The regular dies trial piece in aluminum. These were deliberately struck to show how easily aluminum coined and also for sale to collectors in cased sets several of which are still in existence including the former Garrett set and one in the Eric P. Newman collection. To view the set, click here.
About a half dozen are known to exist including those in the complete sets. An example in ANR's January 2006 sale was analyzed and found to be 94.2% aluminum, 4.1% iron, and 1.5% silicon. David Cassel noted on aluminum postage currency patterns that iron was often added to strengthen the planchet and silicon helped the aluminum resist corrosion.
At least one example is also known struck in nickel J613/P678. ex Siimpson-Heritage 9/20 - PCGS63.
Photo courtesy of Heritage.