IIO PAINTING MATERIALS

solution with a concentrated solution of potassium nitrite (see Beam, p. 79).
The precipitate must be thoroughly washed; otherwise it is not stable. The pig-
ment has a very pure yellow color and a fair hiding power. It is fast to light and
air and is stable with other inorganic pigments, but it may accelerate the fading
of some organic colors and itself turn brown. It is decomposed by heat, by strong
acids and alkalis, and is slightly soluble in cold water. At fairly high magnifica-
tion, it can be observed to be made up of tiny crystals and crystal clusters which
are yellow by transmitted light and appear isotropic in polarized light. The
pigment has been used perhaps more in water color than in oil. The compound,
potassium cobaltinitrite, was discovered by N. W. Fischer in Breslau in 1848
(see Rose, p. 296). It was first introduced as an artist's pigment in 1861 (Laurie,
New Light on Old Master s> p. 44). Messrs Winsor and Newton, Ltd, say (1930
catalogue, p. 14, and in a private communication) that it was first introduced by
them and was popularized by Aaron Penley, a celebrated water color painter.
They also say that they introduced primrose aureolin in 1889. Although avail-
able today in water color medium, cobalt yellow does not appear to be widely
used as an artist's color, one reason being that it is expensive.

Cochineal (carmine lake, crimson lake) is a natural organic dyestuff that is
made from the dried bodies of the female insect, Coccus cacti, which lives on
various cactus plants in Mexico and in Central and South America. It was first
brought to Europe shortly after the discovery of those countries (see Beckmann,
I, 396-404). Eibner says (Entwicklung und Werkstojje der Wandmalerel, table,
p. 51) that it came in after the conquest of Mexico in 1523 and was first described
by Mathioli in 1549. The coloring principle of cochineal extract is carminic acid,

Carmine is an aluminum and calcium salt of carminic acid, and carmine lake
is an aluminum or aluminum-tin lake of cochineal extract. Carminic acid, the
pure extract of "cochineal, gives a scarlet-red solution with water and alcohol, and
a violet solution with sodium hydroxide (Colour Index,, p. 295). Crimson lake is
prepared by striking down an infusion of cochineal with a 5 per cent solution of
alum and cream of tartar. Purple lake is prepared like carmine lake, with the
addition of lime to produce the deep purple tone. Perkin and Everest (pp. 625-
627) describe methods for making the various cochineal-carmine lakes.
The cochineal lakes are not permanent to light. They turn brownish (Church,
p. 1 86) and then fade rapidly in strong sunlight, particularly when used in water
color. In oil, however, they are fairly stable and were used formerly in the prepa-
ration of fine coach colors.
Cologne Earth, (see Van Dyke Brown).
Color is a term used not only to indicate a certain region of the visible spec-
trum but also to indicate the substances of pigments and dyes; or, frequently, as
a synonym for pigment or paint.
Copper Resinate is a green compound formed by dissolving copper acetate,
verdigris, or other copper salt in Venice turpentine, balsam, or similar resinous