Comment by Animats

There's monel metal, which has copper and nickel. That resists corrosion and remains a smooth dull brown for at least a century. There were some monel metal sculptures in the art deco era, but it never caught on.

Stainless steel is an option. That lasts, and you can pressure wash it. There's some nice Art Deco stainless work from the 1930s, most notably at the Chrysler Building. But it's too shiny for most artistic uses.