Editing Pottery (section)

==Production==
[[File:Sèvres - Moulin - boudineuse-désaéreuse 027.jpg|thumb|Clay body being extruded from a de-airing pug]]
The production of pottery includes the following stages:
* Preparing the clay body.
* Shaping
* Drying
* Firing
* Glazing and decorating. (This can be undertaken prior to firing. Also, additional firing stages after decoration may be needed.)
{{Anchor | Shaping | Methods | Methods of shaping }}<!-- This section is linked from [[Throwing]] -->

=== Shaping ===
Before being shaped, clay must be prepared. This may include [[List of pottery terms#K|kneading]] to ensure an even moisture content throughout the body. Air trapped within the clay body needs to be removed, or de-aired, and can be accomplished either by a machine called a vacuum [[List of pottery terms#pug|pug]] or manually by [[List of pottery terms#W|wedging]]. Wedging can also help produce an even moisture content. Once a clay body has been kneaded and de-aired or wedged, it is shaped by a variety of techniques, which include:

* Hand-building: This is the earliest forming method. Wares can be constructed by hand from [[Coiling (pottery)|coils of clay]], combining flat slabs of clay, or [[Pinch pot|pinching]] solid balls of clay or some combination of these. Parts of hand-built vessels are often joined with the aid of [[Slip (ceramics)|slip]]. Some [[studio potters]] find hand-building more conducive for one-of-a-kind works of [[art]].[[File:At_the_potter's_workshop.webm|thumb|A potter using a potter's wheel describes his materials (in Romanian and English)]]
* The [[potter's wheel]]:  In a process called "throwing" (coming from the [[Old English]] word ''thrawan'' which means to twist or turn<ref>{{Cite web |date=June 12, 2019 |title=Why On Earth Do They Call It Throwing? {{pipe}} Contractor Quotes |url=https://contractorquotes.us/earth-call-throwing/ |url-status=dead |archive-url=https://web.archive.org/web/20070203065817/http://www.ceramicstoday.com/articles/why_throwing.htm |archive-date=February 3, 2007}}</ref>) a ball of clay is placed in the centre of a turntable, called the wheel-head, which the potter rotates with a stick, with foot power or with a variable-speed [[electric motor]]. During the process of throwing, the wheel rotates while the solid ball of soft clay is pressed, squeezed and pulled gently upwards and outwards into a hollow shape. Skill and experience are required to throw pots of an acceptable standard and, while the ware may have high artistic merit, the reproducibility of the method is poor.<ref name="ReferenceA2">"Whitewares: Production, Testing And Quality Control." W.Ryan & C.Radford. ''Pergamon Press.'' 1987</ref> Because of its inherent limitations, throwing can only be used to create wares with [[radial symmetry]] on a [[vertical axis]].
* Press moulding: a simple technique of shaping by manually pressing a lump of clay body into a porous mould.<ref>Two Centuries of Hellenistic Pottery Homer A. Thompson. Vol. 3, No. 4, The American Excavations in the Athenian Agora: Fifth Report (1934), pp. 311-476. The American School of Classical Studies at Athens</ref><ref>New Zealand Potter. Vol. 30 No. 1 1988, pp. 7</ref><ref>Forming Techniques - for the Self-Reliant Potter.  Henrik Norsker, James Danisch. Vieweg+1991.Teubner Verlag Wiesbaden</ref>
* Granulate pressing: a highly automated technique of shaping by pressing clay body in a semi-dry and granulated form in a [[Moulding (process)|mould]]. The body is pressed into the mould by a porous die through which water is pumped at high pressure. The fine, free flowing [[Granular material|granulated]] body is prepared by [[spray drying]] a high-solids content slip. Granulate pressing, also known as ''dust pressing'', is widely used in the manufacture of [[ceramic tile]]s and, increasingly, of plates.<ref>Using Polymers as a Binder for Improvement of Mechanical Strength of Tableware in Isostatics Press Technology. A. Arasteh Nodeh. Iranian Chemical Engineering Journal – Vol.9 - No. 48 (2010)</ref><ref>Control And Automation In The Ceramic Industry Evolution. José Gustavo Mallol Gasch. Ceramic Forum International. December 2007 84 (12):E55-E57</ref><ref>Reference Document On Best Available Techniques In The Ceramic Manufacturing Industry. European Commission August 2007</ref>[[File:Sèvres_-_Grand_atelier_-_calibrage_140.jpg|thumb|Jiggering a plate]]
* [[List of pottery terms#J|Jiggering and jolleying]]: These operations are carried out on the potter's wheel and allow the time taken to bring wares to a standardized form to be reduced. ''Jiggering'' is the operation of bringing a shaped tool into contact with the plastic clay of a piece under construction, the piece itself being set on a rotating plaster mould on the wheel. The jigger tool shapes one face while the mould shapes the other. Jiggering is used only in the production of flat wares, such as plates, but a similar operation, ''jolleying'', is used in the production of hollow-wares such as cups. Jiggering and jolleying have been used in the production of pottery since at least the 18th century. In large-scale factory production, jiggering and jolleying are usually automated, which allows the operations to be carried out by semi-skilled labour.
* [[List of pottery terms|Roller-head machine]]: This machine is for shaping wares on a rotating mould, as in jiggering and jolleying, but with a rotary shaping tool replacing the fixed profile. The rotary shaping tool is a shallow cone having the same diameter as the ware being formed and shaped to the desired form of the back of the article being made. Wares may in this way be shaped, using relatively unskilled labour, in one operation at a rate of about twelve pieces per minute, though this varies with the size of the articles being produced. Developed in the UK just after [[World War II]] by the company ''Service Engineers'', roller-heads were quickly adopted by manufacturers around the world; it remains the dominant method for producing both flatware and holloware, such as plates and mugs.<ref>An Introduction To The Technology Of Pottery. Paul Rado. Pergamon Press. 1969</ref>
