TedEd: How to spot a counterfeit bill

A TedEd by Tien Nguyen

Out of every 10,000 US bills, 1 of them is counterfeit. Although that doesn't sound like much, it can add up to millions of dollars. It can cause a wide range of problems, from a few dollars out of your pocket to destabilizing national economies. But you can easily spot these fakes. The counterfeit detection pen is made of a solution of potassium iodide and elemental iodine. Real money is made of a mixture of cotton and linen threaded with tiny red and blue fibers. It is made by one secret company called Crane & Company which has been producing it since Paul Revere asked them to do it to fund the Revolutionary War. However, many counterfeits are made from printer paper strengthened with starch, which is what the pen detects. The starch is made of amylopectin and amylose molecules. Amylose is in a helical structure, which reacts with iodide and leaves a dark mark on the paper. If it is real, the mark will be bright yellow. Another way is using UV light. Since 1996, all bills have a polyester strip one millimeter wide. These will show the bill's value and USA on them in natural light, but shine under UV light. These work because the molecules absorb the amount of energy from UV light, then give off some as heat and the rest as light. There may also be visual clues. The portrait should be lifelike, the seal should have even sawtooth points, the border should be unbroken, and the serial number should be evenly spaced.