By Mike Diamond for CoinWeek…
There are many ways foreign (or foreign-looking) material can end up in a coin. It might have been present in the molten alloy, particularly if the material’s melting point is higher than the alloy’s normal constituents. A slag inclusion is one type of “poured-in” error. It could be a minor constituent of the alloy that wasn’t properly blended or that segregated during cooling, an intrinsic metallic inclusion. It might have been dropped onto the cooling ingot, rolled into the coin metal strip (a “rolled-in” error), or pushed into the strip by the blanking punch (a “punched-in” error). It could have been ground into the strip or planchet (a “scraped-in” error), squeezed into the edge of the planchet, and possibly folded onto one or both faces by the upsetting mill (a “squeezed-in” error). Finally, it could have been forced into the planchet by the strike (a “struck-in” or “retained struck-through” error).
When foreign material falls out of the strip after rolling, falls out of a planchet before the strike, or falls out of a coin after the strike, it leaves behind a recess that records the size, shape, thickness, and texture of the missing object. To further complicate the picture, depressions remain behind when coin metal delaminates or disintegrates. The resulting recesses include so-called lamination errors, split planchets, and crumbling planchets.
As you might imagine, it is sometimes difficult to determine the mechanism responsible for an embedded object or the nature of the recess it leaves behind.
A recently acquired 1970-D Lincoln Memorial Cent presented some initial diagnostic ambiguity. A deep recess with irregular margins occupies the lower left quadrant of the reverse face. It was advertised as a “large strike-through.” Black patches sprinkled in and around the irregular recess certainly resemble struck-in “grease.” The term “grease” is hobby shorthand for a mixture of lubricant, dirt, and metal particles that forms a plaque of variable hardness and viscosity that coats the die face and occupies its recesses. A second 1970-D cent with a large, crusty struck-in grease deposit shows the black color typical of such material. Indistinct design details and shallow recesses mark areas where the grease fell off after the strike.
Diagnosing the 1970-D Cent
Despite these resemblances, it’s clear that the recess in our subject coin is not a struck-through error. First, the coin is underweight at 2.93 grams (normal is 3.11 grams). A coin with a struck-through error will weigh the same as a normal coin because the planchet arrives in the striking chamber with normal specifications. Second, the area opposite the recess on the subject coin’s obverse is unstruck. In a struck-through error, the opposing design should be especially well-struck due to the increased aggregate thickness and the concomitant increase in effective striking pressure.
It’s therefore clear that the depression in our subject coin was present before the strike. But this still leaves a number of possible explanations. One possibility is a pre-strike lamination error. If metal separates from a planchet before the strike, the affected area will be thinner than normal and will strike up poorly (or not at all). A 1962-D Lincoln Memorial Cent struck on a hemi-split planchet shows how the lower half of what would become the reverse face split off before the strike, resulting in a poorly struck upper half of both faces.
The subject coin’s depression shows a rough texture that is compatible with a lamination error. Outside the depression, the surface shows no cracking or peeling metal. Most lamination errors are associated with accessory lamination cracks and other signs of surface friability.
Lamination errors can sometimes be traced to the presence of subsurface contaminants. This 1944-D Lincoln Wheat Cent shows a post-strike lamination error that has exposed a dark plane of separation, presumably stained by contaminants. In a similar manner, the black patches in the floor of the subject coin’s depression could have contributed to the loss of overlying metal. The black material was likely present before the strike because it is level with the coin’s surface (material added after the strike will stand above the coin’s surface). Furthermore, pits and rough patches are seen in the few areas where the black material fell out after the strike. Black flecks lie outside the boundaries of the depression and are sprinkled all over the obverse. This may indicate that the alloy was heavily contaminated with this foreign substance.
Ruling Out Other Explanations
The black substance could be slag, but there is no definitive proof of that. A 1979 Lincoln Memorial Cent with a large slag inclusion shows how over sixty percent of the material fell out after the strike, leaving a large hole in the coin. Slag left over from copper smelting is rich in iron and and is attracted to a magnet, as is true of the 1979 cent. Our subject coin is not attracted to a magnet, but this might be because the black material is too thin and sparse.
The possibility that this black substance was rolled into the cent strip was also considered, with the thickest deposit (in the southwest quadrant of the reverse face) falling out before the strike. This would have left a “rolling indentation” error. A 1942 Lincoln Wheat Cent with a rolling indentation error at the base of Lincoln’s bust illustrates this. Arguing against this scenario is the presence of black patches along the edge of the coin. Rolled-in material would not wrap around the planchet’s edge unless it was smeared over the edge during blanking. This does not appear to be the case here, as there’s no consistent continuity between black patches at the coin’s periphery and black patches on the coin’s edge.
The last scenario considered is that the black material was ground into the surface of the planchet in the course of mechanical damage. A clad Roosevelt Dime struck on a mangled planchet shows how dark material was deposited on both faces, with the largest, thickest deposits appearing on the reverse face. Shallow struck-through errors were left where the material fell off after the strike. It stands to reason that the dark material was deposited at the same time the planchet was being ripped apart. Since our subject coin shows no obvious mechanical damage, there is little likelihood that its black material was ground into its surface.
Conclusion
The depression on the reverse face is a pre-strike lamination error linked to the presence of contaminants that permeated the cent alloy. In a sense, you could consider it a combination lamination/poured-in error.
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