Varnish (aircraft finishing material)
A material used to produce an attractive and protective coating on wood or metal. Varnish is made of a resin dissolved in a solvent and thinned until it has the proper viscosity to spray or brush. The varnish is spread evenly over the surface to be coated, and when the solvents evaporate, a tough film is left.
Aviation Maintenance Technician Handbook — Airframe, p. G-38