Banknote Watermarks Explained: Classification and Verification Techniques

A watermark is a security feature created by varying the thickness of paper fibers during paper production. This variation in paper density results in an image, with darker areas containing more fibers and lighter areas containing fewer fibers.

Watermarks are among the oldest security features of banknotes and travel documents. They were first developed in about 1282 by Italian papermakers in Fabriano. Primarily, they served as “trademarks” of paper makers. The watermarking process was significantly simplified with the invention of the dandy roll by John Marshall in 1826.

Watermark technology has been used for centuries for securing documents and valuable papers, so it’s no wonder today there are several types of these banknote security features of varying complexity. We can classify watermarks based on their location and paper tone.

• General: An image repeated at regular intervals all over the surface, creating a pattern.

• Local: An image located in a certain place. 

• 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.

Local and Cornerstone® watermarks are widely used in banknote production. General watermarks, however, are seldom used for banknotes; they are primarily used to secure passport pages.

Local watermarks depict portraits, representations of local flora and fauna, banknote denominations, or objects of culture.

The Cornerstone® watermark was first used in 2003 and is currently used in more than 200 denominations. It was designed by the British banknote printer and papermaker De La Rue.

• Single-tone: Consists of dark OR light elements compared to the general paper tone.

• Duotone: Consists of dark AND light elements compared to the general paper tone.

• Multitone: Consists of dark and light elements compared to the general paper tone which gradually transform into each other.

• Highlight (electrotype): Extremely light clear single-tone watermark with clear boundaries. 

• Combined: Combines several kinds of watermarks.

Since watermarks are one of the public security features of banknotes, they can be visualized without any forensic equipment: watermarks become visible when banknotes are held up to the light. But, when dealing with authenticity verification on a professional level, it’s necessary to use special forensic devices that contain varied light sources. When carrying out banknote authenticity verification, an expert needs not only to check the watermark in transmitted light, but to distinguish forgery methods and capture evidence if the watermark was forged.

• Clearly visible in transmitted light and almost invisible (or slightly visible) in incident light

• Blurred boundaries of the image because the paper thickness changes gradually (except for highlight watermarks, which have clear boundaries)

• Absence of fluorescence in UV light

• Change of paper thickness where a watermark is located

If there is any doubt when examining a watermark in transmitted light, we recommend observing the banknote in ultraviolet light (UV). A genuine watermark won’t fluoresce in UV light, even though it may be slightly visible. In the majority of cases, if the watermark was imitated using inks or grease, it will fluoresce in UV. 

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.

In the incident white light, the watermark is slightly visible. In transmitted white light, the image of the watermark becomes clearly visible. When viewed from different angles with oblique white light sources, the relief of the watermark area is noticeable due to variations in paper fiber density. 

Although we can see the silhouette of a bird in the ultraviolet light, it is visible because of the thicker layer of paper fibers. If the watermark had been imitated using ink or grease, it could fluoresce or contrast against the background under ultraviolet light. Using transmitted ultraviolet light eases the process, as we can simultaneously observe the watermark image and the absence of a glow in ultraviolet light.

We recommend using the Regula 4115 device for rapid but precise authenticity verification of banknotes. It has a variety of light sources (white, ultraviolet and infrared) and magnification to meticulously examine banknote security features, printing techniques, and relief.

Plus, the device can feature an integrated Information Reference System “Currency” that contains images of more than 5,000 banknotes, both in circulation and outdated. These images captured in different light sources can be used as reference images during banknote examination and assist in detecting questionable areas.

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