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Pottery is the process of forming vessels and other objects with clay and other ceramic materials, which are fired at high temperatures to give them a hard, durable form. Major types include earthenware, stoneware and porcelain. The place where such wares are made by a potter is also called a pottery (plural "potteries"). The definition of pottery used by the American Society for Testing and Materials (ASTM), is "all fired ceramic wares that contain clay when formed, except technical, structural, and refractory products."[2] In archaeology, especially of ancient and prehistoric periods, "pottery" often means vessels only, and figures etc. of the same material are called "terracottas". Clay as a part of the materials used is required by some definitions of pottery, but this is dubious.

Pottery is one of the oldest human inventions, originating before the Neolithic period, with ceramic objects like the Gravettian culture Venus of Dolní Věstonice figurine discovered in the Czech Republic dating back to 29,000–25,000 BC,[3] and pottery vessels that were discovered in Jiangxi, China, which date back to 18,000 BC. Early Neolithic pottery artefacts have been found in places such as Jōmon Japan (10,500 BC),[4] the Russian Far East (14,000 BC),[5] Sub-Saharan Africa and South America.

Pottery is made by forming a ceramic (often clay) body into objects of a desired shape and heating them to high temperatures (600-1600 °C) in a bonfire, pit or kiln and induces reactions that lead to permanent changes including increasing the strength and rigidity of the object.

Clay-based pottery can be divided into three main groups: earthenware, stoneware and porcelain. These require increasingly more specific clay material, and increasingly higher firing temperatures. All three are made in glazed and unglazed varieties, for different purposes. All may also be decorated by various techniques. In many examples the group a piece belongs to is immediately visually apparent, but this is not always the case. The fritware of the Islamic world does not use clay, so technically falls outside these groups. Historic pottery of all these types is often grouped as either "fine" wares, relatively expensive and well-made, and following the aesthetic taste of the culture concerned, or alternatively "coarse", "popular" "folk" or "village" wares, mostly undecorated, or simply so, and often less well-made.

Main types


All the earliest forms of pottery were made from clays that were fired at low temperatures, initially in pit-fires or in open bonfires.

Stoneware is pottery that has been fired in a kiln at a relatively high temperature, from about 1,100 °C to 1,200 °C, and is stronger and non-porous to liquids.[7] The Chinese, who developed stoneware very early on, classify this together with porcelain as high-fired wares.

Stoneware is very tough and practical, and much of it has always been utilitarian, for the kitchen or storage rather than the table.

Porcelain is made by heating materials, generally including kaolin, in a kiln to temperatures between 1,200 and 1,400 °C (2,200 and 2,600 °F). This is higher than used for the other types, and achieving these temperatures was a long struggle, as well as realizing what materials were needed. The toughness, strength and translucence of porcelain, relative to other types of pottery, arises mainly from vitrification and the formation of the mineral mullite within the body at these high temperatures.

Although porcelain was first made in China, the Chinese traditionally do not recognise it as a distinct category, grouping it with stoneware as "high-fired" ware, opposed to "low-fired" earthenware.

Production stages


Before being shaped, clay must be prepared.

  • Greenware refers to unfired objects. 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).
  • Leather-hard
  • 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.
  • Biscuit (or bisque)[10][11] 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 changes the clay body in several ways. Mineral components of the clay body will undergo chemical and physical changes that will change the material.
  • Glaze fired is the final stage of some pottery making, or glost fired.[12] A glaze may be applied to the bisque form 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.

Clay bodies and mineral contents


Body is a term for the main pottery form of a piece, underneath any glaze or decoration. The main ingredient of the body is clay. There are several materials that are referred to as clay. The properties which make them different include: Plasticity, the malleability of the body; the extent to which they will absorb water after firing; and shrinkage, the extent of reduction in size of a body as water is removed. Different clay bodies also differ in the way in which they respond when fired in the kiln. A clay body can be decorated before or after firing. Prior to some shaping processes, clay must be prepared. Each of these different clays is composed of different types and amounts of minerals that determine the characteristics of resulting pottery. There can be regional variations in the properties of raw materials used for the production of pottery, and these can lead to wares that are unique in character to a locality. It is common for clays and other materials to be mixed to produce clay bodies suited to specific purposes. A common component of clay bodies is the mineral kaolinite. Other minerals in the clay, such as feldspar, act as fluxes which lower the vitrification temperature of bodies. Following is a list of different types of clay used for pottery.[13]

  • Kaolin, is sometimes referred to as china clay because it was first used in China. Used for porcelain.
  • Ball clay An extremely plastic, fine grained sedimentary clay, which may contain some organic matter. Small amounts can be added to porcelain bodies to increase plasticity.
  • Fire clay A clay having a slightly lower percentage of fluxes than kaolin, but usually quite plastic. It is highly heat resistant form of clay which can be combined with other clays to increase the firing temperature and may be used as an ingredient to make stoneware type bodies.
  • Stoneware clay Suitable for creating stoneware. Has many of the characteristics between fire clay and ball clay, having finer grain, like ball clay but is more heat resistant like fire clays.
  • Common red clay and shale clay have vegetable and ferric oxide impurities which make them useful for bricks, but are generally unsatisfactory for pottery except under special conditions of a particular deposit.[14]
  • Bentonite An extremely plastic clay which can be added in small quantities to short clay to increase the plasticity.

