History of Bronze

Bronze was developed about 3500 BC by the ancient Sumerians in the Tigris-Euphrates Valley. Historians are unsure how this alloy was discovered, but believe that bronze may have first been made accidentally when rocks rich in ores of copper and tin were used to build campfire rings (enclosures for preventing fires from spreading). As fire heated these stones, the metals may have mixed, forming bronze. This theory is supported by the fact that bronze was not developed in North America, where natural tin and copper ores are rarely found in the same rocks.

Around 3000 BC, bronze-making spread to Persia, where bronze objects such as ornaments, weapons, and chariot fittings have been found. Bronzes appeared in both Egypt and China around 2000 BC. The earliest bronze castings (objects made by pouring liquid metal into molds) were made in sand; later, clay and stone molds were used. Zinc, lead, and silver were added to bronze alloys by Greek and Roman metalworkers for use in tools, weapons, coins, and art objects.

During the Renaissance, a series of cultural movements that occurred in Europe in the 14th, 15th, and 16th centuries, bronze was used to make guns, and artists such as Michelangelo and Benvenuto Cellini used bronze for sculpting. The most accurate and most commonly used method of bronze casting is the lost-wax method.

Today, bronze is used for making products ranging from household items such as doorknobs, drawer handles, and clocks to industrial products such as engine parts, bearings, and wire. Bronze is made by heating and mixing the molten metal constituents. When the molten mixture is poured into a mold and begins to harden, the bronze expands and fills the entire mold. Once the bronze has cooled, it shrinks slightly and can easily be removed from the mold.

Bronze is a metal compound containing copper and other elements. The term bronze was originally applied to an alloy of copper containing tin, but the term is now used to describe a variety of copper-rich material, including aluminum bronze, manganese bronze, and silicon bronze.

Bronze is stronger and harder than any other common alloy except steel. It does not easily break under stress, is corrosion resistant, and is easy to form into finished shapes by molding, casting, or machining.

The strongest bronze alloys contain tin and a small amount of lead. Tin, silicon (see end of this article for specifics on silicon), or aluminum is often added to bronze to improve its resistance. ilicon bronze alloys is used today in art castings. As bronze weathers, a brown or green film forms on the surface. This film inhibits corrosion. For example, many bronze statues erected hundreds of years ago show little sign of corrosion. Bronzes have a low melting point, a characteristic that makes them useful for brazing—that is, for joining two pieces of metal. When used as brazing material, bronze is heated above 430°C (800°F), but not above the melting point of the metals being joined. The molten bronze fuses to the other metals, forming a solid joint after cooling.

Lead is often added to make bronze easier to machine. Silicon bronze is machined into piston rings and screening, and because of its resistance to chemical corrosion it is also used to make chemical containers and in the the making of bronze art. Manganese bronze is used for valve stems and welding rods. Aluminum bronzes are used in engine parts and in marine hardware.

Bronze containing 10 percent or more tin is most often rolled or drawn into wires, sheets, and pipes. Tin bronze, in a powdered form, is sintered (heated without being melted), pressed into a solid mass, saturated with oil, and used to make self-lubricating bearings.

In metallurgy bronze is an alloy of copper, tin, zinc, phosphorus, and sometimes small amounts of other elements. Bronzes are harder than brasses. Most are produced by melting the copper and adding the desired amounts of tin, zinc, and other substances. The properties of the alloy depend on the proportions of its components.

Bronze is used for coins, medals, steam fittings, and gunmetal and was formerly employed for cannon. Because of its particularly echoing quality, bell metal, containing from 20% to 24% tin, is used for casting bells.

Essentially, to produce a bronze casting, the alloy is heated to at least 1,700 degrees F. at which it melts, and then poured into some type of fireproof mold of the original work.

