 In 1867 , Longacre proposed the use of aluminum in coins ; this was rejected as the supply and price of the metal fluctuated considerably , and it then had a high intrinsic value . In 1868 , Wharton 's interests proposed making the dime into a copper @-@ nickel piece and to modify the cent , three @-@ cent piece , and nickel . The project was abandoned when it became clear the base @-@ metal dime would be too large to be effectively struck in the tough copper @-@ nickel alloy , but Longacre prepared a number of half dollar @-@ size patterns . He also began work on re @-@ engraving the designs of the gold pieces , and completed the $ 10 piece by year 's end . 
