K-edge differential radiography for works of art

Digital radiography is a invaluable technique to get information concerning the conservation state of a painting, while it offers qualitative data about the composition of the work of art. On the other hand, K-edge differential radiography maps the distribution of a chosen element in the whole painted surface and can univocally characterize the art work. This technique is subtracting two images obtained by monoenergetic X-rays, bracketing the K-edge of a chemical element. It was initially proposed in the medical field and was successfully applied in angiography and mammography. For the study of paintings, it was formerly applied using X-ray source monochromatized by Bragg diffraction and synchrotron radiation. An alternative method for K-edge RX is filtering a commercial X-ray generator by filters made of adjacent elements in the periodic table, bracketing the absorption edge of the target element. If this method should be effective, it could be easily implemented with any commercial system and applied for in situ applications. First maps of Cadmium in XX century paintings have been obtained filtering by thin slices of Silver (Z = 47), Cadmium (Z = 48) and Indium (Z = 49). Studies are progressing concerning the threshold of sensitivity to Cadmium and other elements in pigments.