X-rays help scientists read Renaissance ‘Letterlocked’ mail



A computer-generated representation of the virtual step-by-step flow of the letter.

A computer-generated representation of the virtual step-by-step flow of the letter.
Picture: Courtesy of the Unlocking History Research Group Archives.

In July 1697, Jacques Sennacques of Lille, France, scribbled a missive to his merchant cousin, Pierre le Pers, in The Hague. The topic of discussion was a death certificate from their loved one, a topic the cousins ​​had previously discussed but which the Pers neglected to follow up. The letter was the Renaissance equivalent of a “by my previous email”, and it has only been read for the first time since it was sealed 324 years ago.

But although it has been read, the letter is still not open. It’s letterlocked, a term coined by MIT conservator Jana Dambrogio for letters that use specific folds and slits to seal, without the need for an envelope. Lock letters was the typical way of sealing messages in the days before mass production of envelopes; Queen Elizabeth I of England had at least five different letter lock variations to privatize her correspondence.

In a unique application of the technology, Dambrogio’s team “unfolded” the Epistle of Sennacques using virtually x-ray microtomography, which allowed researchers to bypass the often damaging process of manually opening a a letter. The team’s search was published Tuesday in the journal Nature Communications.

A virtual unfolding of the centuries-old letter.
GIF: Courtesy of the Unlocking History Research Group Archives.

“I remember a feeling of elation, as in, [oh my god] we finally did it, ”said co-author Rebekah Ahrendt, musicologist at Utrecht University, in an email. “Having worked with this collection for a number of years, the effect of ‘I’m probably the first person to read this since it was written’ has worn off a bit … That said, this letter is such a great example of the concerns of normal people right now.

It is not clear why the Pers never received the letter – given his profession, he may have moved. But the sealed letter remained in the care of the main postmasters of The Hague, Simone de Brienne, and his wife, Marie Germain. The couple did not rule out the attached family affair as at the time the letters were purchased by the recipients and not paid by their senders. Some postmasters kept unclaimed letters in case someone ended up buying them. The couple in charge of The Hague post were either hoarders or decidedly optimistic, as they kept the letters until their deaths. Thousands of letters charged to Brienne and Germain have been kept in an old trunk, and 600 of them are unopened letter messages; it is an astonishing assemblage of European conversations suspended in time, now called the Brienne collection. The collection is housed at the Sound and Vision Museum in The Hague.

X-raying through the letter written by Sennacques produced the smear of iron-rich ink which he noted through each fold of the letter. The intensity of the x-rays was about a third of that used by the same machine for its original purpose: imaging teeth and bones.

The team's readable results, with the slight watermark of the letter in the center.

The team’s readable results, with the slight watermark of the letter in the center.
Picture: Courtesy of the Unlocking History Research Group Archives.

“We start with a very high resolution CT scan of the folded packet of letters, essentially a 3D x-ray image,” said Amanda Ghassaei, co-lead author of the project, algorithm engineer responsible for the project and who previously worked on the simulation of the origami folds, in an email. “From there, our algorithm detects the individual paper layers in the scan and reconstructs the folded geometry. This computational pipeline allows us to observe handwriting, watermarks, seals, internal folds, and any other information hidden inside the bundle of letters without damaging the original artifact. “

But that was not enough. The team also had to decipher the folded letter, understanding which characters were falling where in the unfolded version. To do this, they used a computer flattening script, to deconstruct the letter without touching it. Although an imperceptible jumble of characters from the outside, wrapped in the khaki paper, the research team were able to extract the message without a problem.

The research team did not describe the folded layout of Sennacques’ letter in the code; the algorithm made the heavy geometric lift.

The Renaissance chest contains missives from all over the world sent to The Hague.

The Renaissance chest contains missives from all over the world sent to The Hague.
Photo: Courtesy of the Unlocking History Research Group Archives.

“The message and the complex internal mechanics of these letters are only known to us because they have been virtually reconstructed,” said co-author Holly Jackson, an MIT undergraduate student and algorithmic engineer on the project. “Our methods are fully automatic, unbiased for scan orientation, and require no prior knowledge of the folded geometry of a packet of letters.”

So, to draft the new document, the team used x-rays to detect the ink layout on a centuries-old piece of paper, they built and deployed an algorithm to virtually unfold that paper, and they described the contents of this letter alongside a complex dictionary for the various letter locking techniques as a larger practice a few days before the envelopes. Essentially, the work was threefold.

The sum of these efforts is a clear plan of attack for the approximately 600 letter-shaped objects that remain in the vault. Cousins’ scruples, marital disputes, state secrets – who knows?

It’s as close as history can hold its breath.


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