Editing Wrought iron (section)

==History==
===China===
During the Han dynasty (202 BC – 220 AD), new iron smelting processes led to the manufacture of new wrought iron implements for use in agriculture, such as the [[Seed drill|multi-tube seed drill]] and [[Plough|iron plough]].<ref>{{cite book |title=A Short History of China |last=Kerr |first=Gordon |publisher=Pocket Essentials  |year=2013 |isbn=978-1842439692}}</ref> In addition to accidental lumps of low-carbon wrought iron produced by excessive injected air in ancient Chinese [[cupola furnace]]s. The ancient Chinese created wrought iron by using the [[finery forge]] at least by the 2nd century BC, the earliest specimens of [[Cast iron|cast]] and [[pig iron]] fined into wrought iron and [[steel]] found at the early Han dynasty site at Tieshengguo.<ref>{{cite book |last=Needham |first=Joseph |title=Science and Civilisation in China |year=1995 |volume=5: Chemistry and Chemical Technology |section=Part 3: Spagyrical Discovery and Invention: Historical Survey from Cinnabar Elixirs to Synthetic Insulin |page=105 |publisher=Cambridge University Press |url=https://books.google.com/books?id=oH-TYyjgAj0C|isbn=9780521210287 }}</ref><ref name="Piggot1999">{{cite book |last=Pigott |first=Vincent C. |url=https://books.google.com/books?id=AjUy9SA3vqcC |title=The Archaeometallurgy of the Asian Old World |year=1999 |publisher=UPenn Museum of Archaeology |isbn=9780924171345}}</ref>{{rp|186}} Pigott speculates that the finery forge existed in the previous [[Warring States period]] (403–221 BC), due to the fact that there are wrought iron items from China dating to that period and there is no documented evidence of the [[bloomery]] ever being used in China.<ref name="Piggot1999" />{{rp|186–187}} The fining process involved liquifying cast iron in a fining hearth and [[decarburization|removing carbon]] from the molten cast iron through [[Redox|oxidation]].<ref name="Piggot1999" />{{rp|186}} Wagner writes that in addition to the Han dynasty hearths believed to be fining hearths, there is also pictorial evidence of the fining hearth from a [[Shandong]] tomb mural dated 1st to 2nd century AD, as well as a hint of written evidence in the 4th century AD Daoist text ''[[Taiping Jing]]''.<ref>{{cite book |last=Wagner |first=Rudolf G. |year=2001 |title=The Craft of a Chinese Commentator: Wang Bi on the Laozi |pages=80–83}}</ref>

===Western world===
[[File:Chinese fining.png|thumb|upright|The puddling process of smelting iron ore to make wrought iron from pig iron, illustrated in the ''Tiangong Kaiwu'' [[encyclopedia]] by [[Song Yingxing]], published in 1637.]]

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]], was in use in China since ancient times but was not introduced into Western Europe until the 15th century; even then, due to its brittleness, it could be used for only a limited number of purposes. Throughout much of the Middle Ages, iron was produced by the direct reduction of ore in manually operated [[Bloomery|bloomeries]], although [[water power]] had begun to be employed by 1104.<ref>{{cite book |first=A. |last=Lucas |title=Wind, Water, Work: Ancient and Medieval Milling Technology |publisher=Brill |location=Leiden NL and Boston Mass. |date=2006 |pages=251–255, 347}}</ref>

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 cannot 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]], Sweden and in [[Germany]].

The bloomery and osmond processes were gradually replaced from the 15th century by [[finery forge|finery]] processes, of which there were two versions, the German and Walloon. They were in turn replaced from the late 18th century by [[puddling (metallurgy)|puddling]], with certain variants such as the Swedish [[Lancashire process]]. Those, too, are now obsolete, and wrought iron is no longer manufactured commercially.<!-- For references see below in the Aston process section -->

===Bloomery process===
{{Main|Bloomery}}

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]] and iron ore and then lit. Air was blown in through a [[tuyere]] 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]] from the charcoal would reduce the ore to iron, which formed a spongy mass (called a "bloom") containing iron and also molten silicate minerals (slag) from the ore. The iron remained in the solid state. If the bloomery were 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. However, the design of a bloomery made it difficult to reach the melting point of iron and also prevented the concentration of carbon monoxide from becoming high.<ref name="Tylecote1992" />{{rp|46–57}}

