Also, it might even make counterfeit coin production cheaper if it replaces rather than supplements current detection methods - maybe a counterfeiter can make a plastic or wooden coin of roughly the right shape and paint it with a paint containing the appropriate mixture, and then trick a vending machine into giving them non-counterfeit change.
Usual weight, magnetic and maybe inductance tests apply.
I also wonder about someone's ability to take slices of the surface of a coin and spread that out over other cheaper coins. I guess you have to randomize the test, or make sure it covers more than just a couple predictable spots on the coin.
