Bronze

Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals (including aluminium, manganese, nickel, or zinc) and sometimes non-metals (such as phosphorus) or metalloids (such as arsenic or silicon). These additions produce a range of alloys some of which are harder than copper alone or have other useful properties, such as strength, ductility, or machinability.

The archaeological period during which bronze was the hardest metal in widespread use is known as the Bronze Age. The beginning of the Bronze Age in western Eurasia and India is conventionally dated to the mid-4th millennium BCE (~3500 BCE), and to the early 2nd millennium BCE in China; elsewhere it gradually spread across regions. The Bronze Age was followed by the Iron Age, which started about 1300 BCE and reaching most of Eurasia by about 500 BCE, although bronze continued to be much more widely used than it is in modern times.

Because historical artworks were often made of bronzes and brasses (alloys of copper and zinc) of different metallic compositions, modern museum and scholarly descriptions of older artworks increasingly use the generalized term "copper alloy" instead of the names of individual alloys. This is done (at least in part) to prevent database searches from failing merely because of errors or disagreements in the naming of historic copper alloys.

Etymology

The word bronze (1730–1740) is borrowed from Middle French bronze (1511), itself borrowed from Italian bronzo 'bell metal, brass' (13th century, transcribed in Medieval Latin as bronzium) from either:

bróntion, back-formation from Byzantine Greek brontēsíon (βροντησίον, 11th century), perhaps from Brentḗsion (Βρεντήσιον, 'Brindisi'), reputed for its bronze; or originally:

in its earliest form from Old Persian birinj, (برنج, 'brass', modern berenj) and piring (پرنگ) 'copper', from which also came Georgian brinǯi (ბრინჯი), Turkish pirinç from "bir" (one) "birinç" (primary), and Armenian brinj (բրինձ), also meaning 'bronze'.

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. Initially, bronze was made out of copper and arsenic or from naturally or artificially mixed ores of those metals, forming arsenic bronze.

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.

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 China, Luristan (Iran), Tepe Sialk (Iran), Mundigak (Afghanistan), and Mesopotamia (Iraq).

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 those of arsenic, metallic tin and the fumes from tin refining are not toxic.

Tin became the major non-copper ingredient of bronze in the late 3rd millennium BCE. Ores of copper and the far rarer tin 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.

Transition to iron

Though bronze, whose Vickers hardness is 60–258, is generally harder than wrought iron, with a hardness of 30–80, the Bronze Age gave way to the Iron Age after a serious disruption of the tin trade: the population migrations of around 1200–1100 BCE reduced the shipment of tin around the Mediterranean and from Britain, limiting supplies and raising prices. As the art of working in iron improved, iron became cheaper and improved in quality. As later cultures advanced from hand-wrought iron to machine-forged iron (typically made with trip hammers powered by water), blacksmiths also learned how to make steel, which is stronger and harder than bronze and holds a sharper edge longer. Bronze was still used during the Iron Age and has continued in use for many purposes to the modern day.

Composition

There are many different bronze alloys, but typically modern bronze is about 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, arsenic and 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 suggest that the candlestick was made from a hoard of old coins. The 13th-century Benin Bronzes are in fact brass, and the 12th-century Romanesque Baptismal font at St Bartholomew's Church, Liège is sometimes described as bronze and sometimes as brass.

During the Bronze Age, two forms of bronze were commonly used: "classic bronze", about 10% tin, was used in casting; "mild bronze", about 6% tin, was hammered from ingots to make sheets. Bladed weapons were primarily cast from classic bronze while helmets and armor were hammered from mild bronze.

Modern 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. Plastic bronze contains a significant quantity of lead, which makes for improved plasticity, and may have been used by the ancient Greeks in ship construction. Silicon bronze has a composition of Si: 2.80–3.80%, Mn: 0.50–1.30%, Fe: 0.80% max., Zn: 1.50% max., Pb: 0.05% max., Cu: balance. Other bronze alloys include aluminium bronze, phosphor bronze, manganese bronze, bell metal, arsenical bronze, speculum metal, bismuth bronze, and cymbal alloys.

