Secrets of 'locked' letters revealed Virtual technique was developed to open specially folded letters without damaging their historical contents. By William J. Broad New York Times March 11, 2021 — 10:02pm Text size Copy shortlink: In 1587, hours before her beheading, Mary, Queen of Scots, sent a letter to her brother-in-law Henry III, King of France. But she didn't just sign it and send it off. She folded the paper repeatedly, cut out a piece of the page and left it dangling. She used that strand of paper to sew the letter tight with locking stitches. In an era before sealed envelopes, this technique, now called letterlocking, was as important for deterring snoops as encryption is to e-mail inboxes today. Although this art form faded in the 1830s with the advent of mass-produced envelopes, it has attracted renewed attention from scholars. But they have faced a problem: How do you look at the contents of such locked letters without permanently damaging priceless bits of history?