Brass

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Brass astrolabe Persian astrolabe.jpg
Brass astrolabe
Brass lectern with an eagle. Attributed to Aert van Tricht, Limburg (Netherlands), c. 1500. Brass lectern in the form of an eagle attributed to Aert van Tricht the Elder, Limburg (Netherlands), c. 1500, The Cloisters.jpg
Brass lectern with an eagle. Attributed to Aert van Tricht, Limburg (Netherlands), c. 1500.

Brass is an alloy of copper and zinc, in proportions which can be varied to achieve varying mechanical and electrical properties. [1] It is a substitutional alloy: atoms of the two constituents may replace each other within the same crystal structure.

Alloy mixture or metallic solid solution composed of two or more elements

An alloy is a combination of metals or a combination of one or more metals with non-metallic elements. For example, combining the metallic elements gold and copper produces red gold, gold and silver becomes white gold, and silver combined with copper produces sterling silver. Elemental iron, combined with non-metallic carbon or silicon, produces alloys called steel or silicon steel. The resulting mixture forms a substance with properties that often differ from those of the pure metals, such as increased strength or hardness. Unlike other substances that may contain metallic bases but do not behave as metals, such as aluminium oxide (sapphire), beryllium aluminium silicate (emerald) or sodium chloride (salt), an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, opaqueness, and luster. Alloys are used in a wide variety of applications, from the steel alloys, used in everything from buildings to automobiles to surgical tools, to exotic titanium-alloys used in the aerospace industry, to beryllium-copper alloys for non-sparking tools. In some cases, a combination of metals may reduce the overall cost of the material while preserving important properties. In other cases, the combination of metals imparts synergistic properties to the constituent metal elements such as corrosion resistance or mechanical strength. Examples of alloys are steel, solder, brass, pewter, duralumin, bronze and amalgams.

Copper Chemical element with atomic number 29

Copper is a chemical element with the symbol Cu and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orange color. Copper is used as a conductor of heat and electricity, as a building material, and as a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel used to make marine hardware and coins, and constantan used in strain gauges and thermocouples for temperature measurement.

Zinc Chemical element with atomic number 30

Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a blue-silvery appearance when oxidation is removed. It is the first element in group 12 of the periodic table. In some respects, zinc is chemically similar to magnesium: both elements exhibit only one normal oxidation state (+2), and the Zn2+ and Mg2+ ions are of similar size. Zinc is the 24th most abundant element in Earth's crust and has five stable isotopes. The most common zinc ore is sphalerite (zinc blende), a zinc sulfide mineral. The largest workable lodes are in Australia, Asia, and the United States. Zinc is refined by froth flotation of the ore, roasting, and final extraction using electricity (electrowinning).

Contents

It is similar to bronze, another alloy containing copper, with tin included instead of zinc [2] ; both bronze and brass may include small proportions of a range of other elements including arsenic, lead, phosphorus, aluminum, manganese, and silicon. The distinction between the two alloys is largely historical, [3] and modern practice in museums and archaeology increasingly avoids both terms for historical objects in favour of the more general "copper alloy". [4]

Bronze metal alloy

Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals and sometimes non-metals or metalloids such as arsenic, phosphorus or silicon. These additions produce a range of alloys that may be harder than copper alone, or have other useful properties, such as stiffness, ductility, or machinability.

Tin Chemical element with atomic number 50

Tin is a chemical element with the symbol Sn (from Latin: stannum) and atomic number 50. Tin is a silvery metal that characteristically has a faint yellow hue. Tin, like indium, is soft enough to be cut without much force. When a bar of tin is bent, the so-called tin cry can be heard as a result of sliding tin crystals reforming; this trait is shared by indium, cadmium, and frozen mercury. Pure tin after solidifying keeps a mirror-like appearance similar to most metals. However, in most tin alloys (such as pewter) the metal solidifies with a dull gray color. Tin is a post-transition metal in group 14 of the periodic table of elements. It is obtained chiefly from the mineral cassiterite, which contains stannic oxide, SnO2. Tin shows a chemical similarity to both of its neighbors in group 14, germanium and lead, and has two main oxidation states, +2 and the slightly more stable +4. Tin is the 49th most abundant element on Earth and has, with 10 stable isotopes, the largest number of stable isotopes in the periodic table, thanks to its magic number of protons. It has two main allotropes: at room temperature, the stable allotrope is β-tin, a silvery-white, malleable metal, but at low temperatures, it transforms into the less dense grey α-tin, which has the diamond cubic structure. Metallic tin does not easily oxidize in air.

Chemical element a species of atoms having the same number of protons in the atomic nucleus

A chemical element is a species of atom having the same number of protons in their atomic nuclei. For example, the atomic number of oxygen is 8, so the element oxygen consists of all atoms which have 8 protons.

