Varnishes and Vehicles

When an oil, such as linseed, walnut, or poppy, has been purified and made more quickly drying by one or other of the methods already described, it is often called 'varnish.'

It has acquired the property of rapidly solidifying, when spread as a thin layer, into a tough transparent substance, endowed with a considerable degree of cohesiveness and elasticity, yet rather soft withal. Now oil of this character, although it has many uses in painting, is not quite hard enough for some of the purposes for which a true varnish may be required, but its defects may be amended by associating with it one or more of the resins described in Resins, Waxes, And Solid Paraffins. One class of varnishes is compounded in this manner of two materials, oil and resin, both of which are fixed or non-volatile. A second group of varnishes consists of a resin dissolved in a volatile solvent. And there are also mixed varnishes which contain at least three ingredients - namely, a drying oil, a volatile solvent, and a resin. As the varnishes which consist wholly of oil and resin are thick and intractable, it is usual to thin these according to the purpose for which they are intended, with varying amounts of some volatile liquid or solvent, spirit of turpentine being most frequently thus employed.

In order to avoid too elaborate a classification, it will be advisable to describe those varnishes which contain oil as oil or fat varnishes, and those which consist wholly of a resin and a volatile solvent as spirit varnishes. We describe the latter first, as their manufacture is easier and their constitution simpler. In order to avoid repeated references to the descriptions already given of the several materials employed in making varnishes, it will be convenient to state once for all that the oils used are described in Chapter V., the resins in Chapter VI (Resins, Waxes, And Solid Paraffins)., and the solvents in Chapter X (Solvents And Diluents).