These are a combination of experimental alloys and regular die trial pieces. Metalurgical analysis is recommended.
The following combinations are known:
Copper-Aluminum in a 13 to 1 ratio (93% to 7%) J353/P425. These are described as having a golden color.
Copper-Aluminum in a 19 to 1 ratio (95% to 5%) J354/P425. These are described as having a golden color.
Copper-Aluminum in a 9 to 1 ratio (90% to 10%) J355/P425. These are described as having a yellow color.
Billon J356/P426 and are said to weigh 45 grains. At least a dozen are known.
Copper-nickel J356B/P426A. The Starr example weighing 51 grains was discovered by NGC to be copper-nickel. These are probably mint errors on wrong thickness stock.
Copper or Bronze on thick planchets J356A/P427 with at least a dozen known on planchets of about 73 grains and are extremely rare showing any red color. If these are truly bronze, then they may be mint errors on wrong thickness stock.
Bronze on thin planchets J355A have been delisted as probably being a mint error on wrong thickness stock.
Although not well documented, die varieties exist. On the illustrated coin, the the point of the neck is well past the one in the date whereas on the J353/P425 the one in the date almost touches the tip of the neck. The Goldberg 2/01 sale lots 1203 and 1204 also show these same dies as well.
Photo courtesy of Superior.