[samson1097]

“Many businesses where I shop will routinely swipe some kind of felt-tip marker across the paper of the bill. So there is some kind of chemistry test, too.”

I’m not positive, but I believe that the reason the color changes is due to the ink being absorbed into the paper before it eventually fades.

I worked as a cashier at Home Depot and noticed that if you take a recipt with one glossy side and one regular feeling paper side, and mark both sides with the counterfit pen than the glossy side stays yellow (good) and the regular feeling side turns black (bad).

[sausageseller]

US currency is made from cotton.

Chemical in pen reacts to wood fibers and changes colors.

Slicks sides of receipt paper is treated.

[ASOC]

"will routinely swipe some kind of felt-tip marker across the paper of the bill" Every time I get cash from my credit union, I insist the teller do the felt tip pen swipy thing. There are so many bad bills floating around AK, I am not going to take te chance of being burned. Most are $50s and $100s. When in Russia (well, the Komi Republic) I was out shopping and had a gentleman offer to buy any Rubles I had with - yup, $100 dollar bills. I told him "Нет, KGB я не"