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 such as a blast furnace. The bloom had to be forged mechanically to consolidate it and shape it into a bar, expelling slag in the process.<ref name="Tylecote1992" />{{rp|62–66}}

During the [[Middle Ages]], 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 remain uncertain.<ref name="Tylecote1992" />{{rp|75–76}} That was the culmination of the direct process of ironmaking. It survived in [[Spain]] and southern [[France]] as Catalan Forges to the mid 19th century, in [[Austria]] as the ''stuckofen'' to 1775,<ref name="Tylecote1992" />{{rp|100–101}} and near [[Garstang]] in England until about 1770;<ref>{{cite book |author=Richard Pococke|author-link=Richard Pococke |title=The travels through England&nbsp;... during 1750, 1751, and later years |editor=J.J. Cartwright |publisher=Camden Soc. n.s. 42, 1888 |page=13 }}</ref><ref>{{cite book |first=W. |last=Lewis |title=The Chemical and Mineral History of Iron |type=manuscript at Cardiff Central Library |year=1775 |pages=iv, 76}}</ref> it was still in use with [[hot blast]] in [[New York (state)|New York]] in the 1880s.<ref>{{cite periodical |first=G.C. |last=Pollard |title=Experimentation in 19th-century bloomery iron production: Evidence from the Adirondacks of New York |periodical=Historical Metallurgy |edition=32nd |issue=1 |year=1998 |pages=33–40}}</ref> In [[Japan]] the last of the old ''[[tatara (furnace)|tatara]]'' bloomeries used in production of traditional [[tamahagane]] steel, mainly used in swordmaking, was extinguished only in 1925, though in the late 20th century the production resumed on a low scale to supply the steel to the artisan swordmakers.

===Osmond process===
{{Main|Osmond process}}

[[Osmond iron]] 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.<ref>H. R. Schubert, ''History of the British Iron and Steel Industry from 450 BC to AD 1775 (Routledge and Kegan Paul, London 1957)'', 299–304.</ref> The resultant ball was often forged into bar iron in a hammer mill.

===Finery process===
{{Main|Finery forge}}

In the 15th century, the [[blast furnace]] spread into what is now [[Belgium]] where it was improved. From there, it spread via the [[Pays de Bray]] on the boundary of [[Normandy]] and then to the [[Weald]] in England. With it, the finery forge spread. Those remelted the pig iron and (in effect) burnt out the carbon, producing a bloom, which was then forged into 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. That employed two different hearths, a finery hearth for finishing 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]], 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.<ref>A. den Ouden, 'The production of wrought iron in Finery Hearths' ''Historical Metallurgy'' 15(2) (1981), 63–87 and 16(1) (1982), 29–32.</ref>

The introduction of [[coke (fuel)|coke]] for use in the blast furnace by [[Abraham Darby I|Abraham Darby]] 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===
<!-- A main article is needed. -->
From the late 1750s, ironmasters began to develop processes for making bar iron without charcoal. There were a number of patented processes for that, which are referred to today as [[potting and stamping]]. The earliest were developed by John Wood of [[Wednesbury]] and his brother Charles Wood of Low Mill at [[Egremont, Cumbria|Egremont]], patented in 1763.<ref name="MortonMutton1967">{{cite journal |first1=G.R. |last1=Morton |first2=N. |last2=Mutton |title=The Transition to Cort's Puddling Process |journal=Journal of the Iron and Steel Institute |volume=205 |year=1967}}</ref>{{rp|723–724}} Another was developed for the [[Coalbrookdale]] Company by the [[Cranage brothers]].<ref>{{cite periodical |first=R. |last=Hayman |title=The Cranage brothers and eighteenth-century forge technology |periodical=Historical Metallurgy |edition=28th |issue=2 |year=2004 |pages=113–120}}</ref> Another important one was that of John Wright and Joseph Jesson of [[West Bromwich]].<ref name="MortonMutton1967" />{{rp|725–726}}

===Puddling process===
{{Main|Puddling (metallurgy)}}
[[File:Puddling furnace.jpg|thumb|Schematic drawing of a puddling furnace]]

