Unique errors often pose a diagnostic challenge because there are no precedents to consult. Such is the case with a 1972-D Jefferson 5-cent coin recently sent to me by veteran error collector Steve Mills. A curved (concave) clip in the northwest quadrant is flanked by an unexpected curved groove. The clip shows such hallmarks of authenticity as metal flow in adjacent design elements (like the E of WE) and weakness of the design rim at the pole opposite the clip (the “Blakesley Effect”).

The groove was clearly present before the strike because its margins are flush with the field and design and it widens and narrows in concert with the topography that it crosses.

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Collector speculates

Mills speculated that the groove could be an incomplete clip (incomplete punch). The problem with this idea is that the groove appears on only one face while an incomplete clip always appears on both faces. This is because one punch mark is generated by the blanking die and the other by a hole in a perforated base plate.

Another difficulty with the incomplete clip theory is the failure of the groove to appear on the coin’s edge. An incomplete clip penetrates the surface of the strip, and all but the shallowest will be visible on the edge of the affected blank.

Another explanation

A much more satisfactory interpretation identifies the groove as a novel form of blanking burr. For some reason, as the blanking die sliced through the strip, it produced a burr along the bottom edge of the hole. When this hole was sliced though again by a blanking die to create the clipped blank, the burr remained attached. Later on, during its rough-and-tumble journey to the press, the blanking burr was pushed over onto the surface of the blank. The burr was eventually struck into the coin by the 5-cent obverse die.

There is considerable evidence to support this theory. Whenever a piece of metal is struck into a planchet, it is outlined by a fissure, which is here represented by the curved groove. We can see this effect in association with a more familiar form of blanking burr, the “rolling fold.”

A rolling fold is a blanking burr that protrudes from the blank (rather than the hole), and is thought to be the result of a chipped or locally dulled blanking die. The burr is folded over onto the surface of the planchet during upsetting and is struck into the surface of the coin in the form of a short broad symmetrical tongue of metal. A typical rolling fold, along with its fissure, is shown here on a Washington quarter dollar.

A different kind of burr

Another type of burr is often found in association with straight clips, like the one shown here. Paralleling the straight edge is a fissure that, except for its linear shape, closely resembles the fissure on the 1972-D Jefferson 5-cent coin. It most likely represents a cutting burr generated when the leading or trailing end of the strip was trimmed by a saw or guillotine. Sometime after the blank was punched out from the end of the strip, the burr was pushed over onto the surface of the planchet and was eventually struck into the coin. These straight fissures used to be incorrectly identified as “incomplete straight clips.”

Other ideas include scars from a guide or stop, but these explanations seem less likely.

Returning to the 1972-D Jefferson 5-cent coin, we find additional evidence supporting the blanking burr theory.

The edge of the clip shows only vertical striations; it lacks the more familiar cut-and-tear texture generated as the blank tears away from the bottom of the strip as it’s pushed through by the blanking die. The edge texture suggests that, instead of stopping just short of the bottom surface, the blanking die traveled all the way through the strip, possibly dragging some metal along with it.

The edge of a curved clip should be vertical in cross section. But here, the edge is slightly inclined, tilting outward as one approaches the obverse face. This effect can be attributed to the extra thickness added to the planchet by the pushed-over burr.

Exactly why the burr formed isn’t clear. Perhaps the blanking die was dull, or perhaps the blanking die pushed ahead of it the roughened metal of a breakaway zone that protruded inward to an unusual degree from the side of the hole.