Watermarks can be used as decorative devices, or as functional additions to the paper. In the late 18th century, papermakers began to experiment with watermarks to add functionality to writing paper. Stationery was a blank sheet with size to accept the ink without it soaking into the sheet. In addition, paper was smoothed with stones or large flat metal sheets so that the quill pen would move smoothly across the surface of the paper.
Wire was woven into a uniform screen in the mid 18th century to create wove paper. The uniform surface of wove paper made it possible to treat the surface of the sheet of paper more like a uniform surface like a block of wood or sheet of metal for engraving. Papermakers began to experiment with how they could enhance the surface through watermarks, and a ruled-line watermark was developed where straightened wire was sewn onto the wove cover of the mould. This created a subtle surface of straight lines that could be seen with the aid of a dark sheet of paper placed behind and made it possible for people to write a letter in straight lines. When the dark sheet is removed, the watermark is almost invisible. This innovation was used through the early 19th century as a deluxe stationery product, falling out of favor as paper became machine-made.