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 as illustrated.
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. This is probably a wrong thickness stock mint error.
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.
Bronze on thin planchets J355A have been delisted as probably a mint error.
Although not well documented, die varieties exist. On the illustrated coin, the one in date almost touches the point of the neck where as on J356/P426 the tip of the neck is well past the one in the date. The Goldberg 2/01 sale lots 1203 and 1204 also show these same dies as well.
Photo courtesy of Heritage.