* Pressure casting: Is a development of traditional slipcasting. Specially developed [[Polymeric material|polymeric materials]] allow a mould to be subject to application external pressures of up to 4.0 MPa – so much higher than slip casting in plaster moulds where the capillary forces correspond to a pressure of around 0.1–0.2 MPa. The high pressure leads to much faster casting rates and, hence, faster production cycles. Furthermore, the application of high pressure air through the polymeric moulds upon demoulding the cast means a new casting cycle can be started immediately in the same mould, unlike plaster moulds which require lengthy drying times. The polymeric materials have much greater durability than plaster and, therefore, it is possible to achieve shaped products with better dimensional tolerances and much longer mould life. Pressure casting was developed in the 1970s for the production of sanitaryware although, more recently, it has been applied to tableware.<ref>'Sanitaryware Technology'. Domenico Fortuna. Gruppo Editoriale Faenza Editrice S.p.A. 2000.</ref><ref>{{cite web |title=DGM-E.pdf |url=http://www.dorst.de/dorst_seite/Infolines_PDF/Infoline%20DGM/DGM-E.pdf |access-date=2010-09-04}}{{dead link|date=August 2017|bot=InternetArchiveBot|fix-attempted=yes}}</ref><ref>{{cite web |date=2000-11-21 |title=Ceramicindustry.com |url=http://www.ceramicindustry.com/Articles/Feature_Article/4025c9fbcb9c7010VgnVCM100000f932a8c0____ |url-status=dead |archive-url=https://web.archive.org/web/20110708132727/http://www.ceramicindustry.com/Articles/Feature_Article/4025c9fbcb9c7010VgnVCM100000f932a8c0____ |archive-date=2011-07-08 |access-date=2010-09-04 |website=Ceramic industries.com}}</ref><ref>''Dictionary Of Ceramics''. Arthur Dodd & David Murfin. 3rd edition. The Institute Of Minerals. 1994.</ref>
* [[RAM press]]ing: This is used to shape ware by pressing a bat of prepared clay body into a required shape between two porous moulding plates. After pressing, compressed air is blown through the porous mould plates to release the shaped wares.<ref>Operations Optimization Of RAM Press Machine By Frame Assembly Techniques. Pairoj Bootpeng, Yuttapong Naksopon, Nuttawut Pebkhuntod, Pattana
Charuenying, And Pakawadee Sirilar. Suranaree J. Sci. Technol. 21(2):105-109</ref>[[File:Slip_Casting_di_kilang_Claytan.png|thumb|Filling a plaster mould with slip]][[File:Sèvres_-_petit_coulage_-_démoulage_19.jpg|thumb|De-moulding a large vase after it has been slip cast]]
* [[Slip casting]]: This is suited to the making of shapes that cannot be formed by other methods. A liquid [[Slip (ceramics)|slip]], made by mixing [[clay]] body with water, is poured into a highly absorbent plaster mould. Water from the slip is absorbed into the mould leaving a layer of clay body covering its internal surfaces and taking its internal shape. Excess slip is poured out of the mould, which is then split open and the moulded object removed. Slip casting is widely used in the production of sanitaryware and is also used for making other complex shaped ware such as teapots and figurines.
* [[Injection moulding]]: This is a shape-forming process adapted for the tableware industry from the method long established for the forming of [[thermoplastic]] and some metal components.<ref>"Novel Approach To Injection Moulding." M.Y.Anwar, P.F. Messer, H.A. Davies, B. Ellis. Ceramic Technology International 1996. ''Sterling Publications Ltd.'', London, 1995. pp. 95–96, 98.</ref> It has been called ''Porcelain Injection Moulding'', or ''PIM''.<ref name="autogenerated103">"Injection Moulding Of Porcelain Pieces." A. Odriozola, M.Gutierrez, U.Haupt, A.Centeno. ''Bol. Soc. Esp. Ceram.'' Vidrio 35, No. 2, 1996. pp. 103–07</ref> Suited to the mass production of complex-shaped articles, one significant advantage of the technique is that it allows the production of a [[cup]], including the handle, in a single process, and thereby eliminates the handle-fixing operation and produces a stronger bond between cup and handle.<ref>"Injection Moulding Of Cups With Handles." U.Haupt. ''International Ceramics.'' No. 2, 1998, pp. 48–51.</ref> The feed to the mould die is a mix of approximately 50 to 60 per cent unfired body in powder form, together with 40 to 50 per cent organic additives composed of [[Binder (material)|binders]], [[lubricant]]s and [[Plasticizer|plasticisers]].<ref name="autogenerated103" /> The technique is not as widely used as other shaping methods.<ref>"Injection Moulding Technology In Tableware Production." ''Ceramic World Review.'' 13, No. 54, 2003. pp. 94, 96–97.</ref>
* [[3D printing]]: There are two methods. One involves the layered deposition of soft clay body similar to fused deposition modelling (FDM), and the other uses powder binding techniques where clay body in dry powder form is fused together layer upon layer with a liquid.<ref>Research on The Application of Ceramic 3D Printing Technology. Bin Zhao. March 2021 Journal of Physics Conference Series 1827(1):012057</ref><ref>From Control To Uncertainty In 3d Printing With Clay. Benay Gürsoy. Computing For A Better Tomorrow. Education And Research In Computer Aided Architectural Design In Europe. Pp. 21-30. 2018</ref>
* [[Injection moulding]] of ceramic tableware has been developed, though it has yet to be fully commercialised.<ref>'The Application Of Injection Moulding Technology In Modern Tableware Production. 'P. Quirmbach, S. Schwartz, F. Magerl. Ceramic Forum International 81(3):E24-E31, 2004</ref>

