ANS:D - Drying oil

A common constituent of both paint and oil varnish is drying oil. Drying oils, such as linseed oil, tung oil, and walnut oil, are vegetable oils that polymerize when exposed to air, forming a tough, protective film. In both paint and oil varnish formulations, drying oils serve as binders that hold the pigment particles together and adhere them to the substrate. While extenders, pigments, and thinners are also used in both paints and oil varnishes, drying oils are specifically responsible for forming the film that provides protection and aesthetics to the surface. Extenders are additives that increase the volume of the formulation, pigments provide color and opacity, thinners are solvents used to adjust the viscosity and flow of the mixture, but drying oils are essential for forming the solid film after application.