Watermarks are figurative marks introduced into paper through different paper thicknesses, recognizable by means of light transmission, and were originally used to identify the producing paper mill . Among other things, they are used as a security feature in banknotes and postage stamps as well as in personal documents . Since watermarks require a certain procedure in order to be perceptible (hold paper up to the light), imperceptible markings in digital content, which can also only be detected with a given method, are referred to as digital watermarks .
Watermark in paper
It has been proven that since 1282 in Bologna , Italy , the paper mills marked their goods by attaching a thick wire in the form of a letter or a symbol to the wire mesh of the ladle sieve . The first multilayer, 3D watermark was produced around 1800 . The introduction of the "dandy roll" as a dandy roll in 1826 by John Marshall revolutionized the watermark process and made it easier for producers. This figure leaves an impression in the paper; the fiber layer is thinner there, and when the light shines through, the watermark becomes visible as a more transparent image. Conversely, by partially deepening the sieve, it was possible to achieve an enrichment of the substance, which then got a more cloudy appearance. By cleverly combining deepening and heightening, even semitones can be simulated. This complex process is still used today for watermarks in banknotes . In the early days of European paper production, watermarks were the origin and trade marks of the paper mills.
Since the screens for paper production were worn out after around two years, the recording of datable watermarks with slight deviations that resulted from the manual production made it possible to date the paper. Because paper was usually not stored for long due to its high price, it is a comparatively precise instrument for dating the documents and graphics that have been handed down on paper . This is the working field of filigranology (watermarking), a historical auxiliary science that uses watermarks to research the age and origin of documents. For this purpose, extensive historical watermark collections have been created since the beginning of the 20th century. The first extensive work is Charles-Moïse Briquet's dictionnaire des filigranes , followed by the as yet incompletely printed collection of Gerhard Piccards in the Baden-Württemberg State Archives . Other large collections of watermarks can be found in the German Museum of Books and Writing in the German National Library in Leipzig and in the Düren Paper Museum .
The above-mentioned and a growing number of other watermark cards are now partially digitized . Particular attention is drawn to the following collections:
- the multilingual watermark portal Bernstein - The Memory of Papers , and
- the DFG project Watermark Information System , which brings together the relevant databases.
The digitization of further collections is also increasingly closing the gap in the mapping of the papers used in Eastern Europe .
The dating of the watermarks is primarily done by determining the symbol used according to the systematics of the card indexes and additionally by the height and width of the watermark and the spacing of the web wires. For the dating and localization of the watermarks, their location within the ladle strainer is also important, since watermarks could be warped on the one hand through wear and tear, on the other hand watermarks could also be removed from one ladle strainer and applied to another; a fine determination also requires the consideration of the distance between the warp and weft threads and the attachment points of the watermark structure on the screen.
A distinction is made between real, semi-real and fake watermarks.
Nowadays, real watermarks are mostly created 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 compresses the paper web at a given point. In the case of real watermarks, a distinction is made between attachment watermarks and displacement watermarks . Accumulation watermarks can only be produced on the cylinder sieve machine or - as in the original process - on the hand sieve.
The accumulation watermark is caused by a disturbed deposition of the fibers during the formation process (transition of the fibers from swimming to lying). Depending on the shape of the wire and the length of the fiber, the accumulation watermark can be sharper or more blurred. The typical accumulation of watermarks on the round wire can easily be recognized by the fact that part of the fibers washed under the wire is torn off when the wire is drained and the edge is therefore always somewhat blurred. Trapezoidal wires or rectangular wires that lie flat on the sieve show a razor-sharp image (short pulp ). A distinction is made between two types of attachment watermarks:
- There is the two-level or line watermark , which only has a light-dark effect (e.g. the number under the image in the 50 euro note ). The production of two-stage watermarks is possible with long, inclined and cylinder screens. It takes place on the drainage screen. Metal wires or shaped metal parts, also known as electrotypes , are soldered, glued, sewn or welded onto it. This leads to parts of the screen closing completely. Alternatively, embossing and embossing can be applied to the screen, which reduces or increases the fiber density in the fleece. The transparency of the sheet is increased or decreased in relation to the environment. Bronze is preferably used as the material for this if it is a bronze sieve. In the case of a screen construction made of metal-plastic combinations, in which metal weft threads are woven for strength and plastic warp threads for elasticity , embossing is also possible. Watermarks cannot be embossed in pure plastic screens. This is why these screens are used together with watermark inserts made of perforated hard metal such as metal plates or perforated plastic plates.