Brass is used for decoration for its bright gold-like appearance; for applications where low friction is required such as locks, gears, bearings, doorknobs, ammunition casings and valves; for plumbing and electrical applications; and extensively in brass musical instruments such as horns and bells where a combination of high workability (historically with hand tools) and durability is desired. It is also used in zippers. Brass is often used in situations in which it is important that sparks not be struck, such as in fittings and tools used near flammable or explosive materials. [5]

Friction Force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other

Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction:

Door handle attached device used to open or close a door

The traditional door knob has a bolt or spindle running through it that sits just above a cylinder, to which the spindle is connected. Turning the knob pulls the cylinder in the direction of the turn. The end of the cylinder is the "latch bolt", which protrudes into a space carved out of the door frame, and which prevents the door from being opened if the knob is not turned. A spring or similar mechanism causes the latch to return to its protruding state whenever the knob is not being turned. Escutcheon plates are the keyhole covers, usually circular, through which keys pass to enter the lock body. If the door handles have a square or rectangular plate on which the handle is mounted this is called the backplate. The backplate can be plain, pierced for keyholes, or pierced and fitted with turn knobs and releases. The plate on the front edge of the lock where the latch bolt protrudes is called the faceplate.

Ammunition General term for a wide range of weapon items such as bombs, missiles, mines and projectiles

Ammunition is the material fired, scattered, dropped or detonated from any weapon. Ammunition is both expendable weapons and the component parts of other weapons that create the effect on a target. Nearly all mechanical weapons require some form of ammunition to operate.

Properties

Microstructure of rolled and annealed brass (400x magnification) Microstructure of rolled and annealed brass; magnification 400X.jpg
Microstructure of rolled and annealed brass (400× magnification)

Brass has higher malleability than bronze or zinc. The relatively low melting point of brass (900 to 940 °C, 1,650 to 1,720 °F, depending on composition) and its flow characteristics make it a relatively easy material to cast. By varying the proportions of copper and zinc, the properties of the brass can be changed, allowing hard and soft brasses. The density of brass is 8.4 to 8.73 g/cm3 (0.303 to 0.315 lb/cu in). [6]

Melting point temperature at which a solid turns liquid

The melting point of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at a standard pressure such as 1 atmosphere or 100 kPa.

The density, of a substance is its mass per unit volume. The symbol most often used for density is ρ, although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume:

Today, almost 90% of all brass alloys are recycled. [7] Because brass is not ferromagnetic, it can be separated from ferrous scrap by passing the scrap near a powerful magnet. Brass scrap is collected and transported to the foundry, where it is melted and recast into billets. Billets are heated and extruded into the desired form and size. The general softness of brass means that it can often be machined without the use of cutting fluid, though there are exceptions to this. [8]

Ferromagnetism physical phenomenon

Ferromagnetism is the basic mechanism by which certain materials form permanent magnets, or are attracted to magnets. In physics, several different types of magnetism are distinguished. Ferromagnetism is the strongest type and is responsible for the common phenomenon of magnetism in magnets encountered in everyday life. Substances respond weakly to magnetic fields with three other types of magnetism—paramagnetism, diamagnetism, and antiferromagnetism—but the forces are usually so weak that they can be detected only by sensitive instruments in a laboratory. An everyday example of ferromagnetism is a refrigerator magnet used to hold notes on a refrigerator door. The attraction between a magnet and ferromagnetic material is "the quality of magnetism first apparent to the ancient world, and to us today".

Cutting fluid type of coolant and lubricant designed specifically for metalworking processes, such as machining and stamping

Cutting fluid is a type of coolant and lubricant designed specifically for metalworking processes, such as machining and stamping. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, aerosols (mists), and air or other gases. They may be made from petroleum distillates, animal fats, plant oils, water and air, or other raw ingredients. Depending on context and on which type of cutting fluid is being considered, it may be referred to as cutting fluid, cutting oil, cutting compound, coolant, or lubricant.

Aluminum makes brass stronger and more corrosion-resistant. Aluminum also causes a highly beneficial hard layer of aluminum oxide (Al2O3) to be formed on the surface that is thin, transparent and self-healing. Tin has a similar effect and finds its use especially in seawater applications (naval brasses). Combinations of iron, aluminum, silicon and manganese make brass wear- and tear-resistant. [9]

Seawater Water from a sea or ocean

Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5%. This means that every kilogram of seawater has approximately 35 grams (1.2 oz) of dissolved salts. Average density at the surface is 1.025 kg/L. Seawater is denser than both fresh water and pure water because the dissolved salts increase the mass by a larger proportion than the volume. The freezing point of seawater decreases as salt concentration increases. At typical salinity, it freezes at about −2 °C (28 °F). The coldest seawater ever recorded was in 2010, in a stream under an Antarctic glacier, and measured −2.6 °C (27.3 °F). Seawater pH is typically limited to a range between 7.5 and 8.4. However, there is no universally accepted reference pH-scale for seawater and the difference between measurements based on different reference scales may be up to 0.14 units.

Wear damaging, gradual removal or deformation of material at solid surfaces

Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical or chemical. The study of wear and related processes is referred to as tribology.

Tear resistance is a measure of how well a material can withstand the effects of tearing. It is a useful engineering measurement for a wide variety of materials by many different test methods.

