Letterlocking
There was a cool article on this subject a few weeks ago: https://www.npr.org/2021/03/02/972607811/reading-a-letter-th...Basically, opening centuries-old letters that are sealed with this technique is usually a destructive process: you might end up rendering some portions of the letter unreadable.As such, many of these letters have never been opened! They might contain interesting things, but we have no idea.Some researchers figured out a way to "unfold" X-rays of these intricately-locked letters, to render the letter legible without having to actually open it! It's a pretty cool technique.The underlying paper is here: https://www.nature.com/articles/s41467-021-21326-w