Application of hyperspectral imaging for the study of pigments in paintings

HyperSpectral Imaging (HSI) can be considered as the evolution of classical spectroscopy, where “only” punctual analyses are carried out. The obtained 2D information (i.e. one spectrum for each pixel of the target image) can be thus used to characterize, map and monitor the materials constituting cultural heritage. Such non-invasive diagnostic technique can be applied by mobile devices directly in situ. The adoption of HSI techniques allows the acquisition of the spectra without a direct physical contact and/or sampling of material objects under investigations. This research aims at the development of a methodology to classify different pigments through HSI. Reference samples were prepared using six pigments (i.e. red ocher, yellow ocher, chrome yellow, mineral blue, cobalt green, and malachite) mixed with egg tempera. The obtained products were then applied on two different supports (i.e. canvas and wood) in order to obtain different combinations among pigment/support. The spectral changes of each pigment with different supports were evaluated with reference to the spectrum of the original pigment in powder. The samples were acquired in the SWIR (1000-2500 nm) range by HSI. Results showed as it is possible to identify a pigment on the surface of painting using a reference database of pigments in powder and also to obtain information on the binder and the support from the spectral signature.