Summary
Information has been accidentally or intentionally obscured in countless historic documents, photographs and films. Specifically, legibility of texts and visibility of images may be compromised due to, on the one hand, deterioration of the support, writing or image-forming materials (fading, water damage, biodeterioration…) and, on the other hand, past human interventions (redactions, palimpsests, chemical reagents for ink enhancement…). The massive scale of archival collections, organisations´ finite resources, severity of the damage and the limits of current conservation methods are important obstacles to address this problem. Advanced imaging techniques have been explored as a possible solution to digitally unlock this inaccessible knowledge [1, 2]. This is the goal of the project “The Museum of the Invisible - Spectral Imaging Techniques for the Digital Recovery of Deteriorated Heritage”, which has shown particularly promising results on archive collections with challenging conservation problems [3].The applied methodology comprises a range of complementary imaging techniques, such as multiband and hyperspectral imaging in the UV-VIS-NIR range, X-Ray Fluorescence scanning, Raman imaging and micro CT-scanning. Image processing methods like binarization, Principal Component Analysis (PCA) or Spectral Angle Mapper (SAM) among others, are also investigated to improve the readability of the writing and the contrast of the images.This lecture will give an overview of the main results obtained so far, both on reference samples prepared in the laboratory and on historic case studies from a range of archival collections. Representative successful cases will be shown, analysing the imaging techniques and processing methods that proved more adequate in each case, depending on the variety of document media and causes of information loss. Equally, unresolved challenges and further research needed to access the contents of these invaluable historic materials will be discussed.References:• Tonazzini A. et al. (2019) Analytical and mathematical methods for revealing hidden details in ancient manuscripts and paintings: a review, J. Adv. Res., 17: 31–42. https://doi.org/10.1016/j.jare.2019.01.003 • Perino M. et al. (2024) New Frontiers in the Digital Restoration of Hidden Texts in Manuscripts: A Review of the Technical Approaches. Heritage, 7: 683–696. https://doi.org/10.3390/heritage7020034