A Walloon forge (or Walloon process) is a type of finery forge that decarbonizes

pig iron Pig iron, also known as crude iron, is an intermediate product of the iron industry in the production of steel which is obtained by smelting iron ore in a blast furnace. Pig iron has a high carbon content, typically 3.8–4.7%, along with silic ...

into

wrought iron Wrought iron is an iron alloy with a very low carbon content (less than 0.08%) in contrast to that of cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag Inclusion (mineral), inclusions (up to 2% by weight), which give it a ...

. The process was conceived in the

Liège Liège ( , , ; wa, Lîdje ; nl, Luik ; german: Lüttich ) is a major city and municipality of Wallonia and the capital of the Belgian province of Liège. The city is situated in the valley of the Meuse, in the east of Belgium, not far from b ...

region, and from there extended to France, then England around the end of the 15th century. Louis de Geer brought it to

Roslagen Roslagen is the name of the coastal areas of Uppland province in Sweden, which also constitutes the northern part of the Stockholm archipelago. Historically, it was the name for all the coastal areas of the Baltic Sea, including the eastern par ...

Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...

at the beginning of the 17th century, with Walloon blacksmiths. The Walloon process spread to Sweden in the

Uppland Uppland () is a historical province or ' on the eastern coast of Sweden, just north of Stockholm, the capital. It borders Södermanland, Västmanland and Gästrikland. It is also bounded by lake Mälaren and the Baltic Sea. On the small uninhab ...

province north of

Stockholm Stockholm () is the Capital city, capital and List of urban areas in Sweden by population, largest city of Sweden as well as the List of urban areas in the Nordic countries, largest urban area in Scandinavia. Approximately 980,000 people liv ...

, where it was used to produce a specific kind of wrought iron called

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 port from which the bar iron was shipped. It was produced using the Wal ...

In Sweden

The source material was pig iron produced by a

blast furnace A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally pig iron, but also others such as lead or copper. ''Blast'' refers to the combustion air being "forced" or supplied above atmospheric ...

using

charcoal Charcoal is a lightweight black carbon residue produced by strongly heating wood (or other animal and plant materials) in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, cal ...

and the

manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...

rich

iron ore Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the fo ...

from the

Dannemora mine The Dannemora mine (''Dannemora gruvor'') at Dannemora in Uppsala County, Sweden was once one of the most important iron ore mines in Sweden. The mine was closed by its owners SSAB in 1992. It may have been open since the 13th century, but the ...

. A "V" shaped

hearth A hearth () is the place in a home where a fire is or was traditionally kept for home heating and for cooking, usually constituted by at least a horizontal hearthstone and often enclosed to varying degrees by any combination of reredos (a lo ...

using charcoal was used to heat up the pig iron bar that was presented to a tuyere that decarbonized it and made it melt and fall in drops that solidified in a pool of

slag Slag is a by-product of smelting (pyrometallurgical) ores and used metals. Broadly, it can be classified as ferrous (by-products of processing iron and steel), ferroalloy (by-product of ferroalloy production) or non-ferrous/base metals (by-prod ...

where the decarburization continued.American iron 1607-1900
by Robert Boyd Gordon The iron drops were picked up with an iron bar and presented again in front of the tuyere and one by one agglomerated into a ball. That heterogeneous iron was full of slag and the carbon content ranged from pure iron to nearly pig iron. It was therefore reheated in a

chafery A chafery is a variety of hearth used in ironmaking for reheating a bloom of iron, in the course of its being drawn out into a bar of wrought iron. The equivalent term for a bloomery was string hearth, except in 17th century Cumbria, where the ...

and hammered and folded using a

waterwheel A water wheel is a machine for converting the energy of flowing or falling water into useful forms of power, often in a watermill. A water wheel consists of a wheel (usually constructed from wood or metal), with a number of blades or buckets ...

powered trip hammer. The ore from Dannemora was very low in

sulphur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...

and high in manganese. It is possible the manganese bonded with the impurities during the

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

, creating a pretty pure wrought iron. The use of charcoal prevented the contamination with impurities usually associated with the usage of

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dea ...

or coke, of which Sweden has none. In England, the chafery might use coal or coke, as in this stage the iron is solidified and the contamination remain low. The iron was sold to England, where it was recarbonized into

blister steel The cementation process is an obsolete technology for making steel by carburization of iron. Unlike modern steelmaking, it increased the amount of carbon in the iron. It was apparently developed before the 17th century. Derwentcote Steel Fur ...

using the

cementation process The cementation process is an obsolete technology for making steel by carburization of iron. Unlike modern steelmaking, it increased the amount of carbon in the iron. It was apparently developed before the 17th century. Derwentcote Steel F ...

. This

steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...

still contain some slag, and if the carbon was around 1% at the surface, it was lower in the center. The blister steel was than purchased by Benjamin Huntsman who melted it in a crucible heated using coke and poured it. This modern crucible steel was different from the medieval

wootz Wootz steel, also known as Seric steel, is a crucible steel characterized by a pattern of bands and high carbon content. These bands are formed by sheets of microscopic carbides within a tempered martensite or pearlite matrix in higher carbon st ...

, but was homogeneous and without slag.

References

{{reflist Steelmaking Metallurgical processes