Summary
Our archives and libraries hold invaluable collections of historical documents, some of which have seen their text legibility or image visibility compromised by the ageing of their materials, worsened by various deterioration factors -such as fires, floods, excessive light, pollutants, incorrect temperature or humidity levels, the action of microorganisms and rodents-, or even due to deliberate human intervention, like redactions, erasures and chemical reagents for ink enhancement.When the damage of the documents is beyond the capacity of current conservation treatments, advanced imaging techniques (such as multi and hyperspectral imaging, macroXRF scanning, Raman mapping, or microcomputed tomography) have been explored for their digital recovery.Given the fragility and value of these historical documents, taking samples for analysis or moving them to a laboratory is rarely acceptable. Therefore, counting with a comprehensive reference sample collection of inks, supports, photographic and film materials is key to, on the one hand, improve our understanding of the degradation of the materials in the laboratory and, on the other hand, test and optimise the best imaging strategy for text or image recovery with portable non-invasive techniques, which can then be applied in situ on real documents.This talk will illustrate how an archival materials reference collection was created and how it supported the recovery of readability or image visibility in the most challenging case studies investigated in the project “The Museum of the Invisible”.