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High-Tech Scan looks inside sealed letters from the Renaissance: NPR

A computer-generated unfolding sequence of sealed letter DB-1538. New research describes how “virtual unfolding” was used to read the contents of sealed letter packages from 1

7th-century Europe without physically opening them.

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A computer-generated unfolding sequence of sealed letter DB-1538. New research describes how “virtual unfolding” was used to read the contents of sealed letter packages from 17th-century Europe without physically opening them.

Unlock for the history research group

An unopened letter sent back in 1697 but never delivered has been read by scholars who have developed a way to almost “unfold” sealed letter packages without having to break the seal.

The new technique described in the journal Nature communication, should allow historians to learn more about “letter locking”, the practice of using detailed columns, folds, folds and tucks to transform a flat sheet of paper with a written message into a tamper-resistant package.

Such precautions have been a daily part of life for centuries. “The envelope as we know it, the rubberized envelope, was not invented until the 1830s,” says Jana Dambrogio, a curator at the Massachusetts Institute of Technology Libraries in Cambridge, Mass. “And then before then all the letters were locked.”

An example of an intricate folded letter. This practice was common hundreds of years ago to prevent manipulation. Researchers have figured out how to almost unfold and read some of these letters without harming them. They have used their non-invasive technique to read undelivered letters that have been kept unopened in a postmaster’s trunk for over 300 years.


Text locking technologies varied widely, with people folding and sealing their messages in hundreds of different ways. “They can make it look less secure and have security hidden on the inside,” Dambrogio said. “Or they may make something look very secure, but it’s actually not so secure inside when you open the letter package.”

Letterlocking, however, has not received much attention until recently, and in the past, archivists have opened locked letters by simply cutting them. “What do we lose when we open unopened?” asks Dambrogio.

She was fascinated to hear about a 17th-century postmaster trunk from The Hague in the Netherlands that contained 577 unopened letter packages. Back then, if a letter for some reason could not be delivered, workers would keep it around if the intended recipient ever showed up to demand it and pay the postage.

Dambrogio and a team of scholars now say they have managed to read one of these unopened Renaissance letters using a medical scanner.

“It was originally designed to study teeth. It’s this really high-resolution X-ray scanner,” says Amanda Ghassaei of Adobe Research in San Francisco, who explains that the device can create a detailed three-dimensional X-ray image of a folded letter.

Because the inks used at the time contained a lot of metal, Ghassaei says, the text shows “as a very bright area on the scan, as if the way your bone would appear really light on an x-ray.”

The problem is that the ink markings all look alike because many layers of folded paper are printed close together and words appear to overlap.

“The challenge here was really to try to find a way to manipulate this data and actually almost unfold it so we could get it in a flat state,” she says, “and actually generate something resembling a picture of a letter if it had been opened and flattened. But in reality we have not even touched the letter. “

Their first success using a brutal force algorithm to study a partially opened letter came in late 2016, recalls Holly Jackson, a student at MIT who has worked on the project.

“Since then, we’ve somehow refined this pipeline and tried to make it fully automated, fully generalizable to many different intricate folding patterns,” Jackson says.

The unopened 1697 letter from the postmaster’s trunk has a particularly nice folding pattern, Dambrogio says, though the content of the letter makes it clear that it’s just an ordinary family business where one cousin writes to another to request a copy of an official death. certificate to one of their relatives.

“In a sequence, it makes an arrow shape that folds into itself and is sealed with a small piece of adhesive,” says Dambrogio. “So it’s pretty beautiful, and it’s exciting that we can read it without manipulating the letter package and letting it study like an unopened object.”

The work impressed Brent Seales, a computer scientist at the University of Kentucky in Lexington who has worked on virtually “unpacking” old rolls that are too fragile to be rolled out.

“They revealed the text, which was amazing. Doing so without opening the letter is in itself a kind of miracle that I love,” Seales says. “They were also complete with the technology of the artifact itself, because we can not forget that these things are embodied in physical form. And that is important.”

He notes that the process of sealing written documents goes back to the clay plates used by the Sums, and that it can put historians in a difficult position because to open something is to destroy it in part.

“There’s this idea of ​​the physical artifact that needs to be preserved, and then the scientific work that we want to do, that is, to know what it says,” Seales notes. “How do you break that stalemate?”

Virtual unpacking can provide an answer, he says, but its methods must always be fully described and transparent, as they were in this case, so that others can follow the process step by step. “They told you in their paper what’s inside a letter without ever opening it. You have to have some kind of confidence in it. Because the artifact itself will never be opened,” Seales points out.

Many, many unopened letters await further investigation, including hundreds in the pricing papers, a collection of mail and other material confiscated from enemy ships of Britain from the 17th to the 19th century.

Howard Hotson, a historian at the University of Oxford, believes that studying unopened letters and others that were once locked might “reveal patterns of transcultural, potentially global technological exchange as sophisticated letter-locking techniques are transferred from a country, activity area, or continent to second in the long period in which these techniques were in use. “

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