Using a Counterfeit Pen to Check if Money is Real

Identifying genuine currency is an important skill for individuals and businesses engaging in daily financial transactions. Counterfeit money, though a small percentage of total currency in circulation, can lead to financial losses for those who unknowingly accept it. Understanding the various methods available for currency verification helps protect against such fraud.

The Counterfeit Detection Pen: Mechanism and Use

A counterfeit detection pen utilizes a chemical reaction to determine if a banknote is printed on standard paper. These pens contain an iodine-based solution that reacts with starch, a common component in wood-based paper. Genuine U.S. currency is composed of starch-free cotton and linen fibers.

When the iodine solution is applied to a genuine bill, the mark typically remains pale yellow, clear, or light amber. If the pen marks a counterfeit bill made from wood-based paper, the iodine solution reacts with starch, turning the mark dark brown, black, or dark blue within 2-3 seconds. To use the pen, draw a small line on an inconspicuous area, such as the border, and observe the color change.

The detection pen has limitations. It cannot detect sophisticated counterfeits that use starch-free paper or genuine bills that have been “bleached” of their original low denomination and reprinted with a higher value. In these cases, the paper is authentic, and the pen would incorrectly indicate the bill as genuine. Relying solely on a counterfeit detection pen may not provide complete security.

Key Security Features on U.S. Currency

Beyond the detection pen, U.S. currency incorporates several embedded security features. The watermark is a faint image visible when the bill is held to light. On denominations $10 and higher, the watermark typically matches the portrait, while the $5 bill has a numeral 5 watermark. It is embedded within the paper and visible from both sides.

The security thread is a plastic strip embedded vertically in the paper of denominations $5 and higher. When held to light, it becomes visible, containing microprinted text like “USA” and the bill’s denomination. The denomination is spelled out for $10 and $20 notes and numerical for $5, $50, and $100 notes. Each thread is positioned differently and glows a distinct color under ultraviolet (UV) light:
Blue for $5
Orange for $10
Green for $20
Yellow for $50
Pink for $100

Color-shifting ink is present on denominations of $10 and higher, found on the numeral in the lower right corner. When the bill is tilted, the ink changes color, often from copper to green. The $100 bill also features a color-shifting “Bell in the Inkwell.” Microprinting, tiny words or phrases, is incorporated in various locations on bills $5 and higher and often requires magnification.

Genuine U.S. currency possesses a distinctive tactile quality due to raised printing. Running a finger across the portrait or other printed areas should reveal a slightly rough texture, difficult for counterfeiters to replicate. Tiny red and blue fibers are embedded randomly throughout the paper of all U.S. bills; counterfeiters sometimes simulate this by printing or drawing them onto the surface. Checking multiple security features provides a more reliable assessment of a bill’s authenticity than relying on a single indicator.