Not directly origami, but I came across this in the Guardian about a cache of 17th Century letters (http://www.theguardian.com/world/2015/nov/08/undelivered-letters-17th-century-dutch-society)
The linen-lined leather trunk, covered in official seals, was presented to a postal museum in The Hague in 1926, but the 2,600 letters it held, 600 of them unopened, are only now being studied...Special scanning techniques will be used to examine the contents without opening the sealed letters or damaging the ingenious variety of ways in which the pages were folded to so that the letter became its own envelope. You can see a photo of one of the folded letters. Clare, Perth, Western Australia
