We borrow from M. Lacroix his classification of colors, which is very
practical with regard to their employment in painting:
“CLASSIFICATION OF COLORS WITH RESPECT TO IRON.—Iron plays an important
part in the composition of a great many enamel colors; for this reason I
have taken it as a standard for my classification of colors into three
groups.
“FIRST GROUP.—Colors that do not contain any iron: First, the white;
secondly, the blues; thirdly, the colors from gold.
“A horn or ivory knife is preferable for the use of colors of this
group.
“A glass muller is still better than knives.
“SECOND GROUP.—Colors with but little trace of iron. This group includes
the yellows and greens, several of which colors contain iron in small
quantities.
“Third Group.—Colors with an iron basis, or of which iron is one of the
coloring parts: First, the reds, fleshes, red browns, and violets of
iron; secondly, the browns, yellow browns, ochres, blacks and a greater
part of the greys.”
The enamel colors usually designated by the name of iron colors are: All
the browns; the greys, excepting platina grey; the blacks, minus iridium
black; the ochres; the reds, and the violets of iron.
The enamel colors said to be with a golden basis are: The carmines;
crimson lake; the purples, and the violets of gold.
TESTS.—The amount of flux added to the coloring oxides for the
manufacture of enamel colors varies according to the color; this
difference, joined to the diversity of the chemical elements, causes
actions in the firing which may modify certain colors and even make them
disappear entirely; it is said expressively that they have been _eaten
up, devoured_ by the fire. We shall cite, as an example, the mixture of
ivory yellow with carmine, as one of those which decompose in the
firing. Other causes act likewise on enamel colors during firing; the
intensity, more or less great, of the heat, the thickness, and the
amount of oil in the color, the way it is used, etc.
In order to well understand the various influences, and to secure
yourself against accidents, you must be continually making tests of the
mixtures _yourself_; it is the only way to paint with safety.
It is indispensable for the test to be double, that is, on two small
bits of precisely the same manufacture of china as the piece you wish to
paint. The same mixture is made on both small pieces, they are both
dried, and one only is fired in order to be able to judge what change is
caused by the firing, by comparing it with the unfired test you have
kept by you. Besides, you will be able to make sure of a satisfactory
result by comparing your experiments with the test tiles and plates of
fired colors.
Mixed colors should be stirred with the brush when used; without this
precaution they would separate; light blue would rise on dark blue,
yellow on green, ivory yellow on carnation.
Some hints follow which it will be advantageous to verify and to carry
out by tests. They apply generally to painting on porcelain or
earthenware for the ordinary muffle.
FUSIBILITY. Hard colors (those which require the greatest heat to make
them fuse) spoil and often destroy those of a softer flux (that fuse
more easily). The flux added by the manufacturer to the coloring oxide
lightens the tint of the color; dark colors are therefore generally
harder than light ones. In the palette of M. Lacroix the colors more
fusible than the rest, although taking the same time to fire, are light
sky-blue, light carmine A, pearl grey, warm or russet grey, and ivory
yellow, all light colors.
THICKNESS. The tint of enamel colors get darker when you increase their
thickness. But you must beware of doing it too much. Light and fusible
colors used too thick, blister in firing; it is prudent to give them
only a medium thickness.
You should apply in drops those colors only that are specially designed
for the purpose; permanent white, permanent yellow, and relief. They
hold on earthenware, but their use on porcelain is liable to failure.
MEDIUMS. Experience will prove that if too much oil of turpentine is
added to the colors used, which is called adding “fat,” they will craze
in the firing. Make some trials by exaggerating this fault. You will
remark nevertheless that colors applied very thin, although with much
“fat,” do not craze. The cracks caused in the firing, by the action of
the resinous part of the oil, which evaporates and causes the white of
the enamel to reappear, is called crazing.
CONDUCT OF THE WORK. It is very important in the first painting to use
the most fusible light colors, and those most easily developed in the
first firing, which is the strongest. Commence always on a lighter scale
than the final tint, for in pottery painting any color made too dark in
firing cannot be made light again. When the mixtures have produced, for
example, some browns or russet hues which have not glazed in the first
firing, the glazing is brought back by a little fusible light grey,
applied before the second firing for retouches. These short general
instructions will be resumed and developed in the following lessons.