Page:Cyclopedia of Painting-Armstrong, George D (1908).djvu/252

244 the pigment in oil, the admixture then being more thorough.

Drying Oils. Fifteen parts of lime made into paste with water are added to 100 parts of oil oxidized by peroxide of manganese. The whole is boiled or heated by steam until the water has evaporated; the oil then forms with lime a thick product which is a drier. It may be ground with the ordinary oil of turpentine, or with that of Venice, but the dryer is less powerful than when it has been mixed with oxidized linseed oil. Three to five per cent of this drier are sufficient for a rapid desiccation.

Other driers may be made by combining lime with resins and essence of turpentine in the proportions indicated for fixed oils.

Powdered Drier. Pure sulphate of manganese 1 part, pure acetate of manganese 1 part, calcined sulphate of zinc 1 part, white oxide of zinc 97 parts. The sulphate and acetate are ground in a mortar to an impalpable powder, which is passed through a metallic sieve. Three parts of this powder are dusted over the 97 parts of oxide of zinc, spread over a board or a slab; the whole is then thoroughly mixed and ground. The resulting white and impalpable powder, mixed in the proportion of $1/2$ to 1 per cent with zinc white, will enormously increase the drying property of this product, which will become dry in from ten to twelve hours.

Volatile Oils, procured by distillation from turpentine and other vegetable substances, are almost destitute of the strength of the expressed oils, having hardly more cementing power in painting than water alone, and are principally used as solvents, and media of resinous and other substances introduced into vehicles and other varnishes. In drying they partly evaporate and partly, by combination with oxygen, form resin and become fixed. They are not, however, liable to change color like expressed oils of a drying nature, and, owing to their extreme fluidness, are useful diluents of the latter; they have also a bleaching quality,