Letterlocking in the 16th century
Before the invention of the envelope, people had to devise ways to protect the content of their correspondence. Once the letter was neatly folded, sealing wax was used to keep the letter closed and untampered with.
Initially sealing wax was made of beeswax only, which had a drawback as it could be removed neatly with a thin heated knife and, after the content of the letter was read, the sealing wax was replaced back on the letter with a few drops of melted wax.
So a new type of wax was later invented, made of a blend of shellac, turpentine, chalk and a colouring agent. This was very difficult to remove and replace as it firmly stuck to the writing surface on which it was placed.
I recently stumbled upon a fascinating website (letterlocking.org)dedicated to letterlocking, a term used to describe the different ways to fold and secure letters in the times before the envelope. They have tens of videos on how to fold and seal letters, which inspired me to create my own.