Step 2: The Letter / Envelope
Airmail envelopes like this are no longer able to be mailed, so tracking enough down was quite a process. An outlet store provided most, and a wanted post on Craigslist had enough responses from people who had most of a box in their stationery drawer to round out what we needed. Each envelope was dyed using the same process, but this will ruin the glue portion of the envelope, so have a plan ahead of time. We tried two different ways to solve this - we let them dry closed and then if an envelope would open easily, we just opened it; otherwise, we opened the top with a letter opener. We made a trip to a local stamp collector and purchased grab bags of various worthless old stamps to add to the envelopes.
The final detail necessary to complete the look was to cancel the stamp. We bought a rubber stamp of a postmark at a craft store and then marred it a little with tweezers in order to obscure the location and date. We stamped all our envelopes with black pigment ink and once everything was dry and flat, we popped in Season One of LOST and started collating all the letters.