Women spies for King Charles 1 knew how to letter-lock their communications so that these messages passed to him in secret.
These expertly crafted locked letters would be damaged if opened making resealing impossible. In fact, trying to open them without the unfolding code would often lead to a damaged and unreadable message. Furthermore, each spy had their own locking signature so that King Charles knew that the letter came from who it said it did.
Today, researchers can virtually unfold these historic writings and read their contents without damage. For more about letter-locking see this article, or this entry in Wikipedia.
Astucieux, mais il fallait avoir le temps …merci pour ces infos ..
Tellement vrai. Diane