Special versions of the four different 2009 Lincoln Cents were produced by the United States Mint. These coins use the exact composition that was originally used when the first Lincoln Cents were issued in 1909, consisting of 95% copper and 5% tin and zinc. The same legislation which authorized the four new reverse designs also authorized the Secretary of the Treasury to issue these coins for numismatic purposes:
The Secretary of the Treasury shall issue 1-cent coins in 2009 with the exact metallic content as the 1-cent coin contained in 1909 in such number as the Secretary determines to be appropriate for numismatic purposes.
When the Lincoln Cent debuted in 1909, the composition was 95% copper and 5% tin and zinc, or bronze. The composition was modified several times during the course of the next 100 years. In 1943, the composition was changed for one year to steel coated with zinc. Starting in 1962, the tin was permanently removed from the composition. Most recently in 1982, the was switched to copper coated zinc, with an overall composition 97.5% zinc and 2.5% copper.
The Bronze 2009 Lincoln Cents were only included in certain sets issued by the United States Mint for collectors. All 2009 Lincoln Cents issued for circulation or sold in the US Mint’s two roll sets have the standard zinc based composition.
The 2009 Proof Set and 2009 Silver Proof Set both contain Bronze 2009 Lincoln Cents produced at the San Francisco Mint with a proof finish. Additional products including the special composition proof coins are the 2009 Lincoln Coin and Chronicles Set and the separate 2009 Lincoln Bicentennial Proof Set.
The 2009 Mint Set contains Bronze 2009 Lincoln Cents produced at the Philadelphia and Denver Mints. These coins are struck with a special satin finish, used for the US Mint’s annual uncirculated Mint Sets.