Where free coinage is permitted the supply of money depends upon the relative cost of producing the money material, as compared with the cost of producing other commodities. The value of the money commodity is equal in the long run to the marginal cost of producing it; that is, to the cost of producing that portion of it which is produced at the greatest cost, and anything which tends to increase the marginal cost of producing the money commodity or to decrease its value tends to curtail its supply. Those forms of money of which the government does not permit free coinage have their supply regulated artificially by the government. In this case, of course, there is no direct relation between the cost of producing the money and its value.