U.S. Steel Tower
First building to use steel as an exterior building material. It has a rust-like appearance due to the exterior application and support material Cor-ten. Cor-ten resists the corrosive effects of rain, snow, ice, fog, and other conditions by forming a coating of dark brown oxidation over the metal, which inhibits deeper penetration and negates the need for painting and costly rust-prevention maintenance over the years.
This paper has been withdrawn.