Sales of United States Mint Uncirculated Coin Sets will be delayed from the middle of July until an unspecified date later this year, the Mint announced July 6.
A problem with protecting the uncirculated surfaces of the new Lincoln cent from premature toning is the cause of the delay.
By law, the four new Lincoln cents in the set will be made of the same alloy that the first Lincoln cent was made of in 1909.
That composition, 95 percent copper, 3 percent zinc and 2 percent tin, Mint technicians have discovered has “unique tarnish issues.”
These tarnish issues are of sufficient severity that the Mint has acted to delay mint set sales until they can be resolved.
“Even with normal anti-tarnish treatment,” the problem occurs with the cent’s surfaces.
The normal treatment was developed for use on the copper-coated zinc cents that have been the standard Mint issue since 1982.
“The pure copper surface is not as susceptible to tarnish as the bronze alloy.” the Mint says.
Even when the Mint achieves a satisfactory outcome with the new cents, the coins will be “expected to tarnish more over time than plated zinc cents.”