Properties

Copper-based alloys have lower melting points than steel or iron and are more readily produced from their constituent metals. They are generally about 10 percent denser than steel, although alloys using aluminium or silicon may be slightly less dense. Bronze conducts heat and electricity better than most steels. Copper-base alloys are generally more costly than steels but less so than nickel-base alloys.

Bronzes are typically ductile alloys and are considerably less brittle than cast iron. 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 low-friction properties of bearing bronze (bronze that has a high lead content— 6–8%), the resonant qualities of bell bronze (20% tin, 80% copper), and the resistance to corrosion by seawater of several bronze alloys.

The melting point of bronze is about 950 °C (1,742 °F) but varies depending on the ratio of the alloy components. Bronze is usually nonmagnetic, but certain alloys containing iron or nickel may have magnetic properties. Bronze typically oxidizes only superficially; once a copper oxide (eventually becoming copper carbonate) layer is formed, the underlying metal is protected from further corrosion. This can be seen on statues from the Hellenistic period. If copper chlorides are formed, a corrosion-mode called "bronze disease" will eventually destroy it completely.

Tin bronzes

In the bronze range of the copper -tin system, three different solid solutions form from the melt with different compositions: The α-solid solution corresponds to that of pure copper, which forms a face-centered cubic lattice. The melting point of pure copper is 1083 °C. At around 24% tin, the β-solid solution is present, which has a body-centered cubic lattice; at around 30% tin and above, the γ-solid solution, which is also body-centered cubic, forms. A peritectic subsystem forms between the α and β solid solutions and between β and γ. The technically relevant peritectic α/β occurs at 22% tin and 798 °C. At 586 °C, a eutectoid decomposition of the β-solid solutions into α and γ solid solutions occurs. 

Depending on the alloy composition, two intermetallic compounds can form from the γ-solid solutions upon cooling: The δ-phase corresponds to Cu 31 Sn 8 and thus contains approximately 32.5% tin. It forms an enormously large face-centered cubic unit cell with 416 atoms and is very hard. The orthorhombic ε-phase corresponds to Cu 3 Sn and thus contains approximately 38.4% tin. In the technically relevant range, the δ-phase is formed at 520 °C when the γ-solid solutions decompose into a eutectoid structure of α- and δ-solid solutions with 27% tin. A further eutectoid decomposition of the δ-solid solutions into α- and ε-solid solutions at approximately 350 °C no longer occurs under real technical conditions because diffusion is too severely impeded. To achieve equilibrium, cold forming and annealing lasting several months would be necessary.

The resulting microstructures are primarily determined by the high diffusion inertia of tin, which prevents equilibrium from being established even during crystallization from the melt. Thus, in tin bronze, a microstructure consisting exclusively of α-solid solutions is only present at tin contents below 5–6%; at higher contents, it consists of soft α-solid solutions and the hard α/δ eutectoid.

The addition of tin increases the strength of the alloy, reaching a maximum between 10 and 15% tin. The yield strength increases almost linearly, multiplying compared to pure copper, reaching a maximum at around 20%. Starting from the high values of copper, the elongation at break begins to decrease rapidly beyond 5% tin and approaches zero almost exponentially, which is practically reached between 20 and 25%. Hardness increases steadily, which is further increased with higher tin contents. The density decreases by 0.1 g/cm³ for every 6% tin addition. At 8% tin, it is 8.79 g/cm³.

Alloys and alloying additives

Tin bronzes are standardized as copper-tin alloys and, due to their fundamentally different requirements and properties, are divided into wrought alloys (max. 9% tin), which are suitable for forming, and cast alloys (9% to 13% tin). In addition, so-called bell bronzes with about 20% (maximum 22%) tin are also used.

Phosphorus reduces copper oxide and thus also liquefies the melt. Although tin oxide is not reduced, it can rise more easily into the slag in the deoxidized melt. When phosphorus is added as a deoxidizer, usually in the form of pre-alloyed phosphorus copper with a phosphorus content of 10 or 15%, it must be dosed so that at least 0.01% excess phosphorus remains in the melt after deoxidation. This prevents pouring stream oxidation; castability and physical properties in the casting are improved. Phosphorus only has a negative effect on electrical conductivity. At contents of more than 0.1%, Cu 3 P occurs in the microstructure. This can be desirable for bearing materials; for conductive copper, phosphorus as a deoxidizer must be replaced with manganese copper or another phosphorus-free master alloy.

