The extrusion strike on this 1983 Washington quarter dollar formed when coin metal bulged into a triangular tear in the wall of a crushed die cap.
Common sense and basic Newtonian physics tells us that a die can transfer its design to a planchet only when there is resistance to its impact from the opposite side. Without such direct resistance, no design should form on either face.
Although a coinage press cannot violate Newton’s laws, there are some circumstances in which a die will transfer its design without a direct opposing force. The necessary resistance is instead delivered through an indirect route.
One example is the Type II stutter strike, in which a planchet tips up into the path of the descending hammer as the result of unevenly and prematurely applied striking pressure caused by the presence of an intrusive planchet, coin or foreign object at the opposite pole.
In a Type III stutter strike, a tiny bit of die struck design is left on the apex of a bent coin. Here the resistance is supplied by a temporary arch, the sides of which briefly resist flattening out (see Collectors’ Clearinghouse, Dec. 28, 2009, and July 25, 2011).
These are not the only circumstances that leave die-struck design elements on one face and nothing but the original unstruck surface of the planchet on the opposite face. When crushed flat against a gaping hole, a planchet will sometimes squeeze through in the direction of the hammer or anvil die, with only the apex of the extruded metal making direct contact with the die. Designated “extrusion strikes,” this category of “one-sided” strike has been previously discussed in the March/April 2004 Errorscope and in the Fall 2007 Mint Error News (www.minterrornews.com/issue19).
In one variation of the extrusion strike, coin metal protrudes through a gap in an object interposed between planchet and die. An example is seen here in a 1983 Washington quarter dollar. It was struck through a dislodged and torn late-stage die cap. Coin metal protruded through the triangular tear. The apex of the bulge made direct contact with the obverse die, picking up a weak impression of the base of Washington’s bust and the date. The featureless area on the opposite face is concave and carries the original tumbling marks of the unstruck planchet.
A coin struck in-collar against an incomplete planchet experiences the same conditions. Such coins often show variable development of an extrusion strike as coin metal is forced through the gap in the incomplete planchet and into the path of the die.
A gap in the die itself prompted formation of an extrusion strike an undated quarter dollar illustrated this week. It shows a cud (marginal die break) on the obverse face and a retained cud on the reverse face. The retained cud has left most of the letters of united sitting on a low plateau. This part of the die broke off but was held in place by the collar. Instead, the die fragment simply sank below the plane of the die face. Coin metal bulged into the recess, leaving a full die-struck design on the reverse face and a small, featureless hollow on the obverse face.
A third scenario associated with extrusion strikes involves a planchet that is overlain by a coin, planchet or foreign object and simultaneously confined by a partly deployed collar. Coin metal — trapped between the intrusive object and the immobile collar — bulges into the gap between the two, contacting the hammer die. A New Jersey quarter dollar illustrates what can happen. It has an 80 percent indent on the obverse face and shows a partial collar error. Coin metal bulged into the crescentic gap and collided with the hammer (obverse die) while simultaneously withdrawing from the anvil die. The result is a crescent of die-struck design on the obverse face carrying the legend united states of. The opposite face shows a deeply recessed crescent devoid of design but marked by numerous microscopic stress lines and a coarse, grainy texture.
I can envision additional scenarios that could generate an extrusion strike.
Not all coins involved in the foregoing scenarios will develop extrusion strikes. Scenarios 1 and 3 require striking pressure to be slightly lower than normal. A slight reduction in ram pressure or an increase in minimum die clearance will do the trick.
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