Bronze typically consists of copper, tin, zinc and phosphorus. For some applications, it may also include small amounts of other elements. The specified properties and characteristics of the finished castings determine the exact composition and proportions. Bronze is excellent for valve seats, bearings, heavy-duty bushings and bearings, machine parts, springs, telegraph wires, chemical containers and many other uses. Bronze is one of the earliest alloys to be used by smiths, beginning almost 5,000 years ago in Asia. It is an important enough alloy to have its own time period, the Bronze Age, from 3,300 BC to 1,200 BC.