In sixteenth- and seventeenth-century Europe, ready-made gummed envelopes were not yet for sale. Many letters were folded from the very sheet they were written on.
In one spiral lock documented by historians, a strip left attached to the sheet passed through slits in the packet and through itself. Opening it could tear the strip and leave traces on the paper.
On a letter Catherine de’ Medici sent in 1570, researchers estimate that up to 99% of the paper lock survives, scattered in fragments across the sheet. Wax and extra pieces of paper were part of its closure. The fold here adapts some documented principles; it does not reproduce her letter, seals or exact lock.
Paper and handwriting
The sheet is divided into panels that rotate along its creases; a strip cut from the margin locks the packet. Each mark remains attached to the place where it was made. The wax seal is a drawing: it does not show whether the letter has been opened before and does not prove who sent it.