Publication Type:Journal Article
Source:Studies in Conservation, Volume 52, Number 3, p.161-176 (2007)
Lead soap aggregateshave been-found in lead-containing oil paint layers in paintings from the thirteenth to the twentieth century. They severely affect the stability of the paint layers and disturb the surface of the paintings. Paint cross-sectionsfrom five paintings affected by lead soaps were selected to illustrate and investigate this degradation phenomenon with the analytical imaging techniques of Fourier transform infrared spectroscopy, secondary ion mass spectrometry and scanning electron microscopy combined with X-ray analysis. Examples aregiven of lead soapsforming in a mature paint system or, alternatively, in the early drying stage of the oil; lead soapsforming from various types of lead-containing pigments or driers; lead soapsforming in multiple paint layers; and lead-containing crystallization products inside aggregates. The phenomenon of lead soap aggregatesis multifaceted, and one general scenario describing theformation of lead soap aggregatescannot explain all aspects. However, the integration of the chemical information and its distribution among the paint layers leads to the proposal that reactivefree monocarboxylicfatty acids playa key role in lead soap aggregateformation. The availability and release of thesefatty acids depends on the original paint composition, the build-up of the layers, and the conservation/environmental exposure history of the painting.