The optical properties of varnishes and their effects on image quality

Varnishes have been used to alter the appearance of paintings throughout history. Most significantly, they help to level the surface of the painting and reduce the first-surface diffuse scattering of light. This scattering makes a painting appear desaturated and gives it a much lower contrast. Traditionally, varnishes have been made from natural sources, such as tree resins. Over time these varnishes will dull and add a yellow cast. Also, the repeated cleaning and reapplication may hasten the deterioration of the painting, making the choice of varnish crucial in order to restore the painting to its original appearance and retain this appearance over time. Currently, new synthetic varnishes are being used, but they do not always result in the same appearance as natural varnishes. There is currently a need to assess the various optical properties of synthetic varnishes to help determine the effects they will have on paintings that they may be applied to. This research evaluated the spatial and colorimetric properties of Union Carbide AYAT PVA and Hercules Regalrez varnishes