Nickel, which causes the formation of an additional ϑ-solid solution in the range of 9% tin, increases toughness and reduces the influence of wall thickness on strength. It is therefore only used in casting alloys with a content of up to 2.5%.

Lead forms a separate phase and is finely distributed throughout the structure. It improves machinability and sliding properties, but increases hot brittleness. It is therefore used at 2% in cast alloys for bearing materials, and at 4% in wrought alloys only in the special case of continuous, strip, and wire casting, where subsequent hot forming is no longer necessary and the product must be machinable.

Zinc can, under certain circumstances, replace half the amount of tin; it is used for economic reasons. Its deoxidizing effect eliminates the need for phosphorus. This is used, among other things, in alloys for contact materials.

Copper-tin-based welding consumables and brazing alloys are subject to their own standards.

More bronzes

Alloys containing little or no tin are often called "special bronzes." Their names are derived from the alloying additive: aluminum bronze, manganese bronze, nickel bronze, etc.  Beryllium bronze is a special copper material for non-sparking tools, containing only 2–3% beryllium and a small amount of cobalt.

Lead bronze (also copper-tin-lead bronze) is a bearing alloy with 5–22% lead.

Gunmetal is not a tin bronze, and therefore not bronze in the strict sense, although it is sometimes referred to as machine bronze, cannon bronze, and similar. It is a copper-based alloy whose properties are determined less by the addition of tin than by zinc, lead, and nickel.

In contrast to the expensive real bronze, artificial bronze is an alloy of various metals, usually a mixture of copper, zinc and tin, which can often also be alloyed with other metals such as lead, nickel or aluminum and which has bronze-like properties but is less durable and not as resistant as real bronze. 

Arsenical bronze

The alloy ofcopperwitharsenicIt is the first bronze used by man. It is a whitish alloy, very hard and brittle. It is manufactured in a proportion of 70% copper and 30% arsenic, although it is possible to cast bronzes with arsenic percentages of up to 47.5%. In these cases, the result is a shiny gray material, red-fused and unaltered by boiling water.

Simple exposure of arsenical bronze to air produces a dark patina. This circumstance, and the high toxicity of arsenic, made it a very little used alloy, especially after the discovery ofalpaca, German silver or white bronze, known since ancient times inChinaand manufactured inGermanysince the end of the 18th century. 

Bronze sun

The so-called sun bronze (in German; Sonnenbronze) is an alloy used in jewelry, tough, ductile and very hard, which melts at temperatures close to those of copper (1357 °C) and is made up to 60% cobalt. 

Cuproaluminum

Cuproaluminum or aluminum bronze is a type of bronze, similar in color to gold, in which aluminum is theprimaryalloying metal added to copper. A variety of aluminum bronzes, with different compositions, have found industrial use.

Bronze for firearms

Since the discovery of gunpowder, a cannonbronze consisting of 90–91% copper and 9–10% tin has been used, a proportion commonly referred to as "coarse bronze". Such weapons were known inChinaas early as the 11th century BC, and were used in Europe from the 13th century for both cannons and falconets.

By the 15th century, the Ottoman Empire's artillery included large bronze bombards. Constructed in two pieces, with a total length of 5.20 m and a weight of 16.8 tons, they propelled 300 kg (660 lb) balls to a distance of up to 1,600 meters. Difficult to operate, with a firing capacity of no more than 15 shots per day, they were used in the siege of Constantinoplein 1453. 

Bronze for bells

Bell castings are generally brittle: new pieces vary in color from dark ash to grayish white, with yellowish red or even bluish red tones in alloys with a higher copper content. 

A higher proportion of copper produces deeper, deeper tones for equal mass, while the addition of tin, iron, or zinc produces higher tones. To achieve a more crystalline structure and produce variations in sound, foundry workers have also used other metals such asantimonyorbismuthin small quantities.

The most sonorous alloy for making bells is the so-calledbell metal, which consists of 78% copper and 22% tin. It is relatively easy to cast, has a compact granular structure with a reddish vitreous-conchoidal fracture. This type of bronze was known since ancient times in India for makinggongs. Although uncommon due to its cost, the addition ofsilveris one of the few that further improves the sonority. 

