“Locked” for 300 years: the virtual unfolding has now revealed the secrets of this letter

In 1697, a man named Jacques Sennacque wrote a letter to his cousin, a French merchant named Pierre Le Pers, requesting a death certificate for another man named Daniel Le Pers (presumably also a relative). Sennacque sealed the letter with an intricate method of folding known as “letterlocking”, a type of physical encryption – the best to protect content from prying eyes. That letter was never delivered or opened. More than 300 years later, researchers virtually “unlocked” the letter to reveal its contents for the first time, even the watermark in the shape of a bird. They described their results in a new article published in the journal Nature Communications.

Co-author Jana Dambrogio, a conservative at MIT Libraries, coined the term “letterlocking” after discovering these letters while working in the Vatican Secret Archives in 2000. The Vatican letters dated from the 15th and 16th centuries and had strange cracks and corners that were cut. Dambrogio realized that the letters had originally been folded ingeniously, essentially “locked” by inserting a slice of the paper into a slot and then sealing it with wax. It would not have been possible to open the letter without tearing up that piece of paper – proof that the letter had been tampered with.

Dambrogio has been studying the practice of letterlocking ever since, often creating his own models to show different techniques. The practice dates back to the 13th century – at least in Western history – and there are many different folding and braking techniques that have emerged over the centuries. Queen Elizabeth I, Machiavelli, Galileo Galilei and Marie Antoinette are among the famous characters known for having used letter blocking in their correspondence.

For example, a letter of 8 February 1587 from Mary, Queen of Scots, to her brother-in-law, King Henry III of France, was sealed using a so-called “butterfly lock” – just one of hundreds of locking techniques Dambrogio compiled in a letter blocking dictionary. Other techniques include a simple triangular fold and fold and an ingenious method known as a “dagger trap”, which incorporates a trap disguised as another simpler type of letter lock.

Often, individuals had their own style of blocking letters, most notably the English poet John Donne, who used at least five different letter blocking styles, an exclusive of his own, according to Dambrogio. “So, we have this guy who is known as the most inventive and witty poet of his generation, and he is making one of the most creative, witty and brilliant interconnection methods you could imagine,” she told Atlas Obscura in 2018. “That’s the kind of evidence you can use to say, ‘Ah, so you can really see something about people’s personality in the way they fold the cards.’ “

In 2012, Dambrogio was lucky: a Yale researcher named Rebekah Ahrendt found a 17th century chest with undelivered letters preserved in the postal museum in The Hague, The Netherlands. The chest belonged to Simon and Marie de Brienne, a highly related postmaster and post-manager of his day. Now known as the Brienne Collection, the chest contains 2,600 “locked” letters sent from all over Europe, 600 of which have never been opened.

And there was the challenge. “Once a document, like an unopened letter, is damaged in the opening process, we lose the feeling that the object is intact and intact,” wrote the authors in their article. The virtual opening of these letters helps to preserve “material evidence” about the internal security of a given letter, “including highly ephemeral evidence about folds and layer order, which generally do not leave material traces”.

So Dambrogio et al. it turned to virtual “unwrap” techniques, which are becoming increasingly popular for the study of fragile historical documents. For example, in 2016, an international team of scientists developed a method to virtually unroll a heavily damaged ancient parchment found on the west coast of the Dead Sea, revealing the first verses of the book of Leviticus. The so-called En-Gedi parchment was recovered from the ark of an old synagogue destroyed by fire around 600 CE.

In 2019, we report that German scientists used a combination of cutting-edge physics techniques to “unfold” virtually an ancient Egyptian papyrus, part of an extensive collection housed in the Egyptian Museum in Berlin. The analysis revealed that an apparently blank spot on the papyrus actually contained characters written in what became “invisible ink” after centuries of exposure to light. And earlier this year, we reported that scientists used multispectral images on four supposedly blank Dead Sea Scrolls and found that the scrolls contained hidden text, probably a passage from the book of Ezekiel. Although it took 10 years to determine that Mary’s last letter, Queen of Scots, employed a letter blocking technique, Dambrogio et al. claim that their new method of virtual deployment could make the same determination in a few days.

For the first phase of analyzing the cards in the Brienne collection, Dambrogio created his own test set of 10 model cards, which were then photographed using X-ray tomography by collaborators in the dental research labs at Queen Mary University of London, along with four original letters from the trunk. The scanner in question was designed to be especially sensitive to mapping the mineral content of teeth, but it works the same way with certain types of ink on old paper and parchment. This was followed by the painstaking process of developing algorithms to identify and separate different layers of the folded letters, allowing Dambrogio et al. to unfold and “read” virtually the closed cards. It also allowed them to better explore the various complicated folding systems for each letter, as the algorithm can visualize creasing patterns.

“We were able to use our scanners for the history of X-rays,” said co-author David Mills of Queen Mary University of London. “The scanning technology is similar to medical tomographs, but using much more intense X-rays that allow us to see the small traces of metal in the ink used to write these letters. The rest of the team was then able to take our images and transform them in letters that they could virtually open and read for the first time in more than 300 years. “

In addition to finally reading Jacques Sennacque’s 1697 letter, the team found evidence to track the evolution of letter-blocking technology. The letters in the Brienne collection showed a marked change in letter blocking techniques over time, moving away from the “fold, fold and stick” method, for example, to a more “fold and stick” approach that seems to foreshadow the envelope modern . The subsequent analysis is likely to reveal even deeper historical insights.

“Keeping these records of human interaction with materials intact, while making their secrets visible, allows a new perspective on history that is both kinetic and tactile, and that encourages new ways of thinking about life, emotions and creativity of historical individuals and communities, “wrote the authors. “Doing so also challenges cultural historians to reconceptualize hidden, secret and inaccessible materials as places of critical investigation. Letterlocking and virtual unfolding point to the ways in which history sometimes withstands scrutiny, and that resistance itself deserves patient study.”

A probable source for further study are hundreds of unopened and unopened letters in a file known as the Prize Papers – all confiscated by the British in enemy stores between the 17th and 19th centuries. Ultimately, “we anticipate a complete, data-driven study, covering tens of thousands of known unopened letters and millions more of open letters, gathering letterlocking data globally to make persuasive and consequent statements about historical epistolary security trends,” they concluded the authors. “By synthesizing traditional and computational conservation techniques, we can help integrate computational tools even further into conservation and the humanities – and show that letters are even more revealing when not open.”

DOI: Nature Communications, 2021. 10.1038 / s41467-021-21326-w (About DOIs).

Listing the image by the Unlocking History Research Group file