Influence of the Addition of Crushed Glass on the Physical and Chemical Properties of Lead White Oil Paint

Microscopic particles of transparent colourless silicate glass have been found in numerous oil paintings dating from the fifteenth and sixteenth centuries. The widespread occurrence of such powdered glass has been demonstrated in combination with various pigments and within different pictorial layers in works by artists belonging to the Italian, German, Netherlandish, French, Spanish and Portuguese schools. The aims of this paper are to evaluate the multiple current hypotheses for its use, which include modification of transparency, siccative effects and rheology, and through reconstruction experiments, to gain a better understanding of the modifications of the physical and chemical properties of the paint induced by the addition of glass powder. Experimental works have been carried out using lead white based oil paint mixtures, since this pigment is one of those most frequently mixed with crushed glass in Italian paintings. Optical (reflectance and transmittance), rheological and Fourier transform infrared spectroscopy measurements were carried out on pure lead white paint as well as on paint mixtures containing varying amounts of crushed glass. These experiments indicated that the addition of crushed glass increases the transparency and siccative effect of paint films, without significantly altering rheological properties. (c) 2023 Published by Elsevier Masson SAS on behalf of Consiglio Nazionale delle Ricerche (CNR).