If you look carefully at a medieval page that is made of paper, you notice a shape hidden inside, such as the head of an ox, a bell, or a jester. These little ‘drawings’ that show themselves when you hold a light behind the page are watermarks. They are a byproduct of the production process of paper. The papermaker used a kind of screen to scoop up the mush of cloth from which paper was made.
The water would be pushed through a roster or sift at the bottom of the screen, while the cloth fibers that remained behind formed the pulpy beginning of a page. These screens were fitted with drawings made from thin metal strings. Each papermaker had his own picture with which he ‘branded’ his product. Because the screen was replaced every few years, these watermarks now form a great tool for dating medieval paper manuscripts.