Lead content

To enhance the machinability of brass, lead is often added in concentrations of around 2%. Since lead has a lower melting point than the other constituents of the brass, it tends to migrate towards the grain boundaries in the form of globules as it cools from casting. The pattern the globules form on the surface of the brass increases the available lead surface area which in turn affects the degree of leaching. In addition, cutting operations can smear the lead globules over the surface. These effects can lead to significant lead leaching from brasses of comparatively low lead content. [10]

In October 1999 the California State Attorney General sued 13 key manufacturers and distributors over lead content. In laboratory tests, state researchers found the average brass key, new or old, exceeded the California Proposition 65 limits by an average factor of 19, assuming handling twice a day. [11] In April 2001 manufacturers agreed to reduce lead content to 1.5%, or face a requirement to warn consumers about lead content. Keys plated with other metals are not affected by the settlement, and may continue to use brass alloys with higher percentage of lead content. [12] [13]

Also in California, lead-free materials must be used for "each component that comes into contact with the wetted surface of pipes and pipe fittings, plumbing fittings and fixtures." On January 1, 2010, the maximum amount of lead in "lead-free brass" in California was reduced from 4% to 0.25% lead. [14] [15]

Corrosion-resistant brass for harsh environments

Brass sampling cock with stainless steel handle 00 BMA Automation Sampling cock.JPG
Brass sampling cock with stainless steel handle

Dezincification-resistant (DZR or DR) brasses, sometimes referred to as CR (corrosion resistant) brasses, are used where there is a large corrosion risk and where normal brasses do not meet the standards. Applications with high water temperatures, chlorides present or deviating water qualities (soft water) play a role. DZR-brass is excellent in water boiler systems. This brass alloy must be produced with great care, with special attention placed on a balanced composition and proper production temperatures and parameters to avoid long-term failures.

Use in musical instruments

A collection of brass instruments Trumpets02262006.jpg
A collection of brass instruments

The high malleability and workability, relatively good resistance to corrosion, and traditionally attributed acoustic properties of brass, have made it the usual metal of choice for construction of musical instruments whose acoustic resonators consist of long, relatively narrow tubing, often folded or coiled for compactness; silver and its alloys, and even gold, have been used for the same reasons, but brass is the most economical choice. Collectively known as brass instruments, these include the trombone, tuba, trumpet, cornet, baritone horn, euphonium, tenor horn, and French horn, and many other "horns", many in variously-sized families, such as the saxhorns.

Other wind instruments may be constructed of brass or other metals, and indeed most modern student-model flutes and piccolos are made of some variety of brass, usually a cupronickel alloy similar to nickel silver/German silver. Clarinets, especially low clarinets such as the contrabass and subcontrabass, are sometimes made of metal because of limited supplies of the dense, fine-grained tropical hardwoods traditionally preferred for smaller woodwinds. For the same reason, some low clarinets, bassoons and contrabassoons feature a hybrid construction, with long, straight sections of wood, and curved joints, neck, and/or bell of metal. The use of metal also avoids the risks of exposing wooden instruments to changes in temperature or humidity, which can cause sudden cracking. Even though the saxophones and sarrusaphones are classified as woodwind instruments, they are normally made of brass for similar reasons, and because their wide, conical bores and thin-walled bodies are more easily and efficiently made by forming sheet metal than by machining wood.

The keywork of most modern woodwinds, including wooden-bodied instruments, is also usually made of an alloy such as Nickel Silver/German Silver. Such alloys are stiffer and more durable than the brass used to construct the instrument bodies, but still workable with simple hand tools—a boon to quick repairs. The mouthpieces of both brass instruments and, less commonly, woodwind instruments are often made of brass among other metals as well.

Next to the brass instruments, the most notable use of brass in music is in various percussion instruments, most notably cymbals, gongs, and orchestral (tubular) bells (large "church" bells are normally made of bronze). Small handbells and "jingle bell" are also commonly made of brass.

The harmonica is a free reed aerophone, also often made from brass. In organ pipes of the reed family, brass strips (called tongues) are used as the reeds, which beat against the shallot (or beat "through" the shallot in the case of a "free" reed). Although not part of the brass section, snare drums are also sometimes made of brass. Some parts on electric guitars are also made from brass, especially inertia blocks on tremolo systems for its tonal properties, and for string nuts and saddles for both tonal properties and its low friction.

Germicidal and antimicrobial applications

The bactericidal properties of brass have been observed for centuries, particularly in marine environments where it prevents biofouling. Depending upon the type and concentration of pathogens and the medium they are in, brass kills these microorganisms within a few minutes to hours of contact. [16] [17] [18]

A large number of independent studies [16] [17] [18] [19] [20] [21] [22] confirm this antimicrobial effect, even against antibiotic-resistant bacteria such as MRSA and VRSA. The mechanisms of antimicrobial action by copper and its alloys, including brass, are a subject of intense and ongoing investigation. [17] [23] [24]

Season cracking

Cracking in brass caused by ammonia attack BrassSCC1.jpg
Cracking in brass caused by ammonia attack

Brass is susceptible to stress corrosion cracking, [25] especially from ammonia or substances containing or releasing ammonia. The problem is sometimes known as season cracking after it was first discovered in brass cartridges used for rifle ammunition during the 1920s in the British Indian Army. The problem was caused by high residual stresses from cold forming of the cases during manufacture, together with chemical attack from traces of ammonia in the atmosphere. The cartridges were stored in stables and the ammonia concentration rose during the hot summer months, thus initiating brittle cracks. The problem was resolved by annealing the cases, and storing the cartridges elsewhere.

