In vitro validation of a mobile Raman–XRF micro‐analytical instrument's capabilities on the diagnosis of Byzantine icons

A new mobile instrumentation that takes advantage of the simultaneous utilisation of two micro‐analytical techniques (Raman and XRF) has already been effected within the PRAXIS European project (Competitive and Sustainable growth programme, PRAXIS: A portable Raman–X‐Ray instrument. No G6RD‐CT‐2001‐00602). The instrument permits structural characterisation of the pigments incorporated in a painting under study by evaluation of the Raman spectra together with elemental analysis of the same materials provided by XRF spectra. Although direct structural characterisation with great specificity is directly accomplished by Raman spectroscopy, the signal is often masked by strong fluorescence, a fact that imposes time consumption. On the other hand, the average signal offered by XRF over larger volumes enables unique information to be obtained from invisible under‐layers. Moreover, the detection of trace elements by XRF, not influencing the Raman spectra, renders the characterisation of painting materials more comprehensive. Validation of the instrument's in situ and non‐destructive capabilities was performed after its in vitro application on an experimental icon (painted with traditional Byzantine techniques). The data acquired by the two techniques from the same spots on the painting offer complementary results, which enable the identification of almost all pigments even in the case of over‐painted art objects. Finally, the instrument's abilities on the identification of materials on specimen's cross sections are revealed.