The minting process provides many opportunities for foreign material
to become embedded in a coin. Previous columns have discussed how
foreign material can enter the production stream during smelting and
mixing of an alloy’s constituent metals, pouring of the molten alloy
into ingot molds, the rolling of the coin metal strip, the punching of
a blank, the upsetting of the blank, and the striking of the planchet.
Now Troy Shoopman has discovered a new entry point, one that occurs
after the coin is struck.
Extra production step
For most coins, production ends with the strike. But Presidential
and Native American dollars go through an additional step that
generates the edge design. After it is struck, each otherwise finished
dollar is sent through a lettering device consisting of a rotating
impeller and a fixed lettering die. The coin is rolled and squeezed
between the impeller and the slot-like die.
As the coin rolls against the raised design elements that stick up
from the floor of the slot, assorted incuse letters, numbers, dots,
and stars are impressed into the soft, exposed copper core of these
manganese-brass clad coins.
It stands to reason that debris of one kind or another might get
sucked into the lettering device or might be carried along with the
coins. This debris will then be pressed into the edge of the coin
during the lettering operation.
Spiral of gray metal
While inspecting hundreds of Presidential dollars obtained from his
local bank, Shoopman discovered a 2007-P Thomas Jefferson dollar with
a spiral of gray metal embedded in the edge. Strongly attracted to a
magnet, it appears to be composed of steel. The spiral shape suggests
a metal shaving. The right arm of the letter U from PLURIBUS overlaps
the foreign object. Here the letter is impressed much more deeply than
the other design elements arranged along the edge.
This error is similar in appearance and etiology to foreign matter
that is impressed into the edge of a planchet during the upsetting
process. During upsetting, a rotating drum machined with trapezoidal
grooves rolls and squeezes each blank against a fixed half-circle
bearing identical grooves. The blank is reduced to a smaller diameter
and a low proto-rim is pushed up along the perimeter of what is now a planchet.
On rare occasions bits of metal become trapped between the blank and
upset mill. Several examples have appeared in earlier columns.
Reproduced here is a photo of a 1968-D Lincoln cent with a round
pellet of nonmagnetic, nickel-colored metal that was evidently forced
into the edge during upsetting.
Know the differences
How is it then possible to distinguish these two types of
“squeezed-in” errors? In other words, how can we discriminate between
an upset mill inclusion and a lettering die inclusion?
It mainly boils down to whether the foreign object protrudes beyond
the edge. The pressure used during upsetting is undoubtedly greater
than the pressure used to impress the edge design because the blank
has to undergo controlled deformation. This greater pressure will
likely push the foreign object deep enough so that it is level with
the edge of the planchet. Even if it still protrudes a little bit
after this step, the subsequent strike will leave it flush with the
edge when the coin expands against the collar. The pellet found in the
1968-D cent fulfills these expectations.
The Presidential dollar’s steel spiral protrudes slightly beyond the
coin’s edge, providing persuasive evidence that it was forced in
during lettering. The greater depth of the right arm of the U is also
a predictable outcome since the metal shaving briefly created a much
tighter fit between coin and lettering die.
We can anticipate finding other examples of lettering die
inclusions. They might not always be restricted to the coin’s edge,
however. Wider, thinner items might wrap around one or both faces of
an affected dollar coin, in the same way that foil-like pieces of
metal probably introduced during upsetting have been observed to wrap
around 5-cent coins.
If any such wraparound fragments happen to make their appearance, we
can expect them to sit loosely above the obverse and reverse faces of
the coin. After all, there is nothing beyond normal circulation that
would flatten them against the coin’s surface.
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