Brass types

ClassProportion by weight (%)Notes
CopperZinc
Alpha brasses> 65< 35Alpha brasses are malleable, can be worked cold, and are used in pressing, forging, or similar applications. They contain only one phase, with face-centered cubic crystal structure. With their high proportion of copper, these brasses have a more golden hue than others
Alpha-beta brasses55–6535–45Also called duplex brasses, these are suited for hot working. They contain both α and β' phases; the β'-phase is body-centered cubic and is harder and stronger than α. Alpha-beta brasses are usually worked hot. The higher proportion of zinc means these brasses are brighter than alpha brasses.
Beta brasses[ citation needed ]50–5545–50Beta brasses can only be worked hot, and are harder, stronger, and suitable for casting. The high zinc-low copper content means these are some of the brightest and least-golden of the common brasses.
Gamma brasses33–3961–67There are also Ag-Zn and Au-Zn gamma brasses, Ag 30–50%, Au 41%. [26]
White brass< 50> 50These are too brittle for general use. The term may also refer to certain types of nickel silver alloys as well as Cu-Zn-Sn alloys with high proportions (typically 40%+) of tin and/or zinc, as well as predominantly zinc casting alloys with copper additives. These have virtually no yellow coloring at all, and instead have a much more silvery appearance.

Brass alloys
Alloy nameProportion by weight (%)OtherNotes
CopperZincTinLead
Abyssinian gold9010
Admiralty brass69301Tin inhibits loss of zinc in many environments.
Aich's alloy60.6636.581.021.74% ironDesigned for use in marine service owing to its corrosion resistance, hardness and toughness. A characteristic application is to the protection of ships' bottoms, but more modern methods of cathodic protection have rendered its use less common. Its appearance resembles that of gold. [27]
Aluminum brass77.520.52% aluminumAluminum improves corrosion resistance. It is used for heat exchanger and condenser tubes. [28]
Arsenical brass Arsenic; frequently aluminum Used for boiler fireboxes.
Cartridge brass (C260)7030 0.07 [29] Good cold working properties. Used for ammunition cases, plumbing, and hardware.
Common brass6337Also called rivet brass. Cheap and standard for cold working.
DZR brassArsenicDezincification resistant brass with a small percentage of arsenic.
Delta metal5541–431–3% iron with the balance consisting of various other metals.The proportions used make the material harder and suitable for valves and bearings.
Free machining brass (C360)61.535.530.35% ironAlso called 360 or C360 brass. High machinability. Lead content, 2.5–3.7% [29]
Gilding metal 955Softest type of brass commonly available. Gilding metal is typically used for ammunition bullet "jackets"; e.g., full metal jacket bullets. Almost red in color.
High brass6535Has a high tensile strength and is used for springs, screws, and rivets.
Leaded brass> 0An alpha-beta brass with an addition of lead for improved machinability.
Lead-free brass< 0.25Defined by California Assembly Bill AB 1953 contains "not more than 0.25 percent lead content". [14] Prior upper limit was 4%.
Low brass8020Light golden color, very ductile; used for flexible metal hoses and metal bellows.
Manganese brass70291.3% manganese Most notably used in making golden dollar coins in the United States. [30]
Muntz metal 6040Traces of ironUsed as a lining on boats.
Naval brass59401Similar to admiralty brass. Also known as Tobin bronze. [31]
Nickel brass 7024.55.5% nickelUsed to make pound coins in the pound sterling currency. Also the main constituent of the bi-metallic One Euro coin and the centre part of the Two Euro coin.
Nordic gold 89515% aluminumUsed in 10, 20, and 50 cents euro coins.
Prince's metal7525A type of alpha brass. Due to its yellow color, it is used as an imitation of gold. [32] Also called Prince Rupert's metal, the alloy was named after Prince Rupert of the Rhine.
Red brass, Rose brass (C230)85555Both an American term for the copper-zinc-tin alloy known as gunmetal, and an alloy which is considered both a brass and a bronze. [33] [34] Red brass is also an alternative name for copper alloy C23000, which is composed of 14–16% zinc, a minimum 0.05% iron and minimum 0.07% lead content, [29] and the remainder copper. [35] It may also refer to ounce metal, another copper-zinc-tin alloy.
Rich low brass, Tombac 5–20Often used in jewelry applications.
Silicon tombac 80164% siliconUsed as an alternative for investment cast steel parts.
Tonval brass> 0Also called CW617N or CZ122 or OT58. It is not recommended for sea water use, being susceptible to dezincification. [36] [37]
Yellow brass6733An American term for 33% zinc brass.

