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The first step taken before the bloomery can be used is the preparation of the [[charcoal]] and the iron ore. Charcoal is nearly pure [[carbon]] which when burned, both produces the high temperature needed for the smelting process and provides the carbon monoxide needed for [[Redox|reduction]] of the metal.
The first step taken before the bloomery can be used is the preparation of the [[charcoal]] and the iron ore. Charcoal is nearly pure [[carbon]] which when burned, both produces the high temperature needed for the smelting process and provides the carbon monoxide needed for [[Redox|reduction]] of the metal.


The [[ore]] is broken into small pieces and usually roasted in a fire to remove any moisture in the ore. Any large impurities in the ore can be crushed and removed. Since [[slag]] from previous blooms may have a high iron content, it can also be broken up and [[recycled]] into the bloomery with the new ore.
The [[ore]] is broken into small pieces and usually roasted in a fire, to make rock based ores easier to break up, bake out some impurities, and (to a lesser extent) to remove any moisture in the ore. Any large impurities (as silica) in the ore can be removed as it is crushed. The desired particle size depends primarily on which of several ore types may be available, which will also have a relationship to the layout and operation of the furnace, of which there are a number of regional, historic/traditional forms. Natural iron ores can vary considerably in oxide form (Fe2O3 / Fe3O4 / FeO(OH) ), and importantly in relative iron content. Since [[slag]] from previous blooms may have a high iron content, it can also be broken up and may be[[recycled]] into the bloomery with the new ore.


In operation, after the bloomery is preheated by burning charcoal, iron ore and additional charcoal are introduced through the top in a roughly one-to-one ratio. Inside the furnace, [[carbon monoxide]] from the incomplete [[combustion]] of the charcoal [[redox|reduces]] the iron oxides in the ore to [[Iron|metallic iron]] without melting the ore; this allows the bloomery to operate at lower temperatures than the melting temperature of the ore. As the desired product of a bloomery is iron which is easily [[Forging|forgeable]], it requires a low carbon content. The temperature and ratio of charcoal to iron ore must be carefully controlled to keep the iron from absorbing too much carbon and thus becoming unforgeable. Cast iron occurs when the iron absorbs 2% to 4% carbon. Because the bloomery is self-[[Flux (metallurgy)|fluxing]], the addition of [[limestone]] is not required to form a slag.
In operation, after the bloomery is preheated typically with a wood fire, shifting to burning pre-sized charcoal, iron ore and additional charcoal are introduced through the top. Again, 'traditional' methods vary, but normally smaller charges of ore are added at the start of the main smelting sequence, increasing to larger amounts as the smelt progresses. Overall a typical ratio of total charcoal to ore added will in a roughly one-to-one ratio. Inside the furnace, [[carbon monoxide]] from the incomplete [[combustion]] of the charcoal [[redox|reduces]] the iron oxides in the ore to [[Iron|metallic iron]] without melting the ore; this allows the bloomery to operate at lower temperatures than the melting temperature of the ore. As the desired product of a bloomery is iron which is easily [[Forging|forgeable]], it requires a low carbon content. The temperature and ratio of charcoal to iron ore must be carefully controlled to keep the iron from absorbing too much carbon and thus becoming unforgeable. Cast iron occurs when the iron absorbs 2% to 4% carbon. Because the bloomery is self-[[Flux (metallurgy)|fluxing]], the addition of [[limestone]] is not required to form a slag.


The small particles of iron produced in this way fall to the bottom of the furnace, where they combine with molten slag, often consisting of [[fayalite]], a compound of [[silicon]], [[oxygen]] and iron mixed with other impurities from the ore. The mixed iron and slag cool to form a spongy mass referred to as the bloom. Because the bloom is highly [[porous]], and its open spaces are full of slag, the bloom must later be reheated and beaten with a hammer to drive the molten slag out of it. Iron treated this way is said to be ''wrought'' (worked), and the resulting iron, with reduced amounts of slag, is called ''wrought iron'' or bar iron. It is also possible to produce blooms coated in [[steel]] by manipulating the charge of and air flow to the bloomery.<ref>[http://iron.wlu.edu/reports/Eindhoven%20Smelt%20Report.htm Smelting Enriched Bog Ore in a Low Shaft Bloomery]</ref>
The small particles of iron produced in this way fall to the bottom of the furnace, where they combine with molten slag, often consisting of [[fayalite]], a compound of [[silicon]], [[oxygen]] and iron mixed with other impurities from the ore. The hot liquid slag, running to the bottom of the furnace, cools against the base and lower side walls of the furnace, effectively forming a bowl still containing fluid slag. As the individual iron particles form, they fall into this bowl and sinter together under their own weight, forming a spongy mass referred to as the '''bloom'''. Because the bloom is typically [[porous]], and its open spaces can be full of slag, the extracted mass must beaten with heavy hammers to both compress voids and drive out any molten slag remaining. This process may require several additional heating and compaction cycles, working at high 'welding' temperatures. Iron treated this way is said to be ''wrought'' (worked), and the resulting iron, with reduced amounts of slag, is called ''wrought iron'' or bar iron. Because of the creation process, individual blooms can often have differing carbon contents between the original top and bottom surfaces, differences that will also be somewhat blended together through the flattening, folding and hammer welding sequences. It is also possible to produce blooms coated in [[steel]] (higher carbon) by manipulating the charge of and air flow to the bloomery.<ref>[http://iron.wlu.edu/reports/Eindhoven%20Smelt%20Report.htm Smelting Enriched Bog Ore in a Low Shaft Bloomery]</ref>


