Concentric 'strike lines' don't always indicate multiple
- Published: Dec 16, 2011, 7 PM
Multiple strikes are often hard to spot when no movement of the coin occurs between strikes. Collectors rely on a number of diagnostic clues to identify such “close multi-strikes.” One such clue is the presence of concentric strike lines.
Concentric strike lines are circular or semicircular grooves or steps produced by the edge of the field portion of the die and sometimes the outer edge of the rim gutter of the die. An intermediate strike line can reflect the presence of collar clash, which occurs when the rim gutter is damaged by contact with the top of the collar. Close examination of spacing, contour and stepwise elevation of the strike lines is necessary to distinguish those created by multiple strikes from those that simply result from contact with different parts of the die perimeter.
Strike lines are located in the “slide zone” of off-center and broadstruck coins. The slide zone forms as coin metal squeezes out between the dies and picks up fine radial striations in the process. A strike line interrupts these striations.
It would be nice if strike lines always indicated the presence of extra strikes, but this is not the case. For example, they sometimes form opposite a “stiff collar” error. The planchet represented by the illustrated 2000-P Jefferson 5-cent coin was not perfectly centered in the striking chamber when it was struck. The right side rested against a stiff, but still mobile collar. The obverse face (struck by the anvil die) was left with a sloping, featureless shoulder that terminates laterally in a strong collar scar. On the reverse face, four concentric strike lines can be detected between the edge of the field and the unstruck portion of the planchet.
The multiple strike lines were produced early in the downstroke as the hammer (reverse) die skittered across the surface of the planchet as the collar collapsed.
These strike lines happen to be a minor expression of a Type I stutter strike. Had the bounces been higher and wider, a thin crescent of die-struck design would have been left in the gap between the inner and outer series of strike lines. A Type I stutter strike is shown in the Dec. 28, 2009, “Collectors’ Clearinghouse” column.
I’m not sure what caused the extensive series of strike lines present on the obverse face of the illustrated 1993-P Washington quarter dollar. The broad crescent on the left carries no fewer than six concentric lines. I doubt they represent an incipient stutter strike.
On the reverse face, strangely distant from the die-struck design, are two short but very deep arcs of collar contact, located at 6:00 and 8:30. At this distance, I’m skeptical that the collar could have provided sufficient resistance for even a loose hammer die to skitter. This hypothesis would also have to incorporate the unlikely assumption that the hammer (obverse) die contacted the planchet in a very misaligned position and that it skittered its way to a centered position by the time the downstroke was completed.
An equally dubious scenario has the planchet squeezing out beneath a jittery hammer die. Instead of a “slide zone” forming with conventional radial striations, a series of partial rings was generated. The stumbling block here is that this presumptive slide zone is far too wide relative to the strength of the strike, which was quite modest. The slide zone on the reverse face is extremely narrow.
Almost as puzzling are the two to three concentric strike lines present on the left side of the reverse face of a broadstruck 1998-D Roosevelt dime. The coin shows are no signs of collar contact at all, which would seem to rule out a Type I stutter strike. Here, at least, it seems possible that the planchet squeezed out beneath a jittery hammer (reverse) die, leaving a series of curved lines.
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