History

Although forms of brass have been in use since prehistory, [38] its true nature as a copper-zinc alloy was not understood until the post-medieval period because the zinc vapor which reacted with copper to make brass was not recognised as a metal. [39] The King James Bible makes many references to "brass" [40] to translate "nechosheth" (bronze or copper) from Hebrew to archaic English. The Shakespearean English use of the word 'brass' can mean any bronze alloy, or copper, an even less precise definition than the modern one. [ citation needed ] The earliest brasses may have been natural alloys made by smelting zinc-rich copper ores. [41] By the Roman period brass was being deliberately produced from metallic copper and zinc minerals using the cementation process, the product of which was calamine brass, and variations on this method continued until the mid-19th century. [42] It was eventually replaced by speltering, the direct alloying of copper and zinc metal which was introduced to Europe in the 16th century. [41]

Early copper-zinc alloys

In West Asia and the Eastern Mediterranean early copper-zinc alloys are now known in small numbers from a number of 3rd millennium BC sites in the Aegean, Iraq, the United Arab Emirates, Kalmykia, Turkmenistan and Georgia and from 2nd millennium BC sites in West India, Uzbekistan, Iran, Syria, Iraq and Canaan. [43] However, isolated examples of copper-zinc alloys are known in China from as early as the 5th millennium BC. [44]

The compositions of these early "brass" objects are highly variable and most have zinc contents of between 5% and 15% wt which is lower than in brass produced by cementation. [45] These may be "natural alloys" manufactured by smelting zinc rich copper ores in redox conditions. Many have similar tin contents to contemporary bronze artefacts and it is possible that some copper-zinc alloys were accidental and perhaps not even distinguished from copper. [45] However the large number of copper-zinc alloys now known suggests that at least some were deliberately manufactured and many have zinc contents of more than 12% wt which would have resulted in a distinctive golden color. [45] [46]

By the 8th–7th century BC Assyrian cuneiform tablets mention the exploitation of the "copper of the mountains" and this may refer to "natural" brass. [47] "Oreikhalkon" (mountain copper), [48] the Ancient Greek translation of this term, was later adapted to the Latin aurichalcum meaning "golden copper" which became the standard term for brass. [49] In the 4th century BC Plato knew orichalkos as rare and nearly as valuable as gold [50] and Pliny describes how aurichalcum had come from Cypriot ore deposits which had been exhausted by the 1st century AD. [51] X-ray fluorescence analysis of 39 orichalcum ingots recovered from a 2,600-year-old shipwreck off Sicily found them to be an alloy made with 75–80 percent copper, 15–20 percent zinc and small percentages of nickel, lead and iron. [52] [53]

Brass making in the Roman world

7th-century Persian ewer in brass with copper inlay Iranian - Ewer - Walters 54457 - Profile.jpg
7th-century Persian ewer in brass with copper inlay

During the later part of first millennium BC the use of brass spread across a wide geographical area from Britain [54] and Spain [55] in the west to Iran, and India in the east. [56] This seems to have been encouraged by exports and influence from the Middle East and eastern Mediterranean where deliberate production of brass from metallic copper and zinc ores had been introduced. [57] The 4th century BC writer Theopompus, quoted by Strabo, describes how heating earth from Andeira in Turkey produced "droplets of false silver", probably metallic zinc, which could be used to turn copper into oreichalkos. [58] In the 1st century BC the Greek Dioscorides seems to have recognised a link between zinc minerals and brass describing how Cadmia (zinc oxide) was found on the walls of furnaces used to heat either zinc ore or copper and explaining that it can then be used to make brass. [59]

By the first century BC brass was available in sufficient supply to use as coinage in Phrygia and Bithynia, [60] and after the Augustan currency reform of 23 BC it was also used to make Roman dupondii and sestertii . [61] The uniform use of brass for coinage and military equipment across the Roman world may indicate a degree of state involvement in the industry, [62] [63] and brass even seems to have been deliberately boycotted by Jewish communities in Palestine because of its association with Roman authority. [64]

Brass was produced by the cementation process where copper and zinc ore are heated together until zinc vapor is produced which reacts with the copper. There is good archaeological evidence for this process and crucibles used to produce brass by cementation have been found on Roman period sites including Xanten [65] and Nidda [66] in Germany, Lyon in France [67] and at a number of sites in Britain. [68] They vary in size from tiny acorn sized to large amphorae like vessels but all have elevated levels of zinc on the interior and are lidded. [67] They show no signs of slag or metal prills suggesting that zinc minerals were heated to produce zinc vapor which reacted with metallic copper in a solid state reaction. The fabric of these crucibles is porous, probably designed to prevent a buildup of pressure, and many have small holes in the lids which may be designed to release pressure [67] or to add additional zinc minerals near the end of the process. Dioscorides mentioned that zinc minerals were used for both the working and finishing of brass, perhaps suggesting secondary additions. [69]

Brass made during the early Roman period seems to have varied between 20% to 28% wt zinc. [70] The high content of zinc in coinage and brass objects declined after the first century AD and it has been suggested that this reflects zinc loss during recycling and thus an interruption in the production of new brass. [71] However it is now thought this was probably a deliberate change in composition [72] and overall the use of brass increases over this period making up around 40% of all copper alloys used in the Roman world by the 4th century AD. [73]

Brass making in the medieval period

Baptism of Christ on the 12th-century baptismal font at St Bartholomew's Church, Liege Renier de Huy JPG0.jpg
Baptism of Christ on the 12th-century baptismal font at St Bartholomew's Church, Liège

