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Wrought iron

Wrought iron

Overview
Wrought iron is an iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

 with a very low carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...


content, in comparison to steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

, and has fibrous inclusions
Inclusion (mineral)
In mineralogy, an inclusion is any material that is trapped inside a mineral during its formation.In gemology, an inclusion is a characteristic enclosed within a gemstone, or reaching its surface from the interior....

, known as slag
Slag
Slag is a partially vitreous by-product of smelting ore to separate the metal fraction from the unwanted fraction. It can usually be considered to be a mixture of metal oxides and silicon dioxide. However, slags can contain metal sulfides and metal atoms in the elemental form...

. This is what gives it a "grain" resembling wood, which is visible when it is etched or bent to the point of failure. Wrought iron is tough, malleable, ductile and easily welded
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...

. Historically, it was known as "commercially pure iron"; however, it no longer qualifies because current standards for commercially pure iron require a carbon content of less than 0.008 wt%.

Before the development of effective methods of steelmaking
Steelmaking
Steelmaking is the second step in producing steel from iron ore. In this stage, impurities such as sulfur, phosphorus, and excess carbon are removed from the raw iron, and alloying elements such as manganese, nickel, chromium and vanadium are added to produce the exact steel required.-Older...

 and the availability of large quantities of steel, wrought iron was the most common form of malleable iron.
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Encyclopedia
Wrought iron is an iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

 with a very low carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...


content, in comparison to steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

, and has fibrous inclusions
Inclusion (mineral)
In mineralogy, an inclusion is any material that is trapped inside a mineral during its formation.In gemology, an inclusion is a characteristic enclosed within a gemstone, or reaching its surface from the interior....

, known as slag
Slag
Slag is a partially vitreous by-product of smelting ore to separate the metal fraction from the unwanted fraction. It can usually be considered to be a mixture of metal oxides and silicon dioxide. However, slags can contain metal sulfides and metal atoms in the elemental form...

. This is what gives it a "grain" resembling wood, which is visible when it is etched or bent to the point of failure. Wrought iron is tough, malleable, ductile and easily welded
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...

. Historically, it was known as "commercially pure iron"; however, it no longer qualifies because current standards for commercially pure iron require a carbon content of less than 0.008 wt%.

Before the development of effective methods of steelmaking
Steelmaking
Steelmaking is the second step in producing steel from iron ore. In this stage, impurities such as sulfur, phosphorus, and excess carbon are removed from the raw iron, and alloying elements such as manganese, nickel, chromium and vanadium are added to produce the exact steel required.-Older...

 and the availability of large quantities of steel, wrought iron was the most common form of malleable iron. A modest amount of wrought iron was used as a raw material for manufacturing of steel, which was mainly to produce sword
Sword
A sword is a bladed weapon used primarily for cutting or thrusting. The precise definition of the term varies with the historical epoch or the geographical region under consideration...

s, cutlery
Cutlery
Cutlery refers to any hand implement used in preparing, serving, and especially eating food in the Western world. It is more usually known as silverware or flatware in the United States, where cutlery can have the more specific meaning of knives and other cutting instruments. This is probably the...

, chisels, axes and other edge tools as well as springs and files. Demand for wrought iron reached its peak in the 1860s with the adaptation of ironclad warship
Ironclad warship
An ironclad was a steam-propelled warship in the early part of the second half of the 19th century, protected by iron or steel armor plates. The ironclad was developed as a result of the vulnerability of wooden warships to explosive or incendiary shells. The first ironclad battleship, La Gloire,...

s and railways, but then declined as mild steel became more available.

Before they came to be made of mild steel, items produced from wrought iron included rivets, nails, wire
Wire
A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...

, chains, railway couplings
Coupling (railway)
A coupling is a mechanism for connecting rolling stock in a train. The design of the coupler is standard, and is almost as important as the railway gauge, since flexibility and convenience are maximised if all rolling stock can be coupled together.The equipment that connects the couplings to the...

, water
Water pipe
Water pipes are pipes or tubes, frequently made of polyvinyl chloride , ductile iron, steel, cast iron, polypropylene, polyethylene, or copper, that carry pressurized and treated fresh water to buildings , as well as inside the building.-History:For many centuries, lead was the favoured material...

 and steam pipes, nuts
Nut (hardware)
A nut is a type of hardware fastener with a threaded hole. Nuts are almost always used opposite a mating bolt to fasten a stack of parts together. The two partners are kept together by a combination of their threads' friction, a slight stretch of the bolt, and compression of the parts...

, bolts
Screw
A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...

, horseshoe
Horseshoe
A horseshoe, is a fabricated product, normally made of metal, although sometimes made partially or wholly of modern synthetic materials, designed to protect a horse's hoof from wear and tear. Shoes are attached on the palmar surface of the hooves, usually nailed through the insensitive hoof wall...

s, handrail
Handrail
A handrail is a rail that is designed to be grasped by the hand so as to provide stability or support. Handrails are commonly used while ascending or descending stairways and escalators in order to prevent injurious falls. Other applications include bathroom handrails—which help to prevent falls on...

s, straps for timber roof trusses, and ornamental ironwork.

