At first only copper was traded. Lead and zinc were soon added but only gained official trading status in 1920. The exchange was closed upon the outbreak of World War II and did not re-open for copper trading until 1953. The range of metals traded was extended to include aluminium (1978), nickel (1979), tin (1989), aluminium alloy (1992), steel (2008), and minor metals cobalt and molybdenum (2010). The exchange ceased trading plastics in 2011. The total value of the trade is around $US 11.6 trillion annually.