Editing Pottery (section)

===Firing===
[[File:Firing.jpg|thumb|A modern tunnel kiln]]
Firing produces permanent and irreversible chemical and physical changes in the body. It is only after firing that the article or material is pottery. In lower-fired pottery, the changes include [[sintering]], the fusing together of coarser particles in the body at their points of contact with each other. In the case of porcelain, where higher firing-temperatures are used, the physical, chemical and mineralogical properties of the constituents in the body are greatly altered. In all cases, the reason for firing is to permanently harden the wares, and the firing regime must be appropriate to the materials used.

====Temperature====
As a rough guide, modern earthenwares are normally fired at temperatures in the range of about {{convert|1000|°C|lk=in}} to {{convert|1,200|°C|°F}}; stonewares at between about {{convert|1100|°C|°F}}  to {{convert|1300|°C|°F}}; and porcelains at between about {{convert|1200|°C|°F}}  to {{convert|1400|°C|°F}}. Historically, reaching high temperatures was a long-lasting challenge, and earthenware can be fired effectively as low as {{convert|600|°C}}, achievable in primitive [[Pit fired pottery|pit firing]]. The time spent at any particular temperature is also important, the combination of heat and time is known as [[heatwork]].

[[Kiln]]s can be monitored by [[pyrometer]]s, [[thermocouple]]s and [[Pyrometric device|pyrometric devices]].

====Atmosphere====
[[File:Bottle Kiln.JPG|thumb|A [[bottle kiln]]]]
The atmosphere within a kiln during firing can affect the appearance of the body and glaze. Key to this is the differing colours of the various oxides of iron, such as [[iron(III) oxide]] (also known as ferric oxide or Fe<sub>2</sub>O<sub>3</sub>) which is associated with brown-red colours, whilst [[iron(II) oxide]] (also known as ferrous oxide or FeO) is associated with much darker colours, including black. The oxygen concentration in the kiln influences the type, and relative proportions, of these iron oxides in fired the body and glaze: for example, where there is a lack of oxygen during firing the associated [[carbon monoxide]] (CO) will readily react with oxygen in Fe<sub>2</sub>O<sub>3</sub> in the raw materials and cause it to be reduced to FeO.<ref name="auto">'The Emergence Of Ceramic Technology And Its Evolution As Revealed With The Use Of Scientific Techniques.' Y. Maniatis. Mine to Microscope: Advances in the Study of Ancient. (ed. A.J. Shortland, I.C. Freestone and T. Rehren ) Oxbow Books, Oxford, (2009). Chapter 2.</ref><ref name="auto1">'The Firing Of Clay-Based Ceramics.' W. H. Holmes. Science Progress. Vol. 60, No. 237 (Spring 1972), pg. 98</ref>

An oxygen deficient condition, called a reducing atmosphere, is generated by preventing the complete combustion of the kiln fuel; this is achieved by deliberately restricting the supply of air or by supplying an excess of fuel.<ref name="auto"/><ref name="auto1"/>

==== Methods ====
Firing pottery can be done using a variety of methods, with a [[kiln]] being the usual firing method. Both the maximum temperature and the duration of firing influences the final characteristics of the ceramic. Thus, the maximum temperature within a kiln is often held constant for a period of time to ''soak'' the wares to produce the maturity required in the body of the wares.

Kilns may be heated by burning combustible materials, such as [[wood]], [[coal]] and [[Fuel gas|gas]], or by [[electricity]]. The use of microwave energy has been investigated.<ref>Sutton, W.H. Microwave Processing of Ceramics – An Overview. MRS Online Proceedings Library 269, 3–20 (1992).</ref>

When used as fuels, coal and wood can introduce smoke, soot and ash into the kiln which can affect the appearance of unprotected wares. For this reason, wares fired in wood- or coal-fired kilns are often placed in the kiln in [[saggar]]s, ceramic boxes, to protect them. Modern kilns fuelled by gas or electricity are cleaner and more easily controlled than older wood- or coal-fired kilns and often allow shorter firing times to be used.
[[File:Pottery_firing_Mali.jpg|thumb|Pottery firing mound in [[Kalabougou]], [[Mali]]. Much of the earliest pottery would have been fired in a similar fashion.]]

Niche techniques include:
*In a Western adaptation of traditional Japanese [[raku ware]] firing, wares are removed from the kiln while hot and smothered in ashes, paper or woodchips which produces a distinctive [[carbonization|carbonised]] appearance. This technique is also used in Malaysia in creating traditional ''labu sayung''.<ref>{{cite web |url=http://www.brothers-handmade.com/potteryhistory.html |title=History of Pottery |website=Brothers-handmade.com |access-date=2010-09-04 |url-status=dead |archive-url=https://web.archive.org/web/20130601232455/http://www.brothers-handmade.com/potteryhistory.html |archive-date=2013-06-01 }}</ref><ref>{{cite web |author=Malaxi Teams |url=http://www.malaxi.com/perak/labu_sayong.html |title=Labu Sayong, Perak |website=Malaxi.com |access-date=2010-09-04 |url-status=dead |archive-url=https://web.archive.org/web/20121104011251/http://www.malaxi.com/perak/labu_sayong.html |archive-date=2012-11-04 }}</ref>
*In [[Mali]], a firing mound is used rather than a brick or stone kiln. Unfired pots are first brought to the place where a mound will be built, customarily by the women and girls of the village. The mound's foundation is made by placing sticks on the ground, then:{{blockquote|[...] pots are positioned on and amid the branches and then grass is piled high to complete the mound. Although the mound contains the pots of many women, who are related through their husbands' extended families, each women is responsible for her own or her immediate family's pots within the mound.<p>When a mound is completed and the ground around has been swept clean of residual combustible material, a senior potter lights the fire. A handful of grass is lit and the woman runs around the circumference of the mound touching the burning torch to the dried grass. Some mounds are still being constructed as others are already burning.<ref>{{cite journal|last=Goldner|first=Janet|title=The women of Kalabougou|journal=African Arts|date=Spring 2007|volume=40|issue=1|pages=74–79|doi=10.1162/afar.2007.40.1.74|s2cid=57567441}}</ref></p>}}

====Stages====
* ''[[Biscuit (pottery)|Biscuit]]'' (or bisque)<ref>"The Fast Firing Of Biscuit Earthenware Hollow-Ware In a Single-Layer Tunnel Kiln." Salt D.L. Holmes W.H. RP737. ''Ceram Research''.</ref><ref>"New And Latest Biscuit Firing Technology". Porzellanfabriken Christian Seltmann GmbH. ''Ceram.Forum Int.''/Ber.DKG 87, No. 1/2, pp. E33–E34, E36. 2010</ref> refers to the clay after the object is shaped to the desired form and fired in the kiln for the first time, known as "bisque fired" or "biscuit fired". This firing results in both chemical and physical changes to the minerals of the clay body.
* ''Glaze fired'' is the final stage of some pottery making, or ''glost fired''.<ref name="ReferenceA2" /> A [[Ceramic glaze|glaze]] may be applied to the biscuit ware and the object can be decorated in several ways. After this the object is "glazed fired", which causes the glaze material to melt, then adhere to the object. Depending on the temperature schedule the glaze firing may also further mature the body as chemical and physical changes continue.