Raman microscopy for the identification of pearlescent pigments in acrylic works of art

Abstract

AbstractIn this work, pearlescent pigments used to create luster in poly(methyl methacrylate) artworks by Ângelo de Sousa (1938–2011) were identified in an effort to predict their possible degradation. Raman microscopy was used, in situ, to identify plumbonacrite and bismuth oxychloride. Unequivocal characterization of plumbonacrite and bismuth oxychloride was made possible by comparison with reference materials, synthesized for this study. The vibrational pattern (infrared and Raman) of both pigments is discussed. Based on their Raman ν1 stretching mode at around 1050 cm−1, we show that it is possible to differentiate between the two basic lead carbonates that are both reported in the literature to be pearlescent: hydrocerussite Pb3(CO3)2(OH)2 and plumbonacrite Pb5(CO3)3O(OH)2. Raman microscopy was thus, for the first time, used as fingerprint tool for the molecular identification of pearlescent pigments in plastic materials. Based on these findings, better‐informed conservation strategies for the acrylic sculptures will be developed.