Bronze

Bronze is a special kind of metal made by mixing mostly copper with a little tin, and sometimes adding other metals or non-metals. These extra ingredients make bronze stronger or easier to shape than copper alone.

A very important time in history, called the Bronze Age, started around 3500 BCE in parts of Europe and Asia. During this time, bronze was one of the strongest metals people knew how to make. Later, around 1300 BCE, people began using iron more, but bronze was still used a lot.

Because many beautiful old artworks were made from bronze or similar metals, museums and scholars today often use the term "copper alloy" to describe these items. This helps them talk about old artworks more clearly, even when they aren't sure of the exact mixture of metals used.

Etymology

The word bronze was first used in English between 1730 and 1740. It came from the Middle French word bronze, which itself came from the Italian word bronzo. This Italian word described a special kind of metal used for making bells, called "bell metal" or brass.

The Italian word may have originated from an old Byzantine Greek word, possibly linked to a place called Brindisi, known for its bronze. Another possibility is that it came from very old Persian words for brass and copper. This idea also influenced words in several other languages, including Georgian, Turkish, and Armenian.

History

The discovery of bronze allowed people to make metal objects that were stronger and more lasting than ever before. Bronze was used to make tools, weapons, armor, and beautiful building pieces that were tougher than older stone and copper items.

The oldest bronze object found dates back to around 4650 BCE, in a place called Pločnik in Serbia. It was made from a natural mixture of tin and copper. Other early bronze items were found in places like Egypt, Iran, China, and Iraq. Some bronze contained arsenic, which made it look silver and work easier, but tin became the main ingredient mixed with copper later on because it was easier to control and made stronger bronze. Tin and copper ores are rarely found together, so people had to trade to get both materials. In Europe, tin from Cornwall in the United Kingdom was traded as far as Phoenicia in the eastern Mediterranean. Bronze objects were also a sign of wealth and status. As ironworking improved, iron became cheaper and stronger than bronze, leading to the Iron Age, though bronze is still used today for many things.

Composition

Bronze is made from mixing different metals together. Most modern bronze is about 88% copper and 12% tin. One type, called alpha bronze, has a little tin mixed in with copper and is used for making coins, springs, turbines, and blades.

In the past, people used many different mixtures for bronze, using whatever old pieces of metal they could find. For example, the metal of the 12th-century English Gloucester Candlestick had copper, zinc, tin, lead, nickel, iron, antimony, arsenic, and even some silver. During a time called the Bronze Age, people used two main types of bronze: one with about 10% tin for casting things like weapons, and another with about 6% tin for making sheets that could be hammered into shapes like helmets.

There are also many other bronze mixtures today, including aluminium bronze, phosphor bronze, manganese bronze, bell metal, arsenical bronze, speculum metal, bismuth bronze, and cymbal alloys.

Properties

Copper-based alloys melt at lower temperatures than steel or iron and are easier to make from their metals. They are a bit heavier than steel but not as heavy as some other metals. Bronze carries heat and electricity better than most steels. These metals cost more than steel but less than some special alloys.

Bronze is flexible and not as likely to break as cast iron. Copper and its mixes are used in many ways because of their useful traits. For example, pure copper is great for electricity, some bronze with lead is good for moving parts, and bronze with tin makes beautiful bells. Certain bronze mixes can also resist rust from seawater.

Bronze melts around 950 °C (1,742 °F), but this changes with the mix of metals. Bronze usually isn’t magnetic, but some mixes with iron or nickel can be. Bronze forms a thin layer that protects it from rust, but if it gets a certain type of rust from copper chlorides, it can be badly damaged — this is called “bronze disease”.

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.

Unlike steel, bronze struck against a hard surface will not generate sparks, so it 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.

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.

Architectural bronze

Main articles: Seagram Building and Roman Bronze Works

See also: General Bronze Corporation

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.

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.

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.

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. 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.

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.

Mechanical bearings and springs

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. Bearings are often made of bronze for its friction properties.

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.

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.

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.

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.

Sculptures

See also: Ormolu

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.

Bronze statues were regarded as the highest form of sculpture in Ancient Greek art, though survivals are few, as bronze objects were frequently melted down for reuse throughout the Classical period.

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 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.

Biblical references

The Bible mentions copper and its alloys more than 125 times. In older translations, like the King James Version, these materials were called "brass." But scholars think the ancient Hebrews did not know how to make brass, which needs zinc. Instead, these references likely mean copper mixed with tin, known today as bronze. Bronze was used for many important items in the Tabernacle, such as altars and mirrors. It was also used for decorations in Solomon's Temple, made by a skilled craftsman named Hiram I. Bronze was used for armor in battles, including the famous fight between David and Goliath.