Page:Cyclopedia of Painting-Armstrong, George D (1908).djvu/65

Rh the poisonous particles do not fly about, and the difficulty of grinding is avoided. Scheele's green and Vienna green are also arseniates of copper, and highly poisonous. Chrome green should be made from the oxide of chromium, and is very durable. An inferior chrome green is made by mixing chromate of lead and Prussian blue, as above mentioned, and is called Brunswick green. The chrome should be free from acid or the color will fade; it may be tested by placing it for several days in strong sunlight.

Bremen green is essentially copper hydrate, and forms an extremely loose and pale blue mass, the color of which has, however, a somewhat greenish tinge. When used as a water color it gives a pale blue, but when employed as an oil paint the original blue color turns green in 24 hours, owing to the copper oxide combining with the fatty acids of the oil to a green copper soap.

Reds. Carmine, made from the cochineal insect, is the most brilliant red color known. It is, however, too expensive for ordinary house painting and is not durable. It is sometimes used for inside decoration.

Red lead is produced by raising massicot, which is the commercial name for oxide of lead, to a high temperature, short of fusion, during which it absorbs oxygen from the air and is converted into red lead or minium, also an oxide of lead. The color is lasting, and is unaffected by light when it is pure and used alone, but any preparation containing lead or acids mixed with it deprives it of color, and impure air makes it black. It may be used for a drier, as it possesses many of the properties of litharge; it is also often employed in painting wrought iron work, to which it adheres with a tenacity not equaled by any other paints; it is sometimes objected to for this purpose, on the ground that galvanic action is set up between the lead and iron.

Vermilion is a sulphide of mercury in a natural state as cinnabar. The best comes from China. Artificial vermilion is also made, both in China and in this country, from a