There are 4 hand-made die struck quarter eagle varieties dated 1851, and 3 are part of the same counterfeit family (yet unnamed).  1851 'C-1' is known on both brass and silver planchets, but those on silver plachets appear to be much scarcer (only 2 or 3 have yet been documented). A silver planchet was most likely used because its density is higher than brass, but was probably not used much because it was more costly.
 
This example shows less than 5% of its original gold plating, but some silvery blue toning is present.  Examples are usually weakly struck and show less detail.  This variety is especially diagnostic on the obverse with the boldly repunched 8 to the south.  If you're building a counterfeit quarter eagle set or even a cool type set, this is an example you should consider.