money tracing

[Peter Baumbach]

Thug writes:
> 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.
>[...]
>           3. Magnetic ink detection.  Real bills are printed with magnetic
>              ink, forgeries/photocopies are not.

Magnetic toner for laser printers does exist.  Its purpose is to allow people
to print their own checks.

Peter Baumbach
baumbach at atmel.com