Other Dryers

Borate of lime and borate of zinc have been employed not only for rendering oils more quickly drying, but also in admixture with some of those oil-paints which dry with difficulty. Being colourless they are well adapted for use with white pigments, such as oxide of zinc. Several of the siccative materials sold under various fancy names consist of mixtures of these borates with carbonate of zinc or oxide of zinc, manganese compounds being also sometimes added. Another dryer in common use is white vitriol or sulphate of zinc. Its siccative character is very slight. Most of the other siccatives employed by artists owe their efficacy to lead, or are resinous preparations. Siccatif de Courtrai is a very dangerous mixture, heavily loaded with compounds of lead; Siccatif de Haarlem is a resinous preparation, which produces, on drying, a hard, brilliant, and tough film. This acquires, in course of time, a deep yellow hue, which, however, hardly affects the colour of the paints with which the siccative has been employed, because of the small proportion used.

¶ Here it may be mentioned that spirit of turpentine may be regarded as a fairly efficacious dryer, especially if the picture in which it has been employed is exposed to sunlight. This property of turpentine (terpenes) is not shared by the hydrocarbons of petroleum and of coal-naphtha, such as petroleum spirit, benzene, and toluene. This difference in chemical activity must be borne in mind if we would correctly estimate and foresee the results of employing these several liquids as vehicles or diluents.

It may be well to remark in this place that many of the volatile solvents, described in this chapter, are dangerously inflammable, and some are of a poisonous character.