Bi-directional reflectance of a varnished painting Part 2: Comparison between the effects of the refractive indices, of the surface states and of the absorption of the varnish - experiments and simulations

This study.. based on diffuse reflectance spectrometry compared with simulations, shows that three parameters influence the visual aspect of a painting when a varnish is applied on it. The difference between the refractive indices of air, varnish and painting induces a negligible effect. The levelling of the painted surface by a varnish is more consequent. It induces a vertical downwards translation of the reflectance spectrum of the painting. Absorption by the varnish occurs for small wavelengths, under 450 nm. It induces a second decrease of the spectrum in this range. The refractive indices, the surface state modification due to levelling and the absorption law as a function of the wavelength have been evaluated. These results lead to a successful agreement between simulated and measured spectra. Different paintings and varnishes have been investigated and an example of application is given for an old painting. (C) 2003 Elsevier B.V. All rights reserved.