Non-invasive spectroscopic techniques for the diagnosis and conservation of historic surfaces and wall paintings

The present work illustrates the use of Fibre Optic Reflectance Spectroscopy (FORS) and Imaging Spectroscopy (IS) in the ultraviolet (UV), visible (Vis) and near infrared (NIR) regions. Both spectroscopic techniques are non-invasive, portable, and are primarily used for the identification of pigments and dyes (FORS and IS), evaluation of colour and colour changes (FORS and IS), for the detection of alteration products (FORS), and for mapping different compounds (IS). Furthermore, application of the principal components analysis algorithm to the spectral data, with the pixels as objects and the wavelengths as variables has made it possible to show areas painted with different materials as statistically-uncorrelated images (IS). Limits and advantages of such methodologies when applied to the diagnosis and the conservation of historic surfaces and wall paintings are also presented.