Counterfeit detection pens work because they detect paper starch in phony currency. All real U.S. currency is made of linen and contains no paper starch.

Question

Quizplus · Accepted Answer

Counterfeit detection pens contain an iodine solution that reacts with the starch found in most paper, turning it dark. Genuine U.S. currency is made from a blend of cotton and linen, which does not contain starch, so the pen leaves no mark or only a faint mark on real bills.

Counterfeit Detection Pens Work Because They Detect Paper Starch in Phony