Letterlocking: the long-lost art of using paper-folding to foil snoops

"Letterlocking" is a term coined by MIT Libraries conservator Jana Dambrogio after she discovered a trove of letters while spelunking in the conservation lab of the Vatican Secret Archives; the letters had been ingeniously folded and sealed so that they couldn't be opened and re-closed without revealing that they had been read. Some even contained "booby traps" to catch the unwary. Read the rest