254. GRAYISH BLACK FOR MIXTURES

Yellow ochre, No. 244, 15 parts; oxide of cobalt, 1 part; triturate
and calcine in a crucible until it has the desired tone. A little
oxide of manganese is added in order to make it blacker; sometimes a
little more of oxide of cobalt.


255. DEEP BLACK

Oxide of cobalt, 2 parts; oxide of copper, 2 parts; oxide of
manganese, 1 part; flux No. 1, 6 parts; fused borax, 1/2 part; melt
and add oxide of manganese, 1 part; oxide of copper, 2 parts;
triturate without melting.


256. GENERAL DIRECTIONS

The colours thus prepared after having been rubbed up on a plate of
ground glass with the spirits of turpentine or lavender, thickened
in the air are applied with a hair pencil. Before using them,
however, it is necessary to try them on small pieces of glass, and
expose them to the fire, to ascertain if the desired tone of colour
is produced. The artist must be guided by these proof pieces in
using his colours. The proper glass for receiving these colours
should be uniform, colourless, and difficult of fusion. For this
reason crown glass made with a little alkali or kelp is preferred.
A design must be drawn upon paper and placed beneath the plate of
glass. The upper side of the glass being sponged over with gum-water