Both are warm copper alloys, but they differ in tone and behavior. Brass, an alloy of copper and zinc, is brighter and more golden, and takes a high polish, which suits refined interior railings. Bronze, primarily copper and tin, is warmer and browner and weathers to a stable patina, which makes it the traditional choice outdoors. In Seattle we often use brass for interior statement stairs and bronze for exterior and architectural work, and we will recommend the right one for your project.