Spettroscopia UV-Vis-NIR per lo studio di pigmenti verdi

The identification of artistic materials is often based on invasive and micro-destructive analytical methods. Nevertheless, non-invasive techniques such as the Fibre Optic Reflectance Spectroscopy (FORS) allow identification of several compounds (pigments and dyes) in pictorial layers without any need of sampling. Although FORS is well-established for non-invasive investigations of polychrome surfaces some difficulties can occur in the interpretation of UVVis- NIR reflectance spectra acquired on multilayered paintings or on mixtures, such as those found in modern paintings. This is the case, for example, of paintings belonging to the "Macchiaioli" or to the "Impressionists" artistic movements, developed in the second half of the 19th Century in Tuscany and in France, respectively. The interpretation of FORS data acquired on multilayered pictorial surfaces can be particularly awkward, because reflectance spectra show complex behaviours resulting from several contributions of optically different materials. This work was in particular focused on the interpretation of UV-Vis-NIR spectra of green pigments, lavishly used in plain-air paintings. A series of samples were prepared using different green pigments, already available in the second half of the 19th century, and spectrally characterised in the UV-Vis-NIR spectral region. The materials studied were viridian, chromium oxide, cobalt green, cinnabar green, malachite, verdigris, Schweinfurt green and ultramarine green. The spectral data were analysed and matched in order to emphasise features typical of each material and highlights differences between pure pigments and mixtures. This research has to be considered a part of a wide study on the detection of green pigments by means of non-invasive methodologies.