These envelopes were made with a super-handy envelope template I picked up at a local store. It's a kit with a selection of templates to make envelopes of various sizes and for various functions. My favorite was an accordion-sided envelope with a large back flap, best when made with stout parchment. I thought it was great simply for what it was, but it was especially handy when mailing an especially voluminous letter or a package of fun little extras.
The pictured envelopes are of the standard variety, but I'm coating them in a sheath of kozo paper. This is a Japanese paper made by laying out a large sheet of paper fibers in a room with a ceiling designed to leak profusely. The droplets create the pools and holes in the paper, which is allowed to dry with this random, natural formation.
Obviously it's terrible for making an envelope and worse for writing on, but it is a marvelous decorative feature. I dressed up these plain, lusterless envelopes with a judicious application of kozo and was quite happy with the results. The trick is in finding a way to glue the kozo to the envelope. My technique was to glue-stick the entire outside of the envelope and press the kozo flat. This was a poor idea because it left an envelope with dozens and dozens of sticky little holes all over its surface. A better solution might have been to use a spray adhesive on one side of the kozo.