Characterisation of Surface States on Patrimonial Works of Art

Abstract

A gonio-spectrophotometer is used to analyse the backscattered light in the visible range from a 0·3 cm 2 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 backscattered angle. The probability density of the normal to the surface is then deduced. The ratio roughness root mean square/correlation length is calculated. The method is applied to characterise the different techniques for applying 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 database of mineral pigment spectra. The comparison allows the pigments to be identified and, moreover, to deduce the surface state of the painting layer. Examples of Egyptian and modern paintings will be presented.