Bronze

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Bronze is an alloy consisting primarily of copper, usually with tin as the main additive, but sometimes with other elements such as phosphorus, manganese, aluminum, or silicon. It is hard and brittle, and it was particularly significant in antiquity, giving its name to the Bronze Age.

History

The discovery of bronze enabled people to create metal objects which were harder and more durable than previously possible. Bronze tools, weapons, armor, and building materials such as decorative tiles were harder and more durable than their stone and copper ("Chalcolithic") predecessors. Initially, bronze was made out of copper and arsenic to form arsenical bronze, or from naturally or artificially mixed ores of copper and arsenic, with the earliest artifacts so far known coming from the Iranian plateau in the 5th millennium BCE. It was only later that tin was used, becoming the major non-copper ingredient of bronze in the late 3rd millennium BCE.

Composition and Properties

Bronze is typically 88% copper and 12% tin. Alpha bronze consists of the alpha solid solution of tin in copper. Alpha bronze alloys of 4–5% tin are used to make coins, springs, turbines and blades. Historical bronzes are highly variable in composition, as most metalworkers probably used whatever scrap was on hand; the metal of the 12th-century English Gloucester Candlestick is bronze containing a mixture of copper, zinc, tin, lead, nickel, iron, antimony, and arsenic with an unusually large amount of silver – between 22.5% in the base and 5.76% in the pan below the candle. The proportions of this mixture suggests that the candlestick was made from a hoard of old coins. The Benin Bronzes are in fact brass, and the Romanesque and Renaissance art works in bronze are actually in copper alloys with a high content of zinc.

Applications

Bronze is used for various applications because of its various properties. Not only is it harder than copper, but it also has a lower melting point (900 to 1000 degrees Celsius, depending on composition) and is more fluid, making it easier to cast into complex shapes. It is also more resistant to corrosion than pure copper, making it useful in metal objects that are exposed to the elements.

Sculpture

In the world of art, bronze has been used for centuries for the casting of sculptures. The lost-wax casting method is the most common technique used for the creation of bronze sculptures; a wax model of the sculpture is made, which is then coated with clay and allowed to harden. The wax is melted out and molten bronze is poured into the space left behind. Once the metal cools and solidifies, the clay is broken away, revealing the sculpture.

Musical Instruments

Bronze is also widely used in the manufacture of various musical instruments, particularly brass instruments and, historically, for the strings of lutes, harps, and pianos. The alloy used for these instruments is typically phosphor bronze, which contains a small amount of phosphorus. This alloy is preferred for its durability and clear tone.

Industrial

In the industrial sector, bronze is used for bearings, bushings, and other components where its low metal-on-metal friction is an advantage. Bronze also has a high resistance to fatigue and is used in heavy-duty gear wheels, worm gears, and other machinery parts.

Bronze Age

The Bronze Age is a historical period characterized by the use of bronze, proto-writing, and other early features of urban civilization. The Bronze Age is the second principal period of the three-age Stone-Bronze-Iron system, as proposed in modern times by Christian Jürgensen Thomsen, for classifying and studying ancient societies. An ancient civilization is defined to be in the Bronze Age either by producing bronze by smelting its own copper and alloying with tin, arsenic, or other metals, or by trading for bronze from production areas elsewhere. Bronze itself is harder and more durable than other metals available at the time, allowing Bronze Age civilizations to gain a technological advantage.

See Also

• Copper
• Tin
• Alloy
• Metallurgy
• Iron Age
• Lost-wax casting

Bronze Resources
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