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The Sumitomo copper affair refers to a metal trading scandal in 1995 involving Yasuo Hamanaka, the chief copper trader of the Japanese trading house Sumitomo Corporation. Hamanaka allegedly attempted to corner the entire world's copper market.
Sumitomo lost at least $1.8 billion as a result of what it said were unauthorized trades over a 10-year period by Hamanaka, who was later charged on allegations that he manipulated the price of the metal, which then lost a third of its value on world markets in less than two months.
The affair was a major scandal which is at times compared in magnitude to the Silver Thursday scandal, involving the Hunt family's attempt to corner the world's silver markets. It currently ranks in the top 10 trading losses in financial history.