  Energy-dispersive X-ray diffraction (EDXRD) is extremely insensitive to
sample morphology when implemented in a back-reflection geometry. The
capabilities of this non-invasive technique for cultural heritage applications
have been explored at high resolution at the Diamond Light Source synchrotron.
The results of the XRD analysis of the pigments in 40 paints, commonly used by
20th century artists, are reported here. It was found that synthetic organic
pigments yielded weak diffraction patterns at best, and it was not possible to
unambiguously identify any of these pigments. In contrast, the majority of the
paints containing inorganic pigments yielded good diffraction patterns amenable
to crystallographic analysis. The high resolution of the technique enables the
extraction of a range of detailed information: phase identification (including
solid solutions), highly accurate unit cell parameters, phase quantification,
crystallite size and strain parameters and preferred orientation parameters.
The implications of these results for application to real paintings are
discussed, along with the possibility to transfer the technique away from the
synchrotron and into the laboratory and museum through the use of
state-of-the-art microcalorimeter detectors. The results presented demonstrate
the exciting potential of the technique for art history and authentication
studies, based on the non-invasive acquisition of very high quality
crystallographic data.
