Description: The Museum Bronze Age geometrical vessel, Middle East, 4000-1200 BC The purpose of this vessel (vase, pot or cup) is unclear: drinking, praying, libation cup, medicinal, etc. Height: 2.36 inches = 6 cm; Upper Diameter: 2.9 inches = 7.4 cm = 74 mm; Base diameter: 2.55 inches = 6.5 cm = 65 mm; Weight: 7.5 oz. = 207 g; Condition: covered with amazing genuine patina; Origin: Afghanistan (Kandahar). 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, forming arsenic bronze, or from naturally or artificially mixed ores of copper and arsenic,[ with the earliest artefacts 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 BC. Tin bronze was superior to arsenic bronze in that the alloying process could be more easily controlled, and the resulting alloy was stronger and easier to cast. Also, unlike arsenic, metallic tin and fumes from tin refining are not toxic. The earliest tin-alloy bronze dates to 4500 BCE in a Vin?a culture site in Plo?nik (Serbia). Other early examples date to the late 4th millennium BC in Africa, Susa (Iran) and some ancient sites in China, Luristan (Iran) and Mesopotamia (Iraq). Ores of copper and the far rarer tin are not often found together (exceptions include one ancient site in Thailand and one in Iran), so serious bronze work has always involved trade. Tin sources and trade in ancient times had a major influence on the development of cultures. In Europe, a major source of tin was England's 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 artefacts 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 very clear. These were made in enormous quantities for elite burials, and also used by the living for ritual offerings. Though bronze is generally harder than wrought iron, with Vickers hardness of 60258 vs. 3080, the Bronze Age gave way to the Iron Age because iron was easier to find and easier to process into a usable grade of metal (it can be made into higher grades, but doing so takes significantly more effort and knowledge of techniques). Pure iron is soft, and the process of beating and folding sponge iron to make wrought iron removes from the metal carbon and other impurities which need to be re-introduced to improve hardness. Careful control of the alloying and tempering eventually allowed for wrought iron with properties comparable to modern steel. Bronze was still used during the Iron Age, and has continued in use for many purposes to the modern day. Among other advantages it does not rust. The weaker wrought iron was found to be sufficiently strong for many uses. Archaeologists suspect that a serious disruption of the tin trade precipitated the transition. The population migrations around 12001100 BC reduced the shipping of tin around the Mediterranean (and from Great Britain), limiting supplies and raising prices. As the art of working in iron improved, iron became cheaper, and as cultures advanced from wrought iron (typically forged by hand wrought by blacksmiths) to machine forged iron (typically made with trip hammers powered by water), the blacksmiths learned how to make steel, which is stronger than bronze and holds a sharper edge longer. Composition, alloys There are many different bronze alloys, but typically modern bronze is 88% copper and 12% tin. Alpha bronze consists of the alpha solid solution of tin in copper. Alpha bronze alloys of 45% 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, 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 really brass, and the Romanesque Baptismal font at St Bartholomew's Church, Liège is described as both bronze and brass. In the Bronze Age, two forms of bronze were commonly used: "classic bronze", about 10% tin, was used in casting; and "mild bronze", about 6% tin, was hammered from ingots to make sheets. Bladed weapons were mostly cast from classic bronze, while helmets and armor were hammered from mild bronze. Commercial bronze (90% copper and 10% zinc) and architectural bronze (57% copper, 3% lead, 40% zinc) are more properly regarded as brass alloys because they contain zinc as the main alloying ingredient. They are commonly used in architectural applications. Bismuth bronze is a bronze alloy with a composition of 52% copper, 30% nickel, 12% zinc, 5% lead, and 1% bismuth. It is able to hold a good polish and so is sometimes used in light reflectors and mirrors. Plastic bronze is bronze containing a significant quantity of lead which makes for improved plasticity possibly used by the ancient Greeks in their ship construction. Other bronze alloys include aluminium bronze, phosphor bronze, manganese bronze, bell metal, arsenical bronze, speculum metal and cymbal alloys.
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