<P> In honor of Lincoln's 200th anniversary, special 2009 cents were minted for collectors in the same composition as the 1909 coins . </P> <P> The isotope composition of early coins spanning the period 1828 to 1843 reflects that of copper from Cornish ores from England, while coins after 1850 that reflects that of Keweenaw Peninsula, Michigan ores, a finding consistent with historical records . </P> <P> In 1943, at the peak of World War II, zinc - coated steel cents were made for a short time because of war demands for copper . A few copper cents from 1943 were produced from the 1942 planchets remaining in the bins . Similarly, some 1944 steel cents have been confirmed . From 1944 through 1946, salvaged ammunition shells made their way into the minting process, and it was not uncommon to see coins featuring streaks of brass or having a considerably darker finish than other issues . </P> <P> During the early 1970s, the price of copper rose to the point where the cent contained almost one cent's worth of copper . This led the Mint to test alternative metals, including aluminum and bronze - clad steel . Aluminum was chosen, and over 1.5 million of these pennies were struck and ready for public release before ultimately being rejected . The proposed aluminum pennies were rejected for two reasons: vending machine owners complained the coins would cause mechanical problems; and pediatricians and pediatric radiologists pointed out that the radiodensity of the metal inside the respiratory and gastrointestinal tracts was close to that of soft tissue, and the coins would therefore be difficult to detect in X-ray imaging . One aluminum cent was donated to the Smithsonian Institution . </P>

When did they quit making pennies out of copper