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MIT researchers read a letter without opening it

Signed, sealed, and revealed: An intricately folded 17th-century letter gives up its secrets.

A rare example of an unopened letterpacket with a paper lock.The Brienne Collection

In July of 1697, Jacques Sennacques penned a letter to his cousin Pierre le Pers, a merchant in The Hague. He then painstakingly sealed the letter using an intricate technique known as letterlocking — a method of folding a letter that allows it to serve as its own secure envelope — and dropped it in the mail. What happened next would surprise few present-day Americans: It was never delivered. Instead, Sennacques’s letter was locked away in a trunk in the care of the postmasters of The Hague, awaiting a recipient who did not materialize. There it languished, along with nearly 600 other letters, sealed and unread for centuries.

That began to change in 2016, when researchers at the Massachusetts Institute of Technology, working with teams at institutions around the world, developed a “virtual unfolding” method. This advance allowed them to “read” the letter while leaving it in its letterlocked state.


As the researchers detailed last week in the journal Nature Communications, they combined precise use of X-rays with a computer algorithm that was able to map the folds and layers inside the letter without damaging it. It’s an exercise in seeing the unseen and protecting history at the same time. The algorithm was tested against an opened letter that confirmed the folding pattern. Handwriting experts verified the X-ray-detected text.

When asked why researchers didn’t simply open the letter, researcher Nadine Akkerman of Leider University explained that the sealed letter would be forever changed were it opened. “Imagine you’ve discovered an origami bird you’ve never seen before,” she said. “You unfold it to learn its secrets and it rips as you do so. You may never be able to recreate it.” In fact, in a “Mission: Impossible”-esque twist, many letterlocked papers have self-destruct mechanisms built into them. “People went to great lengths to prevent their letters being opened and read clandestinely,” she says. Some had “built-in traps that actually ripped the paper and could even ruin the message.”


A computer-generated unfolding animation of a sealed letter.Unlocking History Research Group

MIT Library Conservator Jana Dambrogio says that keeping the letter in its locked state preserves history itself. “We may lose valuable evidence about the locking process when we open a historic locked letter,” she says, because the way the paper is folded is itself a valuable trove of historical information. “Many letters found in [the trunk] have internal tucking systems to help keep the letterpacket closed. . . . Those internal tucks are as ephemeral as a sneeze. We lose the letter’s paper engineering evidence when we open [them].”

For those of us hoping for a steamy bit of gossip or a burning love letter to emerge from a pre-Victorian past, we’ll have to keep waiting. “Bridgerton” the Sennacques letter is not. Rather, it is a request for the legal death certificate for a relative and an inquiry about the well-being of the le Pers family. But hundreds of other letterlocked parcels wait to be digitally revealed.

Ben Jackson is a writer and producer in Natick. Follow him on Twitter @benjacksonwrites