Before envelopes, there was letter-locking. This was a European trick, it says here*, for folding a letter and locking it closed with parts of the letter-paper itself, so as to keep its contents concealed from prying eyes. Apparently a recipient judged your folding skills along with your literary talents. This research determined there were a dozen basic styles or techniques for letter-locking.
A fantastic digital manipulation, yes, but not as incredible as blooms.
* “New Technique Reveals Centuries of Secrets in Locked Letters” by William J. Broad, NYTimes, Mar 02.