As the era of modern commercial [[steelmaking]] began, the word ''bloom'' was extended to another [[word sense|sense]] referring to [[semi-finished casting products#Bloom|an intermediate-stage piece of steel]], of a size comparable to many traditional iron blooms, that was ready to be further worked into [[semi-finished casting products#Billet|billet]].
As the era of modern commercial [[steelmaking]] began, the word ''bloom'' was extended to another [[word sense|sense]] referring to [[semi-finished casting products#Bloom|an intermediate-stage piece of steel]], of a size comparable to many traditional iron blooms, that was ready to be further worked into [[semi-finished casting products#Billet|billet]].
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[[File:PSM V38 D159 Persian method of smelting iron.jpg|thumb|A drawing of a simple bloomery and bellows.]]
[[File:PSM V38 D159 Persian method of smelting iron.jpg|thumb|A drawing of a simple bloomery and bellows.]]
[[File:Bas fourneau.png|thumb|Bloomery smelting during the [[Middle Ages]], as depicted in the ''[[De Re Metallica]]'' by [[Georgius Agricola]], 1556]]
[[File:Bas fourneau.png|thumb|Bloomery smelting during the [[Middle Ages]], as depicted in the ''[[De Re Metallica]]'' by [[Georgius Agricola]], 1556]]
The onset of the [[Iron Age]] in most parts of the world coincides with the first widespread use of the bloomery. While earlier examples of iron are found, their high nickel content indicates that this is [[meteoric iron]]. Other early samples of iron may have been produced by accidental introduction of iron ore in [[bronze]] smelting operations. Iron appears to have been smelted in the West as early as 3000 BC, but bronze smiths, not being familiar with iron, did not put it to use until much later. In the West, iron began to be used around 1200 BC.<ref>{{cite web|title=The History of Forging - Now and Then|url=http://cantondropforge.com/history-of-forging|website=Canton Drop Forge|publisher=Canton Drop Forge}}</ref>
The onset of the [[Iron Age]] in most parts of the world coincides with the first widespread use of the bloomery. While earlier examples of iron are found, their high nickel content indicates that this is [[meteoric iron]]. Other early samples of iron may have been produced by accidental introduction of iron ore in copper smelting operations. Iron appears to have been smelted in the Middle East as early as 3000 BC, but copper smiths, not being familiar with iron, did not put it to use until much later. In the West, iron began to be used around 1200 BC.<ref>{{cite web|title=The History of Forging - Now and Then|url=http://cantondropforge.com/history-of-forging|website=Canton Drop Forge|publisher=Canton Drop Forge}}</ref>


===East Asia===
===East Asia===
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Wrought iron was used in the construction of monuments like the [[Iron pillar of Delhi]], built in the 3rd century AD during the [[Gupta Empire]]. The latter was built using a towering series of disc-shaped iron blooms. Similar to China, high-carbon steel was eventually used in India, although cast iron was not used for architecture until modern times.<ref name="METALLURGICAL HERITAGE OF INDIA">Ranganathan, Srinivasa; Srinivasan, Sharada. (1997). [http://dtrinkle.matse.illinois.edu/MatSE584/articles/metallurg_heritage_india/metallurgical_heritage_india.html "METALLURGICAL HERITAGE OF INDIA"], in ''Golden Jubilee Souvenir'', Indian Institute of Science, pp. 29-36, ([[University of Illinois]], Department of Materials Science and Engineering web page). Accessed 30 October 2019.</ref>
Wrought iron was used in the construction of monuments like the [[Iron pillar of Delhi]], built in the 3rd century AD during the [[Gupta Empire]]. The latter was built using a towering series of disc-shaped iron blooms. Similar to China, high-carbon steel was eventually used in India, although cast iron was not used for architecture until modern times.<ref name="METALLURGICAL HERITAGE OF INDIA">Ranganathan, Srinivasa; Srinivasan, Sharada. (1997). [http://dtrinkle.matse.illinois.edu/MatSE584/articles/metallurg_heritage_india/metallurgical_heritage_india.html "METALLURGICAL HERITAGE OF INDIA"], in ''Golden Jubilee Souvenir'', Indian Institute of Science, pp. 29-36, ([[University of Illinois]], Department of Materials Science and Engineering web page). Accessed 30 October 2019.</ref>