Wrought iron is no longer produced on a commercial scale. Many products described as wrought iron, such as guard rail
Guard rail
Guard rail or guardrail, sometimes referred to as guide rail or railing, is a system designed to keep people or vehicles from straying into dangerous or off-limits areas...

s, garden furniture
Garden furniture
Garden furniture, also called patio furniture and outdoor furniture, is a type of furniture specifically designed for outdoor use. It is typically made of weather resistant materials...

 and gate
Gate
A gate is a point of entry to a space enclosed by walls, or a moderately sized opening in a fence. Gates may prevent or control entry or exit, or they may be merely decorative. Other terms for gate include yett and port...

s, are made of mild steel. They retain that description because they are wrought (worked) by hand.

Terminology


The word "wrought" is an archaic past tense form of the verb "to work," and so "wrought iron" literally means "worked iron". Wrought iron is a general term for the commodity, but is also used more specifically for finished iron goods, as manufactured by a blacksmith
Blacksmith
A blacksmith is a person who creates objects from wrought iron or steel by forging the metal; that is, by using tools to hammer, bend, and cut...

 or other smith. It was used in this narrower sense in British
Great Britain
Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...

 Customs
Customs
Customs is an authority or agency in a country responsible for collecting and safeguarding customs duties and for controlling the flow of goods including animals, transports, personal effects and hazardous items in and out of a country...

 records, such manufactured iron being subject to a higher rate of duty than what might be called "unwrought" iron. Cast iron
Cast iron
Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...

, unlike wrought iron, is brittle and cannot be worked either hot or cold. Cast iron can break if struck with a hammer.

In the 17th, 18th and 19th centuries, wrought iron went by a wide variety of terms according to its form, origin, or quality.

While the bloomery
Bloomery
A bloomery is a type of furnace once widely used for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. A bloomery's product is a porous mass of iron and slag called a bloom. This mix of slag and iron in the bloom is termed sponge iron, which...

 process produced wrought iron directly from ore, cast iron
Cast iron
Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...

 or pig iron
Pig iron
Pig iron is the intermediate product of smelting iron ore with a high-carbon fuel such as coke, usually with limestone as a flux. Charcoal and anthracite have also been used as fuel...

 were the starting materials used in the finery forge
Finery forge
Iron tapped from the blast furnace is pig iron, and contains significant amounts of carbon and silicon. To produce malleable wrought iron, it needs to undergo a further process. In the early modern period, this was carried out in a finery forge....

 and puddling furnace. Pig iron and cast iron have high carbon content which make them very brittle, but they have a lower melting point than iron or steel. Cast and especially pig iron have excess slag which must be at least partially removed to produce quality wrought iron.

For several years after the introduction of Bessemer and open hearth steel there were different opinions as to what differentiated iron from steel, some thinking it was the chemical composition and others believing it was whether the iron heated sufficiently to melt and "fuse". Fusion eventually became generally accepted as relatively more important than composition below a given low carbon concentration. Another difference is that steel can be hardened by heat treating.

Form or shapes

  • Bar iron—iron in bars, which are the usual product of the finery forge
    Finery forge
    Iron tapped from the blast furnace is pig iron, and contains significant amounts of carbon and silicon. To produce malleable wrought iron, it needs to undergo a further process. In the early modern period, this was carried out in a finery forge....

    , but not necessarily made by that process. These might be square or flat, and flat bars might be narrow or broad.
  • Rod iron—cut from flat bar iron in a slitting mill
    Slitting mill
    The slitting mill was a watermill for slitting bars of iron into rods. The rods then were passed to nailers who made the rods into nails, by giving them a point and head....

     to provide the raw material for nails.
  • Hoop iron—suitable for the hoops of barrels, made by passing rod iron through flat rolls.
  • Plate iron—sheets of iron suitable for use as boiler
    Boiler
    A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Materials:...

     plate.
  • Blackplate—sheets of iron, perhaps thinner than plate iron, from the black rolling stage of tinplate production.
  • Voyage iron—narrow flat bar iron, made or cut into bars of a particular weight, a commodity for sale in Africa
    Africa
    Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

     for the Atlantic slave trade
    Atlantic slave trade
    The Atlantic slave trade, also known as the trans-atlantic slave trade, refers to the trade in slaves that took place across the Atlantic ocean from the sixteenth through to the nineteenth centuries...

    . The number of bars per ton gradually increased from 70 per ton in the 1660s to 75–80 per ton in 1685 and "near 92 to the ton" in 1731.

Origin

  • Charcoal Iron — Until the end of the eighteenth century, wrought iron was smelted from ore using charcoal, by the bloomery
    Bloomery
    A bloomery is a type of furnace once widely used for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. A bloomery's product is a porous mass of iron and slag called a bloom. This mix of slag and iron in the bloom is termed sponge iron, which...

     process. Wrought iron was also produced from pig iron using a finery forge
    Finery forge
    Iron tapped from the blast furnace is pig iron, and contains significant amounts of carbon and silicon. To produce malleable wrought iron, it needs to undergo a further process. In the early modern period, this was carried out in a finery forge....

     or from the industrial revolution in a Lancashire hearth
    Lancashire hearth
    The Lancashire hearth was used to fine pig iron, removing carbon to produce wrought iron.-Origins:Until the early 19th century, the usual method of producing wrought iron involved a charcoal-fired finery in a finery forge. By the beginning of the century, this was an obsolescent process, which was...

