I could use some help here on this 1992-D Lincoln cent. Do you have
any thoughts, ideas or feedback about the D Mint mark? All information
I am hoping this is the only documented die variety of this date —
that would make it one in 448,673,300 1992-D cents. That would be fascinating.
Robert J. Price Jr.
Reader Price’s 1992-D Lincoln cent is not a die variety or even an
error. Instead, it exhibits a form of surface degradation found on
some copper-plated zinc cents.
What we see on the coin is exposed zinc from the coin’s core
peeking through overly thin copper plating that split along the curve
of the D Mint mark, with a resultant corrosion of the surfaces from
the zinc’s exposure to the atmosphere.
Copper-plated zinc cents were released in 1982 as a replacement
for the 95 percent copper cents that had been issued in every year
since 1864 but one (1943, when copper-coated steel cents were issued).
The copper plating is thin (the copper used in the composition is just
2.5 percent of the total weight of the coin).
Error coin specialists began receiving reports of poor surfaces on
the new zinc-plated cents not long after they entered circulation in
1982, the most prominent being bubbled surfaces resulting from gasses
being trapped between the zinc core and the copper plating. This
bubbling problem was especially prevalent on the cents of 1982 and
1983, and seen somewhat less on later cents.
Another form of surface problem on copper-plated zinc cents was a
result of thinness of the copper plating. During striking, the copper
plating can tear along the edges of the D Mint mark, the edges of the
numerals in the date and the edges of the letters in the inscriptions,
such as along the tops of the letters of IN GOD WE TRUST.
When the copper tears, the mostly zinc core is exposed (the core
contains a miniscule 0.8 percent copper; the rest is zinc).
Zinc is considered quite reactive. When exposed to oxygen, zinc
reacts to form zinc oxide (itself a very common and useful substance);
zinc oxide can then combine with water molecules in the atmosphere to
form zinc hydroxide. Finally, zinc hydroxide combines with carbon
dioxide to form zinc carbonate, a protective coating widely used in industry.
For cents, when the zinc and copper, in contact with each other,
are exposed to the atmosphere, galvanic corrosion occurs. The result
can be substantial deterioration of the cent’s surfaces, as many
collectors have witnessed.
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