Little is known about the production of brass during the centuries immediately after the collapse of the Roman Empire. Disruption in the trade of tin for bronze from Western Europe may have contributed to the increasing popularity of brass in the east and by the 6th–7th centuries AD over 90% of copper alloy artefacts from Egypt were made of brass. [74] However other alloys such as low tin bronze were also used and they vary depending on local cultural attitudes, the purpose of the metal and access to zinc, especially between the Islamic and Byzantine world. [75] Conversely the use of true brass seems to have declined in Western Europe during this period in favour of gunmetals and other mixed alloys [76] but by about 1000 brass artefacts are found in Scandinavian graves in Scotland, [77] brass was being used in the manufacture of coins in Northumbria [78] and there is archaeological and historical evidence for the production of calamine brass in Germany [79] and The Low Countries, [80] areas rich in calamine ore.

These places would remain important centres of brass making throughout the medieval period, [81] especially Dinant. Brass objects are still collectively known as dinanterie in French. The baptismal font at St Bartholomew's Church, Liège in modern Belgium (before 1117) is an outstanding masterpiece of Romanesque brass casting, though also often described as bronze. The metal of the early 12th-century Gloucester Candlestick is unusual even by medieval standards in being a mixture of copper, zinc, tin, lead, nickel, iron, antimony and arsenic with an unusually large amount of silver, ranging from 22.5% in the base to 5.76% in the pan below the candle. The proportions of this mixture may suggest that the candlestick was made from a hoard of old coins, probably Late Roman. [82] Latten is a term for decorative borders and similar objects cut from sheet metal, whether of brass or bronze. Aquamaniles were typically made in brass in both the European and Islamic worlds.

Brass aquamanile from Lower Saxony, Germany, c. 1250 WLA lacma 1250 Aquamanile.jpg
Brass aquamanile from Lower Saxony, Germany, c. 1250

The cementation process continued to be used but literary sources from both Europe and the Islamic world seem to describe variants of a higher temperature liquid process which took place in open-topped crucibles. [83] Islamic cementation seems to have used zinc oxide known as tutiya or tutty rather than zinc ores for brass-making, resulting in a metal with lower iron impurities. [84] A number of Islamic writers and the 13th century Italian Marco Polo describe how this was obtained by sublimation from zinc ores and condensed onto clay or iron bars, archaeological examples of which have been identified at Kush in Iran. [85] It could then be used for brass making or medicinal purposes. In 10th century Yemen al-Hamdani described how spreading al-iglimiya, probably zinc oxide, onto the surface of molten copper produced tutiya vapor which then reacted with the metal. [86] The 13th century Iranian writer al-Kashani describes a more complex process whereby tutiya was mixed with raisins and gently roasted before being added to the surface of the molten metal. A temporary lid was added at this point presumably to minimise the escape of zinc vapor. [87]

In Europe a similar liquid process in open-topped crucibles took place which was probably less efficient than the Roman process and the use of the term tutty by Albertus Magnus in the 13th century suggests influence from Islamic technology. [88] The 12th century German monk Theophilus described how preheated crucibles were one sixth filled with powdered calamine and charcoal then topped up with copper and charcoal before being melted, stirred then filled again. The final product was cast, then again melted with calamine. It has been suggested that this second melting may have taken place at a lower temperature to allow more zinc to be absorbed. [89] Albertus Magnus noted that the "power" of both calamine and tutty could evaporate and described how the addition of powdered glass could create a film to bind it to the metal. [90] German brass making crucibles are known from Dortmund dating to the 10th century AD and from Soest and Schwerte in Westphalia dating to around the 13th century confirm Theophilus' account, as they are open-topped, although ceramic discs from Soest may have served as loose lids which may have been used to reduce zinc evaporation, and have slag on the interior resulting from a liquid process. [91]

Brass in Africa

12th century "Bronze Head from Ife", actually of "heavily leaded zinc-brass" Arte yoruba, nigeria, testa da ife, 12-15mo secolo.JPG
12th century "Bronze Head from Ife", actually of "heavily leaded zinc-brass"

Some of the most famous objects in African art are the lost wax castings of West Africa, mostly from what is now Nigeria, produced first by the Kingdom of Ife and then the Benin Empire. Though normally described as "bronzes", the Benin Bronzes, now mostly in the British Museum and other Western collections, and the large portrait heads such as the Bronze Head from Ife of "heavily leaded zinc-brass" and the Bronze Head of Queen Idia, both also British Museum, are better described as brass, though of variable compositions. [92] Work in brass or bronze continued to be important in Benin art and other West African traditions such as Akan goldweights, where the metal was regarded as a more valuable material than in Europe.