    . The resulting metal was highly variable, both in chemistry and slag content.
  • Puddled Iron — By the late eighteenth century there was a demand from pig iron, an impure form of cast iron
    Cast iron
    Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...

    , to be refined with coal as fuel. This resulted in ‘puddled iron’, which contained less slag, sulfur and had a very low carbon content. The iron was kept separate from the fire in a reverberatory furnace
    Reverberatory furnace
    A reverberatory furnace is a metallurgical or process furnace that isolates the material being processed from contact with the fuel, but not from contact with combustion gases...

     to prevent harmful sulphur and phosphorus from entering the finished iron. Puddled iron, although also variable in its properties, was generally more consistent than the earlier irons, and the method lent itself to the production of far greater quantities. By 1876, annual production of puddled iron in the UK alone was over 4 million tons.
  • Oregrounds iron
    Oregrounds iron
    Oregrounds iron was a grade of iron that was regarded as the best grade available in 18th century England. The term was derived from the small Swedish city of Öregrund. The process to create it is known as the Walloon method....

    —a particularly pure grade of bar iron made ultimately from iron ore from the Dannemora
    Dannemora
    Dannemora may refer to:* Dannemora , New York* Dannemora Prison, colloquial name for the Clinton Correctional Facility in the village of Dannemora* Dannemora , New York* Dannemora, Sweden, a village with 200 inhabitants...

     mine in Sweden
    Sweden
    Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

    . Its most important use was as the raw material for the cementation process
    Cementation process
    The cementation process is an obsolete technique 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 steelmaking.
  • Danks iron — originally iron imported to Great Britain from Gdańsk
    Gdansk
    Gdańsk is a Polish city on the Baltic coast, at the centre of the country's fourth-largest metropolitan area.The city lies on the southern edge of Gdańsk Bay , in a conurbation with the city of Gdynia, spa town of Sopot, and suburban communities, which together form a metropolitan area called the...

    , but in the 18th century more probably the kind of iron (from eastern Sweden) that once came from Gdańsk.
  • Forest iron — iron from the English Forest of Dean
    Forest of Dean
    The Forest of Dean is a geographical, historical and cultural region in the western part of the county of Gloucestershire, England. The forest is a roughly triangular plateau bounded by the River Wye to the west and north, the River Severn to the south, and the City of Gloucester to the east.The...

    , where haematite
    Hematite
    Hematite, also spelled as haematite, is the mineral form of iron oxide , one of several iron oxides. Hematite crystallizes in the rhombohedral system, and it has the same crystal structure as ilmenite and corundum...

     ore enabled tough iron to be produced.
  • Lukes iron — iron imported from Liège, whose Dutch name is "Luik."
  • Ames iron or amys iron — another variety of iron imported to England
    England
    England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

     from northern Europe. Its origin has been suggested to be Amiens
    Amiens
    Amiens is a city and commune in northern France, north of Paris and south-west of Lille. It is the capital of the Somme department in Picardy...

    , but it seems to have been imported from Flanders
    Flanders
    Flanders is the community of the Flemings but also one of the institutions in Belgium, and a geographical region located in parts of present-day Belgium, France and the Netherlands. "Flanders" can also refer to the northern part of Belgium that contains Brussels, Bruges, Ghent and Antwerp...

     in the 15th century and Holland later, suggesting an origin in the Rhine valley. Its origins remain controversial.
  • Botolf iron or Boutall iron — from Bytów
    Bytów
    Bytów is a town in the Middle Pomerania region of northern Poland in the Bytów Lakeland with 16,888 inhabitants . Previously in Słupsk Voivodeship , it is the capital of Bytów County in Pomeranian Voivodeship .-History:...

     (Polish Pomerania
    Pomerania
    Pomerania is a historical region on the south shore of the Baltic Sea. Divided between Germany and Poland, it stretches roughly from the Recknitz River near Stralsund in the West, via the Oder River delta near Szczecin, to the mouth of the Vistula River near Gdańsk in the East...

    ) or Bytom
    Bytom
    Bytom is a city in Silesia in southern Poland, near Katowice. The central-western district of the Upper Silesian Metropolitan Union - metropolis with the population of 2 millions. Bytom is located in the Silesian Highlands, on the Bytomka river .The city belongs to the Silesian Voivodeship since...

     (Polish Silesia
    Silesia
    Silesia is a historical region of Central Europe located mostly in Poland, with smaller parts also in the Czech Republic, and Germany.Silesia is rich in mineral and natural resources, and includes several important industrial areas. Silesia's largest city and historical capital is Wrocław...

    ).
  • Sable iron (or Old Sable) — iron bearing the mark (a sable
    Sable
    The sable is a species of marten which inhabits forest environments, primarily in Russia from the Ural Mountains throughout Siberia, in northern Mongolia and China and on Hokkaidō in Japan. Its range in the wild originally extended through European Russia to Poland and Scandinavia...

