The outdoor wood-burning fireplace is made of Cor-Ten steel, which is almost pure carbon steel, but is machined to have a protective layer on the surface to keep it protected from the various weather. The surface is initially gray, and due to weather conditions it turns reddish-brown (similar to the color of rust), becoming darker over time. When used properly, cold rolled steel is expressive, durable, requires no maintenance, and stands the test of time in its own way.