===Drying===
Prior to firing, the water in an article needs to be removed. A number of different stages, or conditions of the article, can be identified:
* ''[[Greenware (pottery)|Greenware]]'' refers to unfired objects at any stage of dryness, but is most often used to refer to objects ready to be fired. At sufficient moisture content, bodies at this stage are in their most plastic form (as they are soft and malleable, and hence can be easily deformed by handling). Prior to firing, any state of clay may be hydrated or dehydrated into any other unfired stage. 
* ''Plastic'', also known as ''wet'', refers to clay that is malleable and sufficiently wet to shape by hand or on a potter's wheel, but strong enough to hold its shape. At this stage the clay has between 20% and 25% moisture content.<ref>{{Cite web |title=Quick Tip: Reconstituting Clay |url=https://ceramicartsnetwork.org/ceramics-monthly/ceramics-monthly-article/quick-tip-reconstituting-clay# |access-date=2024-10-01 |website=Default |language=en}}</ref> This is the stage most commercial clays are sold at, and at which most of the shaping process is done.
* ''[[Leather-hard]]'' refers to a clay body that has been dried partially. At this stage the clay object has approximately 15% moisture content. Clay bodies at this stage are very firm and only slightly pliable. Trimming and handle attachment often occurs at the leather-hard state.
* ''Bone-dry'' refers to clay bodies when they reach a moisture content at or near 0%. At that moisture content, the item is ready to be fired. Additionally, the piece is extremely brittle at this stage and must be handled with care.<ref>{{Cite web |last=Kim |date=2012-04-02 |title=Need to know: Stages of drying in clay |url=https://www.claygeek.com/ceramics-101/need-to-know-stages-of-drying-for-clay/ |access-date=2024-10-01 |website=ClayGeek |language=en-US}}</ref><ref>{{Cite web |title=The 6 different stages of clay |url=https://www.oxfordclay.co.uk/blog-1/blog-post-title-four-de9r7-9yzl3 |access-date=2024-10-01 |website=Oxford Clay Handmade Ceramics - Eco-conscious pottery |language=en-US}}</ref>

