This experimental piece was supposedly struck in an alloy of 90% silver and 10% nickel but no examples are known.
Examples are known as follows:
Nickel J714/P793 with slightly over a dozen known. Earlier editions of Judd listed these as silver-nickel but all examples tested by Dave Cassel were more or less standard coin nickel (75% copper, 25% nickel) with no silver found at all. With the 8th edition, this number is now listed as nickel.
In addition to the ones listed in Pollock, an example is in the collection of Princeton University.
Copper J715/P794 with about a half dozen known.
Photo courtesy of David Cassel.