How to Check Counterfeit Money With a Pen

Counterfeit currency poses a consistent threat to individuals and businesses, leading to financial losses and broader economic instability. Counterfeit detection pens have become a common tool for quickly checking suspected fake money. This article explains how these pens work and, more importantly, provides a comprehensive guide to identifying fraudulent currency using other reliable security features.

Understanding the Counterfeit Pen

Counterfeit detection pens utilize an iodine-based ink that reacts chemically with starch, a common component found in wood-based paper. Genuine U.S. currency is made from a blend of 75% cotton and 25% linen fibers, which contains no starch. When the pen is used on authentic paper, the mark remains clear or turns a light yellow, indicating the absence of starch.

Conversely, if the pen is used on paper containing starch, the iodine solution reacts, causing the mark to change to a dark brown or black color. This chemical reaction signals that the paper is likely a common wood-pulp paper, not the specialized blend used for legitimate banknotes. The immediate color change provides a quick visual cue, suggesting the bill may be a counterfeit.

Limitations of the Pen Test

Relying solely on a counterfeit detection pen is insufficient for identifying all fraudulent currency. Some counterfeiters employ sophisticated methods that can bypass the pen test entirely. For instance, criminals may bleach lower-denomination genuine bills and then reprint them with higher denominations. Since the original bill was authentic, its paper will not react with the pen, appearing legitimate.

Another limitation arises when counterfeiters use starch-free paper, which mimics the composition of genuine currency. This specialized paper, while uncommon, would also not trigger a dark reaction from the pen, allowing a fake bill to pass this preliminary check. Therefore, the pen should be considered a first-line defense or a quick preliminary assessment, not a definitive verification method for all types of counterfeits.

Key Security Features Beyond the Pen

Genuine United States currency incorporates multiple security features that are difficult for counterfeiters to replicate. Holding a bill up to a light source reveals a faint watermark, which is a duplicate image of the portrait on the front of the bill, located in the unprinted area to the right of the portrait.

A vertical security thread is also embedded within the paper, visible when held to light, and contains microprinted text indicating “USA” followed by the bill’s denomination. Each denomination’s security thread glows a specific color under ultraviolet (UV) light; for example, a $5 bill glows blue, a $10 bill glows orange, and a $20 bill glows green.

The denomination number located on the lower right corner of the front of most newer bills features color-shifting ink. When the bill is tilted, this number changes color from copper to green, an effect difficult to reproduce convincingly.

Genuine currency also has a distinctive texture; it feels crisp and slightly raised due to the printing process, unlike the smoother feel of common paper. Tiny, intricate microprinting can be found in various locations, such as within the security threads or along the borders, which appears as a solid line to the naked eye but is legible text under magnification.

Red and blue security fibers are randomly embedded throughout the paper of genuine bills, adding another layer of complexity for counterfeiters. These small, distinct fibers are part of the paper’s composition and are not simply printed on the surface.

Each bill also has a unique serial number, printed twice on the front of the note. These numbers should match precisely, have consistent spacing, and use a distinct font.

Steps if You Suspect Counterfeit Money

If you suspect a bill is counterfeit, do not return it to the person who passed it, as this could allow them to pass it to someone else. Instead, limit handling to preserve evidence like fingerprints, and place it in a protective envelope or bag.

Note details about the person who presented the bill, including their physical description, any companions, and the circumstances of the transaction. Also note the date, time, and location where the suspected counterfeit was received. Promptly contact your local law enforcement agency or the United States Secret Service field office to report the incident. Knowingly passing counterfeit currency is a federal crime, punishable by fines of up to $250,000 or imprisonment for up to 20 years under 18 U.S.C. § 472.