    ) of the Demidov
    Demidov
    The Demidov family, also Demidoff, were an influential Russian merchant, industrialist and later chivalry family, possibly second only to the Tsar himself in wealth during the late 18th and early 19th centuries.-History:...

     family of Russia
    Russia
    Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

    n ironmaster
    Ironmaster
    An ironmaster is the manager – and usually owner – of a forge or blast furnace for the processing of iron. It is a term mainly associated with the period of the Industrial Revolution, especially in Great Britain....

    s, one of the better brands of Russian iron.

Quality


Tough iron : Tough iron, also spelled "tuf", is not brittle and strong enough to be used for tools.
Blend iron : Blend iron is made using a mixture of different types of pig iron
Pig iron
Pig iron is the intermediate product of smelting iron ore with a high-carbon fuel such as coke, usually with limestone as a flux. Charcoal and anthracite have also been used as fuel...

.
Best iron : Best iron is iron that had gone through several stages of piling and rolling, might reach the stage of being best iron (in the 19th century).
Marked bar iron : This is iron made by members of the Marked Bar Association and marked with the maker's brand mark as a sign of its quality.

Defects


Wrought iron is redshort if it contains sulfur in excess quantity. It has sufficient tenacity when cold, but cracks when bent or finished at a red heat. It is therefore useless for welding or forging.

Coldshort iron, also known as coldshear, colshire or bloodshot, contains excessive phosphorus. It is very brittle when it is cold. It cracks if bent. It may, however, be worked at high temperature. Historically, coldshort iron was considered good enough for nails
Nail (engineering)
In woodworking and construction, a nail is a pin-shaped, sharp object of hard metal or alloy used as a fastener. Formerly wrought iron, today's nails are typically made of steel, often dipped or coated to prevent corrosion in harsh conditions or improve adhesion...

.

Nevertheless, phosphorus is not necessarily detrimental to iron. Ancient Indian smiths did not add lime to their furnaces; the absence of CaO in the slag, and the deliberate use of wood with high phosphorus content during the smelting, induces a higher P content (> 0.1%, average 0.25%) than in modern iron. Analysis of the Iron Pillar of Delhi gives 0.10% in the slags for .18% in the iron itself, for a total P content of 0.28% in the metal and accounts for much of its corrosion resistance. Furthermore, the presence of phosphorus (without carbon) produces a ductile iron suitable for wire drawing
Wire drawing
Wire drawing is a metalworking process used to reduce the cross-section of a wire by pulling the wire through a single, or series of, drawing die. There are many applications for wire drawing, including electrical wiring, cables, tension-loaded structural components, springs, paper clips, spokes...

, for piano
Piano
The piano is a musical instrument played by means of a keyboard. It is one of the most popular instruments in the world. Widely used in classical and jazz music for solo performances, ensemble use, chamber music and accompaniment, the piano is also very popular as an aid to composing and rehearsal...

 wire.

History


Wrought iron has been used for many centuries, and is the "iron" that is referred to throughout western history. The other form of iron, cast iron
Cast iron
Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...

, was not introduced into Western Europe until the 15th century; even then, due to its brittleness, it could only be used for a limited number of purposes. Throughout much of the Middle Ages iron was produced by the direct reduction of ore in manually operated bloomeries
Bloomery
A bloomery is a type of furnace once widely used for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. A bloomery's product is a porous mass of iron and slag called a bloom. This mix of slag and iron in the bloom is termed sponge iron, which...

, although waterpower had begun to be employed by 1104.

The raw material produced by all indirect processes is pig iron. It has a high carbon content and as a consequence it is brittle and could not be used to make hardware. The osmond process was the first of the indirect processes, developed by 1203, but bloomery production continued in many places. The process depended on the development of the blast furnace, of which medieval examples have been discovered at Lapphyttan
Lapphyttan
Lapphyttan in Norberg Municipality, Sweden, may be regarded as the type site for the Medieval Blast Furnace. Its date is probably between 1150 and 1350. It produced cast iron, which was then fined to make balls of iron known as osmonds. Osmonds occur in English Customs records in the 1250s and...

, Sweden and in Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

.

The bloomery and osmond processes were gradually replaced from the 15th century by finery processes, of which there were two versions, the German and Walloon. They were in turn replaced from the late 18th century by puddling
Puddling (metallurgy)
Puddling was an Industrial Revolution means of making iron and steel. In the original puddling technique, molten iron in a reverberatory furnace was stirred with rods, which were consumed in the process...

, with certain variants such as the Swedish Lancashire process. These too are now obsolete, and wrought iron is no longer manufactured commercially.

Bloomery process



Wrought iron was originally produced by a variety of smelting processes, all described today as bloomeries. Different forms of bloomery were used at different places and times. The bloomery was charged with charcoal
Charcoal
Charcoal is the dark grey residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood or other substances in the absence of oxygen...

 and iron ore and then lit. Air was blown in through a tuyere
Tuyere
A tuyere, also can be spelled as tuyère, is a tube, nozzle or pipe through which air is blown into a furnace or hearth.Air or oxygen is injected into a hearth under pressure from bellows or a blast engine or other devices...

 to heat the bloomery to a temperature somewhat below the melting point of iron. In the course of the smelt, slag would melt and run out, and carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

 from the charcoal would reduce the ore to iron, which formed a spongy mass. The iron remained in the solid state. If the bloomery was allowed to become hot enough to melt the iron, carbon would dissolve into it and form pig or cast iron, but that was not the intention.

