due effect to any colored ground upon which they may be superimposed. For purposes of glazing and overgraining, ivory and blue-blacks and Prussian and indigo blue may be used, though the two latter are required seldom.
Prussian blue is a good working and staining color, and a quick drier. Venetian red is cheap but permanent, and must be procured ready ground in oil. It is useful for grounds.
Lemon and orange chromes, when of best quality, are chromates of lead. They are brilliant, have good body and covering power, and make good tints when mixed with white. When used in oil they must be protected by varnishing, especially if exposed to impure air, which in time will turn them black. The chromes destroy Prussian and some other blues. The yellow chromes are made in three shades; the fourth shade is the orange chrome, a deep rich color. The shades are varied by increasing the chromate for deep orange, and lessening it for the pale yellows. These colors are injured by damp and impure air, sulphur fumes and hydrogen, but the orange chrome is said to last better than orange oxide of lead.
Chrome of either middle or orange tint, may be useful to a slight extent in staining ground colors, when very bright and rich imitations are required. Generally, however, chrome conduces neither to good coloring nor to the attainment of a natural woody effect. The chrome-yellow tint sometimes forms a ground for light oak, whilst orange-red is used for medium oak.
White-lead, the basis of all graining grounds, is one of the most frequently used pigments, and also one of the most faulty. It is made by suspending rolls of ordinary thin sheet lead over malt vinegar or pyroligneous acid, in close vessels, the evaporation from the acid being kept up by a steam bath underneath. The lead is thus reduced to a white powder ready for being ground with linseed oil into a paste. White lead improves by keeping and for good
