252. YELLOW FOR BROWNS & GREENS
Antimonic acid, 2 parts; sulphate of iron 1 part; flux No. 1, 9 parts. This colour is melted and sometimes a little Naples Yellow is added if it is too soft, i.e., melts too easily.
253. BLUEISH GREY FOR MIXTURES
Blue previously made by melting together three parts of flux No. 1, and one part of the mixture of oxide of cobalt, 8 parts; oxide of zinc, 1 part; sulphate of iron calcined at a forge heat, 1 part; flux No. 2, 3 parts; triturate and add a little manganese in order to render it more grey.
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 affords, when dry, a surface proper for receiving the colours, without the risk of their running irregularly, as they would be apt to do on the slippery glass. The artist draws on the plate, with a fine pencil all the traces which mark the great outlines and shades of the figures. This is usually done in black, and afterwards, when it is dry, the vitrifying colours are laid on by means of larger hair pencils. The yellow formed with chloride of silver is generally laid on the back of the glass, for it is apt to run with the other colours while heating.