Brass making in Renaissance and post-medieval Europe

The Renaissance saw important changes to both the theory and practice of brassmaking in Europe. By the 15th century there is evidence for the renewed use of lidded cementation crucibles at Zwickau in Germany. [93] These large crucibles were capable of producing c.20 kg of brass. [94] There are traces of slag and pieces of metal on the interior. Their irregular composition suggests that this was a lower temperature, not entirely liquid, process. [95] The crucible lids had small holes which were blocked with clay plugs near the end of the process presumably to maximise zinc absorption in the final stages. [96] Triangular crucibles were then used to melt the brass for casting. [97]

16th-century technical writers such as Biringuccio, Ercker and Agricola described a variety of cementation brass making techniques and came closer to understanding the true nature of the process noting that copper became heavier as it changed to brass and that it became more golden as additional calamine was added. [98] Zinc metal was also becoming more commonplace. By 1513 metallic zinc ingots from India and China were arriving in London and pellets of zinc condensed in furnace flues at the Rammelsberg in Germany were exploited for cementation brass making from around 1550. [99]

Eventually it was discovered that metallic zinc could be alloyed with copper to make brass, a process known as speltering, [100] and by 1657 the German chemist Johann Glauber had recognised that calamine was "nothing else but unmeltable zinc" and that zinc was a "half ripe metal." [101] However some earlier high zinc, low iron brasses such as the 1530 Wightman brass memorial plaque from England may have been made by alloying copper with zinc and include traces of cadmium similar to those found in some zinc ingots from China. [100]

However, the cementation process was not abandoned, and as late as the early 19th century there are descriptions of solid-state cementation in a domed furnace at around 900–950 °C and lasting up to 10 hours. [102] The European brass industry continued to flourish into the post medieval period buoyed by innovations such as the 16th century introduction of water powered hammers for the production of battery wares. [103] By 1559 the Germany city of Aachen alone was capable of producing 300,000 cwt of brass per year. [103] After several false starts during the 16th and 17th centuries the brass industry was also established in England taking advantage of abundant supplies of cheap copper smelted in the new coal fired reverberatory furnace. [104] In 1723 Bristol brass maker Nehemiah Champion patented the use of granulated copper, produced by pouring molten metal into cold water. [105] This increased the surface area of the copper helping it react and zinc contents of up to 33% wt were reported using this new technique. [106]

In 1738 Nehemiah's son William Champion patented a technique for the first industrial scale distillation of metallic zinc known as distillation per descencum or "the English process". [107] [108] This local zinc was used in speltering and allowed greater control over the zinc content of brass and the production of high-zinc copper alloys which would have been difficult or impossible to produce using cementation, for use in expensive objects such as scientific instruments, clocks, brass buttons and costume jewellery. [109] However Champion continued to use the cheaper calamine cementation method to produce lower-zinc brass [109] and the archaeological remains of bee-hive shaped cementation furnaces have been identified at his works at Warmley. [110] By the mid-to-late 18th century developments in cheaper zinc distillation such as John-Jaques Dony's horizontal furnaces in Belgium and the reduction of tariffs on zinc [111] as well as demand for corrosion-resistant high zinc alloys increased the popularity of speltering and as a result cementation was largely abandoned by the mid-19th century. [112]

See also

Related Research Articles

Calamine (mineral) zinc ore group

Calamine is a historic name for an ore of zinc. The name calamine was derived from lapis calaminaris, a Latin corruption of Greek cadmia (καδμία), the old name for zinc ores in general. The name of the Belgian town of Kelmis, La Calamine in French, which was home to a zinc mine, comes from this. In the 18th and 19th centuries large ore mines could be found near the German village of Breinigerberg.

Crucible container in which substances are heated

A crucible is a ceramic or metal container in which metals or other substances may be melted or subjected to very high temperatures. While crucibles historically were usually made from clay, they can be made from any material that withstands temperatures high enough to melt or otherwise alter its contents.

Orichalcum real alloy and fictional material

Orichalcum or aurichalcum is a metal mentioned in several ancient writings, including the story of Atlantis in the Critias of Plato. Within the dialogue, Critias claims that orichalcum had been considered second only to gold in value and had been found and mined in many parts of Atlantis in ancient times, but that by Critias' own time orichalcum was known only by name.

Cementation process

The cementation process is an obsolete technology for making steel by carburization of iron. Unlike modern steelmaking, it increased the amount of carbon in the iron. It was apparently developed before the 17th century. Derwentcote Steel Furnace, built in 1720, is the earliest surviving example of a cementation furnace. Another example in the UK is the cementation furnace in Doncaster Street, Sheffield.

Cupellation

Cupellation is a refining process in metallurgy where ores or alloyed metals are treated under very high temperatures and have controlled operations to separate noble metals, like gold and silver, from base metals, like lead, copper, zinc, arsenic, antimony, or bismuth, present in the ore. The process is based on the principle that precious metals do not oxidise or react chemically, unlike the base metals, so when they are heated at high temperatures, the precious metals remain apart, and the others react, forming slags or other compounds.

The term latten referred loosely to the copper alloys such as brass or bronze that appeared in the Middle Ages and through to the late 18th and early 19th centuries. It was used for monumental brasses, in decorative effects on borders, rivets or other details of metalwork, in livery and pilgrim badges or funerary effigies. Latten commonly contained varying amounts of copper, tin, zinc and lead, giving it characteristics of both brass and bronze. Metalworkers commonly formed latten in thin sheets and used it to make church utensils. Brass of this period is made through the calamine brass process, from copper and zinc ore. Later brass was made with zinc metal from Champion's smelting process and is not generally referred to as latten. This calamine brass was generally manufactured as hammered sheet or "battery brass" and cast brass was rare.

