This pre-mix by Charvin is a tried and true formula. Retouching varnish is used to even out the finish of the painting as some areas may be glossy while other may appear matte. This will disturb the painter's perception of the pictorial substance that he is working on. It also allows painters to see paint layers more clearly then if they were left matte. Finally if you can use Retouching Varnish to speed the curing of the finished painting.