Optical Spectroscopy of Paper Cultural Heritage

Optical spectroscopy is the study of the interaction between matter and ultraviolet, visible and near infrared radiation. It has been widely used as a non-invasive method for the study of cultural heritage materials for several decades. In particular, fibers optical reflectance spectroscopy (FORS), introduced in the 1980s, allows acquiring hundreds of reflectance spectra in situ in a short time, an approach particularly suitable for cultural heritage diagnostics. More recently, optical spectroscopy has been applied to ancient paper with the aim of noninvasive evaluation of the state of degradation of ancient artworks and as a preliminary technique for the analysis of inks, pigments and dyes used as graphic signs on paper. The discoloration phenomena of paper substrate is responsible for visual degradation of ancient artworks. It is due to the development of oxidized groups acting as chromophores in its chief component, cellulose. This contribution shows the interpretation of optical reflectance measurements by using theoretical simulations of the chromophores' optical spectra. By using this approach it has been possible to describe and quantify the chromophores affecting Leonardo da Vinci's drawings which, compared with future measurements, will assess its degradation rate. This is a fundamental information in order to plan appropriate conservation strategies for very important work of art on paper.