March 5, 2024

The old letters were hidden from prying eyes as the sheets of writing paper were carefully folded to become their own secure enclosures.

The first step in their digital opening is to scan a destination letter with an advanced x-ray machine. The resulting three-dimensional image shows – similar to a medical scan – the internal configuration of the letter. A computer then analyzes the image to remove the wrinkles and almost magically turns the layers into a flat sheet, revealing handwritten text that can be read.

The team translated one of the digitally opened letters from the Brienne collection. It was dated July 31, 1697 and sent from Lille, France to a French merchant in The Hague. It turned out that a certified copy of an obituary was requested. The letter also asked for “news about your health”.

Further analyzes of the Brienne collection could enrich studies not only on postal networks in early modern Europe, but also on politics, religion, music, drama and migration patterns in the region.

The team not only announced its technology to unlock the letters without damaging them, but also examined 250,000 historical letters that led to the “first systematization of letter locking techniques”. The scientists found 12 formats of locked letters – the most complex with an overall shape defined by 12 borders – as well as 64 categories that contain manipulations such as tucks, slits and folds. The team gave each blocked letter a security rating.

Dr. Smith of King’s College London, who lectures on early modern English literature, said the art is so diverse that the lock can almost serve as a person’s signature. One letter, he said, “became an ambassador for you and had to represent something of yours.”

Without the ability to digitally unlock letters, it took scientists a decade to conclude that Mary, Queen of Scots, had secured the letter to her brother-in-law with a distinctive spiral stitch. According to the team, the virtual development could have documented this step “in a few days”.