Bronze is of exceptional historical interest and still finds wide applications. The proportions of copper and tin varied widely (from 67 to 95 percent in surviving artifacts), but, by the Middle Ages in Europe, certain proportions were known to yield specific properties. An alloy described in an 11th-century Greek manuscript in the library of St. Mark's, Venice, cites a proportion of one pound copper to two ounces of tin (8 to 1), approximately that used for bronze gunmetal in later times. Some modern bronzes contain no tin at all, substituting other metals such as aluminum, manganese, and even zinc

Bronze is harder than copper as a result of alloying that metal with tin or other metals. Bronze is also more fusible (i.e., more readily melted) and is hence easier to cast. It is also harder than pure iron and far more resistant to corrosion. The substitution of iron for bronze in tools and weapons from about 1000bc was the result of iron's abundance compared to copper and tin rather than any inherent advantages of iron.

Bronze in the Ancient World

In both Europe and the Middle East, bronze was mainly used for weapons and cutting tools—swords, spears, arrowheads, shields, adzes, and axes—although bowls and cauldrons were also made from bronze. During the 1st millennium, bronze was especially prized in Greece and later in Rome for sumptuous and elegant furnishings, such as tripods, bed and table frames, small oil lamps, and tall lampstands, often elaborately decorated with raised animal or leaf decoration.

Chinese Bronzes

In China bronze appears to have been used almost exclusively for bells, mirrors, and vessels in a variety of prescribed forms for distinct functions in religious rites, as well as for weapons and for the decoration of horse trappings and chariots. This first Bronze Age in China lasted from about 1800 to the end of the Qin dynasty (221-206BC. The bronze ritual vessels are especially admired for the nobility of their forms and the vigor of their abstract linear decoration. The decoration consists of highly conventionalized and attenuated masks and mythical monster forms, such as dragons. These vessels were cast from molds prepared with the decoration cut and incised on the inner face, resulting in equivalent projections on the cast vessel.>

European Bronzes

After bronze was superseded by iron for weapons, it remained in use in Europe as an artist's medium. Greek bronze statues, vases, and wine vessels, sometimes of large size and elaborately gilded, were greatly admired in Rome. The wandering tribes who gradually superseded Roman power in Europe (including Italy), also appreciated bronze, but used it more often for portable items such as shields and bowls as well as for buckles and brooches (often inlaid with colored stones or opaque enamel). In church furnishings, bronze continued to be used for larger pieces, such as candlesticks, baptismal fonts, and coffers. Perhaps the most famous bronze sculptures of the Renaissance are Lorenzo Ghiberti's sumptuously ornamental gilded bronze doors—the Gates of Paradise (1425-1452)—for the Baptistery at Florence, consisting of ten self-contained rectangular panels of biblical scenes cast in high relief. Many other Renaissance artists used this medium for smaller cast figure sculptures, often inspired by antique works of the classical era; this prime use for bronze has persisted to the present day.

In the 18th and 19th centuries, and especially in France, gilt bronze attachments—called ormolu—in the form of projecting and richly decorated cast mounts on edgings, drawers, and feet, were added to luxury furniture.

African Bronzes

In Nigeria, between the 14th and 16th centuries, cast bronze sculptures of extreme refinement were made at Benin in a highly developed artistic convention unrelated to European styles.

Silicon Bronze

Silicon, symbol Si, semimetallic element that is the second most common element on earth, after oxygen. The atomic number of silicon is 14. Silicon is in group 14 (or IVa) of the periodic table. It was first isolated from its compounds in 1823 by the Swedish chemist Baron Jons Jakob Berzelius.

Silicon is prepared as a brown amorphous powder or as gray-black crystals. It is obtained by heating silica, or silicon dioxide (SiO2), with a reducing agent, such as carbon or magnesium, in an electric furnace. Crystalline silicon has a hardness of 7, compared to 5 to 7 for glass. Silicon melts at about 1410° C (about 2570° F), boils at about 2355° C (about 4271° F), and has a specific gravity of 2.33.

Silicon constitutes about 28 percent of the earth's crust. It does not occur in the free, elemental state, but is found in the form of silicon dioxide and in the form of complex silicates. Silicon-containing minerals constitute nearly 40 percent of all common minerals, including more than 90 percent of igneous-rock-forming minerals. The mineral quartz, varieties of quartz (such as chrysoprase, onyx, flint, and jasper), and the minerals cristobalite and tridymite are the naturally occurring crystal forms of silica. Silicon dioxide is the principal constituent of sand. The silicates (such as the complex aluminum, calcium, and magnesium silicates) are the chief constituents of clays, soils, and rocks in the form of feldspars, amphiboles, micas, and zeolites, and of semiprecious stones, such as garnet, zircon, topaz, and tourmaline .

