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How do Counterfeit Pen Tests Work?

by Abdullah Beydoun


Detecting counterfeit currency is serious business for merchants, grocery stores, and casinos that turn over a lot of cash and need to maintain a strong reputation for ensuring the validity of the money they accept. Criminals and counterfeiters will quickly identify retailers and other businesses with lax testing processes and can pass thousands of dollars in false bills before anyone notices.

As a result, innovations like the counterfeit banknote detection pen were developed. This device offers a quick and easy means of testing the authenticity of a banknote – but is this method reliable, and does it even work anymore?

In this resource article, we’re investigating one of the most commonly known methods for verifying bank notes – the counterfeit detection pen. We’ll discuss how these devices work, where they are most commonly used, and the extent to which we can trust the results we get when testing bills with one. By the end, we hope you’ll form your own opinion as to whether you can trust counterfeit detection pens to keep your business or banknote collection free of counterfeits.

How Does a Counterfeit Detector Pen Work?

Bank notes today are packed with security features that make them virtually impossible for a casual counterfeiter to replicate. Between microprinting and raised printing technologies that require high-end printing equipment and expensive ink, and newer features like interwoven security thread and 3D security ribbon embedded into banknotes, counterfeiters can never really get everything right when attempting to create a fake banknote.

As a result, most counterfeiters are amateur criminals doing things the amateur way – producing knock-offs of questionable quality and simply hoping that inexperienced cashiers won’t notice them in the few seconds they spend between the counterfeiter’s wallet and the cashier’s till.

The counterfeit detector pen is a logical response to these lazy counterfeiters. Since most of these rip-off operations aren’t very sophisticated, they use regular paper instead of the cotton and linen hybrid that comprises American bills today, and that’s where they get caught.
Counterfeit detector pens contain a solution of iodine that reacts with the starch molecules that are naturally present in wood-based paper, leaving a black stain that exposes the note as fake.

The iodine solution is non-reactive with cotton and linen fibres, as well as the polymer plastic notes used in Canada and the European Union. As a result, the pens are also effective at detecting counterfeits of these currency types as well.

Criticism of Counterfeit Detector Pens

If you create a new security feature for a bank note, folks will praise it until they realize a way in which it isn’t perfect. Then, they’ll tell you that it’s useless because it doesn’t prevent counterfeiting. That’s human nature, and the same types of criticism have been applied to counterfeit detection pens by collectors and merchants around the world.

The truth is that there are inherent flaws associated with counterfeit detector pens, and they have been cracked in several ways that criminals can now use to avoid their fake notes being discovered. First, Vitamin C solutions that are used to prepare invisible ink can also cause counterfeit bills to pass a pen test. A 0.030 M solution of vitamin C, produced by grinding up store-bought supplement tablets, was applied to a fake banknote, inhibiting the iodine-starch reaction and producing a “false negative” (the test showed that the bill was not fake, but it was).

An effective workaround for counterfeiters of American money is bleaching – crime groups organize illegal workers to bleach $1 bills, removing the ink from printing so that the original cotton/linen material can be used to reprint higher-value notes. It has also been found that real banknotes which pass through the laundry and are exposed to bleach and other detergents may fail a pen test, despite being authentic.

Are Counterfeit Detector Pens a Reliable Technology?

A banknote contains numerous security features, and a counterfeit detector pen is a tool that tests just one of them – but what about the rest? The truth is that there are ways to work around this counterfeit detection method, especially by applying other chemicals to counterfeit bank notes that interfere with the iodine-starch reaction.

Still, we shouldn’t throw the baby out with the bathwater when it comes to counterfeit detection. If you’re serious about keeping your collection free of counterfeits, consider incorporating multiple counterfeit detection methods to ensure the authenticity of notes that pass through your hands. A combination of UV light testing, counterfeit detection pen testing, and examination of other built-in security features should produce a reasonable level of confidence that your bank note is either real or fake.


Like any authenticity test, counterfeit detector pens are effective in many scenarios, but flawed in others. There is no silver bullet test when it comes to counterfeit detection. The best approach is to educate yourself on the security features present in the bills you collect, and ensure that you examine notes adequately before purchasing or accepting them. You’ll have to rely on yourself on your faculties, but you can learn the skills that will keep your business or collection safe from counterfeiters.

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