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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