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
It looks so well preserved it could have been made yesterday.
Its Wikipedia article says that its bronze is mixed with some sulfur that prevented it from going green like copper alloys usually do.