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SEM Backscattered-Electron Images of Paint Cross Sections as Information Source for the Presence of the Lead White Pigment and Lead-Related Degradation and Migration Phenomena in Oil Paintings

Published online by Cambridge University Press:  11 April 2011

Katrien Keune ,
Annelies van Loon  and
Jaap J. Boon
Katrien Keune*
Affiliation:
FOM-Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands Private painting research scientist, Kortenaerstraat 82, 2315 TP Leiden, The Netherlands
Annelies van Loon
Affiliation:
FOM-Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands Royal Picture Gallery Mauritshuis, Postbus 536, 2501 CM, The Hague, The Netherlands
Jaap J. Boon
Affiliation:
FOM-Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
*
Corresponding author. E-mail: katrien.keune@gmail.com
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Abstract

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.

Keywords

electron microscopybackscattered-electron imageoil paintingpaint cross sectionlead whitelead soapdegradationmigration
Type
Analysis of Cultural Heritage Special Section
Information
Microscopy and Microanalysis , Volume 17 , Issue 5 , October 2011 , pp. 696 - 701
Copyright
Copyright © Microscopy Society of America 2011

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References

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