Wikipedia

Brass

"Arsenical brass" redirects here. Not to be confused witharsenical bronzeorarsenical copper.
For other uses, seeBrass (disambiguation).

Brassis analloyofcopperandzinc,in proportions which can be varied to achieve different colours and mechanical, electrical, acoustic and chemical properties,[1]but copper typically has the larger proportion, generally 66% copper and 34% zinc. In use since prehistoric times, it is asubstitutional alloy:atoms of the two constituents may replace each other within the same crystal structure.

Islamic Golden Agebrassastrolabe
Brasslecternwith an eagle. Attributed toAert van Tricht,Limburg (Netherlands),c. 1500.

Brass is similar tobronze,a copper alloy that containstininstead of zinc.[2]Both bronze and brass may include small proportions of a range of otherelementsincludingarsenic,lead,phosphorus,aluminium,manganeseandsilicon.Historically, the distinction between the two alloys has been less consistent and clear,[3]and increasingly museums use the more general term "copper alloy".[4]

Brass has long been a popular material for its bright gold-like appearance and is still used fordrawer pullsanddoorknobs.It has also been widely used to make sculpture and utensils because of its low melting point, high workability (both with hand tools and with modernturningandmillingmachines), durability, andelectricalandthermal conductivity.Brasses with higher copper content are softer and more golden in colour; conversely those with less copper and thus more zinc are harder and more silvery in colour.

Brass is still commonly used in applications where corrosion resistance and lowfrictionare required, such aslocks,hinges,gears,bearings,ammunitioncasings,zippers,plumbing,hose couplings,valvesandelectrical plugs and sockets.It is used extensively formusical instrumentssuch ashornsandbells.The composition of brass makes it a favorable substitute for copper incostume jewelryandfashion jewelry,as it exhibits greater resistance to corrosion. Brass is not as hard as bronze and so is not suitable for most weapons and tools. Nor is it suitable for marine uses, because the zinc reacts with minerals in salt water, leaving porous copper behind; marine brass, with added tin, avoids this, as does bronze.

Brass is often used in situations in which it is important thatsparksnot be struck, such as in fittings and tools used near flammable or explosive materials.[5]

Properties

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Microstructureof rolled andannealedbrass (400× magnification)

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

Today, almost 90% of all brass alloys are recycled.[7]Because brass is notferromagnetic,ferrous scrap can be separated from it by passing the scrap near a powerful magnet. Brass scrap is melted and recast intobilletsthat are extruded into the desired form and size. The general softness of brass means that it can often be machined without the use ofcutting fluid,though there are exceptions to this.[8]

Aluminium makes brass stronger and more corrosion-resistant. Aluminium also causes a highly beneficial hard layer ofaluminium 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 inseawaterapplications (naval brasses). Combinations of iron, aluminium, silicon, and manganese make brasswear- andtear-resistant.[9]The addition of as little as 1% iron to a brass alloy will result in an alloy with a noticeable magnetic attraction.[10]

Binary phase diagram

Brass willcorrodein the presence of moisture,chlorides,acetates,ammonia,and certain acids. This often happens when the copper reacts with sulfur to form a brown and eventually black surface layer ofcopper sulfidewhich, if regularly exposed to slightly acidic water such as urban rainwater, can then oxidize in air to form apatinaof green-bluecopper carbonate.Depending on how the patina layer was formed, it may protect the underlying brass from further damage.[11]

Although copper and zinc have a large difference inelectrical potential,the resulting brass alloy does not experience internalizedgalvanic corrosionbecause of the absence of a corrosive environment within the mixture. However, if brass is placed in contact with a more noble metal such as silver or gold in such an environment, the brass will corrode galvanically; conversely, if brass is in contact with a less-noble metal such as zinc or iron, the less noble metal will corrode and the brass will be protected.