===Medieval Europe===
===Early to Medieval Europe===
[[File:PSM V38 D175 A blomary fire.jpg|thumb|A Catalan furnace, with tuyere and bellows on the right]]
[[File:PSM V38 D175 A blomary fire.jpg|thumb|A Catalan furnace, with tuyere and bellows on the right]]
Early European bloomeries were relatively small, smelting less than 1&nbsp;kg{{citation needed|reason=a bloom that SMALL is hard to achieve. Even very small bloomeries produce 5-10kg per run using bellows for air|date=July 2016}} of iron with each firing. Progressively larger bloomeries were constructed in the late 14th century, with a capacity of about 15&nbsp;kg on average, though exceptions did exist. The use of [[waterwheel]]s to power the bellows allowed the bloomery to become larger and hotter. European average bloom sizes quickly rose to 300&nbsp;kg, where they levelled off until the demise of the bloomery.
Early European bloomeries were relatively small, primarily do to the mechanical limits of human powered bellows and the amount of force possible to apply with hand driven sledge hammers. Those known archaeologically from the pre-Roman Iron Age tend to be in the 2 kg range, produced in low shaft furnaces. Roman era production often used furnaces tall enough to create a natural draft effect (into the range of 200 cm tall), and increasing bloom sizes into the range of 10 - 15 kg. <ref> Radomir Pliener, Iron in Archaeology - the European Bloomery Smelters, chapter XII, 2000 </ref> Contemporary experimenters had routinely made blooms using Northern European derived 'short shaft' furnaces with blown air supplies in the 5 - 10 kg range <ref> Darrell Markewitz, 'If you don't get any IRON - Towards an Effective Method for Small Iron Smelting Furnaces', EXARC Journal 2012-1 (https://exarc.net/ark:/88735/10041)</ref> The use of [[waterwheel]], spreading around the turn of the first millennium and used to power more massive bellows allowed the bloomery to become larger and hotter, with associated trip hammers allowing the consolodation forging of the larger blooms created. Progressively larger bloomeries were constructed in the late 14th century, with a capacity of about 15&nbsp;kg on average, though exceptions did exist. European average bloom sizes quickly rose to 300&nbsp;kg, where they levelled off until the demise of the bloomery.


