Transcriber’s Note
Italic text is enclosed in _underscores_; subscripts are enclosed in
{curly brackets}. Additional notes will be found near the end of this
ebook.
THE MANUFACTURE OF
EARTH COLOURS
THE
MANUFACTURE OF
EARTH COLOURS
BY
DR. JOSEF BERSCH
TRANSLATED FROM THE THIRD GERMAN EDITION (AS
REVISED BY PROF. DR. WILHELM BERSCH)
BY
CHARLES SALTER
_WITH THIRTY-ONE ILLUSTRATIONS_
LONDON
SCOTT, GREENWOOD & SON
8 BROADWAY, LUDGATE, E.C.4
1921
[_The sole rights of translation in English remain with
Scott, Greenwood & Son._]
PRINTED IN GREAT BRITAIN BY
RICHARD CLAY & SONS, LIMITED,
PARIS GARDEN, STAMFORD ST., S.E. 1,
AND BUNGAY, SUFFOLK.
PREFACE
Originally issued as a volume of the series on pigments and colouring
matters by the present author’s father, the necessity for a new edition
afforded a welcome opportunity of revising “_Earth Colours_.” Although,
in the nature of things, little progress has been made in this subject
itself, there was a good deal to add in connection with the mechanical
appliances for treating the colour earths and manufacturing them into
pigments. In other respects, too, the work has been carefully gone
through and brought up to date, with new and additional illustrations.
The author desires to express his thanks to the various firms who
have afforded him assistance in his task by furnishing illustrations
and descriptions of new machinery, together with other information.
It is hoped that this third edition will meet the approval of those
interested in the subject; and the author will be glad to receive
supplementary information to render the work more complete in the event
of a future edition being found advisable.
PROF. DR. WILHELM BERSCH.
1918.
CONTENTS
CHAPTER I
PAGE
INTRODUCTORY 1
CHAPTER II
THE RAW MATERIALS FOR EARTH COLOURS 8
(A) White Raw Materials and Pigmentary Earths 11
Limestone (Calcite, Limestone, Chalk) 11
Gypsum (Alabaster) 18
Barytes, or Heavy Spar 19
Talc, Soapstone, Steatite 20
Clay 21
(B) Yellow Earths 23
Brown Ironstone 23
Ochre 25
Yellow Earth 26
Terra di Siena 27
(C) The Red Earths 27
Red Ironstone 28
Bole 31
Alum Sludge 32
Mine Sludge 32
(D) Blue Earths 33
Azurite, or Ultramarine 33
Vivianite 33
(E) Green Earth Pigments 34
Green Earth 34
Malachite 35
(F) Brown Earth Pigments 36
Umber 36
Asphaltum 37
(G) Black Earth 38
Black Schist 38
Graphite 38
CHAPTER III
THE PREPARATION OF THE COLOUR EARTHS 40
Crushing Machinery 43
Crushing and Sifting 77
Calcining 81
Mixing and Improving 81
Moulding 85
CHAPTER IV
WHITE EARTH COLOURS 87
Caustic Lime 87
Pearl White 94
Vienna White 95
Chalk 98
Precipitated Chalk 107
Calcareous Marl 110
Gypsum 111
Kaolin, Pipeclay 112
Barytes, or Heavy Spar 119
Carbonate of Magnesia 123
Talc 124
Steatite or Soapstone 125
CHAPTER V
YELLOW EARTH COLOURS 127
The Ochres 128
Calcining (Burning) Ochre 132
Ochres from Various Deposits 136
Artificial Ochres 138
Ochres as By-products 146
CHAPTER VI
RED EARTH COLOURS 151
Bole 152
Native Ferric Oxide as a Pigment 154
Iron Glance 154
Hematite 155
Raddle 155
Burnt Ferric Oxide and Ochres 158
(_a_) Burning in the Muffle 158
(_b_) Caput Mortuum, Colcothar 160
(_c_) Calcining Ferric Oxide 161
Ferric Oxide Pigments from Alum Sludge 164
CHAPTER VII
BROWN EARTH COLOURS 168
Terra di Siena 168
True Umber 170
Cologne Earth (Cologne Umber) 173
Asphaltum Brown (Bitumen) 174
CHAPTER VIII
GREEN EARTH COLOURS 176
Green Earth, or Celadon Green 176
Artificial Green Earth (Green Ochre) 180
Malachite Green 181
CHAPTER IX
BLUE EARTH COLOURS 183
Malachite Blue (Lazulite) 183
Vivianite or Blue Ochre 184
CHAPTER X
BLACK EARTH COLOURS 185
Graphite 185
Black Chalk 194
CHAPTER XI
THE COMMERCIAL NOMENCLATURE OF THE EARTH COLOURS 197
White Earth Colours 198
Yellow Earth Colours 200
Red Earth Colours 200
Brown Earth Colours 200
Green Earth Colours 201
Blue Earth Colours 202
Grey Earth Colours 202
Black Earth Colours 202
INDEX 203
EARTH COLOURS
CHAPTER I
INTRODUCTORY
Both from the chemical and practical standpoint it is necessary
to divide pigments into clearly defined groups, the following
classification being adopted on the basis and natural history of the
substances concerned:--
(1) Pigments occurring native in a finished condition, and only
requiring mechanical preparation to fit them for use as painters’
colours. (2) Pigments which are not ready formed in Nature, but
contain some metallic compound as pigmentary material, which requires
certain chemical treatment for its full development. (3) Pigments
which, in contrast to these two groups, contain only organic, and no
inorganic, constituents. This last class comprises all the natural
vegetable pigments, together with the large group of colours obtained
artificially from tar products, fresh groups of which are being
continually introduced. Nowadays, there is no longer any strict line
of demarcation between the natural and artificial organic colouring
matters, it being possible to produce even those of the vegetable
series, such as madder and indigo, by artificial means.
