Investigation of mineralization products of lead soaps in a late medieval panel painting.

Abstract

Metal soaps pose significant concerns in the preservation of paintings made with oil as a binding medium. In highly alkaline environments, metal soap aggregates may undergo mineralization processes with the formation of new phases, such as carbonates, chlorides, oxides and sulfates of the metal cations that are present in pigments or paint additives. In this work, we report new examples of the mineralization of lead soaps in paint-cross sections taken from a late-medieval panel painting owned by the Museum of Cultural History at the University of Oslo. Scientific analyses were carried out with optical microscopy under UV and visible light, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and Raman spectroscopy to investigate and characterize the nature of the compounds present in the samples. Lead (II,IV) oxide, which is presumed to be a secondary product in the mineralization of lead soaps, has been identified in lead-based paint.