Yellow
Ultramarine or Permanent Yellow—Zinc Chrome Yellow
—Cadmium Chrome Yellow—Cadmium Yellow—Lead Iodide
—Mars Yellow—Siderin Yellow—Aureolin—Tungsten
Yellow—Nickel Yellow—Mercury Yellow or Turpeth
Mineral—Yellow Arsenic Pigments—Lead Arsenite
—Thallium Pigments.
CHAPTER XV. MOSAIC GOLD 160
Chrysean.
CHAPTER XVI. RED MINERAL PIGMENTS 163
Vermilion—Black Mercuric Sulphide—Red Mercuric Sulphide.
CHAPTER XVII. THE MANUFACTURE OF VERMILION 166
Dry Method: Chinese Vermilion.—Wet Method:
Firmenich’s Method—Liebig’s Process—Infusible
White Precipitate—Electrolytic Process
—Mercuric Iodide.
CHAPTER XVIII. ANTIMONY VERMILION 178
Appendix—Antimony Blue.
CHAPTER XIX. FERRIC OXIDE PIGMENTS 180
Vogel’s Iron Red—Macay’s English Red—Indian Red.
CHAPTER XX. OTHER RED MINERAL PIGMENTS 186
Chrome Red or Chrome Vermilion—Cobalt Red—Cobalt
Magnesia Red—Cobalt Arsenate—Chromium Stannate
—Silver Chromate.
CHAPTER XXI. PURPLE OF CASSIUS 190
Magnesia Gold Purple—Alumina Gold Purple.
CHAPTER XXII. BLUE MINERAL PIGMENTS—IRON-CYANOGEN PIGMENTS 194
Chinese Blue—Prussian Blue—Mineral Blue—Soluble
Prussian Blue—Special Processes for the
Manufacture of Chinese Blue—Turnbull’s Blue
—Antwerp Blue.
CHAPTER XXIII. ULTRAMARINE 204
CHAPTER XXIV. THE MANUFACTURE OF ULTRAMARINE 211
Preparation of Mixtures for Ultramarine—Ultramarine
Violet—Chlorine and Steam Process—Hydrochloric
Acid and Air Process—Ammonium Chloride Process
—Pale Blue Ultramarine—Ultramarine Red.
CHAPTER XXV. BLUE COPPER PIGMENTS 226
Bremen Blue and Green—Neuberg Blue—Lime Blue
—Payen’s Mountain Blue—Oil Blue—Copper Hydroxide.
CHAPTER XXVI. BLUE COBALT PIGMENTS 230
Cobalt Blue, Thénard’s Blue, Cobalt Ultramarine,
King’s Blue, Leyden Blue—Cæruleum—Cobalt
Zinc Phosphate.
CHAPTER XXVII. SMALTS 233
Preparation of the Charge—Fusion of the Charge
—Grinding the Fused Mass—Tungsten Blue
—Tessié du Motay’s Blue—Molybdenum Blue.
CHAPTER XXVIII. GREEN MINERAL PIGMENTS—GREEN COPPER PIGMENTS 240
Green Copper Pigments: Copper Carbonate—Copper Arsenite
—Scheele’s Green—Swedish Green—Brunswick Green
—Green Verditer—Neuwied Green—Copper Oxychloride.
CHAPTER XXIX. EMERALD GREEN 244
Manufacture of Emerald Green from Verdigris—Manufacture
of Emerald Green from Copper Sulphate—Mitis
Green or Vienna Green—Copper Stannate—Kuhlmann’s
Green—Elsner’s Green—Casselmann’s Green—Lime
Green—Patent Green—Copper Borate—Copper Silicate
(Egyptian Blue).
CHAPTER XXX. VERDIGRIS 252
Blue Verdigris—Distilled or Crystallised Verdigris
—German Verdigris.
CHAPTER XXXI. CHROMIUM OXIDE 260
Chrome Green.
CHAPTER XXXII. OTHER GREEN CHROMIUM PIGMENTS 264
Guignet’s Green—Emerald Green—Chrome Green Lake
—Turkish Green—Leaf Green.—Chromium Phosphate
Pigments: Arnaudan’s Green—Plessy’s Green
—Schnitzer’s Green—Chromaventurine—Chrome
Blue (Garnier).
CHAPTER XXXIII. GREEN COBALT PIGMENTS 268
Cobalt Green.
CHAPTER XXXIV. GREEN MANGANESE PIGMENTS 270
Manganese Green—Rosenstiehl’s Green—Böttger’s Barium
Green—Manganous Oxide—Manganese Blue.
CHAPTER XXXV. COMPOUNDED GREEN PIGMENTS 273
Chrome Green—Elsner’s Chrome Green—Silk Green
—Natural Green—Non-arsenical Green.
