Beyond the Page: Solar Loading Thermographic Imaging and Predictive Modeling for Ancient Book Diagnostics—Preliminary Results

Highlights: What are the main findings? Non-destructive techniques (NDTs) effectively detect sub-surface fabricated defects in an ancient book, with improved accuracy for certain material types. Advanced image processing: Multidimensional Fast Iterative Filtering (MdFIF), Principal Component Thermography (PCT), and Robust Principal Component Thermography (RPCT), combined with numerical simulations (COMSOL Multiphysics®), enhance diagnostic precision, especially for difficult to reveal hidden defects. What are the implications of the main findings? These methods significantly enhance the monitoring of the conservation of movable cultural heritage objects, enabling more accurate and timely interventions. The use of a numerical simulation model is particularly advantageous when dealing with movable artworks, especially valuable pieces that cannot be exposed to direct solar loading during testing. This study investigates the application of NDTs for the detection of sub-surface defects in an ancient book, with the aim of improving conservation methods in the field of cultural heritage. A sequence of thermographic images in a solar loading thermography (SLT) scenario was acquired during a diagnostic campaign in Harbin, China, to identify four distinct fabricated dowels made of Wool, Rubber, Teflon®, and Synthetic material. The images were processed in two ways: the first combined advanced image-processing methods: pre-processing via MdFIF, post-processing, PCT and RPCT, applied both to the original sequence and to the MdFIF-filtered thermograms. The second approach employed numerical simulations in COMSOL Multiphysics® to develop a predictive thermal model. The comparison of localized thermal anomalies obtained from the two approaches demonstrated the capability of NDTs to reliably reveal artificial defects, confirming their suitability for diagnostic conservation. Overall, the integration of advanced image processing with numerical simulation enhances diagnostic accuracy, particularly for subtle or low-contrast anomalies, thereby enabling more informed condition assessment and supporting rapid, targeted, and preventive conservation strategies.