Lead content

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To enhance the machinability of brass,leadis often added in concentrations of about 2%. Since lead has a lowermelting pointthan the other constituents of the brass, it tends to migrate towards thegrain boundariesin 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.[12]

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 theCalifornia Proposition 65limits by an average factor of 19, assuming handling twice a day.[13]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 a higher percentage of lead content.[14][15]

Also in California, lead-free materials must be used for "each component that comes into contact with the wetted surface of pipes andpipe fittings, plumbing fittingsand fixtures ". On 1 January 2010, the maximum amount of lead in" lead-free brass "in California was reduced from 4% to 0.25% lead.[16][17]

Corrosion-resistant brass for harsh environments

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Brass sampling cock with stainless steel handle

Dezincification-resistant (DZRor DR) brasses, sometimes referred to as CR (corrosionresistant) brasses, are used where there is a large corrosion risk and where normal brasses do not meet the requirements. Applications with high water temperatures,chloridespresent or deviating water qualities (soft water) play a role. DZR-brass is used in waterboilersystems. 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.[18][19]

An example of DZR brass is the C352 brass, with about 30% zinc, 61–63% copper, 1.7–2.8% lead, and 0.02–0.15% arsenic. The lead and arsenic significantly suppress the zinc loss.[20]

"Red brasses", a family of alloys with high copper proportion and generally less than 15% zinc, are more resistant to zinc loss. One of the metals called "red brass" is 85% copper, 5% tin, 5% lead, and 5% zinc. Copper alloy C23000, which is also known as "red brass", contains 84–86% copper, 0.05% each iron and lead, with the balance being zinc.[21]

Another such material isgunmetal,from the family of red brasses. Gunmetal alloys contain roughly 88% copper, 8–10% tin, and 2–4% zinc. Lead can be added for ease of machining or for bearing alloys.[22]

"Naval brass", for use in seawater, contains 40% zinc but also 1% tin. The tin addition suppresses zinc leaching.[23]

TheNSF Internationalrequires brasses with more than 15% zinc, used inpiping and plumbing fittings,to be dezincification-resistant.[24]

Use in musical instruments

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A collection of brass instruments

The highmalleabilityand workability, relatively good resistance tocorrosion,and traditionally attributedacousticproperties of brass, have made it the usual metal of choice for construction ofmusical instrumentswhose acousticresonatorsconsist of long, relatively narrow tubing, often folded or coiled for compactness;silverand its alloys, and evengold,have been used for the same reasons, but brass is the most economical choice. Collectively known asbrass instruments,or simply 'the brass', these include thetrombone,tuba,trumpet,cornet,flugelhorn,baritone horn,euphonium,tenor horn,andFrench horn,and many other "horns",many in variously sized families, such as thesaxhorns.

Otherwind instrumentsmay be constructed of brass or other metals, and indeed most modern student-modelflutesandpiccolosare made of some variety of brass, usually acupronickelalloysimilar tonickel silver (also known as German silver).Clarinets,especially low clarinets such as thecontrabassandsubcontrabass,are sometimes made of metal because of limited supplies of the dense, fine-grained tropical hardwoods traditionally preferred for smallerwoodwinds.For the same reason, some low clarinets,bassoonsandcontrabassoonsfeature 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 thesaxophonesandsarrusophonesare 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. 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. Themouthpiecesof 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 variouspercussion instruments,most notablycymbals,gongs,andorchestral (tubular) bells(large "church"bellsare normally made ofbronze). Smallhandbellsand "jingle bells"are also commonly made of brass.

Theharmonicais afree reed aerophone,also often made from brass. Inorgan pipesof the reed family, brass strips (called tongues) are used as the reeds, which beat against theshallot(or beat "through" the shallot in the case of a "free" reed). Although not part of the brass section,snare drumsare also sometimes made of brass. Some parts onelectric guitarsare 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.[25]

Germicidal and antimicrobial applications

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Main article:Antimicrobial copper-alloy touch surfaces
See also:Antimicrobial properties of copperandCopper alloys in aquaculture

Thebactericidalproperties of brass have been observed for centuries, particularly in marine environments where it preventsbiofouling.Depending upon the type and concentration ofpathogensand the medium they are in, brass kills thesemicroorganismswithin a few minutes to hours of contact.[26][27][28]

