History
The discovery of bronze enabled people to create metal objects that were harder and more durable than had previously been possible. Bronze tools, weapons, armor, and building materials such as decorative tiles were harder and more durable than their stone and copper ("Chalcolithic") predecessors.
The earliest tin-copper-alloy artifact has been dated to c. 4650 BCE, in a Vinča culture site in Pločnik (Serbia), and believed to have been smelted from a natural tin-copper ore, stannite. Other early examples date to the late 4th millennium BCE in Egypt, Susa (Iran) and some ancient sites in Luristan (Iran), Tepe Sialk (Iran), Mundigak (Afghanistan), and Mesopotamia (Iraq).
Copper–arsenic alloys, from naturally or artificially mixed ores of those metals, forming arsenical bronze, were found to result in a metal of a silver hue, with similarly increased strength, a lower melting point, and simpler to work, than pure copper. The earliest known arsenic–copper alloy artifacts come from a Yahya Culture (Period V 3800–3400 BCE) site, at Tal-i-Iblis on the Iranian plateau, and were smelted from native arsenical copper and copper-arsenides, such as algodonite and domeykite.
Tin became the major non-copper ingredient of bronze in the late 3rd millennium BCE. Tin bronze was superior to arsenic copper in that the alloying process could be more easily controlled, and the resulting alloy was stronger and easier to cast. Also, unlike those of arsenic, metallic tin and the fumes from tin refining are not toxic.
Ores of copper and tin, which is much rarer, are not often found together (exceptions include Cornwall in the United Kingdom, one ancient site in Thailand and one in Iran), so serious bronze work has always involved trade with other regions. Tin sources and trade in ancient times had a major influence on the development of cultures. In Europe, a major source of tin was the British deposits of ore in Cornwall, which were traded as far as Phoenicia in the eastern Mediterranean. In many parts of the world, large hoards of bronze artifacts are found, suggesting that bronze also represented a store of value and an indicator of social status. In Europe, large hoards of bronze tools, typically socketed axes (illustrated above), are found, which mostly show no signs of wear. With Chinese ritual bronzes, which are documented in the inscriptions they carry and from other sources, the case is clear. These were made in enormous quantities for elite burials, and also used by the living for ritual offerings.
An analysis of 324 metallic finds of the Indus Valley Civilisation (2600–1900 BCE), in the 1990s, found 67 (20%) to have some tin content, to be considered bronze artifacts, with 26 (8%) of the artifacts having a tin content in excess of 10%, permitting casting; the source of the tin is unknown, but has been speculated to be from Bukhara or Samarkand, in Uzbekistan.