Alloys containing up to 2% antimonyhave also been used. An alloy containing 80% copper and 20% tin was known in China for making bells, large gongs, and timpani. 

In England, an alloy consisting of 80% copper, 10.25% tin, 5.50%zinc, and 4.25%leadwas used. It is less sonorous, since the lead does not blend with the alloy. 

For bells and small instruments, an alloy of 68% copper and 32% tin was frequently used, resulting in a brittle, ashy-fractured material. 

Several alloys are used for cymbals and gongs, ranging from a tempered alloy of 80% copper and 20% tin(B20), 88% copper and 12% tin (B12, eg, Zildjian ZHT, Paiste Alpha), and the less expensive B8, which consists of only 8% tin and 92% copper (eg, Sabian B8, Paiste201, ZildjianZBT). Temperingis achieved by reheating the casting and rapidly cooling it. 

The largest surviving bell, calledthe Tsar Kolokol, was cast in 1733 by Ivan Motorin, commissioned by Empress Anna of Russia, niece of the Tsar Peter the Great. It weighed 216 tons, was 6.14 m high, and had a diameter of 6.6 m. It was never used as an instrument, as a fire in 1737 destroyed its large wooden supports. Since 1836, it has been on display in the MoscowKremlin.

Kara Kane

Kara -kane (Japanese for "Chinese metal") is a traditional Japanese bell and goldsmith bronze made of 60% copper, 24% tin, and 9% zinc, with addedironand lead.

Many goldsmiths often add small amounts ofarsenicandantimonyto harden the bronze without losing its fusibility and to achieve greater detail in the impression of the molds.

Kara -kane is widely used for crafts and statuary not only because of its low melting point, high fluidity, and good mold-filling characteristics, but also because of its smooth surface that quickly develops a fine patina.

There is a unique variety called seniokuthis, or gilt bronze, originating in theMingDynasty inChina, which is notable for its lustrous texture and golden hue. Patinatechniques are particularly important in its manufacturing.

The large sculptures of Buddha made by Japanese goldsmiths demonstrate the high technical mastery they possessed and, taking into account their large size, most of them had to be cast on site in successive stages. 

Alloys that imitate silver

Tonka metal: an alloy composed of 36%copper, 28%nickel, and equal amounts oftin,lead,iron,zinc, andantimony. It is a difficult-to-melt, slightly ductile metal that is rarely used. 

Silver mine: Made with 57% copper, 40% nickel, 3%tungstenand traces ofaluminum, it has the property of not being attacked bysulfurand has properties very similar tosilver. 

Lead alloys

For the manufacture of bearings and other parts subject to friction, bronze alloys with up to 10%leadare often used, which gives it self-lubricating properties.

The distinctive characteristic of lead is that it does not form an alloy with copper; Therefore, it is distributed throughout the alloy mass according to the casting technique, without becoming intimately mixed. For this reason, excessive heating of a piece of machinery made from this material can lead to lead "bleeding," which appears as mud or sludge. Recycling these parts is also difficult because the lead melts and separates from the alloy long before the copper reaches its melting point. 