- The multi-level watermark , which is characterized by a detailed display and smooth transitions between the individual light-shadow changes (the translucent image of the 50-euro note). Light and shadow watermarks are much more complicated to create. First of all, the motif has to be cut into a wax plate that is lit from behind. The surfaces, lines, light and shadow areas are worked out of the wax at different depths. A cast is made of this wax relief and a negative and a positive relief made of bronze are made from this by galvanizing . A fine copper sieve is placed between these two bronze plates . By pressing firmly together, the shapes are transferred into the sieve. This metal sieve is sewn onto a scooping frame and, when scooping, causes less paper pulp to remain in the raised areas and more paper pulp in the recessed areas. Multi-stage watermarks are only possible in cylinder sieve machines, since here the dewatering sieve is made up of several bronze sieves, usually four on top of each other. The bottom sieve is coarse-meshed and serves as a support fabric. Above this is a finer screen that is cut out in the watermark areas. This is important to give the fibers leeway. In the two even finer sieves above, a metal stamp is used to emboss a relief in the desired shape. Fewer fibers are deposited on the raised areas and thin, translucent areas are created in the paper. A larger number of fibers collect on the recessed areas and dark spots appear in the paper. In this way, smooth transitions and detailed motifs can be created.
The displacement watermark is created on the dandy section and is characterized by the fact that the fiber is displaced at the moment of formation by a dandy wire acting from above. The resulting watermark is characterized by the fact that it is always somewhat blurred (due to the wire shape used and the elasticity of the fleece) and is often provided with slight crushed edges. As a result of the inlet pressure, stock water penetrates through the sieve into the interior of the dandy roll. The flow is oriented in such a way that fibers floating freely in the suspension reach the tissue and are deflocculated there. The fine and fillers can then flow slightly and thus form a very fine, even surface.
In order to create real shadow watermarks , areas are now heated and pressed in during the production of the dandy sieve. Paper fibers collect in these recesses and a partial thickening takes place. Light watermarks are created by raised areas on the screen roller. This is done by soldering stainless wires, called electrical wires, to the top of the wire mesh. These displace the moist paper fibers and thus lead to a lower fiber concentration.
The strength of the watermark can be controlled by increasing the pressure of the dandy roll on the paper fleece or by driving the dandy roll at a greater speed than the paper fleece.
In the attachment process, cellulose can also be marked that can no longer be marked cleanly using the displacement process (long fibers). The following applies to both forms of watermark: The selected wire thickness depends on the later grammage and the thickness of the desired character. Wires of approx. 0.4 to 1.2 mm are suitable for hand paper making with a basis weight in the range from 40 to 300 g / m 2 .
Semi-real watermarks (for example the Molette watermarks ) are created by pressing them into the much drier paper web after it has left the wire section (usually in or after the first press). Most of them can be removed again afterwards through the partial action of caustic soda or water. In contrast to the real 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 pulp. Molette watermarks are usually made with hard rubber rings attached to the Molette (similar to stamps or letterpress types). Typical applications for Molette characters are lettering running along the edge parallel to the direction of the paper. Molette marks are more rarely produced as passport watermarks . The use of ornaments in the Molette is limited to simple line shapes. Flat or shadow watermarks cannot be created in this way.
The second form of semi-real watermark is the calender watermark . These are embossed into the completely dry paper web during calendering (smoothing through a combination of friction and pressure in the roller mill [= calender], historically also 'calendar' or 'calendar'). The paper is compressed hard. 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 notch in the paper. Molette watermarks and calender watermarks are often not exactly distinguishable from one another. Calender watermarks are particularly suitable for line shapes. However, flat shapes are also known.
Fake watermarks (chemical watermarks) are not watermarks in the actual sense, as they are not created during paper production (i.e. not by water). Usually they are printed on afterwards. Very often transparent material (e.g. glycerine , fat dye or sulfuric acid paste → mercerization ) is printed here, which is supposed to simulate a real watermark by adding color pigments. Subsequent embossing in the paper (similar to calendering) corresponds to that of a fake watermark.
A modern form of forging watermarks for shadow watermarks (attachment watermarks) that are difficult to copy consists of sheet production from two sheets of half their final thickness. One of the sheets is printed with the motif before gluing (later lying on the inside), which then appears like a shadow watermark when looking through it. Such sheets are easy with the firing sample or wicking check (see box - / paperboard production).
Fake watermarks can easily be recognized by the lack of thinning / thickening of the paper or by the recognizable color application and can be removed from the paper without residue using chemical reagents (e.g. alcohols).
