Artifacts made of copper and copper alloys, especially bronze and brass, have been used for several millennia. Native copper was first used; as more information was known about the properties of the metal, copper was smelted from pure ores. Bronze was first used around the beginning of the 3rd millennium B.C. The addition of tin to copper may originally have been accidental, but it was found to be beneficial and consequently was added deliberately, the advantage being the strengthening of cast objects. Hammering further hardens the alloy to produce better tools and weapons. Coldworking copper to give a reduction of 70% increases the hardness from 70 to 130 HV, whereas for copper containing 8% tin the increase is much greater, being up to 250 HV. Many articles were probably cast and then hammered in the cold condition giving the distinctive, distorted cored-structure that has been found in the microstructure of artifacts. See AATA 18-742. -- AATA