Some of the materials prized by artists and patrons become more valuable because of these artistic uses; others are valuable for their intrinsic worth as raw substance. From the earliest times, metals such as gold, silver, iron, and copper were used and traded in their natural states, as they came from the earth. They were mixed with other materials to create alloys, used for minting coins and forming sculptural objects. Among the most prominent metal materials first used for art were iron and bronze; forging and casting them were among the earliest complex artistic processes devised. Brass (copper alloyed with tin, lead, and/or other metals) and the harder, more durable bronze have been wide- ly used for grand public monuments that have fine detail, weather well, and can be hollow cast to reduce the amount of metal used. (Figures 3.29 and 3.30). Because forging and casting are complex and highly skilled processes, a viewer should know that an object made of this material was a significant statement for the artist or patron to make, one involving consider- able planning and staging to accomplish the work.