Page:Cyclopedia of Painting-Armstrong, George D (1908).djvu/251

Rh and printing ink, and also for painting and the preparation of japanner's gold size. As dark and transparent colors are in general comparative ill driers, japanner's gold size is sometimes employed as a powerful means of drying them. This material may be prepared in the following manner: Asphaltum, litharge or red lead, burnt umber or manganese, finely powdered, of each 1 ounce; stir them into a pint of linseed oil and simmer the mixture over a gentle fire, or on a sand bath, till solution has taken place, scum ceases to rise, and the fluid thickens on cooling, carefully guarding it from taking fire. If the oil employed be at all acid or rancid, a small portion of powdered chalk, or magnesia, may be usefully added, and will assist the rising of the scum and the clearing of the oil by its subsidence; and, if it be kept at rest in a warm place, it will clear itself, or it may be strained through a cloth and diluted with turpentine for use. Gold size for gilding is commonly made of boiled oil and fine yellow ochre.

There is often a difficulty in obtaining the oils bright; after boiling or heating them with the lead solutions, the best way, on a small scale, is either to filter them through coarse woollen filtering paper, or to expose the bottle for some time to the action of the sun, or to place it in a warm situation; on a large scale, the fine oils are often filtered through Canton flannel bags. The litharge and sulphate of lead used in the above processes may be again rendered available for the same purpose by washing them in hot water to remove the adhering mucilage.

Drier for Zinc White. Purified linseed oil is boiled for six or eight hours, and to every 100 pounds of boiled oil there are added five pounds of powdered peroxide of manganese, which may be kept in a bag like litharge. The liquid is boiled and stirred for five or six hours more and then cooled and filtered. This drying oil is employed in the proportion of from five to ten per cent of the weight of zinc white, and it should be added during the grinding of