As a bloomery's size is increased, the iron ore is exposed to burning charcoal for a longer time. When combined with the strong air blast required to penetrate the large ore and charcoal stack, this may cause part of the iron to melt and become saturated with carbon in the process, producing unforgeable [[pig iron]] which requires [[finery forge|oxidation]] to be reduced into cast iron, steel, and iron. This pig iron was considered a waste product detracting from the largest bloomeries' yield, and it was not until the 14th century that early [[blast furnace]]s, identical in construction but dedicated to the production of molten iron, were built.<ref>Douglas Alan Fisher, The Epic of Steel, Harper & Row 1963, p. 26-29</ref><ref>Blast furnace, theory and practice, American Institute of mining, metallurgical, and petroleum engineers, Gordon and Breach science 1969, p. 4-5</ref>
As a bloomery's size is increased, the iron ore is exposed to burning charcoal for a longer time. When combined with the strong air blast required to penetrate the large ore and charcoal stack, this may cause part of the iron to melt and become saturated with carbon in the process, producing unforgeable [[pig iron]] which requires [[finery forge|oxidation]] to be reduced into cast iron, steel, and iron. This pig iron was considered a waste product detracting from the largest bloomeries' yield, and it was not until the 14th century that early [[blast furnace]]s, identical in construction but dedicated to the production of molten iron, were built.<ref>Douglas Alan Fisher, The Epic of Steel, Harper & Row 1963, p. 26-29</ref><ref>Blast furnace, theory and practice, American Institute of mining, metallurgical, and petroleum engineers, Gordon and Breach science 1969, p. 4-5</ref>
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===The Americas===
===The Americas===
Iron may have been produced by Vikings at [[Point Rosee]] and other locations in [[Newfoundland]] around 1000 CE.<ref>{{cite web|url=http://news.nationalgeographic.com/2016/03/160331-viking-discovery-north-america-canada-archaeology/|title=Discovery Could Rewrite History of Vikings in New World|last=Strauss|first=Mark|date=31 March 2016|website=National Geographic|publisher=National Geographic Partners, LLC.|access-date=25 October 2016}}</ref><ref>{{cite web|url=http://www.sentinelsource.com/news/wapo/an-ancient-site-spotted-from-space-could-rewrite-the-history/article_481a0be0-56ad-5ac1-b82c-973b6e16cfbb.html|title=An ancient site spotted from space could rewrite the history of Vikings in North America|last=Kaplan|first=Sarah|date=2 April 2016|website=SentinelSource.com|publisher=SentinelSource.com, Keene, NH|access-date=25 October 2016}}</ref> Excavations at [[L'Anse aux Meadows]] have found considerable evidence for the processing of bog iron and the production of iron in a bloomery.<ref name=":2">{{Cite journal|last=Bowles, G., R. Bowker, and N. Samsonoff|date=2011|title=Viking expansion and the search for bog iron|url=https://docplayer.net/47076189-Viking-expansion-and-the-search-for-bog-iron.htmlhttps://docplayer.net/47076189-Viking-expansion-and-the-search-for-bog-iron.html|journal=Platforum|volume=12|pages=25–37}}</ref> The settlement at L'Anse aux Meadows was situated immediately east of a sedge peat bog and 15&nbsp;kg of slag was found at the site, which would have produced around 3&nbsp; kg of usable iron.<ref name=":2" /> Analysis of the slag showed that considerably more iron could have been smelted out of the ore, indicating that the workers processing the ore had not been skilled.<ref name=":2" /> This supports the idea that iron processing knowledge was widespread and not restricted to major centers of trade and commerce.<ref name=":2" /> 98 nail fragments were also found at the site as well as considerable evidence for woodworking which points to the iron produced at the site possibly being used only for ship repair and not tool making.<ref name=":2" /><ref>{{Cite book|title=Vinland Revisited: The Norse World at the Turn of the First Millennium|last=Lewis-Simpson, Shannon|publisher=St. John's, Newfoundland: Historic Sites Association of Newfoundland and Labrador, Inc.|year=2000|isbn=0-919735-07-X|location=St. John's, Newfoundland}}</ref>
Excavations at [[L'Anse aux Meadows]] Newfoundland have found considerable evidence for the processing of bog iron and the production of iron in a bloomery by the Norse.<ref name=":2">{{Cite journal|last=Bowles, G., R. Bowker, and N. Samsonoff|date=2011|title=Viking expansion and the search for bog iron|url=https://docplayer.net/47076189-Viking-expansion-and-the-search-for-bog-iron.htmlhttps://docplayer.net/47076189-Viking-expansion-and-the-search-for-bog-iron.html|journal=Platforum|volume=12|pages=25–37}}</ref> The cluster of Viking Age (c 1000 - 1022 AD) at L'Anse aux Meadows are situated on a raised marine terrace, between a sedge peat bog and the ocean. Estimates from the smaller amount of slag recovered archaeologically suggest 15 kg of slag was produced during what appears to have been a single smelting attempt. By comparing the iron content of the primary bog iron ore found in the purpose built 'furnace hut' with the iron remaining in that slag, an estimated 3 kg iron bloom was produced. (At a yield of at best 20% from what is a good iron rich ore, this suggests the workers processing the ore had not been paticularly skilled.<ref name=":2" /> This supports the idea that iron processing knowledge was widespread and not restricted to major centers of trade and commerce.<ref name=":2" /> 98 nail, and importantly, ship rivet fragments, were also found at the site as well as considerable evidence for woodworking - which points to boat or possibly ship repairs being undertaken at the site.<ref name=":2" /><ref>{{Cite book|title=Vinland Revisited: The Norse World at the Turn of the First Millennium|last=Lewis-Simpson, Shannon|publisher=St. John's, Newfoundland: Historic Sites Association of Newfoundland and Labrador, Inc.|year=2000|isbn=0-919735-07-X|location=St. John's, Newfoundland}}</ref> (An important consideration remains that a potential 3 kg raw bloom most certainly does not make enough refined bar to manufacture the 3 kg of recovered nails and rivets!)


[[Image:Mission San Juan Capistrano 4-5-05 100 6559.JPG|thumb|300px|right|A view of the bloomeries ('Catalan forges') at [[Mission San Juan Capistrano]], the oldest (''circa'' 1790s) existing facilities of their kind in California.]]
[[Image:Mission San Juan Capistrano 4-5-05 100 6559.JPG|thumb|300px|right|A view of the bloomeries ('Catalan forges') at [[Mission San Juan Capistrano]], the oldest (''circa'' 1790s) existing facilities of their kind in California.]]
In the [[Spanish colonization of the Americas]], bloomeries or "Catalan forges" were part of 'self sufficiency' at some of the [[:Category:Spanish missions in the Americas|missions]], ''[[encomienda]]s'', and ''[[pueblo]]s''. As part of the [[Spanish missions in California|Franciscan Spanish missions]] in [[Alta California]], the "Catalan forges" at [[Mission San Juan Capistrano]] from the 1790s are the oldest existing facilities of their kind in the present day [[California|state of California]]. The bloomeries' sign proclaims the site as being "...part of [[Orange County, California|Orange County]]'s first industrial complex."
In the [[Spanish colonization of the Americas]], bloomeries or "Catalan forges" were part of 'self sufficiency' at some of the [[:Category:Spanish missions in the Americas|missions]], ''[[encomienda]]s'', and ''[[pueblo]]s''. As part of the [[Spanish missions in California|Franciscan Spanish missions]] in [[Alta California]], the "Catalan forges" at [[Mission San Juan Capistrano]] from the 1790s are the oldest existing facilities of their kind in the present day [[California|state of California]]. The bloomeries' sign proclaims the site as being "...part of [[Orange County, California|Orange County]]'s first industrial complex."


