Watermark

Watermarks were first introduced in Fabriano, Italy, in 1282. At the time, watermarks were created by varying the thickness of the paper during a stage of the manufacturing process while it was still wet. == Processes ==

Dandy roll process Traditionally, a watermark was made by impressing a water-coated metal stamp onto the paper during manufacturing. The invention of the dandy roll in 1826 by John Marshall revolutionized the watermark process and made it easier for producers to watermark their paper. The dandy roll is a lightweight roller covered with material similar to a window screen that is embossed with a pattern. Faint lines are made by laid wires that run parallel to the axis of the dandy roll, and the bold lines are made by chain wires that run around the circumference of the roll secure the laid wires from the outside. Since the chain wires are located on the outside of the laid wires, they have a greater influence on the impression in the pulp, hence their bolder appearance compared to the laid wire lines. This embossing is transferred to the pulp fibres, compressing them and reducing their thickness in the corresponding area. Since the patterned portion of the page is thinner, it transmits more light and therefore has a lighter appearance than the surrounding paper. If these lines are distinct and parallel, and/or there is a watermark, then the paper is called laid paper. If the lines appear as a mesh or are indistinct, and/or there is no watermark, then it is called wove paper. Cylinder mould process Another type of watermark is called the cylinder mould watermark. It is a shaded watermark first used in 1848 that incorporates tonal depth and creates a greyscale image. Instead of using a wire covering for the dandy roll, the shaded watermark is created by areas of relief on the roll's own surface. Once dry, the paper may then be rolled again to produce a watermark of even thickness but with varying density. The resulting watermark is generally much clearer and more detailed than those made by the Dandy Roll process, and as such, Cylinder Mould Watermark Paper is the preferred type of watermarked paper for banknotes, passports, motor vehicle titles, and other documents where it is an important anti-counterfeiting measure. == On postage stamps ==

In philately, the watermark is a key feature of a stamp, and often constitutes the difference between a common and a rare stamp. Collectors who encounter two otherwise identical stamps with different watermarks consider each stamp to be a separate identifiable issue. The "classic" stamp watermark is a small crown or other national symbol, appearing either once on each stamp or a continuous pattern. Watermarks were nearly universal on stamps in the 19th and early 20th centuries, but generally fell out of use, but some countries continue to use them. Some types of embossing, such as that used to make the "cross on oval" design on early stamps of Switzerland, resemble a watermark in that the paper is thinner, but can be distinguished by having sharper edges than is usual for a normal watermark. Stamp paper watermarks also show various designs, letters, numbers and pictorial elements. The process of bringing out the stamp watermark is fairly simple. Sometimes a watermark in stamp paper can be seen just by looking at the unprinted back side of a stamp. More often, the collector must use a few basic items to get a good look at the watermark. For example, watermark fluid may be applied to the back of a stamp to temporarily reveal the watermark. Such devices can be very useful for they can be used without the application of watermark fluid and also allow the collector to look at the watermark for a longer period of time to more easily detect the watermark. ==Watermarks and historical scholarship==

Watermarks can be informative for historians, since they offer clues for when or where a document was prepared. The musicologist Alan Tyson conducted a comprehensive survey of the forms of paper employed by Wolfgang Amadeus Mozart, based primarily on watermarks, and was thus enabled to correct the date (and often place of origin) assigned by earlier scholars to the composer's compositions. Filigranology is the study of watermarks. == See also ==