I've just been watching a program presented by Adam Hart-Davies about how London was built. He showed some paper making, explaining that hand made paper was expensive and a slow process which made printing very expensive. Printing started in the U.K. in the 1500s.
He created a water mark by having stitching on the screen which was used to make the paper. What he also did, was use a sponge to absorb excess water and to cojoin the fibres after he had put the mould onto the blanket (can't remember the proper terms for either the mould or the blanket). I must try both of these one day.