Applications of synchrotron-based micro-imaging techniques to the chemical analysis of ancient paintings

Ancient paintings are complex materials in terms of chemical analysis because they are usually made of organic/mineral, amorphous/crystallized, major/minor mixtures, evolving with time, and organized in micrometric multi-layered arrangements. In this context, synchrotron micro-imaging techniques offer a powerful analytical platform to reveal the two dimensional atomic, molecular and structural compositions of such complex systems, at a micrometre resolution. The two selected examples illustrate the two main concerns of restorers and conservators: looking backwards, to get insight into ancient artistic practices (in particular through the identification of pigments and binders in Bamiyan Buddhist mural paintings); and looking forward, to preserve works of art as long as possible (through a better understanding of cinnabar blackening in Medieval Spanish paintings). From the analytical chemistry point of view, they also illustrate the relevance of combining micro X-ray fluorescence, micro X-ray absorption spectroscopy, micro X-ray diffraction, and micro-FTIR for the complete analysis of painting cross-sections (binders and pigments).