Corten steel has been around since at least the early sixties. 

Here it's used to sheath a building in Manhattan.  There's no need to paint the steel as it naturally rusts and forms a natural weather resistant coating.  The coating has a nice patina, but the rust stains the surfaces below.  When it runs onto light colored concrete, the results aren't too nice.  A detail where the rust falls onto something that conceals this discoloring would be a nice touch.