The May 2005 issue of Financial History Review contains a very interesting contribution on the nature of premodern moneys, written by Luca Fantacci. An abstract has been available online. I quote:
"Debasement has generally been condemned as a defect of premodern money, that was eventually amended by the institution of the gold standard. Building on monetary history and thought from the sixteenth to the eighteenth century, this article argues that debasement was instead an instrument designed to maintain the metal standard where it was needed, in the circuit of long-distance trade, while preserving the possibility of an autonomous distribution within local economies. The theoretical distinction between monetary functions (measure and means of exchange) was made effective by the articulation of ideal and real money (via debasement and enhancement), providing complementary economic areas with complementary currencies. Moreover, the distinction between monetary functions also appears as a constituent feature of money from the perspective of a reappraisal of the milestones of monetary thought, from Smith to Keynes."