A number of processes for making wrought iron without charcoal were devised as the [[Industrial Revolution]] began during the latter half of the 18th century. The most successful of those was puddling, using a puddling furnace (a variety of the [[reverberatory furnace]]), which was invented by [[Henry Cort]] in 1784.<ref>R. A. Mott (ed. P. Singer), ''Henry Cort, The Great Finer'' (The Metals Society, London 1983).</ref> It was later improved by others including [[Joseph Hall (metallurgist)|Joseph Hall]], who was the first to add iron oxide to the charge. In that type of furnace, the metal does not come into contact with the fuel, and so is not contaminated by its impurities. The heat of the combustion products passes over the surface of the puddle and the roof of the furnace reverberates (reflects) the heat onto the metal puddle on the fire bridge of the furnace.

Unless the raw material used is white cast iron, the pig iron or other raw product of the puddling first had to be refined into [[refined iron]], or finers metal. That would be done in a refinery where raw coal was used to remove [[silicon]] and convert carbon within the raw material, found in the form of graphite, to a combination with iron called cementite.

In the fully developed process (of Hall), 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.<ref name="Rajput2000">{{cite book |last=Rajput |first=R. K. |title=Engineering Materials |publisher=S. Chand |year=2000 |page=223 |isbn=81-219-1960-6}}</ref> The mixture was subjected to a strong current of air and stirred with long bars, called puddling bars or rabbles,<ref name="Gale1971">{{cite book |first=W. K. V. |last=Gale |title=The Iron and Steel Industry: a Dictionary of Terms |publisher=David and Charles |location=Newton Abbot |year=1971}}</ref>{{rp|165}}<ref name="mi">{{cite book |last=Overman |first=Fredrick |title=The Manufacture of Iron, in All Its Various Branches |publisher=H. C. Baird |year=1854 |location=Philadelphia |pages=267, 287, 344 |url=https://books.google.com/books?id=Gani2eHvhAkC}}</ref> through working doors.<ref name="Tylecote1991">{{cite book |first=R. F. |last=Tylecote |section=Iron in the Industrial Revolution |title=The Industrial Revolution in Metals |publisher=Institute of Metals |location=London |year=1991}}</ref>{{rp|236–240}} The air, the stirring, and the "boiling" action of the metal helped the oxidizing agents to oxidize the impurities and carbon out of the pig iron. As the impurities oxidize, they formed a molten slag or drifted off as gas, while the remaining iron solidified into spongy wrought iron that floated to the top of the puddle and was fished out of the melt as puddle balls, using puddle bars.<ref name="Rajput2000" />

====Shingling====
{{Main|Shingling (metallurgy)}}

There was still some slag left in the puddle balls, so while they were still hot they would be shingled<ref name="msts">{{cite book |last1=Camp |first1=James McIntyre |last2=Francis |first2=Charles Blaine |title=The Making, Shaping and Treating of Steel |publisher=Carnegie Steel Company |year=1920 |location=Pittsburgh |pages=173–174 |url=https://books.google.com/books?id=P9MxAAAAMAAJ |isbn=1-147-64423-3}}</ref> to remove the remaining slag and cinder.<ref name="Rajput2000" /> That was achieved by forging the balls under a hammer, or by squeezing the bloom in a machine. The material obtained at the end of shingling is known as bloom.<ref name="msts" /> The blooms are not useful in that form, so they were rolled into a final product.

Sometimes European [[ironwork]]s would skip the shingling process completely and roll the puddle balls. The only drawback to that is that the edges of the rough bars were not as well compressed. When the rough bar was reheated, the edges might separate and be lost into the furnace.<ref name="msts" />

====Rolling====
{{Main|Rolling mill}}

The bloom was passed through rollers and to produce bars. The bars of wrought iron were of poor quality, called muck bars<ref name="msts" /><ref name="Gale1971" />{{rp|137}} or puddle bars.<ref name="Rajput2000" /> To improve their quality, the bars were cut up, piled and tied together by wires, a process known as [[Faggoting (metalworking)|faggoting]] or piling.<ref name="msts" /> They were then reheated to a welding state, forge welded, and rolled again into bars. The process could be repeated several times to produce wrought iron of desired quality. Wrought iron that has been rolled multiple times is called merchant bar or merchant iron.<ref name="mi" /><ref>{{cite book |first=W. K. V. |last=Gale |title=The British Iron and Steel Industry |publisher=David and Charles |location=Newton Abbot |year=1967 |pages=79–88}}</ref>

