The replacement of a varnish in also not a simple matter. Conservators must decide whether to replace a natural varnish with another natural varnish, knowing that the natural varnish will yellow and will have to be replaced, or with a synthetic varnish, which may not yellow as rapidly but also may not duplicate the aesthetic effect of the natural varnish. It also should be in sound condition. Frames can display paintings with or without a protective glass covering. Ultraviolet filtering glass is sometimes placed over the painting to protect the painting surface from harmful ultraviolet light and also from dirt and fingerprints. Paintings without a varnish layer collect dirt in the interstices, which can rarely if ever be removed without damaging the paint layer. It has been suggested to display or store these works behind glass or in a dirt controlled atmosphere or, alternatively, to possibly compromise their appearance with the application of a varnish. What does a Varnish do for a Painting? The varnish layer plays a dual role: it has and effect on the final appearance of the painting and also serves as a protective coating for the paint surface.
Many of these natural materials are still in use today by artists and restorers. Numerous synthetic varnishes have also been developed that provide a wide array of surface characteristics. Synthetic varnishes have been popular, however, they do have different properties than natural varnishes.