Page:Cyclopedia of Painting-Armstrong, George D (1908).djvu/71

Rh is more thoroughly done. Spanish white is a name given to Paris white sold in a cylindrical form prepared by moulding the wet material into that form, and allowing it to dry in the open air.

Whiting is a dull white powder of an amorphous character, and soft to the feel. It is quite insoluble in pure water, but is soluble in water containing carbonic acid gas.

Kaolin or China clay is essentially a hydrated silicate of alumina. It is a natural product and only requires levigating and drying to prepare it for use as a pigment. It occurs in large deposits along with other constituents of undecomposed granite, the china clay usually forming from 15 to 20 per cent of the whole deposit.

Kaolin is a fine, white amorphous powder, having slight adhesive properties and adhering to the fingers when moist. The best qualities have a very soft unctuous feel and a pure white tint, while the common qualities are rather rougher and of a more or less yellowish hue.

As a pigment kaolin is quite permanent, resisting exposure to the atmosphere and to light for any length of time. It is, however, not much used as a pigment. In oil it loses its body and becomes more or less transparent. It can be used in water colors and in distemper work with good results, and is emjDloyed in paper-making and paper-staining.

Yellows. Chrome yellows are chromates of lead, produced by mixing dilute solutions of acetate or nitrate of lead and bichromate of potash. This makes a medium tint known as middle chrome. The addition of sulphate of lead makes this paler, when it is known as lemon chrome, whereas the addition of caustic lime makes an orange chrome of a darker color. The chromes mix well with oil and with white lead either in oil or water. They stand the sun well, but like other lead salts, become dark in bad air. Chrome yellow is frequently adulterated with gypsum.

Naples yellow is a salt of lead and antimony, supposed