After smelting was complete, the bloom was removed, and the process could then be started again. It was thus a batch process, rather than a continuous one. The spongy mass contained iron and also silicate (slag) from the ore; this was iron bloom from which the technique got its name. The bloom had to be forged mechanically to consolidate it and shape it into a bar, expelling slag in the process.

During the Middle Ages
Middle Ages
The Middle Ages is a periodization of European history from the 5th century to the 15th century. The Middle Ages follows the fall of the Western Roman Empire in 476 and precedes the Early Modern Era. It is the middle period of a three-period division of Western history: Classic, Medieval and Modern...

, water-power was applied to the process, probably initially for powering bellows, and only later to hammers for forging the blooms. However, while it is certain that water-power was used, the details of this remain uncertain. This was the culmination of the direct process of ironmaking. It survived in Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...

 and southern France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

 as Catalan Forges to the mid 19th century, in Austria
Austria
Austria , officially the Republic of Austria , is a landlocked country of roughly 8.4 million people in Central Europe. It is bordered by the Czech Republic and Germany to the north, Slovakia and Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the...

 as the stuckofen to 1775, and near Garstang
Garstang
Garstang is a town and civil parish within the Wyre borough of Lancashire, England. It is ten miles north-northwest of the city of Preston and eleven miles south of Lancaster, and had a total resident population of 4,074 in 2001....

 in England until about 1770; it was still in use with hot blast
Hot blast
Hot blast refers to the preheating of air blown into a blast furnace or other metallurgical process. This has the result of considerably reducing the fuel consumed in the process...

 in New York State in the 1880s.

Osmond process



Osmond iron
Osmond iron
Osmond iron was wrought iron made by a particular process. This is associated with the first European production of cast iron in furnaces such as Lapphyttan in Sweden....

 consisted of balls of wrought iron, produced by melting pig iron and catching the droplets on a staff, which was spun in front of a blast of air so as to expose as much of it as possible to the air and oxidise its carbon content. The resultant ball was often forged into bar iron in a hammer mill.

Finery process



In the 15th century, the blast furnace spread into what is now Belgium
Belgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...

 and was improved. From there, it spread via the Pays de Bray
Pays de Bray
The Pays de Bray is a small natural region of France situated to the north-east of Rouen, straddling the French départements of the Seine-Maritime and Oise...

 on the boundary of Normandy
Normandy
Normandy is a geographical region corresponding to the former Duchy of Normandy. It is in France.The continental territory covers 30,627 km² and forms the preponderant part of Normandy and roughly 5% of the territory of France. It is divided for administrative purposes into two régions:...

 and then to the Weald
Weald
The Weald is the name given to an area in South East England situated between the parallel chalk escarpments of the North and the South Downs. It should be regarded as three separate parts: the sandstone "High Weald" in the centre; the clay "Low Weald" periphery; and the Greensand Ridge which...

 in England. With it, the finery forge spread. These remelted the pig iron and (in effect) burnt out the carbon, producing a bloom, which was then forged into a bar iron. If rod iron was required, a slitting mill was used.

The finery process existed in two slightly different forms. In Great Britain, France, and parts of Sweden, only the Walloon process was used. This employed two different hearths, a finery hearth for fining the iron and a chafery hearth for reheating it in the course of drawing the bloom out into a bar. The finery always burnt charcoal, but the chafery could be fired with mineral coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

, since its impurities would not harm the iron when it was in the solid state. On the other hand, the German process, used in Germany, Russia, and most of Sweden used a single hearth for all stages.

The introduction of coke
Coke (fuel)
Coke is the solid carbonaceous material derived from destructive distillation of low-ash, low-sulfur bituminous coal. Cokes from coal are grey, hard, and porous. While coke can be formed naturally, the commonly used form is man-made.- History :...

 for use in the blast furnace by Abraham Darby
Abraham Darby I
Abraham Darby I was the first, and most famous, of three generations with that name in an English Quaker family that played an important role in the Industrial Revolution. He developed a method of producing pig iron in a blast furnace fuelled by coke rather than charcoal...

 in 1709 (or perhaps others a little earlier) initially had little effect on wrought iron production. Only in the 1750s was coke pig iron used on any significant scale as the feedstock of finery forges. However, charcoal continued to be the fuel for the finery.

Potting and stamping


From the late 1750s, ironmasters began to develop processes for making bar iron without charcoal. There were a number of patented processes for this, which are referred to today as potting and stamping
Potting and stamping
Potting and stamping is a modern name for one of the 18th century processes for refining pig iron without the use of charcoal.-Inventors:The process was devised by Charles Wood of Lowmill, Egremont in Cumberland and his brother John Wood of Wednesbury and patented by them...

