A coating applied to the surface of a painting. Varnish serves a dual function: it affects visual appearance by providing a uniform surface for the reflection of light (thereby imparting gloss to a painting) and also acts as a protective coating.
A variety of materials have been used as varnishes: waxes, tree resins, fossil resins, oil/resin mixtures and synthetic preparations. Varnishes tend to darken and discolour over time, necessitating their removal and replacement.