Hyperspectral imaging-based approach for the in-situ characterization of ancient Roman wall paintings.

A diagnostic study was recently carried out on fragments of wall paintings belonging to the decorations of an ancient Roman residential villa of the Ager Gabinus, in the locality Pratolungo (Rome, Italy). The study was organized as follows: a first phase, in which small splinters of these painted specimens were embedded in resin and characterized by optical microscopy on polished cross-sections and thin sections; a second phase, in which the specimens were analyzed by Raman spectroscopy and hyperspectral imaging (HSI). The aim of the present work is to verify the potential use in situ of HSI technique in the range of SWIR (1000 nm - 2500 nm), presenting many advantages to punctual techniques of analysis as, i.e., Raman spectroscopy. In particular, the results obtainable by classical methods, such as optical microscopy, were compared to information resulting from non-destructive investigation techniques, as precisely the HSI. The acquired hyperspectral images were processed applying chemometric methods which allow not only the exploration of the data but also their recognition and their distribution over the whole specimen, without sampling. In fact, the use of HSI as a diagnostic tool in the field of cultural heritage is of great interest and it presents high potentialities, being this analysis non-destructive, non-invasive and almost portable. Furthermore, the possibility to couple hyperspectral data with chemometric techniques allows getting qualitative and/or quantitative information on the nature and physical-chemical characteristics of the investigated materials. Combining the results obtained on the samples by HSI and the results by Raman spectroscopy, it is possible to obtain information comparable with optical microscopy, allowing the identification of pigments and the constituent materials, confirming the potential use of this technique as a portable one.