The present study describes the results of research project at the Metropolitan Museum of Art, New York, beginning with an evaluation of the factors contributing to the optical properties of varnishes. Although this aspect of the varnish problem deserves more attention than it receives in this dissertation (e.g. in the form of extensive spectrophotometric and goniophotometric measurements), the information in Chapter 1 demonstrates clearly that a varnish which mimics traditional resin varnishes should be based on resins with very low molecular weight and a relatively high refractive index. All further work in this study has therefore focussed on such resins. Two approaches to solution of the problem were chosen: studies were done to investigate the possibility of inhibiting autoxidative degradation of natural resin and other varnishes with stabilizing additives, and a search for new stable resins with low molecular weights and high refractive indices was carried out. To this end the chemistry of dammar resin, one of the most popular natural resins used in picture varnishes, and the degradation process of films of the resin were studied (Chapters 3 and 4). A survey of polymer stabilizers appears in Chapter 2 and a stabilizer recommended in the literature for dammar varnishes is evaluated in Chapter 5. The dramatic effects in the absence of ultraviolet light of a hindered amine light stabilizer and a benzotriazole type ultraviolet absorber on films of dammar are described in Chapter 6 and the potential of synthetic resins of low molecular weight is the subject of Chapter 7.