Researchers find a way to virtually open a sealed letter from 1697

More than 300 years after it was mailed, a letter sent from one cousin to another in the Netherlands has finally been opened — virtually.

Jana Dambrogio, a conservator with the Massachusetts Institute of Technology Libraries, told NPR that before the gummed envelope was invented in the 1830s, people would secure their letters via "letterlocking," using intricate folds, creases, slits, and holes to transform the piece of paper into a package. While some archivists have used scissors to cut locked letters, Dambrogio worried about what is lost "when we open the unopened."

With a team of researchers, Dambrogio was able to take a locked letter and read it, without disturbing anything. The letter, written in 1697, was found in The Hague in an old postmaster's trunk. Inks at that time contained high amounts of metal, so the team used an X-ray scanner that can create 3D images of teeth to make a 3D image of the letter. The writing showed up "as a very bright region on the scan," like a bone would appear on an X-ray, Amanda Ghassaei of Adobe Research told NPR.

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Because it was folded so many times, the letter had several layers close together, making the words look jumbled. The team had to "find a way to manipulate that data and actually virtually unfold it so that we could get it into a flat state," Ghassaei said. Success came after the researchers used a brute-force algorithm, and they discovered that the letter was sent to request an official death certificate for a relative.

The folding pattern included an arrow shape, and is "quite beautiful," Dambrogio told NPR. She finds it "thrilling" that the note can be read "without tampering with the letter packet, leaving it to study as an unopened object."