Pennell is well known as a gem engraver, glass engraver and medallist. Of the medal he wrote: ‘A Tree for me shows a man wheeling away the last ancient tree in a wheel-barrow – perhaps for preservation in a museum!… On the reverse, three dead trees in a barren landscape’. Obverse engraved on a glass lens, from which moulds were taken and medals cast in silver; the reverse carved on the silver medal, which then served as a master from which moulds were taken.