The English settlers of the [[13 colonies]] were prevented by law from manufacture; for a time, the British sought to situate most of the skilled artisanry at domestic locations. In fact, this was one of the problems which led to the revolution.{{citation needed|date=November 2018}} The [[Falling Creek Ironworks]] was the first in the United States. The [[Neabsco Iron Works]] is an example of the early [[Virginia]]n effort to form a workable American industry.
The archaeology at Jamestown Virginia (cira 1610-15, citation needed), had recoved the remains of a simple short shaft bloomery furnace, likely intended as yet another 'resource test' like the one in Vinland much earlier. The English settlers of the [[13 colonies]] were prevented by law from manufacture; for a time, the British sought to situate most of the skilled artisanry at domestic locations. In fact, this was one of the problems which led to the revolution.{{citation needed|date=November 2018}} The [[Falling Creek Ironworks]] was the first in the United States. The [[Neabsco Iron Works]] is an example of the early [[Virginia]]n effort to form a workable American industry.


In the [[Adirondacks]], New York, new bloomeries using the [[hot blast]] technique were built in the 19th century.<ref name="Adirondacks">Gordon C. Pollard, 'Experimentation in 19th century bloomery production: evidence from the Adirondacks of New York' ''Historical Metallurgy'' 32(1) (1998), 33–40.</ref>
In the [[Adirondacks]], New York, new bloomeries using the [[hot blast]] technique were built in the 19th century.<ref name="Adirondacks">Gordon C. Pollard, 'Experimentation in 19th century bloomery production: evidence from the Adirondacks of New York' ''Historical Metallurgy'' 32(1) (1998), 33–40.</ref>
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* [http://www.ironsmelting.net/ Technology and archaeology of the earliest iron smelting and smithing]
* [http://www.ironsmelting.net/ Technology and archaeology of the earliest iron smelting and smithing]
* [http://iron.wlu.edu/Bloomery_Iron.htm Rockbridge bloomery]
* [http://iron.wlu.edu/Bloomery_Iron.htm Rockbridge bloomery]
* [http://www.warehamforge.ca/ironsmelting/index.html Experimental Iron Smelting (at the Wareham Forge) ]
* [http://www.darkcompany.ca/iron/ Viking-Era Norse techniques by DARC]
* [http://www.darkcompany.ca/iron/ Viking-Era Norse techniques by DARC]
* [http://www.wealdeniron.org.uk/Expt/index.htm WIRG experimental bloomery]
* [http://www.wealdeniron.org.uk/Expt/index.htm WIRG experimental bloomery]

Revision as of 19:16, 23 September 2022

For other uses, see Bloomery (disambiguation).

Look up bloomery in Wiktionary, the free dictionary.
A bloomery in operation. The bloom will eventually be drawn out of the bottom hole.

A bloomery is a type of metallurgical furnace once used widely for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. Bloomeries produce a porous mass of iron and slag called a bloom. The mix of slag and iron in the bloom, termed sponge iron, is usually consolidated and further forged into wrought iron. Blast furnaces, which produce pig iron, have largely superseded bloomeries.

Process

An iron bloom just removed from the furnace. Surrounding it are pieces of slag that have been pounded off by the hammer.

A bloomery consists of a pit or chimney with heat-resistant walls made of earth, clay, or stone. Near the bottom, one or more pipes (made of clay or metal) enter through the side walls. These pipes, called tuyeres, allow air to enter the furnace, either by natural draught or forced with bellows or a trompe. An opening at the bottom of the bloomery may be used to remove the bloom, or the bloomery can be tipped over and the bloom removed from the top.

The first step taken before the bloomery can be used is the preparation of the charcoal and the iron ore. Charcoal is nearly pure carbon which when burned, both produces the high temperature needed for the smelting process and provides the carbon monoxide needed for reduction of the metal.

The ore is broken into small pieces and usually roasted in a fire, to make rock based ores easier to break up, bake out some impurities, and (to a lesser extent) to remove any moisture in the ore. Any large impurities (as silica) in the ore can be removed as it is crushed. The desired particle size depends primarily on which of several ore types may be available, which will also have a relationship to the layout and operation of the furnace, of which there are a number of regional, historic/traditional forms. Natural iron ores can vary considerably in oxide form (Fe2O3 / Fe3O4 / FeO(OH) ), and importantly in relative iron content. Since slag from previous blooms may have a high iron content, it can also be broken up and may berecycled into the bloomery with the new ore.

