Editing Bloomery (section)

==Process==
[[File:Iron bloom.jpg|thumb|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 [[wikt:pit|pit]] or [[chimney]] with heat-resistant walls made of earth, [[clay]], or [[Rock (geology)|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 [[Redox|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 a number of regional, historic/traditional forms exist. Natural iron ores can vary considerably in oxide form ({{chem|Fe|2|O|3}} / {{chem|Fe|3|O|4}} / {{chem|Fe|O|(|O|H|)}}), 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 heated typically with a wood fire, shifting to burning 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 is 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 that 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 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 [[Sintering|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 be 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. Intentionally producing blooms that are coated in [[steel]] (i.e. iron with a higher carbon content) by manipulating the charge of and air flow to the bloomery is also possible.<ref>{{Cite web|url=http://iron.wlu.edu/reports/Eindhoven%20Smelt%20Report.htm|first1=Jonathan |last1=Thornton |first2=Skip |last2=Williams |first3=Aaron |last3=Shugar |title=The Rockbridge Bloomery – Reports: Smelting Enriched Bog Ore in a Low Shaft Bloomery |website=The Smelter's Art: Experimental Iron Production at The Rockbridge Bloomery |publisher=Washington and Lee University |access-date=21 August 2023}}</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]].