Earlier this year, the United States Mint delayed the release of the annual 2009 Mint Set due to unique tarnish issues encountered for the 2009 Lincoln Cents. Despite the extra time taken by the Mint to deal with the issue, the coins still may be susceptible to tarnish over time.
The 2009 Lincoln Cents included in the set are struck in a special composition of 95% copper, 3% zinc, and 2% tin, which matches the composition used for the original 1909 Lincoln Cents. This special composition was specifically provided under the same authorization which allowed the creation of four different reverse designs.
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.
The US Mint has produced these 95% copper Lincoln Cents for inclusion in the 2009 Proof Set, 2009 Silver Proof Set, 2009 Mint Set, 2009 Lincoln Proof Set, and 2009 Lincoln Coin and Chronicles Set. The 2009 Lincoln Cents issued for circulation have a standard copper coated zinc composition with 97.5% zinc and 2.5% copper.
Despite extra time taken by the United States Mint, it appears that over time, the satin finish 95% 2009 Lincoln Cents will still be more susceptible to tarnish than regular zinc composition sets. The following message has been issued by the United States Mint to accompany the 2009 Uncirculated Mint Set:
Given the metallic composition used for the 2009 uncirculated one-cent coins — the same used for the original 1909 Lincoln Cents — the alloy readily tarnishes. The United States Mint has used anti-tarnish treatments to minimize this impact on the appearance of the uncirculated coins. However, the alloy used for the one-cent coins in this year’s uncirculated coin set is expected to tarnish more over time than the previous years’ plated zinc one-cent coins.