Lead carboxylates (lead soaps) have been detected in hundreds of oil paintings, and have been correlated with visual imperfections and affecting the structural integrity of the artwork. Lead soaps are produced when lead pigments, such as lead tin yellow type I (Pb2SnO4) or basic lead white (2Pb(CO3)2Pb(OH)2), react with fatty acids in the oil binding medium. The mechanism that triggers soap formation is not currently well known. Understanding the mechanism of these reactions requires chemical information, which can be obtained with solid-state 207Pb and 13C NMR. We have examined lead soaps, common lead pigments, and paint films subjected to artificial aging. The tensors determined for the lead carboxylates and the pigments provided new information on the structure of lead carboxylates and the reactivity of the pigments. Our work points to novel applications of solid state NMR in materials science as model systems and replication experiments become increasingly significant in elucidating materials issues in art and archeology.

Structural analysis of lead carboxylates and lead pigments found in traditional oil paintings by multinuclear NMR

251st National Meeting (2016)

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