BLACK VARNISH, the general term used to cover a large range of varnishes which have asphalt or bitumen as their essential and characteristic constituent. The different varieties, however, vary greatly in their properties.
The general process used in the manufacture of black varnishes consists in heating asphaltums or pitches, with a proportion of linseed oil and driers consisting of red lead, litharge, and man ganese dioxide, at a temperature of about 45o° F until the whole becomes stringy. The mass is then allowed to cool sufficiently to enable it to be thinned with turpentine to a suitable consistency.
Coachbuilders' black japan is the highest grade of black varnish manufactured ; the best asphaltums and pitches only are used, and a proportion of hard drying copal varnish is incorporated during the process of manufacture.
Berlin black is the name given to a black varnish which dries with a flat or eggshell finish, and is made by adding vegetable black to the ordinary quick-drying black varnishes.
Black stoving or baking enamels are special types of black varnishes used in the cycle and bedstead trades, and are usually applied by dipping and spraying.