The popular Washington obverse design with the "Curved" 2 cents reverse. These were apparently struck late in 1863 as per the following notation in George Eckgeldt's journal.
Examples were struck as follows:
Copper/Bronze J305/P370 on both thin 78 grain and thick circa 92 grain planchets. Metallurgical testing has confirmed the existence of pure copper, bronze and copper-iron alloys. This a relatively common pattern with several dozen known but surprisingly rare in full red.
Copper-nickel J306/P371 with fewer than a dozen confirmed.
Oroide J307/P372. This may not actually exist as the Byron Reed example is now attributed as a J306/P371.
Aluminum J308/P373 with only 3 or 4 specimens believed to exist.
Eckfeldt journal image courtesy of Alan Meghrig.