A large number of independent studies[26][27][28][29][30][31][32]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.[27][33][34]

Season cracking

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Cracking in brass caused byammoniaattack

Brass is susceptible tostress corrosion cracking,[35]especially fromammoniaor substances containing or releasing ammonia. The problem is sometimes known asseason crackingafter it was first discovered in brasscartridgesused forrifleammunitionduring the 1920s in theBritish Indian Army.The problem was caused by highresidual stressesfrom 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 byannealingthe cases, and storing the cartridges elsewhere.

Types

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Class Proportion by weight (%) Notes
Copper Zinc
Alpha brasses > 65 < 35 Alpha brasses are malleable, can be worked cold, and are used in pressing, forging, or similar applications. They contain only one phase, withface-centred cubiccrystal structure.With their high proportion of copper, these brasses have a more golden hue than others. The alpha phase is a substitutionsolid solutionof zinc in copper. It is close in properties to copper, tough, strong, and somewhat difficult to machine. Best formability is with 32% of zinc. Corrosion-resistant red brasses, with 15% of zinc or less, belong here.
Alpha-beta brasses 55–65 35–45 Also calledduplex brasses,these are suited for hot working. They contain both α and β' phases; the β'-phase is orderedbody-centred cubic,with zinc atoms in the centre of the cubes, 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. At 45% of zinc the alloy has the highest strength.
Beta brasses[citation needed] 50–55 45–50 Beta 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 brasses 33–39 61–67 There are also Ag-Zn and Au-Zn gamma brasses, Ag 30–50%, Au 41%.[36]The gamma phase is a cubic-latticeintermetallic compound,Cu5Zn8.
White brass < 50 > 50 These are too brittle for general use. The term may also refer to certain types ofnickel silveralloys 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 colouring at all, and instead have a much more silvery appearance.

Other phases than α, β and γ are ε, a hexagonal intermetallic CuZn3,and η, a solid solution of copper in zinc.