Whilst this group of colours exhibits the greatest variety, and is
constantly being enriched and increased by the progress of colour
chemistry, the case is different with the first group, the natural
earth pigments. Here we have chiefly to do with the preparation of
materials occurring in Nature, or with bringing about certain chemical
results, so that, consequently, the range of variety is far more
restricted, and there is little or no possibility of increasing the
number of these colours by the manufacture of really new products.
The earth colours nevertheless have a high technical and economic
importance, on account of their extremely valuable properties, coupled,
for the most part, with low cost.
If the term “earth colours” were strictly adhered to, the present work
would have to be confined to a description of the physical and chemical
properties of the various pigments, and of the various means by which
they can be brought into suitable condition for use in paints.
However, of late, the term has found wider application than formerly,
since it has been found practicable to modify (shade) certain of the
earth colours by simple operations, and thus considerably increase
the range of tones of the substances known as earth colours. The
progress of chemical industry has also largely increased the number
of the so-called earth colours, certain methods of chemical treatment
having enabled substances that are of little use for other purposes,
to be employed, in large quantities, as pigments. The application of
these--usually cheap--by-products is still further facilitated by the
fact that they can be transformed, by a simple chemical treatment, into
pigments which are distinguished by their beauty of colour and at the
same time possess the great advantages of durability and cheapness.
As an example of this, mention may be made of iron oxide, which occurs
in Nature in the form of various minerals which can be made into
pigments by mechanical treatment. In many cases, this treatment has
already been carried out by Nature, and deposits of iron oxide are
found in which the material has only to be incorporated with a vehicle
to make it fit for immediate use as a painters’ colour.
Moreover, the same oxide is obtained, in large quantities, as a
by-product of the treatment of other minerals. From the point of view
of chemical composition, this by-product is of very low value, by
reason of the large supplies of native oxide available. By means of
a very simple chemical treatment, however, this by-product oxide can
be considerably improved in commercial value, being, in many cases,
convertible, by merely heating it to certain temperatures, into a
variety of colours which sell at remunerative prices.
Consequently, in view of the present condition of the chemical
industry, the term “earth colours” can be enlarged to include a number
of waste products which fetch good prices as colours, though otherwise
practically valueless in themselves.
The number of earth pigments is very large, and comprises
representatives of all the principal colours. For painting purposes,
few pigments beyond the earth colours were known to the ancients;
and most of the colours in the paintings which have come down to us
from antiquity are pure earth pigments, thus affording proof of their
great durability, having retained their freshness unimpaired for
hundreds--and some for thousands--of years.
The earth colours might be divided into such as occur ready-formed
in Nature, and require only mechanical preparation, and which either
require special treatment (_e. g._ calcining), or are artificial
products (like the iron oxide mentioned above). Since, however, such
a classification would not advantage our knowledge of the nature of
this class of colours, it appears useless and superfluous, and we will
therefore simply confine ourselves to arranging the earth pigments
according to their colour--white, yellow, red, etc.
Adopting this classification, the following minerals and chemical
products may be considered as earth colours:--
_White._--These include the varieties of calcium carbonate, such as
chalk, marble, precipitated chalk, calcium phosphate, calcium sulphate
(in the form of gypsum, alabaster, muriacite and the precipitated
gypsum produced as a by-product in many chemical works), heavy spar,
the different varieties of clay, and magnesia.
