Counterfeit banknote detection pen

Counterfeit pens are pens containing an iodine-based ink. They can be used to detect counterfeit Swiss franc, euro and United States banknotes amongst others. Typically, genuine banknotes are printed on paper based on cotton fibers, and do not contain the starches that react with iodine. When the pen is used to mark genuine bills, the mark is yellowish or clear. Counterfeit pens are most effective against notes printed on standard printer or photocopier paper.

1. Pen manufacturers claim such pens will detect a great majority of counterfeit bills
2. but critics suggest the effectiveness is much lower.
Critics claim that professional counterfeiters use starch-free paper, making the pen unable to detect the majority of counterfeit money in circulation.
3. Magician and skeptic James Randi has written about the ineffectiveness of counterfeit pens on numerous occasions
4. The Secret Service does not include such pens in their guidelines for the public's detection of counterfeit US currency.
5. Uses a pen as an example during his lectures.
6. Randi claims to have contacted a United States Secret Service inspector and asked whether the pen works as advertised, to which the inspector replied "it is not dependable."

7. Some US counterfeiters bleach small denominations and print more valuable bills on the resulting blank paper to evade this test,
8. Although changes to the currency since 2004 have made this method easier to detect.

This is one reason that many currencies use different sized notes for different denominations.