Table overview of bronze alloys

Name of the alloy	Components to copper	Characteristics	use
Cast tin bronze	up to 22% tin , predominantly 10–12% tin, density about 8.8024 kg/dm³	elastic, tough, corrosion-resistant	Mainly used as mold casting , up to 6% tin cold-rollable into sheet and embossed material ( medals , coins ), wire drawing up to 10% tin. Bell casting ( bell bronze : about 20–24% tin), historically used for cannon bronze , as well as for musical instruments. Statue bronze for art casting (small bronzes, monuments).
aluminum bronze	5–10% aluminum	seawater-resistant, wear-resistant, elastic, slightly magnetic, gold-colored	spring plate , balance beam , ship propeller , chemical industry
Lead bronze	up to 26% lead	corrosion-resistant, good sliding properties	Bearing metal , composite and molded casting materials, ancient coin bronze often contained lead, from which not all the silver was removed
Manganese bronze	12% manganese	corrosion-resistant, heat-resistant	Electrical resistors (called manganese bronze in the USA despite the 20–40% zinc content in some alloys , for example in some materials manufactured by Ampco)
Silicon bronze	1–2% silicon	highly mechanically and chemically resistant, high conductivity	Overhead lines , sliding contacts , chemical industry , connecting elements in shipbuilding
Beryllium copper (beryllium bronze)	2% beryllium	hard, elastic, toxic	Springs , watches , non-sparking tools
Phosphor bronze	7% tin , 0.5% phosphorus	high density and strength	tough machine parts, axle bearings , guitar strings
Lead bronze	Magnesium , cadmium , zinc (total 3%)	electrical properties similar to copper, but with greater tensile strength	Overhead lines , high-voltage installations
gunmetal	Tin , zinc , lead (total 10–20%)	corrosion-resistant, good sliding properties and castability	Plain bearings , fittings , worm gears , cast iron
Steel bronze	92% copper and 8% tin	high density and strength, was considered a serious alternative to steel in the 1870s	The material was discovered by Franz von Uchatius and used particularly in the Austro-Hungarian artillery .
Corinthian ore (corinthium aes)	1–3% gold , 1–3% silver , sometimes a few percent arsenic , tin or iron	can be dyed black by patination	historical material for statues and luxury items (antique)
Potin	French term for copper- based alloys		Potin gris is a bronze alloy. Potin jaune is cast brass made from old brass . It is also the name for Celtic coin bronze.

Commercial alloys

Code	Denomination	Composition %	Density g/cm³	Brinell hardness	Mod.Elastic Gpa	Electronic resistance Ω/cm	Thermal cond. W/mK	Melting point °C	Applications
SAE40		Cu85Pb5Sn5Zn5	8.82	60	93	1,2 -05	71.9	854
SAE64		Cu80Pb10Sn10	8.88	60	76	1.7 -05	46.9	762
UNS​ C22000	Commercial 90-10	Cu89/91Fe＜ 0.05Pb＜ 0.05Zn12.5	8.80	53	115	3.91 -06	189	1020	printing dies, laminates,screws
UNS C22600	Bronze jewelry	Cu86/89Fe＜ 0.05Pb＜ 0.05Zn12.5	8.78	55	115	4:30 -06	173	1005	zippers, jewelry,coins
UNS C31400	Commercial lead tempering	Cu87.5/90.5Fe＜ 0.1Ni＜ 0.7Pb1.3/2.5Zn9.25 Others < 0.05	8.83		115		180	1010	screws, electrical contacts, tool parts
UNS C31600	Nickel plated tempered	Cu87.5/90Fe＜ 0.1Ni0.7/1.2P0.04/0.1Pb1.2/2.5Zn8.1	8.86		115		140	1010	screws, electrical contacts, tool parts
UNS C40500	High conductivity bronze	Cu95Sn1Zn4	8.83		117		165

Casting technique

The most widely used method for artistic bronze casting is that of "lost wax" ormicrofusion, which - with various variations - follows the following steps: 

Original modeling in clay,plasteror other material.

Taking the main mold, usually made of plaster. Once set, the core (original model) is removed.

The "negative" mold is filled with wax to produce a "positive" of this material.

The wax is covered with a clay mixture. Once dry, it is taken to a kiln, where the wax melts and "is lost."

For small objects, the new mold is used directly for casting the bronze. For larger pieces, it is common to fill it with a layer of wax that will form a film of the desired thickness for the bronze, and the interior (core) is filled withrefractory material. The entire process requires the installation of aerators, casting channels, and various precautions to achieve a homogeneous casting.

Finishing that includes filing imperfections, roughness, and polishing the piece.

Patina, by applying differentacidsand heating with a blowtorch to speed up oxidation.

Uses

Bronze, or bronze-like alloys and mixtures, were used for coins over a longer period. Bronze was especially suitable for use in boat and ship fittings prior to the wide employment of stainless steel owing to its combination of toughness and resistance to salt water corrosion. Bronze is still commonly used in ship propellers and submerged bearings. In the 20th 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. Sculptors may prefer silicon bronze because of the ready availability of silicon bronze brazing rod, which allows color-matched repair of defects in castings. Aluminium is also used for the structural metal aluminium bronze. Bronze parts are tough and typically used for bearings, clips, electrical connectors and springs.

