Commodity money is money whose value comes from a commodity of which it is made. Commodity money consists of objects having value or use in themselves (intrinsic value) as well as their value in buying goods. This is in contrast to representative money, which has no intrinsic value but represents something of value such as gold or silver, in which it can be exchanged, and fiat money, which derives its value from having been established as money by government regulation. Examples of commodities that have been used as media of exchange include gold, silver, copper, salt, peppercorns, tea, decorated belts, shells, alcohol, cigarettes, silk, candy, nails, cocoa beans, cowries and barley. Several types of commodity money were sometimes used together, with fixed relative values, in various commodity valuation or price system economies. Aspects Commodity money is to be distinguished from representative money, which is a certificate or token which can be exchanged for the underlying commodity, but only by a formal process. A key feature of commodity money is that the value is directly perceived by its users, who recognize the utility or beauty of the tokens as goods in themselves. Since payment by commodity generally provides a useful good, commodity money is similar to barter, but is distinguishable from it in having a single recognized unit of exchange. Radford (1945) described the establishment of commodity money in P.O.W camps. Radford documented the way that this 'cigarette currency' was subject to Gresham's law, inflation, and especially deflation. In another example, in US prisons after smoking was banned circa 2003, commodity money has switched in many places to containers of mackerel fish fillets, which have a fairly standard cost and are easy to store. These may be exchanged for many services in prisons where currency is prohibited. Metals In metallic currencies, a government mint will coin money by placing a mark on metal tokens, typically gold or silver, which serves as a guarantee of their weight and purity. In issuing this coinage at a face value higher than its costs, the government gains a profit known as seigniorage. The role of a mint and of coin differs between commodity money and fiat money. In commodity money, the coin retains its value if it is melted and physically altered, while in a fiat money it does not. Usually, in a fiat money the value drops if the coin is converted to metal,