Silicon is used in the steel industry as a constituent of silicon-steel alloys. Silicon steel, which contains from 2.5 to 4 percent silicon, is used in making the cores of electrical transformers because the alloy exhibits low magnetism. Silicon is also used as an alloy in copper, brass, and bronze.

Properties

With the exception of steel, bronze is superior to iron in nearly every application. Although bronze develops a patina, it does not oxidize beyond the surface. It is considerably less brittle than iron and has a lower casting temperature.

Copper-based alloys have lower melting points than steel and are more readily produced from their constituent metals. They are generally about 10 percent heavier than steel, although alloys using aluminum or silicon may be slightly less dense. Bronzes are softer and weaker than steel, bronze springs are less stiff (and so store less energy) for the same bulk. It resists corrosion (especially seawater corrosion) and metal fatigue better than steel and also conducts heat and electricity better than most steels. The cost of copper-base alloys is generally higher than that of steels but lower than that of nickel-base alloys.

Copper and its alloys have a huge variety of uses that reflect their versatile physical, mechanical, and chemical properties. Some common examples are the high electrical conductivity of pure copper, the excellent deep-drawing qualities of cartridge case brass, the low-friction properties of bearing bronze, the resonant qualities of bell bronze, and the resistance to corrosion by sea water of several bronze alloys.

In the twentieth century, silicon was introduced as the primary alloying element, creating an alloy with wide application in industry and the major form used in contemporary statuary. Aluminum is also used for the structural metal aluminum bronze.

Bronze is the most popular metal for top-quality bells and cymbals, and more recently, saxophones. It is also widely used for cast metal sculpture (see bronze sculpture). Common bronze alloys often have the unusual and very desirable property of expanding slightly just before they set, thus filling in the finest details of a mould. Bronze parts are tough and typically used for bearings, clips, electrical connectors and springs.

Bronze also has very little metal-on-metal friction, which made it invaluable for the building of cannons where iron cannonballs would otherwise stick in the barrel. It is still widely used today for springs, bearings, bushings, automobile transmission pilot bearings, and similar fittings, and is particularly common in the bearings of small electric motors. Phosphor bronze is particularly suited to precision-grade bearings and springs.

Bronze is typically 60% copper and 40% 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.

Commercial bronze (otherwise known as brass) is 90% copper and 10% zinc, and contains no tin. It is stronger than copper and it has equivalent ductility. It is used for screws and wires.

Another useful property of bronze is that it is non-sparking. That is, when struck against a hard surface, unlike steel, it will not generate sparks. This is used to advantage to make hammers, mallets, wrenches and other durable tools to be used in explosive atmospheres or in the presence of flammable vapors.

Bronze Age

The Bronze Age was a period in the civilization's development when the most advanced metalworking (at least in systematic and widespread use) consisted of techniques for smelting copper and tin from naturally occurring outcroppings of ore, and then alloying those metals in order to cast bronze. The Bronze Age forms part of the three-age system for prehistoric societies. In that system, it follows the Neolithic in some areas of the world. In many parts of sub-Saharan Africa, the Neolithic is directly followed by the Iron Age.

Origins

The place and time of the invention of bronze are controversial, and it is possible that bronzing was invented independently in multiple places. The earliest known tin bronzes are from what is now Iran and Iraq and date to the late 4th millennium BC, but there are claims of an earlier appearance of tin bronze in Thailand in the 5th millennium BC. Arsenical bronzes were made in Anatolia and on both sides of the Caucasus by the early 3rd millennium BC. Some scholars date some arsenical bronze artefacts of the Maykop culture in the North Caucasus as far back as the mid 4th millennium BC, which would make them the oldest known bronzes, but others date the same Maykop artefacts to the mid 3rd millennium BC .

