20 Balboas Panama Canal

Panama's 20 Balboa series has used the silver proof format since the 1970s to commemorate the canal that defines the country's modern economic existence. The 2016 issue appeared during a particularly charged moment: the expanded canal — a third set of locks capable of handling post-Panamax vessels — opened in June of that year after a nine-year construction project and a cost overrun dispute between the Panamanian government and the Sacyr-led construction consortium that nearly halted work entirely.

The .9999 fineness is notably purer than the .925 sterling used in earlier issues of this series.