Ring the changes

[Bert]

Why do genuine coins "ring" when you toss them with a flick of your thumb, or when they are allowed to rotate till they stop on a table, and why don't counterfeit coins ring (unless they are really, really good, I suppose).

[heathfield]

The 'ring' will generally depend on the hardness of the metal. And again, generally, the harder a metal, the higher the melting point. Counterfeit coins tend to be of low melting point metal, because they're easier to make by casting in a mould. Making a die and stamping out coins from hard metal could be an expensive business, and so not worthwhile, based on the returns. If there were �20 coins, things might be different!