Three hundred years ago, before envelopes, passwords, and security codes, writers often struggled to keep the thoughts, worries, and dreams expressed in their letters private.
One popular way was to use a technique called letter locking – the intricate folding of a flat sheet of paper to make your own envelope. This security strategy posed a challenge when 577 locked letters delivered to The Hague in the Netherlands between 1689 and 1706 were found in the trunk of undelivered mail.
They had the letters they never reached their final recipients, and conservationists did not want to open them up and damage them. Instead, a team found a way to read one of the letters without breaking its seal or unfolding it in any way. Using a highly sensitive X-ray scanner and computer algorithms, the researchers practically deployed the unopened letter.
This is a computer-generated unfolding sequence of a sealed letter from 17th-century Europe. Virtual deployment was used to read the contents of the letter without physically opening it. Credit: Courtesy of the archives of the Unlocking History Research Group
“This algorithm takes us straight to the heart of a locked letter,” the research team said in a statement.
“Sometimes the past opposes verification. We could have simply cut these letters, but instead took the time to study them for their hidden, secret, and inaccessible qualities. We learned that letters can be much more revealing when left unopened.”
The technique reveals the contents of a letter dated July 31, 1697. It contains a request from Jacques Sennac to his cousin Pierre Le Per, a French merchant in The Hague, for a certified copy of the death notice of Daniel Le Per.
The details may seem prosaic, but researchers say the letter gives a fascinating picture of ordinary people’s lives – a snapshot of the early modern world in the course of their business.
This trunk of unsent 17th-century letters was bequeathed to the Dutch Postal Museum in The Hague in 1926. A letter from this trunk was scanned by X-ray microtomography and practically unfolded to reveal its contents for the first time in centuries. Credit: Courtesy of the archives of the Unlocking History Research Group
In addition to the unopened letters, it contains 2,571 open letters and fragments which, for one reason or another, never reached their destination.
At that time, there was no such thing as a postage stamp, and the recipients, not the senders, were responsible for postage and delivery charges. If the recipient has died or rejected the letter, no fees can be collected and the letters have not been delivered.
A new way of obtaining historical documents
X-ray scanners were originally designed to map the mineral content of teeth and have been used in dental research – until now.
“We were able to use our X-ray scanners,” said study author David Mills, a researcher at Queen Mary University in London.
“The scanning technology is similar to medical scanners, but uses much more intense X-rays, which allow us to see small traces of metal in the ink used to write these letters. The rest of the team was then able to take our scanned images and they turn them into letters that can be opened virtually and read for the first time in over 300 years. “
The letter contained a message from Jacques Sennac dated July 31, 1697 to his cousin Pierre Le Per, a French merchant. A watermark in the center containing an image of a bird is also visible. Credit: Courtesy of the archives of the Unlocking History Research Group
The new technique has the potential to unlock new historical evidence from Brien’s trunk and other collections of unopened letters and documents, the study said.
“Using a virtual deployment to read an intimate story that has never seen the light of day – and has not even reached its recipient – is truly extraordinary,” the researchers said in a statement.
The study was published in the journal Nature Communications on Tuesday.