From macro to micro: An advanced macro X-ray fluorescence (MA-XRF) imaging approach for the study of painted surfaces

In the recent years, an increasing interest has been devoted to the development of compact macro X-ray fluorescence (MA-XRF) systems, establishing the technique as one of the most powerful non-invasive method for the characterization of artworks. Nevertheless, important information may be lost due to the poor signal-to-noise ratio, which characterises spectra collected with a limited acquisition time. Moreover, well-known drawbacks of the XRF analysis, such as the matrix effect and the penetration depth of X-rays, have to be also considered. In the attempt to overcome such limitations, without compromising the potentialities of a MA-XRF imaging analysis in terms of dimension of investigated surface and time of analysis, a specific methodological strategy is proposed. In particular, high signal-to-noise ratio maps were acquired on regions of interest selected after preliminary fast scans on the entire painting. Subsequently, the elaboration of the dataset was supported by the use of ad hoc analytical tools, such as correlation diagrams, averaged extracted spectra and line emission maps for each element. The correct interpretation of the non-invasive results allowed to define a proper sampling strategy. The proposed experimental workflow has been applied to a masterpiece panel painting by Cimabue (1240–1302) depicting “Madonna Enthroned with the Child and Two Angels”, disclosing new knowledge on the adopted execution technique, about which little is known. Thus, for the first time a painting created by Cimabue was investigated under a material and technical point of view. Due to the relevance of the information obtained by MA-XRF analyses, micro-destructive investigations were carried out. Thus, the joint evaluation of elemental distribution and the stratigraphic composition of the selected samples allowed to obtain information about Cimabue painting technique. Particular attention was devoted to the characterization of the throne decorations, pointing out new questions on a non-conventional middle-age gilding technique that need still to be investigated.