In late 1973, the cost of copper rose rapidly, making it a real possibility that the cost of manufacturing a penny would rise above one cent. In an effort to resolve this dilemma the mint in Philadelphia made over 1.5 million pennies out of aluminum, dated 1974. Once test samples reached the hands of vending machine makers, it was decided that the change over would be too costly. The vending machines thought they were fake and it would require major upgrades to get the machines to accept them. All the coins were supposed to returned to the mint and after being individually counted, melted. Thirteen of them remained outstanding, the owners mainly congressmen who claimed they had lost them. One was preserved for the Smithsonian. If one came to the market today it would fetch at least five figures, however its ownership in the U.S. is probably illegal. (see coins you cannot legally own)