CHAPTER XXXVI. VIOLET MINERAL PIGMENTS 276
Chromic Chloride—Manganese Violet—Tin Violet,
Mineral Lake—Copper Violet, Guyard’s Violet.
CHAPTER XXXVII. BROWN MINERAL PIGMENTS 279
Lead Brown—Manganese Brown—Pyrolusite Brown
—Prussian Brown—Iron Brown—Copper Brown
—Chrome Brown—Cobalt Brown.
CHAPTER XXXVIII. BROWN DECOMPOSITION PRODUCTS 283
Humins—Bistre.
CHAPTER XXXIX. BLACK PIGMENTS 285
Charcoal Blacks: True Charcoal Black—Vine Black
—Vine Black from Wine Lees—Vine Black from
Pressed Grapes—Bone Black or Ivory Black.
CHAPTER XL. MANUFACTURE OF SOOT PIGMENTS 294
The Manufacture of Soot Blacks on the Large Scale.
CHAPTER XLI. MANUFACTURE OF LAMP BLACK 307
Calcination of the Soot—Pine Black.
CHAPTER XLII. THE MANUFACTURE OF SOOT BLACK WITHOUT CHAMBERS 313
CHAPTER XLIII. INDIAN INK 316
Neutral Tint Black—Appendix: Black Mineral Pigments
—Chrome Copper Black—Chrome Black.
CHAPTER XLIV. ENAMEL COLOURS 319
White Enamels—Coloured Enamels: Yellow Enamels—Red
Enamel—Blue Enamels—Green Enamel—Violet Enamel
—Black Enamel.
CHAPTER XLV. METALLIC PIGMENTS 326
Shell-Gold—Shell-Silver—Imitation Silver.
CHAPTER XLVI. BRONZE PIGMENTS 329
Electrolytic Copper Bronze—Tungsten Bronze Pigments.
CHAPTER XLVII. VEGETABLE BRONZE PIGMENTS 339
Appendix: The Brocade Pigments.
PIGMENTS OF ORGANIC ORIGIN.
CHAPTER XLVIII. LAKES 343
CHAPTER XLIX. YELLOW LAKES 348
Dutch Pink—Weld Lake—Gamboge Lake—Prepared
Gamboge—Fustic Lake—Quercitron Lake—Purree
or Indian Yellow—The Colouring Matter of
Saffron—Colouring Matter of Gardinia Grandiflora.
CHAPTER L. RED LAKES 354
Cochineal and Carmine
CHAPTER LI. THE MANUFACTURE OF CARMINE 357
Cenette’s Method—Munich, Vienna, Paris or Florentine
Lake—Ammonia-Cochineal.
CHAPTER LII. THE COLOURING MATTER OF LAC 363
Lac Dye.
CHAPTER LIII. SAFFLOWER OR CARTHAMINE RED 366
Safflower Carmine—Alkanet.
CHAPTER LIV. MADDER AND ITS COLOURING MATTERS 370
Garancin—Garanceux—Madder Extract—The Constituents
of Madder.
CHAPTER LV. MADDER LAKES 375
Madder Carmine.
CHAPTER LVI. MANJIT (INDIAN MADDER) 378
Chica Red, Curucuru, Carajuru—Bigonia Chica.
CHAPTER LVII. LICHEN COLOURING MATTERS 380
Archil—French Purple—Cudbear—Litmus.
CHAPTER LVIII. RED WOOD LAKES 384
CHAPTER LIX. THE COLOURING MATTERS OF SANDALWOOD
AND OTHER DYE-WOODS 388
CHAPTER LX. BLUE LAKES 390
Indigo—The Constituents of Indigo.
CHAPTER LXI. INDIGO CARMINE 394
Indigo Mills—Blue Lake.
CHAPTER LXII. THE COLOURING MATTER OF LOGWOOD 398
Logwood Extract—Kohlrausch’s Process for Obtaining
Concentrated Extracts of Colouring Matters
and Tannins.
CHAPTER LXIII. GREEN LAKES 409
Chlorophyll—Sap Green—Chinese Green, Lokao
—Charvin’s Green.
CHAPTER LXIV. BROWN ORGANIC PIGMENTS 414
Asphaltum—Sepia.
CHAPTER LXV. SAP COLOURS 416
CHAPTER LXVI. WATER COLOURS 419
Moist Water Colours.
CHAPTER LXVII. CRAYONS 423
Crayons for Earthenware.
CHAPTER LXVIII. CONFECTIONERY COLOURS 427
CHAPTER LXIX. THE PREPARATION OF PIGMENTS FOR PAINTING 429
Paint Mills.