Brass alloys

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Alloy name Proportion by weight (%) Other Notes
Copper Zinc Tin Lead
Abyssinian gold (Commercial bronze [C220]) 90 10
Admiralty brass 69 30 1 Tin inhibitsloss of zincin many environments.
Aich's alloy 60.66 36.58 1.02 1.74% iron Designed 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.[37]
Aluminium brass 77.5 20.5 2% aluminium Aluminium improves corrosion resistance. It is used for heat exchanger and condenser tubes.[38]
Arsenical brass Arsenic;frequentlyaluminium Used for boilerfireboxes.[39][40]
Arsenical brass 259 70 29.5 ≤0.05 Arsenic 0.2-0.6, Iron ≤0.05 Heat exchangers, plumbing requiring excellent corrosion resistance in water.[40]
Brastil - - - - Copper, Silicon, Zinc An alloy of copper, zinc, and silicon which has an incredibly high tensile strength and is corrosion resistant. Doehler Die Casting Co. of Toledo, Ohio were known for the production of Brastil.[41][42]It was notably tested in 1932 on anM1911 pistolas it was cheaper than steel at the time as a cost-effective measure.
California lead-free brass < 0.25 Defined by California Assembly Bill AB 1953 contains "not more than 0.25 percent lead content".[16]Prior upper limit was 4%.
Cartridge brass (C260) 70 30 — ≤0.07[43] Goodcold workingproperties. Used for ammunition cases, plumbing, and hardware.
Common brass 63 37 Also calledrivet brass.Cheap and standard for cold working.
DZR brass Arsenic Dezincification resistant brass with a small percentage of arsenic.
Delta metal 55 41–43 1–3% 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) 61.5 35.5 2.5–3.7 0.35% iron Also called 360 or C360 brass. High machinability.[43]
Gilding metal 95 5 Softest type of brass commonly available. Gilding metal is typically used for ammunition bullet "jackets"; e.g.,full metal jacketbullets. Almost red in colour.
Gunmetal 88 10 2 Eg British Admiralty gunmetal. Has variations.
High brass 65 35 Has a hightensile strengthand is used forsprings,screws,andrivets.
Leaded brass > 0 An alpha-beta brass with an addition ofleadfor improved machinability.
Low brass 80 20 Light golden colour, very ductile; used for flexible metal hoses and metalbellows.
Manganese brass 77 12 7%manganese,4%nickel Used as cladding for United Statesgolden dollarcoins.[44]Other manganese brass alloy compositions exist.
Muntz metal 60 40 Traces of iron Used as a lining on boats.
Naval brass (C464) 59 40 1 Similar to admiralty brass. Also known as Tobin bronze, 464, or C464.[45]
Naval brass, high lead (C485) 60.5 37.5 1.8 0.7 Naval brass with added lead for machinability. Also known as 485, or C485.[46]
Nickel brass 70–76 20–24.5 4–5.5% nickel The outer ring of the bi-metallicone poundandtwo poundsterling coins and theone euro coin,plus the centre part of the two euro coin. Formerly used for the round one pound coin.
Nordic gold 89 5 1 5% aluminum Used in 10, 20, and 50 centseuro coins.
Orichalcum 75-80 15-20 Trace Trace amounts of nickel and iron Determined from 39 ingots recovered from an ancient shipwreck inGela,Sicily.
Pinchbeck 89% or 93% 11% or 7% Invented in the early 18th century by Christopher Pinchbeck. Resembles gold to a point where people can buy the metal as budget gold "effect" jewelry.
Prince's metal 75 25 A type of alpha brass. Due to its yellow colour, it is used as an imitation of gold.[47]Also calledPrince Rupert's metal,the alloy was named afterPrince Rupert of the Rhine.
ounce metal 85 5 5 5 Sometimes called "red brass"
copper alloy C23000 84-85.9 14-16 minimum 0.07% minimum 0.05% iron [43][48]Sometimes called "red brass"
Red brass, Rose brass (C230) 85 5 5 5 Both an American term for the copper-zinc-tin alloy known asgunmetal,and an alloy which is considered both a brass and a bronze.[49][50]Red brass is also an alternative name forcopper alloy C23000,which is composed of 14–16% zinc, a minimum 0.05% iron and minimum 0.07% lead content,[43]and the remainder copper.[51]It may also refer toounce metal(Cu 85.0, Zn 5.0, Pb 5.0, Sn 5.0).
Rich low brass,Tombac 80-97 5–20 Often used in jewelry applications. Many variations.
Silicon tombac 80 16 4% silicon Used as an alternative for investment cast steel parts.
Tonval brass >0 Also called CW617N or CZ122 or OT58. It is not recommended for sea water use, being susceptible to dezincification.[52][53]
Yellow brass 67 33 An American term for 33% zinc brass.

History

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Further information:Art in bronze and brass

Although forms of brass have been in use sinceprehistory,[54]its true nature as a copper-zinc alloy was not understood until the post-medieval period because the zincvaporwhich reacted with copper to make brass was not recognized as ametal.[55]TheKing James Biblemakes many references to "brass"[56]to translate "nechosheth" (bronze or copper) from Hebrew to English. The earliest brasses may have been natural alloys made bysmeltingzinc-rich copperores.[57]By theRomanperiod brass was being deliberately produced from metallic copper and zinc minerals using thecementationprocess, the product of which wascalamine brass,and variations on this method continued until the mid-19th century.[58]It was eventually replaced byspeltering,the direct alloying of copper and zinc metal which was introduced toEuropein the 16th century.[57]

Brass has sometimes historically been referred to as "yellow copper".[59][60]

Early copper-zinc alloys

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InWest Asiaand theEastern Mediterraneanearly copper-zinc alloys are now known in small numbers from a number of 3rd millennium BC sites in theAegean,Iraq,theUnited Arab Emirates,Kalmykia,TurkmenistanandGeorgiaand from 2nd millennium BC sites inwestern India,Uzbekistan,Iran,Syria,Iraq andCanaan.[61]Isolated examples of copper-zincalloysare known inChinafrom the 1st century AD, long after bronze was widely used.[62]

