For most of its history, from 1909 to 1982, the Lincoln cent was made of bronze (an alloy of about 95% copper and 5% zinc). However, there is one exception: in 1943, pennies were instead produced using steel.
During World War II, demand for copper, tin, and other metals increased tremendously. Copper, in particular, was vital for the production of shell casings and other military equipment. One simple way for the US government to conserve metal was to modify the production of circulating coinage. Even though pennies contained only a small amount of tin, the removal of this metal from the alloy in January 1942 was expected to save over 100,000 pounds of that metal. In October 1942, the composition of the nickel was also modified to reduce its copper content.
Nonetheless, the metal shortages continued. The government encouraged the public to turn in their pennies and nickels, but these efforts proved insufficient. By authorization of Congress in December 1942, the composition of pennies and nickels was to be modified for the following year and through 1946.
In anticipation of this change, the US Mint experimented with various alternative materials for the cent throughout 1942. Some more unorthodox materials included fibers, plastics, and glass, but eventually, a steel composition was chosen. The steel core was coated with a very fine layer of zinc to prevent rust. Thus, it is the only circulation coin ever produced by the US Mint that does not contain any copper (even silver and gold coins contained some copper, and modern pennies still contain about 2.5% copper). It is also the only US coin which can be picked up with a magnet.
Because of its magnetic properties, the coin instantly caused problems in circulation, especially with vending machines. Other problems arose due to the thin zinc coating wearing off and rust appearing. The steel cent’s silvery appearance and similar size caused many people to confuse them with dimes. Public opposition to the steel cent began to foment almost as soon as they were released to the public in February 1943.
By the fall, the Treasury announced that the much-hated steel cents would not be produced in 1944. The Mint had by then developed a process to produce bronze cents using recycled shell casings. This process was used through 1946. Nonetheless, the Mint did produce more than a billion of the steel cents in 1943 across all three mints (Philadelphia, Denver, and San Francisco), saving a tremendous amount of copper for the war effort. Because they were produced in such quantity, 1943 steel cents are not particularly valuable, even in uncirculated condition.
A small number of 1943 bronze cents were produced in error – it is suspected that a few bronze planchets were accidentally mixed in with the steel planchets at some point. Approximately 13 of the 1943 bronze cents have been identified so far, though more may exist. Some examples have sold for over $1 million. Likewise, some steel cents were accidentally produced in 1944. These are slightly less rare; it is estimated that there is a few dozen extant.