What Color Is the Mark on a Fake Bill?

Counterfeit currency poses a challenge to individuals and businesses. Understanding how to identify fake bills is important for safeguarding transactions. This article explores the counterfeit detection pen, its operation, and other reliable security features on U.S. currency, offering a guide to recognizing legitimate tender.

The Counterfeit Pen and Its Mark

A counterfeit detection pen quickly assesses currency authenticity. When applied, its ink reacts with the paper. On genuine U.S. banknotes, the mark appears light (pale yellow or clear), indicating starch-free paper, a characteristic of authentic currency.

Conversely, if printed on common starch-containing paper, the pen’s mark turns dark (black, dark blue, or brown), signaling likely counterfeit currency. The pen provides a rapid initial check for quick verification.

The Science Behind the Pen’s Reaction

The pen’s marks result from a chemical reaction involving an iodine-based solution, typically containing potassium iodide. This solution reacts specifically with starch molecules. Most common papers, like those used in printers, contain wood-based starch. When the iodine solution contacts this starch, a chemical interaction results in a dark blue, black, or brown stain.

Genuine U.S. currency is printed on a unique blend of 75% cotton and 25% linen fibers. This specialized paper is starch-free, so no chemical reaction occurs when the pen’s iodine solution is applied. The mark remains pale yellow or clear on authentic bills, distinguishing them from counterfeits. While useful, these pens are not foolproof, as sophisticated counterfeiters may bypass this test.

Additional Security Features to Look For

While the counterfeit pen offers a quick check, it does not provide a definitive authentication for all types of fake currency. More advanced counterfeits might use paper treated to mimic genuine currency or even bleached genuine bills of lower denominations reprinted as higher ones. Therefore, examining multiple security features is important for thorough verification. U.S. currency incorporates several layered features designed to deter counterfeiting.

• Watermarks: Faint images embedded in the paper, visible from both sides when held to light. They typically match the portrait or show a numeral.
• Security Thread: A clear strip woven vertically into the paper, inscribed with the denomination. It glows a specific color under ultraviolet (UV) light.
• Color-Shifting Ink: Found on denominations $10 and higher, the numeral in the lower right corner changes color when tilted, typically from copper to green.
• Microprinting: Tiny words or numbers that appear as a solid line to the unaided eye. These texts should be clear and sharp.
• Raised Ink/Texture: Genuine U.S. currency has a distinctive texture from the intaglio printing process, creating slightly raised ink that can be felt.
• Security Fibers: The paper contains small, randomly dispersed red and blue security fibers.

Responding to Suspected Counterfeit Bills

If you suspect a counterfeit bill, immediate action is important. Knowingly passing a counterfeit bill has serious legal consequences, even if received unknowingly. While federal law requires intent to defraud for criminal charges, possession of counterfeit currency can still lead to problems.

If you suspect a bill is counterfeit, do not return it to the passer. Limit handling to preserve evidence by placing it in a protective cover, plastic bag, or envelope.

Note details about the passer, such as their physical description and any vehicle information. Contact your local police department or the U.S. Secret Service field office to report the suspected counterfeit.

You will need to surrender the note to law enforcement. There is typically no financial compensation for surrendering a counterfeit bill, but it aids in combating counterfeiting.