Image spectroscopy for diagnostic and conservation of contemporary art materials

To works of art is often assigned a specific value of cultural and expressive testimony of an artist or, more generally, of a culture. Preserve this value means keeping intact the appearance of the work and its component material in order for the message to reach the public, without alteration. A good knowledge of the materials constituting the work is needed to preserve them appropriately. My research work is focused on the study of modern and contemporary paintings and of materials used, which are not well known compared to traditional materials. The main goal of this work was to investigate some of the most popular art materials to track even the weakest changes, which are index of degradation and occur in the form of chromatic alterations. Image spectroscopy (IS) was the scientific technique on which we focused the attention, since it helps to reveal early alterations using imaging, in a complete non-invasive way. Spectral data in the VIS-NIR range were processed by multivariate statistical analysis. The use of Principal Component Analysis (PCA) on IS spectra was applied to modern painting materials, as Titanium White, Artificial Ultramarine Blue in acrylic and oil binders in a test panel. IS + PCA has proven to be an effective method for the early identification of chromatic alterations, although of faint amounts. Moreover, colorimetric data have provided useful and complementary information, recognizing the alterations trends. Unexpectedly, IS has also demonstrated a discriminant power for some materials. The most striking case was the identification of white Lithopone for an absorption band in the visible range, due to the presence of cobalt as vicariant element of Zinc. The knowledge of changes in the chemical composition of this pigment in a specific time period has allowed the recognition of a fake in contemporary artwork. Other scientific methodologies have been used. X-ray fluorescence was used to collect more detailed information about the materials. This can be the case of examinations on Jean Metzinger’s work, present in the Peggy Guggenheim Collection (Venice). Image diagnostics, as Ultraviolet fluorescence, Wide band infrared reflectography, have proved useful to collect information on the state of conservation of works in non-quantitative way. The common features of such techniques are to be non-invasive, non-destructive, to be used in situ.