A popular convention for fictional works stuck in Medieval Stasis or otherwise "primitive" settings is to have money handled by the exchange of precious metals. In almost all of these cases, there will be different denominations of coins differentiated entirely by what metal they're made out of. Usually this takes the form of the Olympic metals -- gold as the highest, silver second, and bronze last (though in coinage, copper is used instead of bronze more often than not). Sometimes more valuable metals are added above gold -- commonly platinum. Examples of Gold-Silver-Copper Standard include: