Elemental maps with X-Ray Fluorescence (XRF)

Diagnostics referred to Cultural Heritage (CH) is a well-established research field. Among all the techniques for CH diagnostics, X-ray fluorescence (XRF) is one of the most used because it allows for multi-elemental, non-invasive, non-destructive and in situ analyses. Traditionally, XRF spectrometers have been used for single point measurements, where a small area is irradiated and the corresponding spectrum is acquired. In this case, it can be questioned whether the point investigated is significant or not for the chemical composition of the sample, as most of the objects of artistic or historical interest have quite unhomogeneous structures, even within apparently uniform areas, and these "anomalous" points may be difficult to identify by visual examination. Therefore, traditional ‘‘single spot’’ XRF analysis can result in misleading information about the composition of the material. In order to overcome the outlined risk of misleading or ambiguous information, many efforts have been dedicated by the scientific community to develop X-ray fluorescence imaging techniques. At the LABEC laboratory a first generation XRF scanner (XRF1) was also developed. This instrument allows for acquiring information both on material composition and on the distribution of the characteristic elements. Reconstructing elemental maps over a whole surface of relatively large area leads to achieve results by far more significant and reliable than those obtained from multiple single-spot analyses.Thanks to the results obtained working with the XRF1 scanner, it was possible to point out the pros and cons of this instrument, and thus, to develop a second generation XRF2 scanner. This instrument is by far more compact, lightweight and easy-to-handle with respect to the XRF1 and it has extended capabilities. Hardware and software upgrades and a new Graphical Users Interface (GUI) were developed, which has proved “on field” to be robust, fail-safe and “user-friendly” .The most important upgrades are: the dynamic positioning system and the helium-flow control system. The former, maintaining constant the sample-to-scanner distance, allows for the XRF imaging of objects of complex structure, with non-planar surfaces. The latter allows for detecting low atomic number elements down to sodium, thus noticeably extending the range of detectable elements, controlling the parameter directly in the GUI. Other functions which make the XRF2 easy to use, both for acquisition and data analyses, were implemented. This second generation spectrometer was designed exploiting the experience acquired during the PhD training and considering also the performance obtained by methodological test on standard laboratory samples and measurements on Cultural Heritage real cases. Tests were carried out to verify the effectiveness and reliability of the developed solutions for the XRF imaging of objects of complex structure. In order to accomplish this task, during the three year of my PhD training, I carried out a wide diagnostic campaign on a total of 30 artworks, among which paintings by the “Old Masters”, such as Simone Martini, Botticelli, Leonardo, Raffaello, Carracci and by modern painters, such as Manet, Previati, Lazzari, Leger, Buffet, Picasso (proposed attribution) and a Roman mosaic. All the measurements on these masterworks have been possible thanks to the collaborations with many museums, conservation scientists, privates interested in CH diagnostic and with the Opificio delle Pietre Dure (OPD) of Florence, one of the world’s most renowned centres for artistic restoration. Exploiting XRF imaging analyses, and thus, the characterisation of the material chemical composition, it has been possible to provide the restorers information about original materials, manufacturing processes, conservation state of the artworks and restorations or alterations occurred over time, which has allowed them to choose the most suitable conservation/restoration treatments.