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.[63]These may be "natural alloys" manufactured by smelting zinc rich copper ores inredoxconditions. Many have similar tin contents to contemporary bronzeartefactsand it is possible that some copper-zinc alloys were accidental and perhaps not even distinguished from copper.[63]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 colour.[63][64]

By the 8th–7th century BCAssyriancuneiformtablets mention the exploitation of the "copper of the mountains" and this may refer to "natural" brass.[65]"Oreikhalkon" (mountain copper),[66]theAncient Greektranslation of this term, was later adapted to theLatinaurichalcummeaning "golden copper" which became the standard term for brass.[67]In the 4th century BCPlatokneworichalkosas rare and nearly as valuable as gold[68]andPlinydescribes howaurichalcumhad come fromCypriotore deposits which had been exhausted by the 1st century AD.[69]X-ray fluorescenceanalysis of 39orichalcumingots recovered from a 2,600-year-old shipwreck off Sicily found them to be an alloy made with 75–80% copper, 15–20% zinc and small percentages of nickel, lead and iron.[70][71]

Roman world

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7th-century Persianewerin brass with copper inlay,Walters Art Museum,Baltimore,Maryland, US

During the later part of first millennium BC the use of brass spread across a wide geographical area fromBritain[72]andSpain[73]in the west toIran,andIndiain the east.[74]This seems to have been encouraged by exports and influence from theMiddle Eastand eastern Mediterranean where deliberate production of brass from metallic copper and zinc ores had been introduced.[75]The 4th century BC writerTheopompus,quoted byStrabo,describes how heating earth fromAndeirainTurkeyproduced "droplets of false silver", probably metallic zinc, which could be used to turn copper into oreichalkos.[76]In the 1st century BC the GreekDioscoridesseems to have recognized a link between zincmineralsand brass describing howCadmia(zinc oxide) was found on the walls offurnacesused to heat either zinc ore or copper and explaining that it can then be used to make brass.[77]

By the first century BC brass was available in sufficient supply to use ascoinageinPhrygiaandBithynia,[78]and after the Augustancurrency reformof 23 BC it was also used to make Romandupondiiandsestertii.[79]The uniform use of brass for coinage and military equipment across theRoman worldmay indicate a degree of state involvement in the industry,[80][81]and brass even seems to have been deliberately boycotted byJewishcommunities in Palestine because of its association with Roman authority.[82]

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 andcruciblesused to produce brass by cementation have been found onRoman periodsites includingXanten[83]andNidda[84]inGermany,LyoninFrance[85]and at a number of sites in Britain.[86]They vary in size from tiny acorn sized to largeamphoraelike vessels but all have elevated levels of zinc on the interior and are lidded.[85]They show no signs ofslagor metalprillssuggesting that zinc minerals were heated to produce zinc vapor which reacted with metallic copper in asolid 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[85]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.[87]

Brass made during the early Roman period seems to have varied between 20% and 28% wt zinc.[87]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 duringrecyclingand thus an interruption in the production of new brass.[79]However it is now thought this was probably a deliberate change in composition[88]and overall the use of brass increases over this period making up around 40% of allcopper alloysused in the Roman world by the 4th century AD.[89]

Medieval period

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Baptism of Christon the 12th-centurybaptismal font at St Bartholomew's Church, Liège

Little is known about the production of brass during the centuries immediately after the collapse of theRoman Empire.Disruption in the trade of tin for bronze fromWestern Europemay have contributed to the increasing popularity of brass in the east and by the 6th–7th centuries AD over 90% ofcopper alloyartefacts fromEgyptwere made of brass.[90]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 theIslamicandByzantineworld.[91]Conversely the use of true brass seems to have declined in Western Europe during this period in favor ofgunmetalsand other mixed alloys[92]but by about 1000 brass artefacts are found inScandinaviangraves inScotland,[93]brass was being used in the manufacture of coins inNorthumbria[94]and there is archaeological and historical evidence for the production ofcalamine brassin Germany[83]andthe Low Countries,[95]areas rich incalamineore.

