Identification of pigments in different layers of illuminated manuscripts by X-ray fluorescence mapping and Raman spectroscopy

We propose a non-invasive approach for the study of illuminated manuscripts based on the combination of near-infrared reflectance imaging, X-ray fluorescence mapping, and Raman spectroscopy. Taking advantage of the different absorption coefficient of the characteristic X-ray emission lines of a specific element, we have implemented a differential mapping method to distinguish the X-ray emissions from two paint layers of a manuscript. This approach was applied to a coat-of-arms of a precious illuminated manuscript belonging to the Trivulziana library collection and revealed specific patterns through the mapping of the spatial distribution of lead in different paint layers. Multivariate methods, including principal component analysis and non-negative matrix factorization, applied to the X-ray fluorescence mapping dataset demonstrate the spatial correlation between different elements. The use of complementary Raman and X-ray fluorescence spectroscopy has hence permitted the identification of the pigments employed in the original and overpainting layers found on the coat-of-arms. Through analysis, it was possible to identify the patron of the Salterium, attributed to Fracesco dei librai, as 15th C. bishop Bernardo de' Rossi.