===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.

=== Decorating ===
Pottery may be decorated in many different ways. Some decoration can be done before or after the firing, and may be undertaken before or after glazing.

====Methods====
[[File:Pottery in China 2.jpg|thumb|Hand painting a vase.]]
* Painting has been used since early prehistoric times, and can be very elaborate. The painting is often applied to pottery that has been fired once, and may then be overlaid with a glaze afterwards. Many [[pigment]]s change colour when fired, and the painter must allow for this.
* [[Ceramic glaze|Glaze]]: Perhaps the most common form of decoration, that also serves as protection to the pottery, by being tougher and keeping liquid from penetrating the pottery. Glaze may be colourless, especially over painting, or coloured and opaque.
* Crystalline glaze: acharacterised by crystalline clusters of various shapes and colours embedded in a more uniform and opaque glaze. Produced by the slow cooling of the glost fire.
* [[Carving]]: Pottery vessels may be decorated by shallow carving of the clay body, typically with a knife or similar instrument used on the wheel. This is common in Chinese porcelain of the classic periods.
* [[Burnishing (pottery)|Burnishing]]: The surface of pottery wares may be ''burnished'' prior to firing by rubbing with a suitable instrument of wood, steel or stone to produce a polished finish that survives firing. It is possible to produce very highly polished wares when fine clays are used or when the polishing is carried out on wares that have been partially dried and contain little water, though wares in this condition are extremely fragile and the risk of breakage is high.
* [[Terra Sigillata]] is an ancient form of decorating ceramics that was first developed in Ancient Greece.
* [[Lithography]], also called litho, although the alternative names of [[Transfer-print|transfer print]] or "''decal''" are also common. These are used to apply designs to articles. The litho comprises three layers: the colour, or image, layer which comprises the decorative design; the cover coat, a clear protective layer, which may incorporate a low-melting glass; and the backing paper on which the design is printed by screen printing or lithography. There are various methods of transferring the design while removing the backing-paper, some of which are suited to machine application.
* Banding is the application by hand or by machine of a band of colour to the edge of a plate or cup. Also known as "lining", this operation is often carried out on a potter's wheel.
* [[Agateware]]: named after its resemblance to the mineral [[agate]], is produced by partially blending clays of differing colours. In Japan the term "''neriage''" is used, whilst in China, where such things have been made since at least the [[Tang dynasty]], they are called "''marbled''" wares.
* [[Wikt:engobe|Engobe]]: a [[clay slip]] is used to coat the surface of pottery, usually before firing. Its purpose is often decorative though it can also be used to mask undesirable features in the clay to which it is applied. The engobe may be applied by painting or by dipping to provide a uniform, smooth, coating. Such decoration is characteristic of [[slipware]]. For [[sgraffito]] decoration a layer of engobe is scratched through to reveal the underlying clay.
* Gold: Decoration with gold is used on some high quality ware. Different methods exist for its application, including:[[File:Sèvres - brunissage 13.jpg|thumb|Burnishing a plate's gold decoration]]
** ''Best gold'' – a suspension of gold powder in essential oils mixed with a flux and a mercury salt extended. This can be applied by a painting technique. From the kiln, the decoration is dull and requires burnishing to reveal the full colour
** ''Acid Gold'' – a form of gold decoration developed in the early 1860s at the English factory of [[Mintons Ltd]]. The glazed surface is etched with diluted [[hydrofluoric acid]] prior to application of the gold. The process demands great skill and is used for the decoration only of ware of the highest class.
** ''Bright Gold'' – consists of a solution of gold sulphoresinate together with other metal resonates and a flux. The name derives from the appearance of the decoration immediately after removal from the kiln as it requires no burnishing
** ''Mussel Gold'' – an old method of gold decoration. It was made by rubbing together gold leaf, sugar and salt, followed by washing to remove solubles
** [[Underglaze]] decoration is applied, by a number of techniques, onto ware before it is glazed; an example is [[Blue and white porcelain|blue and white wares]]. Can be applied by a number of techniques.
** [[In-glaze decoration]] is applied on the surface of the [[Ceramic glaze|glaze]] before the [[glost firing]].
** [[On-glaze decoration]] is applied on top of the already fired, glazed surface, and then fixed in a second firing at a relatively low temperature.

