Typer Yip writes:
since 1990, the Treasury has placed a nylon strip inside the paper of most of the printed money ($10's and above, I believe). This strip has letters on it, spelling out "USA TWENTY" (for the $20 bill) such that it can only be seen if light is passed through the note. This was officially meant to prevent the high quality scanners and color printers from being able to forge money, since the scanner would not be able to reproduce the reflectively-invisible letters in the strip.
Wonder if they could include such a technique in money tracking. Has anyone ever checked the green ink on money for magnetic resonance?
The black ink that is used to print the front side of U.S. cash contains a very finely ground black iron oxide powder. The ink is magnetic. This magnetism is used mostly by vending & change machines to distinguish real bills from forgeries/photocopies. A vending machine that accepts paper money typically has three tests for cash validity. 1. A digital image scan and imagage signature comparison. This test also determines the denomination of the bill. (good photocopies of bills can get past this test) 2. Ultraviolet light test. Real bills (printed on non-chemically treated paper) do not glow. Most other papers, especially chemically whitened papers do glow, and are flagged as fakes. 3. Magnetic ink detection. Real bills are printed with magnetic ink, forgeries/photocopies are not. Thug