Bronze also has low friction against dissimilar metals, making it important for cannons prior to modern tolerancing, 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. It is also used in guitar and piano strings. Unlike steel, bronze struck against a hard surface will not generate sparks, so it (along with beryllium copper) is used to make hammers, mallets, wrenches and other durable tools to be used in explosive atmospheres or in the presence of flammable vapors. Bronze is used to make bronze wool for woodworking applications where steel wool would discolor oak. Phosphor bronze is used for ships' propellers, musical instruments, and electrical contacts. Bearings are often made of bronze for its friction properties. It can be impregnated with oil to make the proprietary Oilite and similar material for bearings. Aluminium bronze is hard and wear-resistant, and is used for bearings and machine tool ways. The Doehler Die Casting Co. of Toledo, Ohio were known for the production of Brastil, a high tensile corrosion resistant bronze alloy.

Architectural bronze

The Seagram Building on New York City's Park Avenue is the "iconic glass box sheathed in bronze, designed by Mies van der Rohe." The Seagram Building was the first time that an entire building was sheathed in bronze. The General Bronze Corporation fabricated 3,200,000 pounds (1,600 tons) of bronze at its plant in Garden City, New York. The Seagram Building is a 38-story, 516-foot bronze-and-topaz-tinted glass building. The building looks like a "squarish 38-story tower clad in a restrained curtain wall of metal and glass." "Bronze was selected because of its color, both before and after aging, its corrosion resistance, and its extrusion properties. In 1958, it was not only the most expensive building of its time — $36 million — but it was the first building in the world with floor-to-ceiling glass walls. Mies van der Rohe achieved the crisp edges that were custom-made with specific detailing by General Bronze and "even the screws that hold in the fixed glass-plate windows were made of brass."

Sculptures

Bronze is widely used for casting bronze sculptures. Common bronze alloys have the unusual and desirable property of expanding slightly just before they set, thus filling the finest details of a mould. Then, as the bronze cools, it shrinks a little, making it easier to separate from the mould. The Assyrian king Sennacherib (704–681 BCE) claims to have been the first to cast monumental bronze statues (of up to 30 tonnes) using two-part moulds instead of the lost-wax method.

Bronze statues were regarded as the highest form of sculpture in Ancient Greek art, though survivals are few, as bronze was a valuable material in short supply in the Late Antique and medieval periods. Many of the most famous Greek bronze sculptures are known through Roman copies in marble, which were more likely to survive. In India, bronze sculptures from the Kushana (Chausa hoard) and Gupta periods (Brahma from Mirpur-Khas, Akota Hoard, Sultanganj Buddha) and later periods (Hansi Hoard) have been found. Indian Hindu artisans from the period of the Chola empire in Tamil Nadu used bronze to create intricate statues via the lost-wax casting method with ornate detailing depicting the deities of Hinduism. The art form survives to this day, with many silpis, craftsmen, working in the areas of Swamimalai and Chennai.

In antiquity other cultures also produced works of high art using bronze. For example: in Africa, the bronze heads of the Kingdom of Benin; in Europe, Grecian bronzes typically of figures from Greek mythology; in east Asia, Chinese ritual bronzes of the Shang and Zhou dynasty—more often ceremonial vessels but including some figurine examples. Bronze continues into modern times as one of the materials of choice for monumental statuary.

Lamps

Tiffany Glass Studios, made famous by Louis C. Tiffany commonly referred to his product as favrile glass or "Tiffany glass," and used bronze in their artisan work for his Tiffany lamps.

Fountains and doors

The largest and most ornate bronze fountain known to be cast in the world was by the Roman Bronze Works and General Bronze Corporation in 1952. The material used for the fountain, known as statuary bronze, is a quaternary alloy made of copper, zinc, tin, and lead, and traditionally golden brown in color. This was made for the Andrew W. Mellon Memorial Fountain in Federal Triangle in Washington, DC. Another example of the massive, ornate design projects of bronze, and attributed to General Bronze/Roman Bronze Works were the massive bronze doors to the United States Supreme Court Building in Washington, DC.

