Varnish is a transparent, hard, protective finish of film primarily used in wood finishing but also for other materials. Varnish is traditionally a combination of a drying oil, resin, and a thinner or solvent. Varnish finishes are usually glossy but may be designed to produce satin or semi-gloss sheens by the addition of "flatting" agents. Varnish has little or no colour, is transparent and has no added pigment, as opposed to paints or wood stains, which contain pigment and generally range from oapque to translucent. Varnishes are also applied over wood stains as a final step to achieve a film for gloss and protection. Some products are marketed as a combined stain and varnish.

A resin dissolved by heating into a drying oil such as linseed or walnut oil to create a thick liquid varnish. An excellent varnish can be made from the mixture of boiled oil and by adding a little of bichromate of potash. In the mean time after half hour add up little of linseed oil, copal, turpentine and a bit ceresine. These are two ways of getting leather varnishes.