A watermark is an area of a paper sheet where the fibers are less thick allowing for a design or signature to be detected when the paper is held up to the light. In handmade paper a watermark is created by thickening up some of the wires on the mould on which the paper is formed. This is usually done by winding wire around the mesh of the mould, as you can see in the photo below.

Mould detail from Simon Barcham Greene’s website

 

The original purpose of a watermark seems uncertain: the circumstantial evidence suggests that they were used as a sort of trademark, an indication of which mill had made the paper. The suggestion that watermarks may have been used to identify different paper sizes and qualities, while superficially plausible, collapses under a complete lack of evidence. (See Foolscap.)

My theory of the watermark’s origin is that they started as a personal mark, identifying the individual vatman who made the sheet. After all a craftsman would in all probability provide his own tools, and how better to mark your own mould than to wind wires into it carrying your own mark? Over the centuries this watermark might easily become linked to the mill at which this craftsman ruled the roost. Of course, however plausible this suggestion may be, it too is not supported by any hard evidence.

You can see them creating the watermark on a mould at 6 minutes into this fascinating video (if you don’t see the video, click on the title of the post so you can view it in your browser). You will have to click through to YouTube to see it as Anglia Television seem to have restricted access.

The Gravell Watermark Archive at the University of Delaware provides a searchable database where the many and various watermarks used by papermakers may be consulted. Their information page does indeed provide much information.

Nowadays, commercial book papers made on Fourdinier machines can, and often do, have a watermark. Although it works in the same way by thinning out the paper to form a translucent design, the watermark is now applied after the sheet has been formed, by putting a raised design on the dandy roll, whose main function is to extract water from the sheet and to even out its formation. Papers for currency incorporate several different types of security feature including watermarks, some of a more complex chemical origin than a mere dandy roll kiss.