In operation, after the bloomery is preheated typically with a wood fire, shifting to burning pre-sized charcoal, iron ore and additional charcoal are introduced through the top. Again, 'traditional' methods vary, but normally smaller charges of ore are added at the start of the main smelting sequence, increasing to larger amounts as the smelt progresses. Overall a typical ratio of total charcoal to ore added will in a roughly one-to-one ratio. Inside the furnace, carbon monoxide from the incomplete combustion of the charcoal reduces the iron oxides in the ore to metallic iron without melting the ore; this allows the bloomery to operate at lower temperatures than the melting temperature of the ore. As the desired product of a bloomery is iron which is easily forgeable, it requires a low carbon content. The temperature and ratio of charcoal to iron ore must be carefully controlled to keep the iron from absorbing too much carbon and thus becoming unforgeable. Cast iron occurs when the iron absorbs 2% to 4% carbon. Because the bloomery is self-fluxing, the addition of limestone is not required to form a slag.

The small particles of iron produced in this way fall to the bottom of the furnace, where they combine with molten slag, often consisting of fayalite, a compound of silicon, oxygen and iron mixed with other impurities from the ore. The hot liquid slag, running to the bottom of the furnace, cools against the base and lower side walls of the furnace, effectively forming a bowl still containing fluid slag. As the individual iron particles form, they fall into this bowl and sinter together under their own weight, forming a spongy mass referred to as the bloom. Because the bloom is typically porous, and its open spaces can be full of slag, the extracted mass must beaten with heavy hammers to both compress voids and drive out any molten slag remaining. This process may require several additional heating and compaction cycles, working at high 'welding' temperatures. Iron treated this way is said to be wrought (worked), and the resulting iron, with reduced amounts of slag, is called wrought iron or bar iron. Because of the creation process, individual blooms can often have differing carbon contents between the original top and bottom surfaces, differences that will also be somewhat blended together through the flattening, folding and hammer welding sequences. It is also possible to produce blooms coated in steel (higher carbon) by manipulating the charge of and air flow to the bloomery.[1]

As the era of modern commercial steelmaking began, the word bloom was extended to another sense referring to an intermediate-stage piece of steel, of a size comparable to many traditional iron blooms, that was ready to be further worked into billet.

History

See also: Early iron smelting, History of ferrous metallurgy, and Bronze Age
A drawing of a simple bloomery and bellows.
Bloomery smelting during the Middle Ages, as depicted in the De Re Metallica by Georgius Agricola, 1556

The onset of the Iron Age in most parts of the world coincides with the first widespread use of the bloomery. While earlier examples of iron are found, their high nickel content indicates that this is meteoric iron. Other early samples of iron may have been produced by accidental introduction of iron ore in copper smelting operations. Iron appears to have been smelted in the Middle East as early as 3000 BC, but copper smiths, not being familiar with iron, did not put it to use until much later. In the West, iron began to be used around 1200 BC.[2]

East Asia

China has long been considered the exception to the general use of bloomeries. It was thought that the Chinese skipped the bloomery process completely, starting with the blast furnace and the finery forge to produce wrought iron: by the 5th century BC, metalworkers in the southern state of Wu had invented the blast furnace and the means to both cast iron and to decarburize the carbon-rich pig iron produced in a blast furnace to a low-carbon, wrought iron-like material. Recent evidence, however, shows that bloomeries were used earlier in ancient China, migrating in from the west as early as 800 BC, before being supplanted by the locally developed blast furnace. Supporting this theory was the discovery of 'more than ten' iron digging implements found in the tomb of Duke Jing of Qin (d. 537 BCE), whose tomb is located in Fengxiang County, Shaanxi (a museum exists on the site today).[3]

Sub-Saharan Africa

All traditional sub-Saharan African iron smelting processes are variants of the bloomery process.[4] There is considerable discussion about the origins of iron metallurgy in Africa. Smelting in bloomery type furnaces in West Africa and forging of tools appeared in the Nok culture of central Nigeria by at least 550 BC and possibly several centuries earlier.[5][6] There is also evidence of iron smelting with bloomery style furnaces dated to 750 BC in Opi (Augustin Holl 2009) and Lejja dated to 2,000 BC (Pamela Eze-Uzomaka 2009), both sites in the Nsukka region of southeast Nigeria in what is now Igboland.[7][8][6] The site of Gbabiri, in the Central African Republic, has also yielded evidence of iron metallurgy, from a reduction furnace and blacksmith workshop; with earliest dates of 896-773 BC and 907-796 BC respectively.[6] The earliest records of bloomery-type furnaces in East Africa are discoveries of smelted iron and carbon in Nubia in ancient Sudan dated at least to the 7th to the 6th century BC. The ancient bloomeries that produced metal tools for the Nubians and Kushites produced a surplus for sale.[9][10][11]

South Asia

Wrought iron was used in the construction of monuments like the Iron pillar of Delhi, built in the 3rd century AD during the Gupta Empire. The latter was built using a towering series of disc-shaped iron blooms. Similar to China, high-carbon steel was eventually used in India, although cast iron was not used for architecture until modern times.[12]

