Term: Varnish

Picture varnishes are transparent, protective coatings added to paintings when they are dry. Finish varnish is applied as the final layer of a painting. It is most often used when a painting is not going to be put under glass (with mediums such as oil or acrylic rather than watercolor or pastel). Finish varnish protects the painting against particulates in the air, abrasion against the surface, and fading through exposure to light. It also gives the painting a uniform look, making all parts of the surface equally glossy, satin, or matte. Most finish varnishes are temporary so they can be removed and replaced when they become discolored or dirty.

Retouch varnish is different than finish varnish as it is applied to an oil painting while it is still drying (which may take many months). For instance, retouch varnish can be used to improve the look of a new painting that is going to be exhibited before it is old enough for finish varnish. Retouch varnish can also be used to compensate for the sinking in that occurs when a painting is still in progress. This is possible because retouch varnish is considered permanent and new paint can be safely applied over it.

No varnish should not be used as a medium, since this will make the colors sensitive to solvent. Where this is done, attempts to clean the painting in the future may remove elements of the painting instead.