I’m liking this a lot, envelopes are one of those thing I’ve always taken for granted.
“The use of pre-made envelopes for standard mail is a relatively new practice. Before their use became common it was standard to fold the sheet of paper a letter was written on in a way making it suitable for posting.”
GHH who host a variety of obscure sites have instructions and a great many variations on how to fold a letter into an envelope.
“If you are not into envelope and letter folding you may wonder why one should go to the trouble of folding up an envelope when you could just buy one from a stationery store. Well, first off, it is the very nature of hobbies that they tend not to be entirely practical.”
Ha, ‘because it’s not entirely practical’ that good enough reason for me, from now I’ll be folding all mine!
Take some pictures for your instruction. It’s not easy to read and understand from the picture you posted.