Ancinet Near East

The Bronze Age in the Near East is divided into three main periods (the dates are very approximate):

* EBA - Early Bronze Age (c.3500-2000 BC)

* MBA - Middle Bronze Age (c.2000-1600 BC)

* LBA - Late Bronze Age (c.1600-1200 BC)

Each main period can be divided into shorter subcategories such as EB I, EB II, MB IIa etc.

Metallurgy developed first in Anatolia, modern Turkey. The mountains in the Anatolian highland possessed rich deposits of copper and tin. Copper was also mined in Cyprus, Egypt, the Negev desert, Iran and around the Persian Gulf. Copper was usually mixed with arsenic, yet the growing demand for tin resulted in the establishment of distant trade routes in and out of Anatolia. The precious copper was also imported by sea routes to the great kingdoms of Ancient Egypt and Mesopotamia .

The Early Bronze Age saw the rise of urbanization into organized city states and the invention of writing (the Uruk period in the fifth millennium BC). In the Middle Bronze Age movements of people partially changed the political pattern of the Near East (Amorites, Hittites, Hurrians, Hyksos and possibly the Israelites). The Late Bronze Age is characterized by competing powerful kingdoms and their vassal states (Ancient Egypt, Assyria, Babylonia, Hittites, Mitanni). Extensive contacts were made with the Aegean civilization (Ahhiyawa, Alashiya) in which the copper trade played an important role. This period ended in a widespread collapse which affected much of the Eastern Mediterranean and Middle East.

Iron began to be worked already in Late Bronze Age Anatolia. The transition into the Iron Age c.1200 BC was more of a political change in the Near East rather than of new developments in metalworking.

Indian Bronze Age

The Bronze Age on the Indian subcontinent began around 3300 BC with the beginning of the Indus Valley civilization. Inhabitants of the ancient Indus Valley, the Harappans, developed new techniques in metallurgy and produced copper, bronze, lead and tin.

East Asia

Bronze artifacts were exhumed in historic site of Majiayao culture (3100 BC to 2700 BC) of China. However, it is commonly accepted that China's Bronze Age began from around 2100 BC during the Xia dynasty.

The Erlitou culture, Shang Dynasty and Sanxingdui culture of early China used bronze vessels for rituals as well as farming implements and weapons

Southeast Asia

In Ban Chiang, Thailand, (Southeast Asia) bronze artifacts have been discovered dating to 2100 BC .

Korean peninsula

The Middle Mumun pottery period culture of the southern Korean Peninsula gradually adopted bronze production (circa 700-600? BC) after a period when Liaoning-style bronze daggers and other bronze artifacts were exchanged as far as the interior part of the Southern Peninsula (circa 900-700 BC). The bronze daggers lent prestige and authority to the personages who wielded and were buried with them in high-status megalithic burials at south-coastal centres such as the Igeum-dong site. Bronze was an important element in ceremonies and as for mortuary offerings until AD 100.

Aegean

The Aegean Bronze Age civilizations established a far-ranging trade network. This network imported tin and charcoal to Cyprus, where copper was mined and alloyed with the tin to produce bronze. Bronze objects were then exported far and wide, and supported the trade. Isotopic analysis of the tin in some Mediterranean bronze objects indicates it came from as far away as Great Britain.

Knowledge of navigation was well developed at this time, and reached a peak of skill not exceeded until a method was discovered (or perhaps rediscovered) to determine longitude around 1750 AD, with the notable exception of the Polynesian sailors.

The Minoan civilization based from Knossos appears to have coordinated and defended its Bronze Age trade.

One crucial lack in this period was that modern methods of accounting were not available. Numerous authorities[citation needed] believe that ancient empires were prone to misvalue staples in favor of luxuries, and thereby perish by famines created by uneconomic trading.

How the Bronze Age ended in this region is still being studied. There is evidence that Mycenaean administration of the regional trade empire followed the decline of Minoan primacy. Evidence also exists that supports the assumption that several Minoan client states lost large portions of their respective populations to extreme famines and/or pestilence, which in turn would indicate that the trade network may have failed at some point, preventing the trade that would have previously relieved such famines and prevented some forms of illness (by nutrition). It is also known that the breadbasket of the Minoan empire, the area north of the Black Sea, also suddenly lost significant portions of its population, and thus probably some degree of cultivation in this era.

