A varnish is a clear coat applied over the top of an artwork. It has two main functions - to give an even sheen to the work, which will in turn help to bring out the full intensity and beauty of the pigments, and to protect it from several different areas of attack such as wear and tear and airborne grime and chemicals.
When selecting a varnish, one of the first questions that arises is that of the gloss level required. In general, good quality acrylics will have a similar sheen level across their colour range. However, the addition of water or many of the other mediums available to the artist, may change the gloss levels dramatically. One must determine the level of gloss that is required. Most gloss and matt varnishes of the same type may be mixed to obtain the desired sheen level. For more information on varnishing techniques and application