The pewter version of the 1791 Washington Liverpool Halfpenny is believed to be unique. The pewter version is different from the copper Liverpool Halfpennies is a couple of ways:
1. The edge of the pewter version is plain; the edges on the copper versions are lettered.
2. Both the pewter and copper versions share the same obverse; the reverses are similar, but with substantial differences. The rigging on the ship is completely different and the shape of the wreaths beneath the ship also differ greatly.
3. The pewter version is on a slightly larger planchet, allowing most of the legends and devices to fit onto the coin. The copper versions are on undersized planchets, which usually lops off the tops of some of the lettering.