If you ask someone with no experience in checking banknotes to name a banknote security feature, they will likely mention watermarks first. Watermarks are widely recognized public security features that are easy to check.
However, this widespread recognition also makes them a common target for counterfeiters. To identify an imitation and verify a watermark with confidence, it is essential to understand the basics: how genuine watermarks are made, what types exist, how they appear under different light sources, and which professional tools are used to verify their authenticity. We cover all these topics in this article.
In brief: Watermarks are among the oldest security features and should be examined not only under transmitted white light but also under incident white, oblique white, and ultraviolet light. These light sources provide a more comprehensive picture of a watermark’s authenticity.
What is a watermark?
A watermark is a security feature created during paper production by varying the thickness of wet paper fibers — hence its name. The difference in paper density forms an image: areas containing more fibers appear darker when viewed in transmitted light, while areas containing fewer fibers appear lighter.
Watermarks are among the oldest security features used to protect valuable papers and documents. They date back to around 1282, when papermakers in Fabriano, Italy, began using them primarily as trademarks to identify the origin of their paper.
Commemorative Vietnamese dong issued in 2016.
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What types of watermarks are there?
Watermark technology has been used for centuries for securing documents and valuable papers, so it’s no wonder that today there are several types of these banknote security features of varying complexity. We can classify watermarks based on their location and paper tone.
According to the location:
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General: An image repeated at regular intervals all over the surface, creating a pattern.
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Local: An image located in a certain place.
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Cornerstone®: Consists of parallel diagonal lines located in the corners of the banknote. It is specifically designed to physically strengthen the edges of the banknote or document page.
General watermarks are rarely used on banknotes; they are primarily used to secure passport pages. However, they do appear on some currencies, including the Lao kip series issued in 1998, 2003, and 2020.
Local watermarks usually depict portraits, local flora and fauna, banknote denominations, or culturally significant objects. For example, the Japanese 10,000-yen banknote issued in 2004 features a local watermark depicting the prominent Japanese figure Fukuzawa Yukichi.
The Cornerstone® watermark was developed by British banknote printer and papermaker De La Rue. First used in 2003, it now appears in more than 200 denominations. For example, the Cape Verdean escudo banknote issued in 2014 features both a Cornerstone® watermark and a local watermark.
According to the paper tone of the watermark:
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Single-tone: Consists of dark OR light elements compared to the general paper tone.
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Duotone: Consists of dark AND light elements compared to the general paper tone.
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Multitone: Consists of dark and light elements compared to the general paper tone which gradually transform into each other.
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Highlight (electrotype): Extremely light clear single-tone watermark with clear boundaries.
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Combined: Combines several kinds of watermarks.
Euro issued in 2002. The banknote contains a single-tone dark watermark and a highlight watermark depicting the denomination.
Cambodian riel issued in 2002 and 2004. The banknote contains a duotone watermark.
Gibraltar pound issued in 2011. The banknote contains a multitone portrait of Queen Elizabeth II.
Commemorative Czech koruna issued in 2023. The banknote denomination is a highlight watermark.
Afghan Afghani issued in 2016 and 2022. Combined type. The banknote contains examples of dark single-tone (Cornerstone®), highlight, and multitone watermarks.
If you are interested in learning what watermarks look like on polycarbonate pages, don't hesitate to read Building Trust with Plastic: 7 Noteworthy Security Features in Modern Passports and IDs
How to check watermarks?
Since watermarks are a public security feature, they can be examined without forensic equipment: they become visible when a banknote is held up to the light. The same effect can be achieved under controlled conditions using transmitted white light.
However, transmitted light alone may be insufficient for professional authenticity verification. If there is any doubt, an expert may need to use additional light sources, magnify the watermark area, and capture evidence of possible forgery. All these tasks can be performed using devices for forensic document examination.
The process of watermark authenticity examination may include the following:
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Examination under incident white light. Any authenticity examination typically begins with white light, and watermark examinations are no exception. Under incident white light, a watermark should be almost invisible or only slightly visible.
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Examination under transmitted white light. A watermark becomes clearly visible in transmitted light. Besides, a genuine watermark features blurred boundaries because paper thickness changes gradually (except for highlight watermarks, which have clear boundaries).
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Examination under ultraviolet (UV) light. If there is any doubt after examining a watermark in transmitted light, inspect the banknote under UV light. A genuine watermark does not fluoresce, although its outline may remain slightly visible. Imitations made with ink or grease, by contrast, often fluoresce or contrast with the surrounding paper.
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Examination under oblique white light. Oblique lighting helps reveal changes in the paper’s surface relief within the watermark area — an important characteristic of a genuine watermark.
Let’s examine the Aruban florin issued in 2019.
We captured the front side of the banknote to see how the watermark area changes in different light sources. The images are captured using the Dual-Video Spectral Comparator Regula 4308M.
Zoomed-in watermark on the Aruban florin issued in 2019. The images are captured using the Dual-Video Spectral Comparator Regula 4308M.
What forensic devices are effective for in-depth watermark examination?
As the examples above demonstrate, professional watermark examination involves much more than viewing a banknote in transmitted light. Experts need access to different light sources, sufficient magnification, and tools for capturing evidence.
For in-depth authenticity verification and evidence capture, we recommend our flagship video spectral comparator, the Regula 4308M. Its advanced optics and wide range of light sources and filters enable experts not only to examine watermarks but also to conduct a comprehensive banknote authenticity check, including the examination of security features, printing techniques, paper substrates, and the spectral characteristics of inks.
The video spectral comparator’s capabilities can be further enhanced with the integrated Information Reference System “Currency”. It contains reference images of more than 5,000 current and withdrawn banknotes captured under different light sources. These images show each banknote’s overall appearance, security features, and printing techniques, allowing experts to compare them with the banknote under examination and identify suspicious areas.
The Regula 4308M features 40+ light sources and 30+ light filters for multi-level inspection, 320x magnification, a motorized object stage for precise banknote positioning, and a built-in spectrometer for spectral analysis of ink characteristics.
Conclusion
Watermarks are among the oldest security features. Although they may seem simple, they come in various types and appearances. Effective watermark examination, as part of a comprehensive banknote analysis, requires access to different light sources and appropriate levels of magnification.
If you have questions about banknote or questioned document examination — or need help choosing the right tools for a particular verification task — contact us. Our experts will be happy to assist you and recommend the most suitable solution for your examination needs.