===Glazing===
{{Main|Ceramic glaze}}
[[File:Sèvres - Émaillage - insufflation 050.jpg|thumb|Spraying glaze onto a vase]]
Glaze is a glassy coating on pottery, and reasons to use it include decoration, ensuring the item is impermeable to liquids, and minimizing the adherence of pollutants.

Glaze may be applied by spraying, dipping, trailing or brushing on an aqueous suspension of the unfired glaze. The colour of a glaze after it has been fired may be significantly different from before firing. To prevent glazed wares sticking to [[kiln furniture]] during firing, either a small part of the object being fired (for example, the foot) is left unglazed or, alternatively, special refractory "''spurs''" are used as supports. These are removed and discarded after the firing.

Some specialised glazing techniques include:
* [[Salt glaze pottery|Salt-glazing]] – [[common salt]] is introduced to the kiln during the firing process. The high temperatures cause the salt to volatilise, depositing it on the surface of the ware to react with the body to form a sodium aluminosilicate glaze. In the 17th and 18th centuries, salt-glazing was used in the manufacture of domestic pottery. Now, except for use by some studio potters, the process is obsolete. The last large-scale application before its demise in the face of environmental clean air restrictions was in the production of salt-glazed [[Sanitary sewer|sewer-pipes]].<ref>"Clay Sewer Pipe Manufacture. Part II – The Effect Of Variable Alumina, Silica And Iron Oxide In Clays On Some Properties Of Salt Glazes." H.G. Schurecht. ''The Journal of the American Ceramic Society.'' Volume 6. Issue 6, pp. 717–29.</ref><ref>"Dictionary Of Ceramics." Arthur Dodd & David Murfin. 3rd edition. ''The Institute Of Minerals.'' 1994.</ref>[[File:Large jar, Sanage ware, Heian period, 9th century, ash glaze - Tokyo National Museum - DSC05227.JPG|thumb|Ash glazed jar from 9th century, Japan.]]
* [[Ash glaze|Ash glazing]] – ash from the combustion of plant matter has been used as the flux component of glazes. The source of the ash was generally the combustion waste from the fuelling of kilns although the potential of ash derived from arable crop wastes has been investigated.<ref>"Ash Glaze Research." C. Metcalfe. ''Ceramic Review'' No. 202. 2003. pp. 48–50.</ref> Ash glazes are of historical interest in the Far East although there are reports of small-scale use in other locations such as the [[Catawba Valley Pottery]] in the United States. They are now limited to small numbers of studio potters who value the unpredictability arising from the variable nature of the raw material.<ref>"Glaze From Wood Ashes And Their Colour Characteristics." Y-S. Han, B-H. Lee. ''Korean Ceramic Society'' 41. No. 2. 2004.</ref>

===Health and environmental issues===
Although many of the environmental effects of pottery production have existed for millennia, some of these have been amplified with modern technology and scales of production. The principal factors for consideration fall into two categories:
* Effects on workers: Notable risks include [[silicosis]], [[toxic heavy metal|heavy metal poisoning]], poor [[indoor air quality]], [[noise health effects|dangerous sound levels]] and possible [[over-illumination]].
* Effects on the general environment.