In addition, nowadays watermarks based on ultraviolet radiation (UV) are increasingly used as security features for papers that are worth protecting. UV watermarks are brightly visible in backlight and appear fluorescent under black light . To increase the security level, these UV watermarks can be used in coated and colored papers.
Digital watermarks are media files introduced information . The main goal here is usually (as with a traditional watermark) that the actual information and that which makes up the watermark can no longer be separated from one another. There is a separate procedure for each type of media (images, audio, video) that is adapted to the respective coding and data format . The techniques used are closely related to steganography .
- Gerhard Piccard: The watermark research as a historical auxiliary science. In: Archival Journal . Vol. 52, 1956, pp. 62-115.
- Karl Theodor Weiß : Handbook of watermarking. Edited and edited by Wisso Weiß. Fachbuchverlag, Leipzig 1962, ISBN 978-3-598-07208-6 .
- Theodor Gerardy : Dating with the help of watermarks, exemplified by the total production of the Schaumburg paper mill in Arensburg from 1604–1650. (= Schaumburg studies. Booklet) Grimme, Bückeburg 1964.
- Ralph Günter Brachvogel: Critical thoughts on watermarking as a dating aid. In: Acta Congressus Internationalis Historiae Pharmaziae Pragae MCMLXXI (= publications of the International Society for the History of Pharmacy, Volume 38), Stuttgart 1972.
- Ulrich Konrad : "... recognized the period of time from the music paper." The importance of paper and watermark research for musicology. In: Gutenberg yearbook. Volume 74, 1999, pp. 20-34.
- Peter Rückert et al. : Ox head and mermaid - paper history and watermarks from the Middle Ages to modern times. Accompanying book and catalog for the exhibition of the Baden-Wuerttemberg State Archives, Main State Archives Stuttgart and the Austrian Academy of Sciences, Commission for Medieval Writing and Books, Vienna, Project Bernstein (Ed.), 3rd, further expanded edition. Stuttgart / Vienna 2009, ISBN 978-3-00-026752-9 .
- Peter F. Tschudin: Fundamentals of the history of paper. 2nd, supplemented edition. Hiersemann, Stuttgart 2012, contains pp. 275–365 as Appendix II: IPH draft standard with illustrated watermark type catalog (English, German, French, Spanish), ISBN 978-3-7772-1212-8 .
- Wisso Weiß: Historical watermarks. Bibliographisches Institut, Leipzig 1986, ISBN 978-3-323-00001-8 .
- Wisso Weiß: On the history of the development of watermarks in European hand-made paper. In: Gutenberg yearbook . Vol. 62, 1987, pp. 109-124.
- Rolf Buscher: From watermarks to branded paper [electronic resource] - paper marking as a means of sales policy in the 20th century. Trier, Univ., Diss., 2007, digitized
- Some references are also listed in: International Bibliography on Paper History (IBP) , De Gruyter Saur, Munich 2003, 4 volumes
- Erwin Frauenknecht, watermark. In: Südwestdeutsche Archivalienkunde , as of December 18, 2017.
- Literature on the keyword watermark in the catalog of the German National Library
- Piccard Online, Piccard watermark index of the Baden-Württemberg State Archives
- WZMA - watermarks of the Middle Ages , description
- WILC - Watermarks in Incunabula printed in the Low Countries
- WIES - Watermarks in Incunabula printed in España
- Watermark Database, Nederlands Interuniversitair Kunsthistorisch Instituut te Florence
- Bernstein - the Memory of Paper
- Watermark Information System
- Richard Leslie Hills: Papermaking in Britain 1488-1988: A Short History. Bloomsbury Publishing, 2015, ISBN 978-1-4742-4127-4 (Reprint), pp. 43, 177 ff.
- Ursula Rautenberg (Ed.): Reclams Sachlexikon des Buch. 3rd edition, Reclam-Verlag 2003, ISBN 978-3-15-011022-5 , p. 532.
- Maria Stieglecker, Emanuel Wenger: The project Bernstein . In: Ox head and mermaid - paper history and watermarks from the Middle Ages to modern times. Stuttgart and Vienna 2009.
- Watermark Information System
- Cf. Theo Gerardy : Collecting, organizing and cataloging watermarks. In: paper history. 9, Roether, Darmstadt 1959, pp. 1-12.
- See also publications by E. G. Loeber, Wisso Weiß, Karl Theodor Weiß and others. a.