Cor-Ten steel. Also known generically as weathering steel, its specific alloys produce a stable rust layer that becomes a protective coating. It’s durability in appropriate applications is unmatched, and its patina improves with age.
Pomegranate~Corten Steel "Pomegranate" sculpture, I see it as a symbol of fertility. Laser Cut Corten Weathering Steel sculpture, commissioned for a client in Adelaide using 6mm thick corten steel, this sculpture is flat pack and easy to assemble with no bolts.