Computational tools reveal the secrets of sealed letters from collection Sound & Vision in The Hague

Virtually unfolding intricately folded letters allows an interdisciplinary team to preserve valuable physical evidence in historic documents.

In a world first, an international team of researchers has read an unopened letter from Renaissance Europe – without breaking its seal or damaging it in any way. The team’s findings appear on march the 2nd in Nature Communications in an article titled “Unlocking history through automated virtual unfolding of sealed documents imaged by X-ray microtomography.” The article has been published open access.

Computational flattening algorithms were applied to X-ray microtomography scans of unopened letters from a 17th-century postal trunk full of undelivered mail. The senders of these letters had closed them using “letterlocking,” the historical process of folding and securing a flat sheet of paper to become its own envelope. The team was able to examine letters’ contents without irrevocably damaging the systems that secured them – a breakthrough for the study of historic documents, as the papers’ folds, tucks, and slits are themselves valuable evidence for historians and conservators.  

This process was used to reveal the contents of a letter dated July 31,1697. It contains a request from Jacques Sennacques to his cousin Pierre Le Pers, a French merchant in The Hague, for a certified copy of a death notice of one Daniel Le Pers (full transcript and images available). The letter gives us a fascinating insight into the lives and concerns of ordinary people in a tumultuous period of European history, when correspondence networks held families, communities, and commerce together over vast distances.

“This algorithm takes us right into the heart of a locked letter,” the research team explains. “Sometimes the past resists scrutiny. We could simply have cut these letters open, but instead we took the time to study them for their hidden, secret, and inaccessible qualities. We’ve learned that letters can be a lot more revealing when they are left unopened. Using virtual unfolding to read an intimate story that has never seen the light of day – and never even reached its recipient – is truly extraordinary.”

The research team includes Jana Dambrogio, Thomas F. Peterson (1957) Conservator, MIT Libraries; Amanda Ghassaei, research engineer, Adobe Research; Daniel Starza Smith, lecturer in Early Modern English Literature, King’s College London; Holly Jackson, MIT undergraduate class of 2022; Erik Demaine, professor, Department of Electrical Engineering and Computer Science (EECS), MIT; Martin Demaine, robotics engineer, CSAIL, and Angelika and Barton Weller Artist-in-Residence in EECS, MIT; Graham Davis and David Mills, Queen Mary University of London, Institute of Dentistry; Rebekah Ahrendt, associate professor of musicology in the Department of Media and Culture Studies, Utrecht University; Nadine Akkerman, reader in early modern English literature, Leiden University; and David van der Linden, assistant professor in early modern history, Radboud University Nijmegen.