This is a bronze sword found in southern Hubei province, China, in 1965. It is inscribed with bird-worm seal script characters reading "King Goujian of Yue made this sword for [his] personal use".
Picture by Wikipedia user Windmemories used under a Creative Commons Attribution-Share Alike 4.0 International
Its Wikipedia article says that its bronze is mixed with some sulfur that prevented it from going green like copper alloys usually do.