Gunmetal alloy of copper, tin, and zinc

Gunmetal, also known as red brass in the United States, is a type of bronze – an alloy of copper, tin, and zinc. Proportions vary but 88% copper, 8–10% tin, and 2–4% zinc is an approximation. Originally used chiefly for making guns, it has largely been replaced by steel. Gunmetal, which casts and machines well and is resistant to corrosion from steam and salt water, is used to make steam and hydraulic castings, valves, gears, statues, and various small objects, such as buttons. It has a tensile strength of 221 to 310 MPa, a specific gravity of 8.7, a Brinell hardness of 65 to 74, and a melting point of around 1,000 degrees Celsius.

History of metallurgy in the Indian subcontinent

The history of metallurgy in the Indian subcontinent began prior to the 3rd millennium BCE and continued well into the British Raj. Metals and related concepts were mentioned in various early Vedic age texts. The Rigveda already uses the Sanskrit term Ayas (metal). The Indian cultural and commercial contacts with the Near East and the Greco-Roman world enabled an exchange of metallurgic sciences. With the advent of the Mughals, India's Mughal Empire further improved the established tradition of metallurgy and metal working in India.

Calamine brass is brass produced by a particular alloying technique using the zinc ore calamine directly, rather than first refining it to metallic zinc. Direct zinc smelting appears to have been unknown in Europe until the mid-18th century, even though the alloyed calamine brass was in use for centuries, and metallic zinc was produced directly via reducing-atmosphere smelting in India and China from the 12th century CE onwards.

Corinthian bronze

Corinthian bronze, also named Corinthian brass or æs Corinthiacum, was a highly valuable metal alloy in classical antiquity. It is thought to be an alloy of copper with gold or silver, although it has also been contended that it was simply a very high grade of bronze, or a kind of bronze that was manufactured in Corinth. It is referred to in various ancient texts, but no certain examples of Corinthian bronze exist today. However, it has been increasingly suggested that a number of artefacts previously described as niello in fact use a technique of patinated metal that may be the same as Corinthian bronze and is similar to the Japanese Shakudō.

Architectural metals

Metals used for architectural purposes include lead, for water pipes, roofing, and windows; tin, formed into tinplate; zinc, copper and aluminium, in a range of applications including roofing and decoration; and iron, which has structural and other uses in the form of cast iron or wrought iron, or made into steel. Metal alloys used in building include bronze ; brass ; monel metal and nickel silver, mainly consisting of nickel and copper; and stainless steel, with important components of nickel and chromium.

Zinc smelting is the process of converting zinc concentrates into pure zinc. Zinc smelting has historically been more difficult than the smelting of other metals, e.g. iron, because in contrast, zinc has a low boiling point. At temperatures typically used for smelting metals, zinc is a gas that will escape from a furnace with the flue gas and be lost, unless specific measures are taken to prevent it.

Metals and metal working had been known to the people of modern Italy since the Bronze Age. By 53 BC, Rome had expanded to control an immense expanse of the Mediterranean. This included Italy and its islands, Spain, Macedonia, Africa, Asia Minor, Syria and Greece; by the end of the Emperor Trajan's reign, the Roman Empire had grown further to encompass parts of Britain, Egypt, all of modern Germany west of the Rhine, Dacia, Noricum, Judea, Armenia, Illyria, and Thrace. As the empire grew, so did its need for metals.

Gold parting

Gold parting is the separating of gold from silver. Gold and silver are often extracted from the same ores and are chemically similar and therefore hard to separate. Over the centuries special means of separation have been invented.

C41100 Lubaloy is a wrought copper alloy that is composed mainly of copper and zinc. Lubaloy possesses many favorable characteristics making it, and other types of brass, a popular choice in manufacturing. It is a source material in many processes including the creation of electrical components and bullet-making. Documented use of brass dates back to early Romans, and is referenced in the King James Bible. There are both positive and negative health effects that are associated with the use of this material.

Bronze and brass ornamental work

The use of bronze dates from remote antiquity. This important metal is an alloy composed of copper and tin, in proportion which vary slightly, but may be normally considered as nine parts of copper to one of tin. Other ingredients which are occasionally found are more or less accidental. The result is a metal of a rich golden brown colour, capable of being worked by casting — a process little applicable to its component parts, but peculiarly successful with bronze, the density and hardness of the metal allowing it to take any impression of a mould, however delicate. It is thus possible to create ornamental work of various kinds.

Non-ferrous extractive metallurgy metallurgy process

Non-ferrous extractive metallurgy is one of the two branches of extractive metallurgy which pertains to the processes of reducing valuable, non-iron metals from ores or raw material. Metals like zinc, copper, lead, aluminium as well as rare and noble metals are of particular interest in this field, while the more common metal, iron, is considered a major impurity. Like ferrous extraction, non-ferrous extraction primarily focuses on the economic optimization of extraction processes in separating qualitatively and quantitatively marketable metals from its impurities (gangue).

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