. The earliest were developed by John Wood of Wednesbury
Wednesbury
Wednesbury is a market town in England's Black Country, part of the Sandwell metropolitan borough in West Midlands, near the source of the River Tame. Similarly to the word Wednesday, it is pronounced .-Pre-Medieval and Medieval times:...

 and his brother Charles Wood of Low Mill at Egremont
Egremont, Cumbria
Egremont is a market town and civil parish in the Borough of Copeland in Cumbria, England, south of Whitehaven and on the River Ehen. The town, which lies at the foot of Uldale Valley and Dent Fell, was historically within Cumberland and has a long industrial heritage including dyeing, weaving and...

, patented in 1763. Another was developed for the Coalbrookdale
Coalbrookdale
Coalbrookdale is a village in the Ironbridge Gorge in Shropshire, England, containing a settlement of great significance in the history of iron ore smelting. This is where iron ore was first smelted by Abraham Darby using easily mined "coking coal". The coal was drawn from drift mines in the sides...

 Company by the Cranage brothers. Another important one was that of John Wright and Joseph Jesson of West Bromwich
West Bromwich
West Bromwich is a town within the Metropolitan Borough of Sandwell, in the West Midlands, England. It is north west of Birmingham lying on the A41 London-to-Birkenhead road. West Bromwich is part of the Black Country...

.

Puddling process



A number of processes for making wrought iron without charcoal were devised as the Industrial Revolution
Industrial Revolution
The Industrial Revolution was a period from the 18th to the 19th century where major changes in agriculture, manufacturing, mining, transportation, and technology had a profound effect on the social, economic and cultural conditions of the times...

 began during the latter half of the 18th century. The most successful of these was puddling, using a puddling furnace (a variety of the reverberatory furnace
Reverberatory furnace
A reverberatory furnace is a metallurgical or process furnace that isolates the material being processed from contact with the fuel, but not from contact with combustion gases...

). This was invented by Henry Cort
Henry Cort
Henry Cort was an English ironmaster. During the Industrial Revolution in England, Cort began refining iron from pig iron to wrought iron using innovative production systems. In 1783 he patented the puddling process for refining iron ore...

 in 1784. It was later improved by others including Joseph Hall
Joseph Hall (metallurgist)
Joseph Hall 1789 – 1862, the inventor of 'Wet Puddling', was born in 1789 and apprenticed in 1806 as a puddler to use Henry Cort's puddling process. He tried adding old iron to the charge of the puddling furnace and later puddler's bosh cinder to the charge. This caused the charge to boil...

. In this type of furnace, the metal does not come into contact with the fuel, and so is not contaminated by impurities in it. The flame from the fire is reverberated or sent back down onto the metal on the fire bridge of the furnace.

Unless the raw material used is white cast iron, the pig iron or other raw material first had to be refined into refined iron or finers metal. This would be done in a refinery where raw coal is used to remove silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

 and convert carbon from a graphitic form to a combined form.

This metal was placed into the hearth of the puddling furnace where it was melted. The hearth was lined with oxidizing agents such as haematite and iron oxide. This mixture is subjected to a strong current of air and stirred with long bars, called puddling bars or rabbles, through working doors. The air, stirring, and "boiling" action of the metal help the oxidizing agents to oxidize the impurities and carbon out of the pig iron to their maximum capability. As the impurities oxidize, they form a molten slag while the retaining iron particles solidifiy into spongy wrought iron balls, called puddle balls.

Shingling


There is still some slag left in the puddle balls, so while they are still hot they must be shingled to remove the remaining slag and cinder. It may be achieved by forging the balls under a power hammer, or by squeezing the bloom in a machine. The material obtained at the end of shingling is known as bloom and it is still red-hot. The blooms are not useful in this form, so they must be rolled into a final product.

Sometimes European ironworks would skip this step completely and roll the puddle balls. The only drawback to this is that the edges of the rough bars are not as well compressed. When the rough bar is reheated, the edges may separate and be lost into the furnace.

Rolling



The bloom is passed through grooved rollers and flat bars were produced. These bars of wrought iron were of poor quality, called muck bars or puddle bars. To improve the quality of wrought iron, these bars were cut up, piled and tied together by wires, a process known as faggoting or piling. They were then reheated and rolled again in merchant rolls. This process may be repeated several times to get wrought iron of desired quality. Wrought iron that has been rolled multiple times is called merchant bar or merchant iron.

Lancashire process



The advantage of puddling was that it used coal, not charcoal as fuel. However this was little advantage in Sweden, which lacks coal. Gustaf Ekman observed charcoal fineries at Ulverston
Ulverston
Ulverston is a market town and civil parish in the South Lakeland district of Cumbria in north-west England. Historically part of Lancashire, the town is located in the Furness area, close to the Lake District, and just north of Morecambe Bay....

e, which were quite different from any in Sweden. After his return to Sweden in the 1830s, he experimented and developed a process similar to puddling but using forewood and charcoal, which was widely adopted in the Bergslagen
Bergslagen
Bergslagen is a historically, culturally, and linguistically distinct mining district located north of Lake Mälaren in northern Svealand, Sweden. In Bergslagen mining and metallurgic industry have been important since the Middle Ages...

 in the following decades.