Mirrors

Before it became possible to produce glass with acceptably flat surfaces, bronze was a standard material for mirrors. Bronze was used for this purpose in many parts of the world, probably based on independent discoveries. Bronze mirrors survive from the Egyptian Middle Kingdom (2040–1750 BCE), and China from at least c. 550 BCE. In Europe, the Etruscans were making bronze mirrors in the sixth century BCE, and Greek and Roman mirrors followed the same pattern. Although other materials such as speculum metal had come into use, and Western glass mirrors had largely taken over, bronze mirrors were still being made in Japan and elsewhere in the eighteenth century, and are still made on a small scale in Kerala, India.

Musical instruments

Bronze is the preferred metal for bells in the form of a high tin bronze alloy known as bell metal, which is typically about 23% tin.

Nearly all professional cymbals are made from bronze, which gives a desirable balance of durability and timbre. Several types of bronze are used, commonly B20 bronze, which is roughly 20% tin, 80% copper, with traces of silver, or the tougher B8 bronze made from 8% tin and 92% copper. As the tin content in a bell or cymbal rises, the timbre drops.

Bronze is also used for the windings of steel and nylon strings of various stringed instruments such as the double bass, piano, harpsichord, and guitar. Bronze strings are commonly reserved on pianoforte for the lower pitch tones, as they possess a superior sustain quality to that of high-tensile steel.

Bronzes of various metallurgical properties are widely used in struck idiophones around the world, notably bells, singing bowls, gongs, cymbals, and other idiophones from Asia. Examples include Tibetan singing bowls, temple bells of many sizes and shapes, Javanese gamelan, and other bronze musical instruments. The earliest bronze archeological finds in Indonesia date from 1–2 BCE, including flat plates probably suspended and struck by a wooden or bone mallet. Ancient bronze drums from Thailand and Vietnam date back 2,000 years. Bronze bells from Thailand and Cambodia date back to 3600 BCE.

Some companies are now making saxophones from phosphor bronze (3.5 to 10% tin and up to 1% phosphorus content). Bell bronze/B20 is used to make the tone rings of many professional model banjos. The tone ring is a heavy (usually 3 lb; 1.4 kg) folded or arched metal ring attached to a thick wood rim, over which a skin, or most often, a plastic membrane (or head) is stretched – it is the bell bronze that gives the banjo a crisp powerful lower register and clear bell-like treble register.

Coins and medals

Bronze has also been used in coins; most "copper" coins are actually bronze, with about 4 percent tin and 1 percent zinc.

As with coins, bronze has been used in the manufacture of various types of medals for centuries, and "bronze medals" are known in contemporary times for being awarded for third place in sporting competitions and other events. The term is now often used for third place even when no actual bronze medal is awarded. The usage in part arose from the trio of gold, silver and bronze to represent the first three Ages of Man in Greek mythology: the Golden Age, when men lived among the gods; the Silver age, where youth lasted a hundred years; and the Bronze Age, the era of heroes. It was first adopted for a sports event at the 1904 Summer Olympics. At the 1896 event, silver was awarded to winners and bronze to runners-up, while at 1900 other prizes were given rather than medals.

Bronze is the normal material for the related form of the plaquette, normally a rectangular work of art with a scene in relief, for a collectors' market.

Bronze is also associated with eighth wedding anniversaries.

Biblical references

There are over 125 references to bronze ('nehoshet'), which appears to be the Hebrew word used for copper and any of its alloys. However, the Old Testament era Hebrews are not thought to have had the capability to manufacture zinc (needed to make brass) and so it is likely that 'nehoshet' refers to copper and its alloys with tin, now called bronze. In the King James Version, there is no use of the word 'bronze' and 'nehoshet' was translated as 'brass'. Modern translations use 'bronze'. Bronze (nehoshet) was used widely in the Tabernacle for items such as the bronze altar (Exodus Ch.27), bronze laver (Exodus Ch.30), utensils, and mirror (Exodus Ch.38). It was mentioned in the account of Moses holding up a bronze snake on a pole in Numbers Ch.21. In First Kings, it is mentioned that Hiram was very skilled in working with bronze, and he made many furnishings for Solomon's Temple including pillars, capitals, stands, wheels, bowls, and plates, some of which were highly decorative (see I Kings 7:13-47). Bronze was also widely used as battle armor and helmet, as in the battle of David and Goliath in I Samuel 17:5-6;38 (also see II Chron. 12:10).

Sourced from Wikipedia