Cor-Ten or corten steel is a type of steel that resists corrosion. Unlike regular steel, corten develops a light rust layer that once formed, will protect the underlying material and prevent further corrosion. Because of its corrosion- resistant properties, it has been widely used by architects and artists, include Richard Serra (my favorite artist). However, corten is not rust-proof. In fact, it needs wet-dry cycles in order for it to form it's protective layer. If the corten steel is submerged in water or buried in wet grounds, it will NOT form the protective rust layer. In addition, if the corten is used in an area that is right on or really close to the ocean, this protective layer may not form in time to protect the underlying steel. Now, for the metal geeks out there, Cor-Ten is actually the trademarked named for a weathering steel developed by US Steel. Although it is correct to say that only US Steel can make Cor-Ten, many other steel mills make a similar product and the correct designation would be ASTM A588 (weathering plate) or ASTM A606 (weathering sheet / coil).