_Yellow._--This group comprises ferric hydroxide (hydrated oxide of
iron) in the form of the various minerals known as ochre; all the
preparations chiefly composed of this hydroxide, and all those prepared
by artificial means. A very important member of this group is orpiment;
the other arsenical compounds frequently met with native, being
however, on account of their poisonous properties, no longer used as
pigments.
_Red._--Chief among the red earth colours are those consisting of
ferric oxide (iron oxide), under various names. The only other member
of the group is the far rarer vermilion.
_Blue._--The blue earth colours are few in number and of no particular
beauty; but they are of importance on account of their cheapness and
because all the artificial blue pigments are rather expensive. Two
products in particular merit attention in this connection, namely,
ultramarine, and the mineral known as blue ochre or blue ironstone.
The latter, as a matter of fact, cannot be used for anything else
than a painters’ colour, and can be obtained at a low price; whereas
ultramarine also forms a valuable raw material for the recovery of
copper, and is therefore dearer.
_Green._--This group, again, contains only two members, viz. malachite
green (chrysocolla), and the green earths (seladonite), known as
Verona, etc., green. These occur fairly often in Nature, and the green
earths in particular find a wide industrial application by reason
of their low price. Malachite green is very similar, in chemical
constitution, to ultramarine; and both form sources of copper and are
consequently expensive.
It should be mentioned that both ultramarine and malachite green
can only be profitably made into pigments where the minerals can
be obtained cheaply, since both of them can be manufactured where
artificial pigments are produced, and are put on the market under the
same names as the native articles. The very low price of the green
earths makes them highly popular as colouring matters in certain
branches of industry, and they are very largely used by wall-paper
manufacturers.
_Brown._--This is a large group, and the pigments composing it are
specially distinguished for their beauty and depth of colour, on
which account they are used in the finest paintings. Here, again,
it is ferric oxide, in combination with water--and therefore ferric
hydroxide--that furnishes a large number of the members of the group.
Like the renowned Siena earth, the artists’ colours known as Vandyck
brown, bole, Lemnos earth, umber, etc., mainly consist of more or
less pure ferric hydroxide. These minerals are, moreover, specially
important to the colour manufacturer, inasmuch as most of them enable a
large number of different shades to be obtained by a simple method of
treatment consisting merely of the application of heat in a suitable
manner; and these colours are among the most excellent we possess, by
reason of their beauty and permanence. Amongst this series must also be
classed native manganese brown, which chiefly consists of a mixture of
manganese oxide and the hydrated peroxide of the same metal.
_Black._--There is really only one member of this class, which,
however, is frequently used, viz. that form of carbon occurring as
hexagonal crystals and known as graphite. Another natural black natural
product, occasionally used as a painters’ colour is the so-called black
chalk. However, since black pigments can be produced very cheaply by
artificial means, the natural colours find only a limited application;
and only in one instance is graphite used alone, viz. for making
blacklead pencils.
As already mentioned, certain chemical industries furnish by-products
which are of very little value in themselves, and many of them, indeed,
may be classed as worthless, since chemical manufacturers naturally
endeavour to get everything possible out of their materials in the
course of manufacture.
Some of these by-products, however, can advantageously be used as
pigments, a good example of this being afforded by the iron oxide
formed as a by-product in the manufacture of fuming sulphuric acid
(Nordhausen oil of vitriol), by the old process, from green vitriol
(ferrous sulphate). In itself, this oxide is practically valueless,
but, by very simple treatment, it can be converted into very valuable
pigments which have a market value far in excess of the original
material. Although it has hitherto been the custom to confine the term
earth colours to such as occur ready-formed in Nature and only require
simple mechanical treatment to make them ready for immediate use as
pigments, the author is nevertheless of opinion that a book dealing
exhaustively with earth colours should also make some mention of all
the mineral colouring matters which can be easily made into pigments
by simple processes, such as calcination or bringing into association
with other substances. In accordance with this view, the present work
will describe all the pigments that are obtainable in this manner.
Most of the earth colours consist of decomposition products of certain
minerals; and this applies particularly to such of them as contain
iron oxide. According as the decomposition of the original mineral has
been more or less extensive, the natural product exhibits different
properties; and the manufacturer must consequently endeavour to treat
them in such a manner as to ensure that the pigment obtained will be
as uniform as possible in shade and permanence. In order to accomplish
this it is essential to have an accurate knowledge of the origin of
the raw material under treatment, and of its chemical and physical
properties. In view of this, the author considers it necessary to deal
more fully with the pigmentary earths forming the raw materials of the
earth colours, before passing on to the preparation of the colours
themselves.