only difference was the coins in antiquity were backed by the metal they contained.
even copper therefore bronze was harder to come by and probably more valuable back then
because the difficulty in mining and refining.
OK, I am ready to knocked down over this next comment
However, not totally true surely, as many of the "barbarous" imitations were often significantly smaller and lighter than the official versions. So the "type" of coin must have had a value for people in spite of the metal weight, or is there evidence that a "barbarous" Constantinian follis was worth less than an official one?