Historically, [[lead poisoning]] (''plumbism'') was a significant health concern to those glazing pottery. This was recognised at least as early as the nineteenth century. The first legislation in the UK to limit pottery workers exposure to lead was included in the [[Factory Acts#Factories Act Extension Act 1867|Factories Act Extension Act in 1864]], with further introduced in 1899.<ref name=autogenerated1>{{Cite web |url=http://www.stokemuseums.org.uk/collections/browse_collections/ceramics/research_resources/general/health_risks_pottery |title=Stoke Museums – Health Risks in a Victorian Pottery Industry |date=7 July 2012 |website= |access-date=23 February 2022 |archive-url=https://web.archive.org/web/20120707001548/http://www.stokemuseums.org.uk/collections/browse_collections/ceramics/research_resources/general/health_risks_pottery |archive-date=7 July 2012 |url-status=dead}}</ref><ref>{{cite web | url=https://www.historyofosh.org.uk/timeline.html | title=Timeline – History of Occupational Safety and Health }}</ref>

[[Silicosis]] is an [[occupational lung disease]] caused by inhaling large amounts of crystalline silica dust, usually over many years. Workers in the ceramic industry can develop it due to exposure to [[silica]] dust in the raw materials; colloquially it has been known as 'Potter's rot'. Less than 10 years after its introduction, in 1720, as a raw material to the British ceramics industry the negative effects of calcined flint on the lungs of workers had been noted.<ref>'The Successful Prevention Of Silicosis Among China Biscuit Workers In The North Staffordshire Potteries.' A. Meiklejohn. British Journal Of Industrial Medicine, October 1963; 20(4): 255–263</ref> In one study reported in 2022, of 106 UK pottery workers 55 per cent had at least some stage of silicosis.<ref>'A Case Of Silicosis In The Ceramic Sector. 
Y. Yurt, M. Turk. EJMI. 2018; 2(1): 50–52</ref><ref>[https://www.nhs.uk/conditions/silicosis/ Silicosis], nhs.uk</ref><ref>[https://www.express.co.uk/life-style/health/1639348/cancer-warning-silicosis-risk-lung-cancer Cancer warning: The type of dust linked to a higher risk of lung cancer – 'harmful'], express.co.uk, 12 July 2022</ref> Exposure to siliceous dusts is reduced by either processing and using the source materials as aqueous suspension or as damp solids, or by the use of dust control measures such as [[Engineering controls#Local exhaust ventilation|local exhaust ventilation]]. These have been mandated by legislation, such as ''The Pottery (Health and Welfare) Special Regulations 1950'' in the UK.<ref>{{Cite web|url=https://www.legislation.gov.uk/uksi/1950/65/regulation/17/made|title=The Pottery (Health and Welfare) Special Regulations 1950}}</ref><ref>'Whitewares: Production, Testing And Quality Control." W.Ryan & C.Radford. Pergamon Press. 1987</ref> The [[Health and Safety Executive]] in the UK has produced guidelines<ref>UK Health and Safety Executive [https://www.hse.gov.uk/coshh/essentials/direct-advice/ceramics-silica.htm guidelines].</ref> on controlling exposure to respirable crystalline silica in potteries, and the British Ceramics Federation provide a guidance booklet.<ref>British Ceramics Federation [https://www.ceramfed.co.uk/resource/respirable-crystalline-silica-guide-2018/ guidance booklet]. {{Webarchive|url=https://web.archive.org/web/20230419090744/https://www.ceramfed.co.uk/resource/respirable-crystalline-silica-guide-2018/|date=2023-04-19}}</ref>

Environmental concerns include off-site [[water pollution]], [[air pollution]], disposal of [[hazardous materials]], disposal of rejected ware and fuel consumption.<ref>{{Cite web |date=2020-07-14 |title=Is Pottery Clay Eco-Friendly? – or is it Costing the Earth? |url=https://thepotterywheel.com/pottery-clay-eco-friendly/ |access-date=2022-05-10 |website=Pottery Tips by the Pottery Wheel |language=en-US}}</ref>