Signed, sealed and undelivered for 300 years - 'locked' letters finally read by virtually unfolding them

Embargoed until: Publicly released: 2021-03-03 03:00

International

Computer-generated unfolding sequence of sealed letter DB-1538. In our paper we describe how “virtual unfolding” was used to read the contents of sealed letterpackets from 17th-century Europe without physically opening them. Credit: Unlocking History Research Group (email address: jld@mit.edu)

Sealed letters from Renaissance Europe have been read for the first time without opening them, by using computers to virtually open them. The letters were folded in intricate ways in a process known as letterlocking, a common way to ensure secure communication before modern envelopes came into use. Until now these letterpackets could only be studied and read by cutting them open, often damaging the historical documents. Using a computer algorithm, the researchers were able to virtually unfold and read surviving letters from a postmaster’s trunk of undelivered letters sent from all over Europe to The Hague between 1680 and 1706. The trunk included a letter which has remained unopened for 300 years, which contains a message from Jacques Sennacques dated 31 July, 1697, to his cousin Pierre Le Pers, a French merchant, for a certified copy of a death notice of one Daniel Le Pers.

Media release

From: Springer Nature

Imaging: Reading unopened Renaissance letters with virtual unfolding *IMAGES & VIDEO*

Sealed letters from Renaissance Europe have been read for the first time without opening them, by using a computational approach. The study, which could contribute to our understanding of historical communication security, is described in Nature Communications this week.

Folding letters in intricate ways, known as letterlocking, was a common practice for secure communication before modern envelopes came into use. Until now these letterpackets could only be studied and read by cutting them open, often damaging the historical documents.

By developing an automatic computational algorithm, Jana Dambrogio, Amanda Ghassaei and colleagues, were able to virtually unfold and read surviving letters from the Brienne Collection (a postmaster’s trunk containing undelivered letters sent from all over Europe to The Hague between 1680 and 1706), including one which has remained unopened for 300 years. They do this by first scanning the letterpackets with X-ray microtomography, producing a 3D reconstruction. The algorithm then identifies and separates different layers of the folded letter. The content of the letter becomes visible, since most inks produce a different contrast than the paper it is written on. The virtual unfolding algorithm allows the authors not only to read the unopened letters, but also to visualise the crease patterns and recreate the step-by-step locking process.

The authors suggest that the virtual unfolding method, and categorization of folding techniques, could help researchers to understand this historical version of physical cryptography, while at the same time conserving their cultural heritage.

Multimedia

Letterpacket DB-1627 was virtually unfolded and read

Computer-generated unfolding animation of sealed letter DB-1538

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conference: Nature Communications

Research:Paper

Organisation/s: Massachusetts Institute of Technology (MIT) Libraries, USA, Adobe Research, USA

Funder: Funding for the Signed, Sealed, and Undelivered project from an Internationalization in the Humanities Grant from the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (Dutch Research Council; project code 236-69-010); Metamorfoze; and Sound and Vision The Hague. J.D. acknowledges funding from The Seaver Institute; MIT Libraries; the MIT Undergraduate Research Opportunity Program (UROP); The Gladys Krieble Delmas Foundation; Bodleian Libraries, University of Oxford; with thanks to Kaija Langley, Mary Hurley, Tess Olson, Emilie Hardman, and MIT Office of Foundation Relations. A.G. acknowledges funding from Adobe Research. D.S.S. acknowledges funding from The British Academy; The John Fell Fund at Oxford University Press; The Zilkha Fund at Lincoln College, University of Oxford; and three sources at King’s College London: the English Department; the International Collaboration Fund, Faculty of Arts and Humanities; and the King’s Undergraduate Research Fellow (KURF) scheme. A.G. and H.J. acknowledge support from sponsors of the MIT Center for Bits and Atoms and MIT Computer Science and Artificial Intelligence Laboratory.

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