Page:Cyclopedia of Painting-Armstrong, George D (1908).djvu/67

Rh than is required for red lead. It is a brighter and better color.

Chinese red and Persian red are chromates of lead, produced by boiling white lead with a solution of bichromate of potash. The tint of Persian red is obtained by the employment of sulphuric acid.

Venetian red is obtained by heating sulphate of iron produced as a waste product at tin and copper works. It is often adulterated by mixing sulphate of lime with it during the manufacture. When pure, it is called bright red. Special tints of purple and brown are frequently required, which greatly enhance the value of the material. These tints should be obtained in the process of manufacture, and not produced by mixing together a variety of different shades of color. When the tint desired is attempted to be obtained by this latter course it is never so good, and the materials produced are known to the trade as faced colors, and are of inferior value.

Venetian red originally consisted of a native ferric oxide or red hematite. But of recent years the name appears to have been transferred to a particular quality of artificial ferric oxide made by calcining green vitriol. When this salt is heated in a crucible the upper portion of the product, which has been less strongly heated than the lower, is of a brighter red than the remainder, and after washing and grinding is sold as Venetian red.

Rose pink is made of a sort of chalk or whiting stained with a tincture of Brazil wood. It fades very quickly, but is used for paper-hangings, common distemper and for staining cheap furniture.

Lakes are made by precipitating colored vegetable tinctures by means of alum and carbonate of potash. The alumina combines with the organic coloring matter and separates it from the solution. The tincture used varies in the different descriptions of lake. The best, made from cochineal or madder, is used for internal work. Drop lake