IOO

PAINTING MATERIALS

Mineral acids decompose them with a yellow to orange-red solution. They are
not stable in strong light. Brazil-wood dyes are said to have been used in great
quantities in mediaeval times in dyeing, in painting, and in inks, perhaps more
than madder at an early date (Thompson, he. cit., pp. 120-121), but were later
replaced by more brilliant colors.
Bronze Powders are metal flake pigments made commonly from copper-zinc
alloys (brass), but for some powders copper-tin alloys (bronze) are also used.
The copper-zinc powders go into imitation gold paint. Formerly all metal bronze
powders were made by the same method: first rolling or beating into foil or leaf,
and then powdering. This method was expensive. Since about 1860 to 1865, they
have been made directly from sheet metal, up to one eighth inch thick, in special
stamping machines (see Otto Von-Schlenk, 'The Manufacture of Bronze Powder/
The Metal Industry [New York], XIV [1917], pp. 77-78, 161-163, 200-203).
Numerous shades and colors, ranging from citron yellow to orange, can be made,
depending upon alloy composition. The alloy, Cu, 95 : Zn, 5, gives a powder the
color of nine-carat gold; 90 : 10 is pale gold; 85 : 15 is yellow gold; 70 : 30 is
greenish gold, etc. (see Oliver Smalley, 'The Manufacture of High-Grade Alumi-
num and Bronze Powders/ The Metal Industry [London], XXVII [1925], pp. 1-2).
The flakes of these powders are very thin: in the order of 1/50,000 to 1/100,000
inch (Von-Schlenk, he. cit.3 p. 77). In spite of thinness, the flakes are quite opaque
when viewed under the microscope; they have fairly regular and uniform dimen-
sions and contain little impurity (see three photomicrographs shown by Smalley,
op. tit., XXVII [1925], p. 186).
Bronzing liquids are generally solutions of nitrocellulose in amyl acetate
(banana oil) or other organic solvents.
Brown Madder is made by the gentle charring of madder lake or alizarin to
give a dull, brownish red color. Although it is not permanent and seems to be an
unnecessary color in these days, it is still listed by a few colormen. Paints now
sold under this name may be mixtures of pure alizarin with burnt sienna or
another similar earth color.
Brown Ochre (see Ochre).
Brown Pink (see Pink).
Buckthorn Berries (see Persian Berries Lake).
Burnt Sienna (see Sienna).
Burnt Umber (see Umber).
Cadmium Green is not a color produced by any pure cadmium compound
but is the name given to a warm green made from a mechanical mixture of trans-
parent oxide of chromium (hydrated green or viridian) with cadmium yellow.
That produced by one manufacturer is said to be 93 to 94 per cent hydrated
green plus cadmium yellow (Gardner, p. 1349).
Cadmium Orange (see also Cadmium Yellow) is one of the color modifications
of cadmium sulphide (CdS). Toch (The Chemistry and Technology of Paints,