These places would remain important centres of brass making throughout theMiddle Agesperiod,[96]especiallyDinant.Brass objects are still collectively known asdinanderiein French. Thebaptismal font at St Bartholomew's Church, Liègein modernBelgium(before 1117) is an outstanding masterpiece ofRomanesquebrass casting, though also often described as bronze. The metal of the early 12th-centuryGloucester Candlestickis unusual even by medieval standards in being a mixture of copper, zinc, tin, lead,nickel,iron,antimonyandarsenicwith an unusually large amount ofsilver,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.[97]Lattenis a term for medieval alloys of uncertain and often variable composition often covering decorative borders and similar objects cut from sheet metal, whether of brass or bronze. Especially inTibetan art,analysis of some objects shows very different compositions from different ends of a large piece.Aquamanileswere typically made in brass in both the European and Islamic worlds.

BrassaquamanilefromLower Saxony,Germany, c. 1250

The cementation process continued to be used but literary sources from both Europe and theIslamic worldseem to describe variants of a higher temperature liquid process which took place in open-topped crucibles.[98]Islamic cementation seems to have used zinc oxide known astutiyaortuttyrather than zinc ores for brass-making, resulting in a metal with lowerironimpurities.[99]A number of Islamic writers and the 13th centuryItalianMarco Polodescribe how this was obtained bysublimationfrom zinc ores andcondensedontoclayor iron bars, archaeological examples of which have been identified atKushin Iran.[100]It could then be used for brass making or medicinal purposes. In 10th centuryYemenal-Hamdanidescribed how spreadingal-iglimiya,probably zinc oxide, onto the surface of molten copper produced tutiya vapor which then reacted with the metal.[101]The 13th century Iranian writeral-Kashanidescribes a more complex process wherebytutiyawas mixed withraisinsand gently roasted before being added to the surface of the molten metal. A temporary lid was added at this point presumably to minimize the escape of zinc vapor.[102]

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 byAlbertus Magnusin the 13th century suggests influence from Islamic technology.[103]The 12th centuryGermanmonkTheophilusdescribed how preheated crucibles were one sixth filled with powdered calamine andcharcoalthen topped up with copper and charcoal before being melted, stirred then filled again. The final product wascast,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 beabsorbed.[104]Albertus Magnus noted that the "power" of both calamine and tutty couldevaporateand described how the addition of powderedglasscould create a film to bind it to the metal.[105] German brass making crucibles are known fromDortmunddating to the 10th century AD and fromSoestandSchwerteinWestphaliadating to around the 13th century confirm Theophilus' account, as they are open-topped, althoughceramicdiscs from Soest may have served as loose lids which may have been used to reduce zincevaporation,and have slag on the interior resulting from a liquid process.[106]

Africa

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12th century "Bronze Head from Ife",actually of" heavily leaded zinc-brass "

Some of the most famous objects inAfrican artare thelost waxcastings of West Africa, mostly from what is nowNigeria,produced first by theKingdom of Ifeand then theBenin Empire.Though normally described as "bronzes", theBenin Bronzes,now mostly in theBritish Museumand other Western collections, and the large portrait heads such as theBronze Head from Ifeof "heavily leaded zinc-brass" and theBronze Head of Queen Idia,both also British Museum, are better described as brass, though of variable compositions.[107]Work in brass or bronze continued to be important inBenin artand other West African traditions such asAkan goldweights,where the metal was regarded as a more valuable material than in Europe.

