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
It seems almost impossible to find these videos or channels intentionally, you can only stumble upon them.
I remember when they figured out how to use spectral analysis to 'see' the solvents that soak into paper from the ink, allowing them to read words that had flaked off due to the ink or the paper delaminating, especially at the edges of paper.
If sealing wax is going to be used anyway, why not just fold the letter and seal with wax like normal?
Not that I've ever done that, as a courier, in a live-roleplay game, ever. Repeatedly ;D
Depending on the security level of the letter, of course, a non-letterlocked letter might be pretty readable even if sealed. A simple letter where the seal authenticates the sender but doesn't protect the contents might simply be folded in three and sealed closed - you can bend and flex such a letter without breaking the seal to read most of it. A more important letter being _protected_ by a seal might be folded into an ersatz envelope and then sealed on the join ... but that's most of the way to a basic letterlock.
So, like all communications there's a tradeoff between complexity and security, and whether you're using the seal merely to authenticate the sender (which was pretty common) or also to protect the contents.
So it's not so much that the seal holds the lock closed, as that the seal obscures the lock to the point that opening non-destructively is much harder.
Well now I'd love to hear more about this!
If there are other pieces of paper held in the wax like a 3D matrix of sorts, it gets much more difficult to undo then redo the seal.
Rumor has it that Cardinal Richelieu's men had ways to read wax sealed documents.
How many of these documents have multiple layers of meaning embedded in them? Steganography, euphemisms, inside jokes, shibboleths, what have you. I wonder how many things these letters say that we simply cannot read.