CHAPTER LXX. THE EXAMINATION OP PIGMENTS 434
Mineral Pigments—Examination with the Blowpipe
—Reactions of the White Pigments—Reactions
of the Yellow Pigments—Reactions of the Red
Pigments—Reactions of the Blue Pigments
—Reactions of the Green Pigments—Reactions
of the Brown Pigments—Reactions of the Black
Pigments.
CHAPTER LXXI. EXAMINATION OF LAKES 445
Reactions of the Organic Colouring Matters.
CHAPTER LXXII. THE TESTING OF DYE-WOODS 449
The Colorimeter.
CHAPTER LXXIII. THE DESIGN OF A COLOUR WORKS 457
CHAPTER LXXIV. COMMERCIAL NAMES OF PIGMENTS 460
APPENDIX.
THE CONVERSION OF METRIC INTO ENGLISH WEIGHTS AND MEASURES
—CENTIGRADE AND FAHRENHEIT THERMOMETER SCALES 469
INDEX.
CHAPTER I.
INTRODUCTION.
It is doubtful whether another branch of applied chemistry is recorded
of so great an age as the colour industry; at the present time there
is hardly a race on the face of the earth which does not make use of
colours in some form, either for the decoration of their persons or
surroundings. The art of preparing colours is as ancient as their
use. It is true that we find from the most remote historical records
that the so-called earth colours were almost solely employed, and
principally those which exist ready formed in nature. But these natural
colours also require their particular process of preparation before
they fulfil their object, even though this be merely a mechanical
operation, such as powdering or levigating. That the oldest nations of
whom we possess lasting records, either written or otherwise, really
understood the preparation of colours by chemical processes is shown
by the common occurrence in the Egyptian mural pictures of figures
clad in brightly coloured garments, a proof that the Egyptians not
only understood the science of colour manufacturing, but also the more
advanced art of fastening colours upon fabrics—dyeing.
The writings of the ancient Greeks, and in part also the scanty remains
of their buildings, prove to us completely that they understood the
use of colours to such an advanced degree that they already employed
them for pictures as works of art. That the Greeks were also acquainted
with the preparation of colours and dyeing follows from various
passages from the classical writers, in which magnificently decorated
rooms and beautifully coloured garments are often described.
Among the Romans, who were the pupils of the Greeks in the arts and
manufactures, the prodigal luxury which existed in Rome, especially
under the emperors, caused a great demand for colours, which were used
in the most profuse manner for the decoration of house and attire. The
Roman colour makers had advanced so far in their art that they could
colour the human hair rose-red.
A glance at East Indian fabrics and pictures, or at the ancient Chinese
buildings, whose colouring is a matter of marvel to-day, shows that
the Oriental were not behind the Western nations in the discovery of
colours and the art of manufacturing them.
In so old an industry it is not remarkable that great changes have
taken place in the course of time. The thousands and thousands of
experiments made by the alchemists in the attempt to prepare gold
failed in their main object, but the tremendous expenditure of time and
trouble in this work was not fruitless; upon the great mass of chemical
facts discovered by the alchemists were laid the foundations of
scientific chemistry. We find on reading the writings of the alchemists
that the colour industry is indebted to them for an immense number of
its products; the reason being that the alchemists worked by preference
on metals, earths and mineral compounds, and from these substances a
large number of colours are obtainable, of which many are still in use
to-day, and, on account of their cheapness, will continue in use.
The period in which the painters were also the colour makers lies not
far behind us. The preparation of many a colour of particular beauty
was treated by the fortunate owner of the recipe as a great secret. It
was sold by him at a great price. What a difference between that time
and the present! There is now no painter among civilised races to whom
it would occur to prepare his own colours; the chemical works provide
them for him at a low price and in such a condition that they can be
immediately used for painting. The Italian painters prepared the highly
prized blue pigment, ultramarine, by laborious toil from the costly
_lapis lazuli_; to-day, this same colour, more beautiful and deeper
in hue, is made by several works, and sold at a price which bears no
comparison with that of the colour obtained from the mineral. The
latter was worth many times its weight in gold: a pound of the finest
ultramarine can now be bought for a shilling or two.
We find a similar comparison in the case of the fine scarlet pigment
known as vermilion: formerly the natural vermilion, cinnabar, was
sold at a very high price; at the present time the finest vermilion,
prepared artificially, can be bought at a low rate. It is no longer
necessary for any one to use natural Chinese vermilion as an artists’
colour.
Whilst formerly mineral colours were used in great preponderance, we
now know a great number of vegetable and animal colouring matters. The
discovery of the sea route to India and the discovery of America had an
important influence in this development. From these countries, as from
other tropical lands, come the majority of the plants which contain
colouring matters. The attempt to change these colouring matters into
insoluble compounds led to the discovery of the lake pigments.