The Aston process


In 1925, James Aston of the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 developed a process for manufacturing wrought iron quickly and economically. It involves taking molten steel from a Bessemer converter
Bessemer process
The Bessemer process was the first inexpensive industrial process for the mass-production of steel from molten pig iron. The process is named after its inventor, Henry Bessemer, who took out a patent on the process in 1855. The process was independently discovered in 1851 by William Kelly...

 and pouring it into cooler liquid slag. The temperature of the steel is about 1500 °C and the liquid slag is maintained at approximately 1200 °C. The molten steel contains a large amount of dissolved gases so when the liquid steel hits the cooler surfaces of the liquid slag the gases are liberated. The molten steel then freezes to yield a spongy mass having a temperature of about 1370 °C. This spongy mass must then be finished by being shingled
Shingling (metallurgy)
Shingling was a stage in the production of bar iron or steel, in the finery and puddling processes. As with many ironmaking terms, this is derived from the French - cinglage....

 and rolled as described under puddling (above). Three to four tons can be converted per batch with this method.

Wrought iron as Pure Iron


Dr Gerry McDonnell in 2010 England, demonstrated by analysis that a wrought iron bloom, from a traditional smelt, could be worked into 99.7% pure iron with no evidence of carbon. It was found that the stringers common to other wrought irons were not present thus making it very malleable for the smith to work hot and cold. A commercial source of pure iron is available and is used by smiths as an alternative to traditional wrought iron and other new generation ferrous metals.

The end of wrought iron


Steel began to replace iron for rails as soon as Bessemer production began (ca. 1860s). Iron remained dominant for structural applications until the 1880s because of problems with brittle steel, caused by high carbon, excess phosphorous or excessive temperature during rolling or too rapid rolling. By 1890 steel had largely replaced iron for structural applications.

Sheet iron (Armco 99.97% pure iron) had good properties for use in appliances including being well suited for enameling and welding and being rust resistant.

In the 1960s the price of steel production was dropping due to recycling and even using the Aston process wrought iron production was a labor-intensive process. It has been estimated that the production of wrought iron costs approximately twice as much as the production of low carbon steel. In the United States the last plant closed in 1969. The last in Great Britain (and the world) was the Atlas Ironworks of Thomas Walmsley Ltd in Bolton
Bolton
Bolton is a town in Greater Manchester, in the North West of England. Close to the West Pennine Moors, it is north west of the city of Manchester. Bolton is surrounded by several smaller towns and villages which together form the Metropolitan Borough of Bolton, of which Bolton is the...

, which closed in 1973. Its equipment, of a type dating from the 1860s, was moved to the Blists Hill site
Blists Hill Victorian Town
Blists Hill is an open air museum, one of ten museums operated by the Ironbridge Gorge Museum Trust, built on a former industrial complex located in the Madeley area of Telford, Shropshire, England...

 of Ironbridge Gorge Museum
Ironbridge Gorge Museum Trust
Ironbridge Gorge Museum Trust is an industrial heritage organisation which runs ten museums and manages 35 historic sites within the Ironbridge Gorge in Shropshire, England, widely considered as the birthplace of the Industrial Revolution....

 for preservation. Some wrought iron is still being produced for heritage restoration purposes, but only by recycling scrap.

Properties


The slag inclusions, or stringers
Stringer (slag)
Stringers are filaments of slag left in wrought iron after the production process. In their correct proportions their presence is beneficial, as they help to control the ductility of the finished product, but when the proportion of slag is too high, or when the filaments run at right angles to the...

, in wrought iron give it properties not found in other forms of ferrous metal. There are approximately 250,000 inclusions per square inch. A fresh fracture shows a clear bluish color with a high silky luster and fibrous appearance.

Wrought iron lacks the carbon content necessary for hardening through heat treatment
Heat treatment
Heat treating is a group of industrial and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass...

, but in areas where steel was uncommon or unknown, tools were sometimes cold-worked (hence cold iron) in order to harden them. An advantage of its low carbon content is its excellent weldability. Furthermore, sheet wrought iron cannot bend as much as steel sheet metal (when cold worked). Wrought iron can be cast, however there is no engineering advantage as compared to cast iron; cast iron is much easier to produce and thus cheaper, so it is exclusively chosen over wrought iron.

Due to the variations in iron ore origin and iron manufacture, wrought iron can be inferior or superior in corrosion resistance compared to other iron alloys. There are many mechanisms behind this corrosion resistance. Chilton and Evans found that nickel enrichment bands reduce corrosion. They also found that in puddled and forged and piled the working over of the iron spread out copper, nickel and tin impurities, which produce electrochemical conditions that slow down corrosion. The slag inclusions have been shown to disperse corrosion in to an even film to resist pitting. Another study has shown that slag inclusions are pathways to corrosion. Other studies show that sulfur impurities in the wrought iron decrease corrosion resistance, but phosphorus increase corrosion resistance. Environments with a high concentration of chlorine ions also decreases wrought iron's corrosion resistance.

