Non-destructive multitechnique and digital image processing analysis of cultural heritage: case study of the Santi Quattro Coronati complex (Rome, Italy)

This PhD thesis investigates a collection of previously unpublished archaeological artefacts recovered from a disposal pit within the historic complex of Santi Quattro Coronati in Rome. The analysed materials include wax seals, handwritten paper, and parchment fragments—artefacts of considerable historical value, likely connected to the administrative and religious functions of the complex, which played a central role in medieval Rome. The primary aim was to characterize these artefacts in terms of material composition and conservation state, employing a multi-analytical, non-invasive approach. Techniques included Fourier Transform Infrared Spectroscopy (FTIR and micro-FTIR), X-ray Fluorescence (XRF), X-ray Absorption Spectroscopy (XAS), Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS), X-ray microfocus Computed Tomography (micro-CT), and Fiber Optics Reflectance Spectroscopy (FORS). Data analysis was supported by chemometric tools such as Principal Component Analysis (PCA) and hierarchical clustering, alongside custom image processing algorithms for ink segmentation, text enhancement, and three-dimensional (3D) structural analysis. Wax seals were found to contain primarily beeswax, protein-based materials, and cinnabar as the red pigment. Signs of degradation included chemical changes and physical damage. Ink fading was observed in both paper and parchment fragments. The inks on paper were consistent with iron gall ink, whose composition and aging were further studied using laboratory mockups. These helped identify chemical changes in the iron compounds of the ink related to aging, shedding light on the ink’s deterioration process. In parchment samples, advanced degradation caused collagen shrinkage and severe deformation, resulting in tightly folded and compressed internal layers. Micro-CT imaging enabled non-invasive exploration of these regions and detailed morphological study of the parchment’s collagen substrate in the 3D domain. Although hidden and faded text in the inner folds was not detected in the original parchment fragments, virtual unfolding techniques were successfully validated on parchment roll mockups, allowing visualization of flattened surfaces and navigation across folded layers to reveal inner text. This demonstrates the potential for digital recovery of obscured writings in fragile artefacts. This interdisciplinary research advances the material science of cultural heritage by integrating high-resolution imaging, spectroscopy, and computational methods. It provides new understanding of the manufacturing processes, use, and deterioration of historical artifacts, and can provide improved strategies for their conservation, documentation, and digital restoration.