From fires to floods, from invisible inks to redactions, information has been accidentally or intentionally obscured on countless documents, maps and photographs, in collections from archives, libraries, and museums across the world. Removed from catalogues and reading rooms and therefore inaccessible to researchers and the general public, what new knowledge would these obscured documents reveal if we were able to read them? This paper demonstrates that current imaging technologies can be used to unlock this lost content. We used High Resolution Multiband Imaging (MBI), Reflectance Imaging Spectroscopy (RIS) and micro X Ray Fluorescence (µXRF) imaging to reveal illegible letter-forms and whole words written in iron gall ink on parchment from medieval documents relevant to the 'Virtual Record Treasury of Ireland' project, a digital reconstruction of archives destroyed in 1922 at the Public Record Office of Ireland at the outset of the Irish Civil War. The readability of text in historic documents with faded iron gall ink and/or parchment obscured by damp stains and ingrained dirt was successfully enhanced with MBI techniques, such as UV-induced visible luminescence (UVL) and UV reflected (UVR) imaging, which were able to recover the contrast of the ink. However, visualising text in documents showing chemical damage caused by the application of reagents for ink enhancement in the 19^th century (a practice known as “galling”) was more challenging because of the similar composition of the ink and the staining. RIS proved helpful to read documents with moderate to severe chemical damage, particularly after applying Principal Component Analysis (PCA). Text in documents that were severely damaged by galling was also recoverable with µXRF imaging of the distribution of iron from the ink. This also posed several challenges, such as minimising movement of the parchment during overnight scans and separating the data corresponding to iron on the front of the parchment which was combined with the signal from the back. Through subtraction of elemental maps during post-processing, we managed to tackle the latter issue. The combination of these different imaging techniques enabled palaeographers and medieval records specialists to identify individual characters and whole words, thereby recovering the meaning of texts that were previously indecipherable. Further research will adapt the methodology to the broad range of causes of information loss, including other reagents historically used for ink enhancement, as well as the variety of document media and temporalities, which require an extensive and multi-faceted approach of advanced imaging and post-processing techniques, in balance with the preservation needs of these fragile and invaluable historic materials.

Research was conducted at the British Museum to investigate the potential of Er:YAG lasers to address challenging conservation problems where traditional conservation methods had failed. The approach followed was to perform laser tests on model samples and unregistered objects to determine the laser alteration threshold fluence on each substrate and the ability of the laser to remove contaminants, such as inorganic crusts and organic coatings. The effects of the laser were assessed by means of optical microscopy, scanning electron microscopy and colour measurements. If tests were successful on the samples and unregistered objects, the laser was then used on artefacts from the collection of the British Museum. This article details the successful results obtained using Er:YAG lasers for the removal of corrosion from metals, remains of old adhesives from ceramics and shells, mould from polychromed limestone and terracotta, modern overpainting and varnish from a fresco painting.

This article presents the results of the examination by means of optical coherence tomography (OCT) of two of the nine monumental ceiling paintings by Peter Paul Rubens and his studio, still located in their original location at the Banqueting House, the only surviving building of the former Whitehall Palace in London. OCT is a non-invasive technique of structural imaging of layers semi-permeable to infrared light. The aim of the 2018 research campaign at the Banqueting House, conducted within the MOLAB programme under the IPERION CH project, was to determine the present condition of the paintings and thus inform decisions about future conservation planning for these unique paintings. GRAPHICAL ABSTRACT