Once the letter was nice and dry, it's time to encapsulate it in polyester film (or Mylar for those of you who prefer that term). There is no adhesive involved. The edges are sealed with our ultrasonic welder and it melts them to seal it. We decided to seal it on all four sides to keep it from air, dust, etc. The air has been forced out from in-between the layers of film using weights before welding the edges. This also keeps a suction seal inside and the pieces cannot slide around (right now, it's one sheet of paper but there is a small tear in the middle). You can see in this picture that it is lying between the sheets of polyester film and the weight is lying on top of it. This final flap will be folded over, leaving only a small edge of polyester film to be welded shut.
Ta da! All four sides are sealed and it's time to trim the edges. You can see a close-up of the sealed corners here on the left, particularly if you click on the picture. Usually, we seal both of the longer sides first and then finish up with the shorter sides (if we are completely enclosing it). If the item was extremely large and couldn't fit into the welder, we may resort to using archival double-sided tape to seal the film. Luckily, this letter was a nice and easy size. Because this letter is exceedingly rare and valuable, I don't want to risk trimming the edges on our large guillotine-style cutter. (I must find you a picture of it). Instead, I trimmed the edges very carefully with scissors. I left a little bit of room on the inside bordering the letter just in case we need to open it up again. If necessary, we can re-use the same pieces of polyester film and weld them shut again.
Apologies if any of the layouts of this post come across as wonky on your browser. I switched to the new editing software that Blogger has and though it's supposed to be easier, it really wasn't. Especially with putting in pictures and getting the text not to look too weird.