The Potential for
Fluorescent X-ray Mapping and Depth Profiling of Oil Paintings at CHESS
Jennifer L. Mass
Scientific Research and Analysis Laboratory
Winterthur Museum, Garden, and Library
Winterthur, DE
X-rays have been central to the examination of paintings since Roentgen collected the first x-radiograph of a painting in 1896. X-radiography and open architecture air-path x-ray fluorescence are the primary methods for nondestructive characterization of oil paintings by museum scientists and art conservators. However, x-radiographs typically reveal little more than information about the painting’s structural integrity and the distribution of lead white ([2Pb(CO3).Pb(OH)2]) below the presentation layer. X-ray fluorescence can provide an indication of the pigments below the presentation layer, but its inability to provide stratigraphic information about these pigments restricts its use to authentication questions and to the identification of previous restorations. Stratigraphic information on paint layers is currently obtained through SEM-EDS of millimeter-sized samples removed from damaged areas of a painting. Such analyses are undesirable because they are destructive and ultimately of limited utility due to the ethical constraints that preclude sampling the most prominent regions of a painting, such as the face in a portrait. The most recent advance in the analysis of paintings by x-ray fluorescence has been the development of polycapillary lenses that provide increased lateral resolution, permitting finer details to be examined without interference from adjacent pigments. The use of capillary optics for the selective collection of fluorescent x-rays from a painting is desired so that a depth profile of paint layer composition can be established. Such a depth profile, assembled at regular intervals across a painting’s surface, could be used to generate a three-dimensional map that would provide invaluable information about artists’ technique in addition to authenticity and condition information. The ability to selectively collect fluorescence from a layered microstructure could also be of great utility in the characterization of ceramic surfaces decorated with both glaze and enamel layers.