PIGMENTS £05

Laurie says that the cool grays of Frans Hals are a mixture of white lead
charcoal black (New Light on Old Masters, p. 127).
China Clay (pipe clay, kaolin, white bole), the natural hydrated silicate of
aluminum, AUOa-aSiCVaEkO (kaolinite), is found in vast beds in many parts
of the world and is the essential raw material of the ceramic arts (see Ladoo,
pp. 138-161). The term is usually reserved, however, for the nearly pure (iron
oxide free) white clay with satin lustre that is used in the manufacture of fine
porcelain. Its plastic qualities, when it is mixed and worked with water, are of
great importance for ceramic purposes. In European paintings, China clay was,
on rare occasions, mixed with glue for a ground or priming material on canvas or
panel. Among painters it has been known as 'white bole,' which is closely related
to the red bole (see Bole) used so commonly as a ground for gilding. The Chinese
appear to have used it rather extensively in the priming for clay wall paintings
(see Gettens, * Pigments in a Wall Painting from Central China'). The term,
kaolin, is Chinese in origin and is said to be a corruption of Kaulingy meaning
'high ridge/ the name of a hill near Jauchau Fu, where the material is obtained
(see Dana, p. 578). Kaolin is not very characteristic microscopically, although
with suitable magnification vermicular crystals can be seen. It is semi-transparent,
finely divided, and homogeneous. The refractive index is low (0 = 1.565), and
it is only weakly birefracting. It is inert chemically. When heated, it loses water
and becomes harder, as in the firing of pottery. It is unaffected by strong acids
or alkalis.
Chinese Blue (see Prussian Blue).
Chinese Ink (India ink) has been the favorite writing and painting material
of the East for centuries. It is lamp black (see Lamp Black and Carbon Black)
which is prepared by the imperfect burning of pine-wood or oil in earthenware
lamps. Beam says (p. 129): *The soot formed is mixed with fish glue size, scented
with musk or camphor and moulded into sticks and dried/ For use, the stick is
rubbed with water on a slate-like slab. The modern India ink, waterproof, pre-
pared for draughting, is a proprietary material with a resin in the binding medium.
Chinese Vermilion (see Vermilion).
Chinese White (see Zinc White).
Chrome Green (cinnabar green) is a name that has come into very common
use for a green pigment that is made by mixing Prussian blue (see Prussian Blue)
and lead chromate (see Chrome Yellow). In the 'wet' method of preparation, a
slurry of Prussian blue is added to a pulp of barytes, China clay, and chrome
yellow, and the whole is stirred until thoroughly mixed (see Beam, p. 96). The
product is a very homogeneous mixture and usually the components can not be
distinguished microscopically. In the light and medium varieties, the Prussian
blue seems to be smeared thinly and evenly over the yellow grains, but in the
darker varieties, separate particles of blue can be seen. Because this green has
excellent hiding power and has body and can be produced at low cost, it is the