Characterization of surface states on patrimonial works of art

Abstract

A goniospectrophotometer is used to analyze the back-scattered light, in the visible range, by a 0.3 cm2 surface. The measurement is non-destructive, without contact and can be implemented in situ. For a metallic surface, the reflected intensity is measured as a function of the back-scattered angle. The probability density of the normal to the surface is then deduced. The ratio roughness r.m.s. / correlation length is calculated. The method is applied to characterize the different techniques for gold backgrounds in primitive European paintings. For a non-metallic surface, the reflected intensity is measured as a function of the wavelength. The spectrum is compared with a data bank of mineral pigment spectra. The comparison allows to identify pigments and, moreover, to deduce the surface state of the painting layer. Examples of Egyptian and modern paintings will be presented.