Demonstrably since 1282 in Bologna/Italy, paper mills marked their goods by attaching a thicker wire (on the dandy roll on the paper machine) in the form of a letter or symbol to the scoop.
This figure leaves an imprint in the paper: the fiber layer is thinner there, and when the light shines through, the so-called watermark becomes visible as a more transparent image. Conversely, by partially deepening the screen, it was possible to achieve a fabric enrichment, which thus took on a duller appearance in the view.
By cleverly combining deepening and heightening, it was even possible to simulate halftones. This elaborate process is still used today for banknote watermarks.
Watermarks often provide information about the paper mill, papermaker and thus about the period of manufacture of the paper. They are an important aid in dating documents and graphics. Extensive historical watermark collections can be found in the German Book and Type Museum of the German Library in Leipzig, in the Paper Museum in Düren and in the watermark index of the State Archives of Baden-Württemberg (so-called Piccard), which has been accessible online since December 2005. A distinction is made between genuine, semi-genuine and non-genuine watermarks.
Nowadays, real watermarks are usually created on/in the wire section of the paper machine. The matted fibers are still very moist and a fixed rotating roller (dandy roll) on the wire section thins or partially densifies the paper web at a specified point.
A distinction is made between deposit watermarks and displacement watermarks.
Accumulation watermarks can be produced exclusively on the cylinder mould machine or, as in the original process, on the hand wire.
The deposit watermark is caused by a disturbed deposition of the fibers during the forming process (transition of the fiber from floating to lying).
Depending on the shape of the wire and the length of the fibers, the deposit watermark can be sharper or blurrier.
The typical deposition watermark on round wire is easily recognized by the fact that part of the fibers washed under the wire are torn off during the couching process, so that the edge is always somewhat blurred. Trapezoidal wires or rectangular wires that lie flat on the screen show a razor-sharp image (short pulp).
The displacement watermark is formed on the egotteur section and is characterized by the fiber being displaced at the moment of formation by an egotteur wire acting from above.
The resulting watermark is characterized by the fact that it is always somewhat blurred (due to the shape of the wire used and the elasticity of the nonwoven) and often has slight squeeze marks.The buildup process can also be used to mark pulps that can no longer be marked cleanly in the displacement process (long fibers).
The following applies to both forms of watermarking: The wire thickness selected depends on the subsequent grammage and the thickness of the desired mark. For hand papermaking in the 40-300 g/m² range, wires of approx. 0.4-1.2 mm are suitable.
Semi-fast watermarks (e.g. Molette watermarks) are formed by pressing them into the already much drier paper web after it leaves the wire section (usually in or after the first press). They can be largely removed again later by partial exposure to caustic soda or water.
In contrast to the genuine watermark, here the paper fiber web is primarily embossed and the fiber structure is not significantly changed. There is no significant reduction or increase in the thickness of the fiber web. Molette watermarks are usually produced with hard rubber rings (similar to stamps or letterpress types) mounted on the molette.
Typical applications for molette characters are lettering running along the edge parallel to the running direction of the paper. Less commonly, molette characters are made as password watermarks. The use of ornaments is limited to simple line forms in the molette. Two-dimensional or shadow watermarks cannot be created in this way.
The second form of semi-authentic watermark is the calender watermark. Calender watermarks are imprinted in the completely dry paper web during calendering (smoothing by a combination of friction and pressure in the roller unit = calender, hist. also “calendar” or “calender”) of the paper. The paper is compressed hard in the process.
The calender watermark can be removed from the paper by swelling with water. Calender watermarks can be recognized by the extremely hard edge contour and the cut-like indentation of the paper.
Molette watermarks and calender watermarks often cannot be precisely distinguished from each other. Calender watermarks are primarily suitable for line forms. However, two-dimensional shapes are also known. A specialist for machine-made and thus also for the semi-genuine watermarks is Mr. S. Feyerabend from Hamburg.
Fake watermarks are not watermarks in the true sense of the word, since they are not created during paper production (i.e. not by water). They are usually printed on afterwards.
Very often, transparent mass (e.g. glycerine, fat color carrier or sulfuric acid paste -> mercerizing) is printed here, which is supposed to simulate a real watermark by adding some color pigments.
Subsequent embossing into the paper (similar to calendering) also meets the “requirements” of a fake watermark.
A modern form of watermark forgery for the difficult-to-copy shadow watermarks (accumulation watermarks) consists in sheet production from two sheets of half end thickness. In this case, one of the sheets is printed with the motif before gluing (later lying inside), which then appears like a shadow watermark when viewed through. Such sheets can be easily unmasked with the burn test or a suction test (see cardboard/board production).
Fake watermarks are easily recognizable by the lack of thinning/thickening of the paper or by the discernible ink application.
Fake watermarks can be removed from the paper without residue using chemical reagents (e.g. alcohols).