Evaluating the integration of Thermal Quasi-Reflectography in manuscript imaging diagnostic protocols to improve non-invasive materials investigation

Abstract

Multispectral imaging techniques applied to book heritage are useful to scholars to obtain information on the materials under investigation. The novel introduction of Thermal Quasi-Reflectography (TQR) technique, operating in the medium wave infrared (MWIR) spectral range, can flank conventional diagnostic techniques such as UV-based methods and IR imaging techniques in the 850–1700 nm range on manuscript acquisition. As proof of concept, this work investigates the application of TQR on the Ms. XL (38) palimpsest, known as Vergilius Veronensis, of the Biblioteca Capitolare of Verona. While investigating the manuscript with full-field imaging technique, this work focuses its application to improve the mapping of conservation materials. The manuscript contains several traces of reagents and conservation treatments applied during its conservation history. The study compared the manuscript materials response obtained with TQR with the response collected using UV-induced visible fluorescence (UVL), UV reflected imaging (UVR), and NIR imaging in the 850–1050 nm and 900–1700 nm bands. Being the TQR technique sensitive to surface materials with MWIR reflectance features, it may especially provide more accurate documentation of the restoration history of the object. TQR imaging discriminated non-homogeneities of products in the surface layer thanks to an enhanced MWIR contrast. The TQR image response on manuscript materials should be further investigated and compared to reflectance spectroscopic data. The results of this study demonstrate the added value of TQR imaging for manuscript diagnostics, for which integration of the TQR technique in the standard protocol is desirable.