Sleuths read old booby trapped letters without opening them

On July 31 1697 Jacques Sennacques sends a letter to his cousin – one Pierre Le Pers, a French merchant living in The Hague – begging him for Pete’s (which is paraphrased) love for a death certificate for his family member, Daniel Le Pers , to send to him. . In a 17th century version of the dreaded ‘according to my previous email’, Sennacques wrote: ‘I am writing to you a second time to remind you of the pain I have done on your behalf.’ Actually, you owe me a favor, and I came to get it.

Sennacques put down his pen and folded the letter intricately and turned it into his own envelope. Historians today call this technique ‘letterlock’. In Sennacques’ time, people devised a galaxy of different ways to fold their letters – some so characteristic that they acted as a kind of signature for the sender. They do this not because they want to save money on envelopes, but because they want privacy. By folding the paper and inserting corners, they were able to arrange it in such a way that the reader had to tear it in certain places to open the correspondence. If the intended recipient opens the letter and finds that it has already been torn, they would know that a sniff has come in. Whole pieces of paper can tear off, so if they open the letter and do not feel or hear tear, yet a piece falls out, they will know that they are not the first person to read its contents.

It was the version of the early modern period of one of the seals that invalidates the warranty of a device if you break it. Unlike the self-destructive messages of Impossible mission, you would still be able to read a torn letter, and if you were familiar with the technique of the person who sent it to you, you would even know tricks to prevent you from tearing it. Yet the letter-blocking set up traps that exposed spies.

Unfortunately for all involved, Sennacques’ second letter never made it to his cousin. Instead, it ends up in a tribe, known as the Brienne Collection, containing 2,600 letters sent to The Hague between 1689 and 1706 from all over Europe. Sennacques’ letter is one of hundreds that remain unopened, and folded tightly on itself.

How then do we know that the man has lost patience with his cousin? Write in the journal today Nature communication, researchers describe how they used an advanced 3D imaging technique – originally designed to map the mineral content of teeth – to scan four old letters from the Brienne collection to virtually unfold them, no crack needed. “The letters in his trunk are so moving, they tell such important stories about family and loss and love and religion,” said literary historian King’s College London, Daniel Starza Smith, a co-author of the paper. “But also what letterlocking does is give us a language to talk about kinds of technologies of human communication security, secrecy and discretion and privacy.”