In 1697, a man wrote to a merchant in the Netherlands to request a copy of an official death certificate for his cousin. The tightly folded letter has never been opened, but researchers have managed to read its contents without breaking the seal by using a high-resolution X-ray scanner designed for dental research, the Wall Street Journal reports. The letter was among around 600 sealed and unclaimed letters left in a trunk by Simon de Brienne and Marie Germain, early postmasters in The Hague. They are intricately folded in a practice called "letterlocking," common before envelopes were widely used, which made reading the contents a major challenge. Researchers say they were able to read the letter by scanning for traces of metal in the ink and using an algorithm to "virtually unfold it," reports CNN.
The researchers say unfolding the letter could have destroyed valuable evidence for historians. "We could simply have cut these letters open, but instead we took the time to study them for their hidden, secret, and inaccessible qualities," the researchers wrote in a study in the journal Nature Communications. "We’ve learned that letters can be a lot more revealing when they are left unopened." Letters in The Brienne collection, which also contains around 2,000 opened letters, were sent to The Hague from all over Europe between 1689 and 1706. Researchers say the technology will be used to read more unopened letters from the collection and it could also be used to unlock many more historical secrets, including the hundreds of unopened letters in the Prize Papers, a collection of documents seized from enemy ships by the British between the 17th and 19th centuries, NPR reports (Read more discoveries stories.)