When I was in junior high school, in those better days before texting, kids communicated by passing intricately-folded handwritten notes. Using complex folding techniques so that the paper becomes its own envelope, a process called "letter locking" actually dates back hundreds of years. Recently, conservationists examining an antique trunk containing more than 2,500 pieces of undelivered mail—nearly 600 of which were "locked letters—used X-ray scanners to virtually "unlock" one of them without risking likely damage of physically unfolding it.
"Sometimes the past resists scrutiny," the researchers from MIT, Queen Mary University of London, and other institutions said in an announcement. "We could simply have cut these letters open, but instead we took the time to study them for their hidden, secret, and inaccessible qualities. We've learned that letters can be a lot more revealing when they are left unopened."
According to their scientific paper, the team applied computational flattening algorithms to the X-rays enabling "reconstructing and virtually unfolding volumetric scans of a locked letter with complex internal folding, producing legible images of the letter's contents and crease pattern while preserving letterlocking evidence."
Learn more at the Unlocking History Research Group site.
And here's what's in the letter seen in the image below:
Dear sir & cousin,
It has been a few weeks since I wrote to you in order to ask you to have drawn up for me a legalized excerpt of the death of sieur Daniel Le Pers, which took place in The Hague in the month of December 1695, without hearing from you. This is f…g I am writing to you a second time in order to remind you of the pains that I took on your behalf. It is important to me to have this extract you will do me a great pleasure to procure it for me to send me at the same time news of your health of all the family.
I also pray that God maintains you in His Sainted graces & covers you with the blessings necessary to your salvation. Nothing more for the time being, except that I pray you to believe that I am completely, sir and cousin, your most humble & very obedient servant,
"Unlocking history through automated virtual unfolding of sealed documents imaged by X-ray microtomography" (Nature Communications)