Renaissance and post-medieval Europe

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TheRenaissancesaw 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 atZwickauin Germany.[108]These large crucibles were capable of producing c.20 kg of brass.[109]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.[110]The crucible lids had small holes which were blocked with clay plugs near the end of the process presumably to maximize zincabsorptionin the final stages.[111]Triangular crucibles were then used to melt the brass forcasting.[112]

16th-century technical writers such asBiringuccio,ErckerandAgricoladescribed 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.[113]Zinc metal was also becoming more commonplace. By 1513 metallic zincingotsfrom India and China were arriving inLondonand pellets of zinc condensed infurnaceflues at theRammelsbergin Germany were exploited for cementation brass making from around 1550.[114]

Eventually it was discovered that metallic zinc could bealloyedwith copper to make brass, a process known as speltering,[115]and by 1657 the German chemistJohann Glauberhad recognized that calamine was "nothing else but unmeltable zinc" and that zinc was a "half ripe metal".[116]However some earlier high zinc, low iron brasses such as the 1530 Wightman brass memorialplaquefrom England may have been made by alloying copper withzincand include traces ofcadmiumsimilar to those found in some zinc ingots from China.[115]

However, the cementation process was not abandoned, and as late as the early 19th century there are descriptions ofsolid-statecementation in a domed furnace at around 900–950 °C and lasting up to 10 hours.[117]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 wares such as pots.[118]By 1559 the Germany city ofAachenalone was capable of producing 300,000cwtof brass per year.[118]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 coppersmeltedin the newcoalfiredreverberatory furnace.[119]In 1723Bristolbrass maker Nehemiah Champion patented the use ofgranulatedcopper, produced by pouring molten metal into cold water.[120]This increased thesurface areaof the copper helping it react and zinc contents of up to 33% wt were reported using this new technique.[121]

In 1738 Nehemiah's sonWilliam Championpatented a technique for the first industrial scaledistillationof metallic zinc known asdistillation per descencumor "the English process".[122][123]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 asscientific instruments,clocks,brassbuttonsandcostume jewelry.[124]However Champion continued to use the cheaper calamine cementation method to produce lower-zinc brass[124]and the archaeological remains of bee-hive shaped cementation furnaces have been identified at his works atWarmley.[125]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[126]as well as demand forcorrosion-resistant high zinc alloys increased the popularity of speltering and as a result cementation was largely abandoned by the mid-19th century.[127]

See also

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Citations

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  4. ^"copper alloy (Scope note)".British Museum.The term copper alloy should be searched for full retrievals on objects made of bronze or brass. This is because bronze and brass have at times been used interchangeably in the old documentation, and copper alloy is the Broad Term of both. In addition, the public may refer to certain collections by their popular name, such as 'TheBenin Bronzes' most of which are actually made of brass.
  5. ^"Hand Tools – Non-sparking tools".Canadian Center for Occupational Health and Safety.1 December 2017.Retrieved30 April2022.
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  8. ^Frederick James Camm (1949).Newnes Engineer's Reference Book.George Newnes. p. 594.
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General references

edit
  • Bayley, J. (1990). "The Production of Brass in Antiquity with Particular Reference to Roman Britain". In Craddock, P. T. (ed.).2000 Years of Zinc and Brass.London: British Museum.
  • Craddock, P. T. and Eckstein, K (2003). "Production of Brass in Antiquity by Direct Reduction". In Craddock, P. T. and Lang, J. (eds.).Mining and Metal Production Through the Ages.London: British Museum.
  • Day, J. (1990). "Brass and Zinc in Europe from the Middle Ages until the 19th century". In Craddock, P. T. (ed.).2000 Years of Zinc and Brass.London: British Museum.
  • Day, J. (1991). "Copper, Zinc and Brass Production". In Day, J. and Tylecote, R. F. (eds.).The Industrial Revolution in Metals.London: The Institute of Metals.
  • Martinon Torres, M.; Rehren, T. (2002). "Agricola and Zwickau: theory and practice of Renaissance brass production in SE Germany".Historical Metallurgy.36(2): 95–111.
  • Rehren, T. and Martinon Torres, M. (2008) "Naturam ars imitate: European brassmaking between craft and science". In Martinon-Torres, M. and Rehren, T. (eds.).Archaeology, History and Science: Integrating Approaches to Ancient Material.Left Coast Press.
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