The problem is, when pressing the coins it might be difficult or impossible to apply such a layer properly.
If the verification is done with a part of the electromagnetic spectrum that somewhat penetrates the coin, then you'll need a very thick, "obvious fake" layer. I am not a physicist so this is just vague speculation.
If the verification is done with a part of the electromagnetic spectrum that somewhat penetrates the coin, then you'll need a very thick, "obvious fake" layer. I am not a physicist so this is just vague speculation.