Beginning in 1965, circulation-quality coins from dimes to dollars
have, for the most part, been a base metal composite arranged in three
layers. The two outer layers are thin and on the vast majority of
coins below the dollar denomination, composed of an alloy of 75
percent copper and 25 percent nickel. These two “clad” layers surround
a much thicker layer of pure copper.”
The sandwich is assembled in the “bonding mill.” Here the three
constituent coils of metal are fed between two rollers. Under immense
pressure, the two outer strips of copper-nickel are fused to the
middle strip of pure copper. The composite strip then makes several
additional passes through the “rolling mill” until it is squeezed down
to coin thickness.
Every so often a collector comes across a coin with the copper
core partly or completely exposed on one face. These “missing clad
layer” errors fall into several categories.
For the sake of simplicity, I will limit my discussion to coins in
which the clad layer is completely missing on one face.
Most are bonding errors
The vast majority of missing clad layer errors are bonding errors.
If insufficient tonnage is applied, or if the facing surfaces are
inadequately cleaned, the clad strip fails to bond to the core strip.
The loose clad layer then falls away some time after the coin blank is
punched out by the blanking press.
Most times the clad layer falls off before the planchet reaches
the coinage press, as seen in the illustrated 1977 Washington quarter
dollar. Since a quarter dollar clad layer weighs approximately 1 gram,
the error coin should weigh about 4.67 grams. This example weighs 4.7 grams.
Every so often the clad layer separates after a coin is struck.
This leaves the exposed copper core with a blurred design, as shown by
the accompanying 1968-D Washington quarter dollar. Despite a little
bit of cladding retained at the 12:00 position, the coin is somewhat
lighter than expected at 4.53 grams. This may be due to the clad layer
having carried off a thin veneer of copper. Or perhaps the intact
blank was underweight to begin with.
The rarest form
The rarest form of missing clad error is not caused by an insecure
bond at all. It is a rolling error that traces back to the bonding
mill. Three potential scenarios are involved:
1. The leading end of one clad strip lags behind the leading end
of the core strip and the other clad strip.
2. The trailing end of one clad strip ends prematurely.
3. A large gap is present in one clad strip.
In each case, you end up with a stretch of composite strip
composed of only two layers, one of copper and one of copper-nickel.
This length of strip is eventually rolled to normal coin thickness
during subsequent passes through the rolling mill. Any blank punched
from this area will weigh the same as a normal coin.
The rarity of such errors may be due, in part, to the habit of
trimming the ends of the composite strip before it is sent through the
The first example of this rare error type is a 1976 Bicentennial
quarter dollar. It weighs 5.39 grams. The reason it’s 0.28 gram short
of normal weight is that the right side shows a taper. This is
consistent with an origin at the leading or trailing end of the strip.
Also showing a slight taper is a 2005-P West Virginia quarter
dollar sent to me several years ago by error dealer Fred Weinberg. At
5.57 grams, it’s only one-tenth of a gram shy of normal weight.
At the recently concluded Central States Numismatic Society
convention, Weinberg handed me a piece of copper-nickel clad strip
that shows the kind of rolling error I’ve been talking about (see
photos). On each side, the clad layer runs out prematurely. The
remaining stretch of pure copper would have yielded a full-weight,
pure copper blank. This piece of composite strip is 2.37 millimeters
thick, considerably thicker than a quarter dollar blank I measured
(1.38 millimeters). I fully anticipate it being thicker than a half
dollar blank as well. Evidently this piece of strip was sliced off
before the composite strip had been rolled to final thickness.
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