The edge of a newly-struck coin is ordinarily flat and vertical. However, certain errors will leave the edge with an overhanging lip or a slanted cross-sectional profile.
The most familiar source of edge overhangs is the partial collar error. A partially deployed collar will surround only the lower portion of the planchet’s edge. The upper portion of the edge will be free to expand.
Illustrated this week is a 1977 Washington quarter dollar struck on a blank that was surrounded by a tilted partial collar. In other words, the top of the collar wasn’t parallel to the horizontal plane. In this case, the collar dipped below the plane of the anvil die face at one pole, leaving the edge completely smooth for about 90 arc degrees. The photograph shows how the reeded lower portion of the edge is separated from the smooth upper portion by a clearly defined step.
A different kind of edge overhang is produced when an expanding coin grazes the top of a collar and forces it down. Instead of a clearly-defined step, the edge shows a continuous bevel. Reeding traces are smeared and indistinct. Such errors are called “forced broadstrikes.” A centered, isolated planchet yields a 360 degree forced broadstrike. If the planchet’s upper surface is partly covered by a planchet or coin, the result is a unipolar forced broadstrike.
The effect of forced expansion against a collapsing collar is seen on the reverse face of a 1998-P Washington quarter dollar whose obverse face carries a partial brockage. Radial expansion of the coin was temporally and spatially asymmetrical, commencing where the two discs overlapped.
Here the expanding edge of the bottom planchet forced the collar down, leaving a beveled edge with smeared reeding traces. Beyond the limits of the brockage, the edge is almost smooth, because by the time this part of the coin began its expansion, the collar had already been depressed.
Another kind of overhang is produced when a planchet or coin is struck into an underlying planchet that is confined by the collar. The increased effective striking pressure generated by the aggregate double thickness forces coin metal over the top of the collar to form a horizontal lip.
The illustrated 1981-D Lincoln cent was brockaged by an off-center cent while remaining fully surrounded by the collar. Horizontal lipping is seen along the outer margin of the brockage.
A fourth type of overhang is produced when an off-center planchet is forced down into a collar frozen in the “up” position. The resulting stiff collar error leaves a rounded shoulder on the lower face and a thick vertical flange on the upper face. It also produces a horizontal lip, as seen in the illustrated 1998-P Washington quarter dollar. The lip lies immediately above a strongly marked collar scar.
It should be noted that partial collar errors often co-occur with the three other types of edge overhang discussed here. This adds to the general confusion and conflation that prevails among these errors.