Early to Medieval Europe

A Catalan furnace, with tuyere and bellows on the right

Early European bloomeries were relatively small, primarily do to the mechanical limits of human powered bellows and the amount of force possible to apply with hand driven sledge hammers. Those known archaeologically from the pre-Roman Iron Age tend to be in the 2 kg range, produced in low shaft furnaces. Roman era production often used furnaces tall enough to create a natural draft effect (into the range of 200 cm tall), and increasing bloom sizes into the range of 10 - 15 kg. [13] Contemporary experimenters had routinely made blooms using Northern European derived 'short shaft' furnaces with blown air supplies in the 5 - 10 kg range [14] The use of waterwheel, spreading around the turn of the first millennium and used to power more massive bellows allowed the bloomery to become larger and hotter, with associated trip hammers allowing the consolodation forging of the larger blooms created. Progressively larger bloomeries were constructed in the late 14th century, with a capacity of about 15 kg on average, though exceptions did exist. European average bloom sizes quickly rose to 300 kg, where they levelled off until the demise of the bloomery.

As a bloomery's size is increased, the iron ore is exposed to burning charcoal for a longer time. When combined with the strong air blast required to penetrate the large ore and charcoal stack, this may cause part of the iron to melt and become saturated with carbon in the process, producing unforgeable pig iron which requires oxidation to be reduced into cast iron, steel, and iron. This pig iron was considered a waste product detracting from the largest bloomeries' yield, and it was not until the 14th century that early blast furnaces, identical in construction but dedicated to the production of molten iron, were built.[15][16]

Bloomery type furnaces typically produced a range of iron products from very low carbon iron to steel containing approximately 0.2% to 1.5% carbon. The master smith had to select pieces of low carbon iron, carburize them, and pattern-weld them together to make steel sheets. Even when applied to a non-carburized bloom, this pound, fold and weld process resulted in a more homogeneous product and removed much of the slag. The process had to be repeated up to 15 times when high quality steel was needed, as for a sword. The alternative was to carburize the surface of a finished product. Each welding's heat oxidises some carbon, so the master smith had to make sure there was enough carbon in the starting mixture.[17][18]

In England and Wales, despite the arrival of the blast furnace in the Weald in about 1491, bloomery forges, probably using water-power for the hammer as well as the bellows, were operating in the West Midlands region beyond 1580. In Furness and Cumberland, they operated into the early 17th century and the last one in England (near Garstang) did not close until about 1770.[19]

One of the oldest known blast furnaces in Europe has been found in Lapphyttan in Sweden, carbon-14 dated to be from the 12th century.[20] The oldest bloomery in Sweden, also found in the same area, has been carbon-14 dated to 700 BCE.[21]

Bloomeries survived in Spain and southern France as Catalan forges into the mid-19th century,[22] and in Austria as the Stückofen [fr] to 1775.

The Americas

Excavations at L'Anse aux Meadows Newfoundland have found considerable evidence for the processing of bog iron and the production of iron in a bloomery by the Norse.[23] The cluster of Viking Age (c 1000 - 1022 AD) at L'Anse aux Meadows are situated on a raised marine terrace, between a sedge peat bog and the ocean. Estimates from the smaller amount of slag recovered archaeologically suggest 15 kg of slag was produced during what appears to have been a single smelting attempt. By comparing the iron content of the primary bog iron ore found in the purpose built 'furnace hut' with the iron remaining in that slag, an estimated 3 kg iron bloom was produced. (At a yield of at best 20% from what is a good iron rich ore, this suggests the workers processing the ore had not been paticularly skilled.[23] This supports the idea that iron processing knowledge was widespread and not restricted to major centers of trade and commerce.[23] 98 nail, and importantly, ship rivet fragments, were also found at the site as well as considerable evidence for woodworking - which points to boat or possibly ship repairs being undertaken at the site.[23][24] (An important consideration remains that a potential 3 kg raw bloom most certainly does not make enough refined bar to manufacture the 3 kg of recovered nails and rivets!)

A view of the bloomeries ('Catalan forges') at Mission San Juan Capistrano, the oldest (circa 1790s) existing facilities of their kind in California.

In the Spanish colonization of the Americas, bloomeries or "Catalan forges" were part of 'self sufficiency' at some of the missions, encomiendas, and pueblos. As part of the Franciscan Spanish missions in Alta California, the "Catalan forges" at Mission San Juan Capistrano from the 1790s are the oldest existing facilities of their kind in the present day state of California. The bloomeries' sign proclaims the site as being "...part of Orange County's first industrial complex."

The archaeology at Jamestown Virginia (cira 1610-15, citation needed), had recoved the remains of a simple short shaft bloomery furnace, likely intended as yet another 'resource test' like the one in Vinland much earlier. The English settlers of the 13 colonies were prevented by law from manufacture; for a time, the British sought to situate most of the skilled artisanry at domestic locations. In fact, this was one of the problems which led to the revolution.[citation needed] The Falling Creek Ironworks was the first in the United States. The Neabsco Iron Works is an example of the early Virginian effort to form a workable American industry.