===Lancashire process===
{{Main|Lancashire hearth}}

The advantage of puddling was that it used coal, not charcoal as fuel. However, that was of little advantage in Sweden, which lacked coal. [[Gustaf Ekman]] observed charcoal fineries at [[Ulverston]], 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 used firewood and charcoal, which was widely adopted in the [[Bergslagen]] in the following decades.<ref>{{cite book |first=G. |last=Rydén |editor1-first=G. |editor1-last=Rydén |editor2-first=C. |editor2-last=Evans |section=Responses to Coal Technology without Coal: Swedish Iron Making in the Nineteenth Century |title=The Industrial Revolution in Iron: The impact of British coal technology in 19th century Europe |publisher=Ashgate |location=[[Aldershot]] |year=2005 |pages=121–124}}</ref><ref name="Evans2007" />{{rp|282–285}}

===Aston process===
In 1925, James Aston of the [[United States]] developed a process for manufacturing wrought iron quickly and economically. It involved taking molten steel from a [[Bessemer process|Bessemer converter]] and pouring it into cooler liquid slag. The temperature of the steel is about 1500&nbsp;°C and the liquid slag is maintained at approximately 1200&nbsp;°C. The molten steel contains a large amount of dissolved gases so when the liquid steel hit the cooler surfaces of the liquid slag the gases were liberated. The molten steel then froze to yield a spongy mass having a temperature of about 1370&nbsp;°C.<ref name="Rajput2000" /> The spongy mass would then be finished by being [[Shingling (metallurgy)|shingled]] and [[Rolling mill|rolled]] as described under puddling (above). Three to four tons could be converted per batch with the method.<ref name="Rajput2000" /><ref>{{Cite book|title=Wrought Iron, Its Manufacture, Characteristics, and Applications|last=Aston|first=James|last2=Story|first2=Edward B.|publisher=A.M. Byers Co.|year=1957|edition=4|location=Pittsburgh|oclc=1966102}}</ref>

===Decline===
[[Steel]] began to replace iron for railroad rails as soon as the [[Bessemer process]] for its manufacture was adopted (1865 on). Iron remained dominant for structural applications until the 1880s, because of problems with brittle steel, caused by introduced nitrogen, high carbon, excess phosphorus, or excessive temperature during or too-rapid rolling.<ref name="Misa1995" />{{rp|144–151}}{{refn|group=note|From Misa, T.J. (1995):<ref name="Misa1995" />''"Quality problems with rails gave Bessemer steel such a bad reputation that engineers and architects refused to specify it for structural applications. Open hearth steel had a better reputation and displaced structural iron by 1889..."''}} By 1890 steel had largely replaced iron for structural applications.

Sheet iron (Armco 99.97% pure iron) had good properties for use in appliances, being well-suited for enamelling and welding, and being rust-resistant.<ref name="Misa1995"/>{{rp|242}}

In the 1960s, the price of steel production was dropping due to recycling, and even using the Aston process, wrought iron production was labor-intensive. It has been estimated that the production of wrought iron is approximately twice as expensive as that of low-carbon steel.<ref name="Daniel1993" /> In the United States, the last plant closed in 1969.<ref name="Daniel1993" /> The last in the world was the Atlas Forge of [[Thomas Walmsley and Sons]] in [[Bolton]], Great Britain, which closed in 1973. Its 1860s-era equipment was moved to the [[Blists Hill Victorian Town|Blists Hill site]] of [[Ironbridge Gorge Museum Trust|Ironbridge Gorge Museum]] for preservation.<ref>{{cite periodical |first1=Stuart B |last1=Smith |first2=W.K.V. |last2=Gale |title=Wrought iron again: the Blists Hill Ironworks officially opened |periodical=Historical Metallurgy |edition=21st |issue=1 |year=1987 |pages=44–45}}</ref> Some wrought iron is still being produced for heritage restoration purposes, but only by recycling scrap.