Watermark

Watermarks are originally introduced in the paper by different thicknesses of paper, using light transmission recognizable brands image and served to identify the producing paper mill. Today they are used inter alia as a security feature for banknotes and stamps. Since watermarks need a specific procedure to be noticeable ( up to the light ), are non- perceptible marks in digital content that can also be detected only with a predetermined method, referred to as digital watermarks.

Watermarks in paper

Proven since 1282 in Bologna, Italy marked the paper mills their goods, as on the wire mesh of the suction strainer ( since the 19th century in part then on the dandy roll ) a thicker wire in the form of a letter or symbol attached. This figure leaves an impression in the paper; the fiber layer is thinner there, and when light, the watermark is visible as a transparent image. Conversely, one could achieve a fuel enrichment, thus in the view got a turbid appearance due to a partial depth of the screen. By skillfully combining between depression and increase even halftones can be simulated. This intricate process is still used in watermark for banknotes. In the early days of European papermaking watermarks were home and business character of the paper mills.

Since the wires were worn for making paper after about two years, allowing the collection of datable watermarks with slight differences that emerged by the craftsmanship, the dating of the paper. Because paper is usually not stored because of its high price, long, this results in a relatively accurate instrument for dating the traditional on paper documents and graphics dar. For this purpose, since the beginning of the 20th century were created extensive historical watermark collections. The first comprehensive work presents Charles- Moïse Briquet represents dictionnaire of filigree, he was followed by the as yet incompletely printed collection Gerhard Piccard in the State Archive of Baden -Württemberg. Other large collections of watermarks are located in the German Book and Writing Museum of the German National Library in Leipzig and the Paper Museum Düren.

The above and a growing circle of other watermarks card indexes are now available partially digitized. Especially it should be noted on the following collections: the seven -speaking watermark portal Bernstein - The Memory of the papers, and the DFG project watermark information system, which summarizes the relevant databases. The digitization of other collections, the gap in mapping the papers used in Eastern Europe is increasingly closed.

The dating of the watermark is mainly done by the determination of the symbol used according to the systematics of the files and in addition by the height and width of the watermark, and the distance of the link wires. On the dating and localization of the watermark also, on the other hand could also be removed by a Schöpfsieb and applied to another their seat within the suction strainer of importance as watermark could on the one hand forgiven by wear watermark; fine determination also requires taking into account the spacing of the warp and weft yarns as well as the attachment points of the watermark on the wire structure.

A distinction will be made into real, half real and imitation watermark.

Genuine watermark

Genuine watermarks are nowadays mostly in the forming section of the paper machine. The matted fibers are still very moist, and a fixed-position rotating roller ( dandy roll ) diluted to the wire section or partially compacted paper web at the point indicated. In the real watermark is distinguished in addition watermark and displacement watermark. Adducts watermark can only be on the cylinder mold or - are produced on the hand-held screen - just as in the original procedure.

The addition watermark is produced by an impaired deposition of the fibers during the formation process (transition of the fiber from swimming to lie ). Depending on the form of wire and fiber length, the addition watermarks can turn sharper or blurrier. The typical annealing watermark on round wire can be easily seen by the fact that the Abgautschen part of geschwemmten under the wire fibers will be torn down and thus the edge is always slightly out of focus. Trapeze wires or rectangular wires that lie flat on the screen, show a razor-sharp image ( short pulp).

The displacement watermark is produced on the Egotteurpartie and is characterized in that the fiber is displaced by a pressure acting from above Egotteurdraht at the moment of formation. The resulting watermark is characterized in that it is always slightly out of focus (the wire shape and elasticity of the web for used) and often with slight dot fringes.

In addition process is also still pulps mark that can not be marked clean in the displacement method ( long fiber ). For both watermarks forms: The selected wire size depends on the later grammage and thickness of the desired character. For the Handpapiermacherei in the range 40 to 300 g / m² there are wires of about 0.4 to 1.2 mm.

Half True watermarks

Half True watermarks ( for example, the serrated roller - watermark ) created by pressing it into the already much drier paper web after leaving the wire section (usually in or after the first press). They can be mostly removed again afterwards by partial action of caustic soda or water. In contrast to the real watermark here the paper fiber web is primarily geared and not significantly changed in the fiber structure. There is no appreciable reduction or increase of the Faserbreidicke. Serrated roller - watermarks are usually manufactured with serrated roller fitted to the hard rubber rings ( designed similar to stamp or printing types). Typical applications for serrated roller - signs are along the edge of continuous strokes parallel to the running direction of the paper. Rare Molette characters are made ​​as pass watermark. The use of ornaments is limited in the serrated roller on simple line shapes. Scale or shadow watermarks can not be produced in this way.

The second form of semi- genuine watermark is the Kalanderwasserzeichen. Kalanderwasserzeichen be in calendering ( smoothing by a combination of friction and pressure in the rolling mill = calender, historically also " Calendar " or " Calender " ) stamped the paper in the completely dry paper web. The paper is compacted hard. The Kalanderwasserzeichen can be removed from the paper by swelling with water.

Kalanderwasserzeichen is evident from the extremely hard edge contour and the cut -like indentation of the paper. Molette watermark and Kalanderwasserzeichen are often not accurately distinguished from each other. Kalanderwasserzeichen are preferably suitable for line shapes. But there are also known two-dimensional shapes.

Loggerhead watermark

Loggerhead watermarks are no watermarks in the strict sense, since they do not (ie not by water) arise in papermaking. They are usually printed subsequently. Very common here Transparent mass ( for example, glycerol, fat color carrier or sulfuric acid paste → Merzerisation ) printed up, which is to simulate by adding some color pigments a genuine watermark. A subsequent embossing in the paper (similar to calendering ) corresponds to the " requirements " of a fake watermark.

A modern form of watermarks for counterfeiting difficult to copy shadow watermarks (Addition watermark ) is the leaf production of two sheets halfway final thickness. This is one of the sheets before gluing printed with the motif ( later lying inside ) which is then like a shadow watermark appears in the review. Such sheets are easy to expose to the internal sample or a wicking (see cardboard / paperboard production).

Loggerhead watermarks are easily recognizable by the lack of dilution / thickening of the paper or on the evident color order and leave no residue by chemical reagents ( eg, alcohols ) from the paper to remove.

Digital watermark

→ Main article: Digital watermark

Digital watermarks are introduced into media files information. The essential goal is usually (as in a "traditional" watermark ) that the actual information and those that make the watermark can not be separated more. There are for each type of media ( images, audio, video, ...) different methods that are adapted to the respective codes and the data format. The techniques used are closely related to steganography.