Detectives read old letter bombs without opening them

July 31 1697, Jacques Sennacques sends a letter to his cousin – a Pierre Le Pers, a French merchant living in The Hague – begging him, for the love of Pete (this is paraphrased), to send him a death certificate for his relative , Daniel Le Pers. In a 17th century version of the dreaded “according to my previous e-mail”, Sennacques wrote: “I am writing to you a second time to remind you of the pains I have taken on your behalf. Fundamentally, you owe me a favor, and I came to collect.

Sennacques put down his quill and finely folded the letter, turning it into his own envelope. Today, historians call this technique “letterlocking”. By the time of Sennacques, people had invented a galaxy of different ways of folding their letters – some so characteristic, in fact, that they acted as a sort of signature for the sender. They weren’t doing this because they wanted to save money on envelopes, but because they wanted privacy. By folding the paper and folding the corners, they could store it in such a way that in order to open the correspondence, the reader had to tear it in some places. If the intended recipient opened the letter and found it already torn, he would know that a nosy had crept inside. Entire pieces of paper could tear, so if they opened the letter and didn’t feel or hear any tears, but a piece still fell off, they would know they weren’t the first person to read it. content.

It was the modern period version of one of those seals that voids a device’s warranty if you break it. Unlike the self-destructive messages of Impossible mission, you could still read a torn letter, and if you were familiar with the technique of the person who sent it to you, you might even know some tips to avoid tearing it in the first place. Yet the letterlock posed traps that exposed the spies.

Unfortunately for all parties involved, Sennacques’ second letter never reached his merchant cousin. Instead, it ended up in a trunk, known as the Brienne Collection, which contains 2,600 letters sent between 1689 and 1706 from all over Europe to The Hague. Sennacques’ letter is one of hundreds that remain unopened, folded in on itself.

How, then, do we know that the man was losing patience with his cousin? Writing today in the newspaper Communications of nature, The 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, without tearing. “The letters in his trunk are so poignant they tell such important stories about family, loss, love and religion,” says King’s College London literary historian Daniel Starza Smith, co-author from Journal. “But also, what the letter lock does is give us a language to talk about kinds of security technologies and human communication secrecy, stealth and privacy.”