Wrought iron may be welded in the same manner as mild steel, but the presence of oxide or inclusions will give defective results.
The material has a rough surface so it can hold platings and coatings better. For instance, a galvanic zinc finish is approximately 25–40% thicker than the same finish on steel. In Table 1, the chemical composition of wrought iron is compared to that of pig iron and carbon steel. Although it appears that wrought iron and plain carbon steel have similar chemical compositions, this is deceiving. Most of the manganese, sulfur, phosphorus, and silicon are incorporated into the slag fibers present in the wrought iron, so wrought iron really is purer than plain carbon steel.
Table 1: Chemical composition comparison of pig iron, plain carbon steel, and wrought iron
Material Iron Carbon Manganese Sulfur Phosphorus Silicon
Pig iron 91–94 3.5–4.5 0.5–2.5 0.018–0.1 0.03–0.1 0.25–3.5
Carbon steel 98.1–99.5 0.07–1.3 0.3–1.0 0.02–0.06 0.002–0.1 0.005–0.5
Wrought iron 99–99.8 0.05–0.25 0.01–0.1 0.02–0.1 0.05–0.2 0.02–0.2
All units are percent weight

Table 2: Properties of wrought iron
Property Value
Ultimate tensile strength [psi (MPa)] 34,000–54,000 (234–372)
Ultimate compression strength [psi (MPa)] 34,000–54,000 (234–372)
Ultimate shear strength [psi (MPa)] 28,000–45,000 (193–310)
Yield point [psi (MPa)] 23,000–32,000 (159–221)
Modulus of elasticity (in tension) [psi (MPa)] 28,000,000 (193,100)
Melting point [°F (°C)] 2,800 (1,540)
Specific gravity 7.6–7.9
7.5–7.8


Amongst its other properties, wrought iron becomes soft at red heat
Red heat
The practice of using colours to determine the temperature of a piece of ferrous metal comes from blacksmithing. Long before thermometers were widely available it was necessary to know what state the metal was in for heat treating it and the only way to do this was to heat it up to a colour which...

, and can be easily forged
Forged
Forged is a book written by biblical scholar, Bart D. Ehrman which attempts to analyze the historical accuracy of the Christian Bible. The book posits that 11 or more books out of the 27 books of the Christian New Testament canon were written as certain types of forgeries related to the politics...

 and forge welded. It can be used to form temporary magnet
Magnet
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...

s, but cannot be magnetized permanently, and is ductile, malleable and tough
Toughness
In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing; Material toughness is defined as the amount of energy per volume that a material can absorb before rupturing...

.

The importance of ductility


For most purposes, ductility is a more important measure of the quality of wrought iron than tensile strength. In tensile testing, the best irons are able to undergo considerable elongation before failure. Higher tensile wrought iron is brittle.

Because of the large number of boiler explosions on steamboats, the U.S. Congress passed legislation in 1830 which approved funds for correcting the problem. The treasury awarded a $1500 contract to the Franklin Institute to conduct a study. As part of the study Walter R. Johnson and Benjamin Reeves conducted strength tests on various boiler iron using a tester they had built in 1832 based on the design of one by Lagerhjelm in Sweden. Unfortunately, because of the misunderstanding of tensile strength and ductility, this work did little to reduce failures.

The importance of ductility was recognized by some very early in the development of tube boilers, such as Thurston's comment:

‘If made of such good iron as the makers claimed to have put into them “which worked like lead,” they would, as also claimed, when ruptured, open by tearing, and discharge their contents without producing the usual disastrous consequences of a boiler explosion.’


By the late 19 th century when metallurgy was able to better understand what properties and processes made good iron, it was being displaced by steel.

Applications


Wrought iron furniture has a long history, dating back to Roman
Ancient Rome
Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....

 times. There are thirteenth century wrought iron gates in Westminster Abbey
Westminster Abbey
The Collegiate Church of St Peter at Westminster, popularly known as Westminster Abbey, is a large, mainly Gothic church, in the City of Westminster, London, United Kingdom, located just to the west of the Palace of Westminster. It is the traditional place of coronation and burial site for English,...

 in London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

, and wrought iron furniture appeared to reach its peak popularity (in Britain) in the seventeenth century during the reign of William and Mary
William and Mary
The phrase William and Mary usually refers to the coregency over the Kingdoms of England, Scotland and Ireland, of King William III & II and Queen Mary II...

. However, cast iron and cheaper steel caused a gradual decline in wrought iron manufacture, with the last wrought ironworks in Britain closing in 1974.

It is also used to make home decor items such as baker's racks
Baker's Rack
A baker's rack is a type of furniture with shelves, typically made of wrought iron or some other metal. Traditionally the wire shelves served to help cool a baker's goods such as hot pies. The heat-conducting metal shelving allows for heat to be quickly transferred from the bowl to the shelf...

, wine rack
Wine rack
A wine rack is a device that stores and organizes wine. Wine racks can be built out of a number of different materials. The size of the rack and the number of bottles it can hold can vary widely...

s, pot rack
Pot rack
A pot rack is a functional piece of kitchen furniture that is used to hang or store cooking pots and pans. Steel, wood, wrought iron, and a few other metals are the most common types of materials used for pot racks. Pot racks also usually have some type of finish or stain to help them match pots...

s, etagere
Etagere
An étagère is a piece of light furniture very similar to the English what-not, which was extensively made in France during the latter part of the 18th century. It consists of a series of stages or shelves for the reception of ornaments or other small articles...

s, table bases, desks, gates, beds, candle holders, curtain rods, bars and bar stools.

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