The project was part of SIK-ISEA’s Fellowship Programme.
Synchrotron x-ray microtomography (SRXTM) is a powerful non-destructive technique ideal for high resolution investigation of a wide range of materials. At the PSI in nearby Villigen, the 2.9 T superbend-generated high brilliance photons allow imaging at high energies (above 20 keV) of electronically dense materials, such as those often found in paintings. In this project we have – in collaboration with PSI’s TOMCAT beamline (Tomographic Microscopy and Coherent Radiology Experiments) – pioneered the application of SRXTM to painting studies.
What new information does SRXTM bring that is not accessible with conventional techniques?
Conventional research methodology for paint microsamples can be categorised into one and two dimensional techniques. One dimensional, i.e. bulk material analysis techniques, provide detailed data on chemical composition, but do not give spatially resolved information.
Spatially resolved information (i.e. information on the location and distribution of the different chemical phases) can to some extent be gained through two dimensional, i.e. analytical imaging techniques. Although restricted to a single exposed polished surface of a sample, this approach has proved very useful in the past towards the understanding of chemical processes on or below the picture surface. However, since three dimensional measurements were tested, it has become clear that a two dimensional image is not sufficiently representative for the accurate study of the composition and degradation of paint layers.
The tomograpic data can be studied in a virtual domain in any direction.
With SRXTM samples can be imaged as three dimensional data sets down to 370 nm pixel size. This can be done without any preparatory manipulation of the sample, thus avoiding the introduction of embedding and polishing related artefacts. It has become clear that SRXTM is uniquely powerful for the visualisation of the internal structure of paint layers and for the study of porosity, particle morphology, and degradation phenomena.
During our exploratory studies, different materials were investigated with SRXTM. Examples include the characterisation of ground layers and the study of the mechanisms of the formation of calcium soaps.
The project was supported by:
Swiss Re, Zürich
Ferreira E. S. B., Boon J. J., van der Horst J., Scherrer N. C., Marone F., Stampanoni M., «3D Synchrotron x-ray microtomography of paint samples», in: Luca Pezzati, Renzo Salimbeni (ed.), O3A: Optics for Arts, Architecture, and Archaeology II, Proceedings of SPIE Europe 2009, Vol. 7391, 73910L • © 2009 SPIE • doi: 10.1117/12.827511