What is a paper watermark?

Watermarks are designs or patterns put into paper during its production, by making thinner or thicker the layer of pulp when it is still wet.
Paper watermarks can be seen holding the paper against the light or, in some cases, over a black surface. Usually, they show themanufacturers name, and geometric designs, or images of animals, etc.
The object of watermarks in paper is, essentially, identifying the paper, as a signature of the manufacturer, or as a security measure to avoid forgery of important documents as bank notes, passports, entry tickets.
Today, good quality writing paper, as well as art drawing paper or paper for bibliophile publishing, usually carry an identifying watermark. Nevertheless, it is easier to find watermarks in old papers from envelopes, letters, books... Indeed, watermarks are a good help in the study of old documents, as they can suggest their origin or date.
 

Links to very good websites about watermarks in paper

International Association of Paper Historians
The IPH integrates professionals of different branches and all friends of paper within the field of ?
paper history. It coordinates all interests and activities in paper history as an international specialist association co-operating with international, regional and local organizations not only of paper historians but also of keepers of archives and libraries, conservators, art historians,specialists in books, printing and technology, associations of the paper industry, the publishing trade etc., including handicraft and artistic activities in connection with paper.
 

Paper Federation of Great Britain
The Paper Federation of Great Britain is the trade association representing UK manufacturers of pulp, paper and board. Site includes industry key statistics.