For all the high-tech wizardry of modern financial markets, there’s one corner of the commodity world that still depends almost entirely on printed paper – making it an easy target for crooks. Buyers and sellers of base metals like copper, aluminum and nickel use documents known as warehouse receipts to prove every pound involved in a transaction actually exists and who owns it. The receipts, from a long list of issuers who often stamp them with holograms and secret codes, have become the linchpin of bank loans backed by the metal as collateral.