With the advance of chemical knowledge the number of colours grew
apace; _e.g._, the discovery of chromium was of great importance
to the colour industry: it presented us with a large number of new
colours. To a more limited extent, the discovery and study of uranium,
molybdenum and other metals were the occasions for the invention of new
colours.
In more recent times, efforts in the colour industry have been
especially directed to making colours more permanent and, at the same
time, harmless. In the first respect, the position at present leaves
much to be desired; but, as regards the second property, great advances
have been made. The colours in use in former days were almost all very
poisonous compounds; the greater number were derived from lead, copper,
mercury or arsenic. More recently these poisonous substances have
been in many cases replaced by innocuous materials, so that among the
colours now in use, though the list is much more comprehensive than of
old, there are but few poisonous to a high degree.
In all civilised states the use of poisonous colours has been much
restricted by law, and in those cases in which an article is to be
manufactured for use as food the employment of such colouring matters
has been absolutely forbidden. For example, in Germany by the law
of 5th July, 1887, concerning the use of dangerous colours in the
preparation of foods and condiments, the application of the permissible
colours has been exactly defined.
During the last decades the colour industry and, still more, dyeing
have undergone a complete change. The momentous discoveries which have
been made in these departments leave far behind the advances which have
been made in other branches of chemical technology, the manufacture
of explosives, perhaps, excepted. We allude here to the beautiful
colours which have been made from coal-tar, colours which far surpass
in beauty all hitherto known, and which we can already prepare in
every shade and hue. Unfortunately, we can only employ the coal-tar
colours, as such, in a restricted measure among the pigments; they
are of more importance in dyeing. We use the term pigments here in
the narrow sense of such substances which, when spread out on certain
materials, provoke a certain sensation of colour. Dyeing is, on the
contrary, that branch of colour chemistry which generally has for its
object the simultaneous production of the colour and its fixation upon
a fabric. This definition was at least applicable to the majority of
the colours which were in use before the discovery of the coal-tar
colours and their introduction into the industry. Since, however,
the latter have acquired so great a preponderance in dyeing, it is
no longer applicable, for the dyers use at present a large number of
substances which are included in the narrow definition of pigments. The
greater part of the coal-tar colours are substances which, in solution,
when brought in contact with a fabric, adhere to it and colour it
permanently.
According to their use and preparation, pigments are divided into a
number of classes, and one speaks of painters’, artists’, enamel,
porcelain and glass colours, also of oil, honey, water and cake
colours. Although this division is important for trade purposes, it
is of little moment for the colour maker, for he can prepare the same
colour for both purposes, either for oil or water colour. What is of
the greatest interest for the colour maker is the preparation of the
pigment itself. The conversion of the prepared pigment into (oil or
water) paint is unaccompanied by difficulties.
When we look for a practical classification for pigments, we find that
there are colours which exist ready formed in nature, and others which
can only be obtained by certain chemical processes, at times very
complicated.
As regards the first group of pigments—those which exist ready formed
in nature—the processes which they undergo at the hands of the colour
maker are almost entirely mechanical treatments—grinding, sieving,
levigating and similar operations—in order to convert them into such
a condition that they can be used for painting. Since a large number
of these pigments belong to that class of minerals which mineralogists
call earths, these pigments have also been designated earth pigments,
a term which we shall retain on account of its general use, although
it is incorrect, since many of the so-called earth pigments are not
obtained from “earths” in the mineralogical sense.
Among the pigments which are prepared by human skill many divisions can
be drawn. A large number of pigments are prepared from mineral sources;
an equally important number are derived from the animal and vegetable
kingdom, the latter consisting of combinations of organic materials
with certain inorganic substances. Some few pigments (putting aside the
coal-tar colours) are simply organic products, as, for example, the
majority of the black pigments, which consist of carbon.
The following classification is drawn up on the lines indicated above:—
1. _Natural Colours or Earth Pigments._—Found ready formed in nature
and requiring only mechanical preparation to be usable. A large number
of handsome and also cheap colours belong to this class.
2. _Artificially Prepared Mineral Pigments._—Obtained by certain
chemical processes, and, according to their composition, either
compounds of metals with sulphur, oxygen, iodine, cyanogen, etc., or of
oxides with acids, i.e., salts.
3. _Lakes._—Compounds of colouring matters from the animal or vegetable
kingdom with a mineral substance, such as lead oxide or alumina.
As a fourth group we might take those colours which do not fall into
the previous classes, as, for example, the black pigments composed of
carbon; but since this division is not made in practice we shall not
regard this species of pigment as a particular group, but shall discuss
them in the proper place.
As an entirely new group of colours are to be classed those which are
generally called coal-tar colours. These colours, which, at present,
are the most important in dyeing and calico printing, are prepared from
so-called organic compounds (more properly, carbon compounds). The
manufacture of these colours is a separate branch of chemical industry.