In the Adirondacks, New York, new bloomeries using the hot blast technique were built in the 19th century.[25]

See also

References

Bloomery iron furnace along Bloomery Pike (West Virginia Route 127) near Bloomery, West Virginia, United States.
  1. ^ Smelting Enriched Bog Ore in a Low Shaft Bloomery
  2. ^ "The History of Forging - Now and Then". Canton Drop Forge. Canton Drop Forge.
  3. ^ "The Earliest Use of Iron in China" by Donald B. Wagner in Metals in Antiquity, by Suzanne M. M. Young, A. Mark Pollard, Paul Budd and Robert A. Ixer (BAR International Series, 792), Oxford: Archaeopress, 1999, pp. 1–9.
  4. ^ Cline, W.W. (1937) Mining and Metallurgy in Negro Africa. Menasha, WI: George Banta
  5. ^ Eggert, Manfred (2014). "Early iron in West and Central Africa". In Breunig, P (ed.). Nok: African Sculpture in Archaeological Context. Frankfurt, Germany: Africa Magna Verlag Press. pp. 51–59.
  6. ^ a b c Eggert, Manfred (2014). "Early iron in West and Central Africa". In Breunig, P (ed.). Nok: African Sculpture in Archaeological Context. Frankfurt, Germany: Africa Magna Verlag Press. pp. 53–54. ISBN 9783937248462.
  7. ^ Eze–Uzomaka, Pamela. "Iron and its influence on the prehistoric site of Lejja". Academia.edu. University of Nigeria,Nsukka, Nigeria. Retrieved 12 December 2014.
  8. ^ Holl, Augustin F. C. (6 November 2009). "Early West African Metallurgies: New Data and Old Orthodoxy". Journal of World Prehistory. 22 (4): 415–438. doi:10.1007/s10963-009-9030-6. S2CID 161611760.
  9. ^ Collins, Robert O.; Burns, James M. (8 February 2007). A History of Sub-Saharan Africa. Cambridge University Press. ISBN 9780521867467 – via Google Books.
  10. ^ Edwards, David N. (29 July 2004). The Nubian Past: An Archaeology of the Sudan. Taylor & Francis. ISBN 9780203482766 – via Google Books.
  11. ^ Humphris J, Charlton MF, Keen J, Sauder L, Alshishani F (June 2018). "Iron Smelting in Sudan: Experimental Archaeology at The Royal City of Meroe". Journal of Field Archaeology. 43 (5): 399–416. doi:10.1080/00934690.2018.1479085.
  12. ^ Ranganathan, Srinivasa; Srinivasan, Sharada. (1997). "METALLURGICAL HERITAGE OF INDIA", in Golden Jubilee Souvenir, Indian Institute of Science, pp. 29-36, (University of Illinois, Department of Materials Science and Engineering web page). Accessed 30 October 2019.
  13. ^ Radomir Pliener, Iron in Archaeology - the European Bloomery Smelters, chapter XII, 2000
  14. ^ Darrell Markewitz, 'If you don't get any IRON - Towards an Effective Method for Small Iron Smelting Furnaces', EXARC Journal 2012-1 (https://exarc.net/ark:/88735/10041)
  15. ^ Douglas Alan Fisher, The Epic of Steel, Harper & Row 1963, p. 26-29
  16. ^ Blast furnace, theory and practice, American Institute of mining, metallurgical, and petroleum engineers, Gordon and Breach science 1969, p. 4-5
  17. ^ "Some Aspects of the Metallurgy and Production of European Armor". Archived from the original on 22 April 2002. Retrieved 14 July 2012.
  18. ^ Alan R. Williams, Methods of manufacture of swords in medieval Europe, Gladius 1977, p. 70-77
  19. ^ H. R. Schubert, History of the British Iron and Steel Industry (1957). R. F. Tylecote, History of Metallurgy (1991).
  20. ^ "The blast furnace in earlier times".
  21. ^ Magnusson G (2015) Järnet och Sveriges medeltida modernisering. Jernkontoret, Stockholm
  22. ^ "Bloomery process". Encyclopædia Britannica. Retrieved 15 July 2017. The final version of this kind of bloomery hearth survived in Spain until the 19th century.
  23. ^ a b c d Bowles, G., R. Bowker, and N. Samsonoff (2011). "Viking expansion and the search for bog iron". Platforum. 12: 25–37.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  24. ^ Lewis-Simpson, Shannon (2000). Vinland Revisited: The Norse World at the Turn of the First Millennium. St. John's, Newfoundland: St. John's, Newfoundland: Historic Sites Association of Newfoundland and Labrador, Inc. ISBN 0-919735-07-X.
  25. ^ Gordon C. Pollard, 'Experimentation in 19th century bloomery production: evidence from the Adirondacks of New York' Historical Metallurgy 32(1) (1998), 33–40.
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