Metastructure of illuminations by infrared thermography

In this work, the capability of Infrared Thermography to characterize in a non-destructive way the main features of illuminated manuscripts has been assessed. It has been shown how this technique can be exploited for a general investigation of the book materials, structure and decorative apparatus, providing information on the manufacturing method, the preservation state and the changes operated throughout the history of the artefact. The used thermographic approach provided infrared images which show also the non-visible surface and subsurface elements that constitute the illumination metastructure, intended as the structure of the entire pictorial system. A number of aspects, like the verification of the adhesion state of the gold leaf, the recovery of the pentimenti, the detection of metal foil residues and the characterization of the damage produced by fungi and bacteria have been studied. For each of the investigated features an interpretative model accounting for the infrared emission processes responsible of the thermogram generation has been proposed. Moreover, for every studied aspect, it has been shown how, based on the thermographic results, other complementary analyses can be directed like Infrared Reflectography, Scanning Electron Microscopy, X-ray Fluorescence and the Energy Dispersion Spectroscopy. The effectiveness of the proposed approach has been tested in the study of Liber Regulae S. Spiritus de Saxia, a 14th century illuminated manuscript of great historical importance and artistic value, since the wide spectrum of the employed materials and the complexity of the structural changes operated during its history by extensive restoration make it a valid test-bed.