The coating, synthetic or natural resin, is used to provide saturation and to protect the paint underneath from dirt, abrasion and moisture. Natural varnish resins are hard or semihard tree saps, insect secretions, or fossil deposits formed by decaying vegetation. The names of the resins may be derived from their places of origin or the port that ships them. As a coating, they provide an unmatched saturation of the pigments. Their main drawback is that they yellow considerably with age.
Synthetic resins are acrylic or ketone compounds dissolved in an appropriate organic solvent.
They form a tough transparent film that may not yellow as rapidly with age. The Lifetime of a Painting From the moment a painting is made, it begins to age. Depending upon the quality, combination and nature of the materials which have gone into its construction as well as its environment, a painting may age well or not. A new painting in good condition will begin to deteriorate as a result of time alone. Cracks appear as the paint films dry and shrink.