Recent research has discredited the theory that exhaustion of the Cypriot forests caused the end of the bronze trade. The Cypriot forests are known to have existed into later times, and experiments have shown that charcoal production on the scale necessary for the bronze production of the late Bronze Age would have exhausted them in less than fifty years.

One theory says that as iron tools became more common, the main justification of the tin trade ended, and that trade network ceased to function as it once did. The individual colonies of the Minoan empire then suffered drought, famine, war, or some combination of these three factors, and thus they had no access to the far-flung resources of an empire by which they could easily recover.

Another family of theories looks to Knossos itself. The Thera eruption occurred at this time, 40 miles north of Crete. Some authorities speculate that a tsunami from Thera destroyed Cretan cities. Others say that perhaps a tsunami destroyed the Cretan navy in its home harbor, which then lost crucial naval battles; so that in the LMIB/LMII event (c. 1450 BC) the cities of Crete burned and the Mycenaean civilization took over Knossos. If the eruption occurred in the late 17th century BC (as most chronologists now think), then its immediate effects belong to the Middle Bronze to Late Bronze Age transition, and not to the end of the Late Bronze Age; but it could have triggered the instability which led to the collapse first of Knossos and then of Bronze Age society overall. One such theory looks to the role of Cretan expertise in administering the empire, post-Thera. If this expertise was concentrated in Crete, then the Mycenaeans may have made crucial political and commercial mistakes when administering the Cretans' empire.

More recent archaeological findings, including on the island of Thera (more commonly known today as Santorini), suggest that the center of Minoan Civilization at the time of the eruption was actually on this island rather than on Crete. Some think that this was the fabled Atlantis (a map drawn on a wall of a Minoan palace in Crete depicts an island similar to that described by Plato and similar too to the form Thera very likely had prior to its explosion). According to this theory, the catastrophic loss of the political, administrative and economic center by the eruption as well as the damage wrought by the tsunami to the coastal towns and villages of Crete precipitated the decline of the Minoans. A weakened political entity with a reduced economic and military capability and fabled riches would have then been more vulnerable to human predators.

Each of these theories is persuasive, and aspects of all of them may have some validity in describing the end of the Bronze Age in this region.

Europe

Central Europe

Bronze Age weaponry and ornaments

In Central Europe, the early Bronze Age Unetice culture (1800-1600 BC) includes numerous smaller groups like the Straubingen, Adlerberg and Hatvan cultures. Some very rich burials, such as the one located at Leubingen with grave gifts crafted from gold, point to an increase of social stratification already present in the Unetice culture. All in all, cemeteries of this period are rare and of small size. The Unetice culture is followed by the middle Bronze Age (1600-1200 BC) Tumulus culture, which is characterised by inhumation burials in tumuli (barrows). In the eastern Hungarian Körös tributaries, the early Bronze Age first saw the introduction of the Mako culture, followed by the Ottomany and Gyulavarsand cultures.

The late Bronze Age urnfield culture, (1300 BC-700 BC) is characterized by cremation burials. It includes the Lusatian culture in eastern Germany and Poland ((1300-500 BC) that continues into the Iron Age. The Central European Bronze Age is followed by the Iron Age Hallstatt culture (700-450 BC).

Important sites include:

* Biskupin (Poland)

* Nebra (Germany)

* Zug-Sumpf, Zug, Switzerland

History of Bronze

Bronze in the Ancient World

Chinese Bronzes

European Bronzes

African Bronzes

Silicon Bronze

Properties

Bronze Age

Origins

Ancinet Near East

Indian Bronze Age

East Asia

Aegean

Europe

Central Europe

Bronze Age weaponry and ornaments

Important sites include:

Northern Europe

Ireland

Americans

Andean Bronze Age

Americans

Andean Bronze Age

From stone to copper:

The Corded Ware culture

The Bellbeaker culture

The transfer period

The Aunjetitz culture

The Nordic circle

From copper to bronze

The Bronze Age cultures:

The Urnfield culture

The Hallstatt culture

The Nordic bronze cultures

Bronze Age religion