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Scanning electron microscopy backscattered-electron images of paint cross sections show the compositional contrast within the paint system. They not only give valuable information about the pigment composition and layer structure but also about the aging processes in the paint. This article focuses on the reading of backscatter images of lead white-containing samples from traditional oil paintings (17th–19th centuries). In contrast to modern lead white, traditional stack process lead white is characterized by a wide particle size distribution. Changes in particle morphology and distribution are indications of chemical/physical reactivity in the paint. Lead white can be affected by free fatty acids to form lead soaps. The dissolution of lead white can be recognized in the backscatter image by gray (less scattering) peripheries around particles and gray amorphous areas as opposed to the well-defined, highly scattering intact lead white particles. The small particles react away first, while the larger particles/lumps can still be visible. Formed lead soaps appear to migrate or diffuse through the semipermeable paint system. Lead-rich bands around particles, at layer interfaces and in the paint medium, are indications of transport. The presence of lead-containing crystals at the paint surface or inside aggregates furthermore point to the migration and mineralization of lead soaps.

The condition of The Art of Painting by Johannes Vermeer painted c. 1667 is now considered too fragile for traveling exhibition and required further investigation into the causes of the paint loss [1]. Samples were taken from a fragile green drapery, the white tile floor and close to the rim to investigate the buildup and composition of the ground and paint layers. Various types of microscopy i.e. Light Microscopy, imaging FTIR microscopy, Raman microscopy, F-SEM and SEM-EDX-mapping were performed on hand polished sections. The flaking paint loss from the white floor was also investigated with Xray tomographic microscopy.

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2006