Methods of shaping


Pottery can be shaped by a range of methods that include:

  • 3D printing: This is the latest advance in forming ceramic objects. There are two methods. One involves the layered deposition of soft clay similar to FDM printing the other and powder binding techniques where dry clay powder is fused together layer upon layer with a liquid.

Decorating and glazing


Pottery may be decorated in many different ways.

  • 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 pigments change colour when fired, and the painter must allow for this.
  • 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 clear, especially over painting, or coloured and opaque. There is more detail in the section below.
  • 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 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.
  • Additives can be worked into the clay body prior to forming, to produce desired effects in the fired wares.
  • Lithography, also called litho, although the alternative names of 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.
  • Agateware is named after its resemblance to the quartz mineral agate which has bands or layers of colour that are blended together, agatewares are made by blending clays of differing colours together but not mixing them to the extent that they lose their individual identities. The wares have a distinctive veined or mottled appearance. The term "agateware" is used to describe such wares in the United Kingdom; in Japan the term "neriage" is used and in China, where such things have been made since at least the Tang Dynasty, they are called "marbled" wares. Great care is required in the selection of clays to be used for making agatewares as the clays used must have matching thermal movement characteristics.
  • Engobe: This is a clay slip, that 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. Engobe slip may be applied by painting or by dipping to provide a uniform, smooth, coating. Engobe has been used by potters from pre-historic times until the present day and is sometimes combined with sgraffito decoration, where a layer of engobe is scratched through to reveal the colour of the underlying clay. With care it is possible to apply a second coat of engobe of a different colour to the first and to incise decoration through the second coat to expose the colour of the underlying coat. Engobes used in this way often contain substantial amounts of silica, sometimes approaching the composition of a glaze.
  • Gold: Decoration with gold is used on some high quality ware.

Glaze is a glassy coating on pottery, the primary purposes of which are decoration and protection.

Some specialised glazing techniques include:

  • Salt-glazing, where common salt is introduced to the kiln during the firing process. The high temperatures cause the salt to volatize, 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 sewer-pipes.[25][26]
  • 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.[27] 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.[28]
  • Underglaze decoration (in the manner of many blue and white wares). Underglaze may be applied by brush strokes, air brush, or by pouring the underglaze into the mould, covering the inside, creating a swirling effect, then the mould is filled with slip.
  • In-glaze decoration
  • On-glaze decoration
  • Enamel

Firing


Firing produces irreversible changes in the body.

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.

The atmosphere within a kiln during firing can affect the appearance of the finished wares.

Kilns may be heated by burning wood, coal and gas, or by electricity. 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 saggars, ceramic boxes, to protect them. Modern kilns powered 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. 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 carbonised appearance. This technique is also used in Malaysia in creating traditional labu sayung.[29][30]

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:

History


A great part of the history of pottery is prehistoric, part of past pre-literate cultures. Therefore, much of this history can only be found among the artifacts of archaeology. Because pottery is so durable, pottery and shards of pottery survive from millennia at archaeological sites, and are typically the most common and important type of artifact to survive. Many prehistoric cultures are named after the pottery that is the easiest way to identify their sites, and archaeologists develop the ability to recognise different types from the chemistry of small shards.

Before pottery becomes part of a culture, several conditions must generally be met.

  • First, there must be usable clay available.
  • Second, it must be possible to heat the pottery to temperatures that will achieve the transformation from raw clay to ceramic.
  • Third, the potter must have time available to prepare, shape and fire the clay into pottery.
  • Fourth, there must be a sufficient need for pottery in order to justify the resources required for its production.[32]
  • Methods of forming: Hand-shaping was the earliest method used to form vessels.
  • Firing: The earliest method for firing pottery wares was the use of bonfires pit fired pottery. Firing times might be short but the peak-temperatures achieved in the fire could be high, perhaps in the region of 900 °C (1,650 °F), and were reached very quickly.[33]
  • Clay: Early potters used whatever clay was available to them in their geographic vicinity.
  • Form: In the main, early bonfire-fired wares were made with rounded bottoms to avoid sharp angles that might be susceptible to cracking.
  • Glazing: the earliest pots were not glazed.
  • The potter's wheel was invented in Mesopotamia sometime between 6,000 and 4,000 BC (Ubaid period) and revolutionised pottery production.
  • Moulds were used to a limited extent as early as the 5th and 6th century BC by the Etruscans[34] and more extensively by the Romans.[35]
  • Slipcasting, a popular method for shaping irregular shaped articles. It was first practised, to a limited extent, in China as early as the Tang dynasty.[36]
  • Transition to kilns: The earliest intentionally constructed were pit-kilns or trench-kilns—holes dug in the ground and covered with fuel. Holes in the ground provided insulation and resulted in better control over firing.[37]
  • Kilns: Pit fire methods were adequate for creating simple earthenware, but other pottery types needed more sophisticated kilns (see below kilns).

Pottery may well have been discovered independently in various places, probably by accidentally creating it at the bottom of fires on a clay soil.

Sherds have been found in China and Japan from a period between 12,000 and perhaps as long as 18,000 years ago.[5][40] As of 2012, the earliest pottery found anywhere in the world,[41] dating to 20,000 to 19,000 years before the present, was found at Xianrendong Cave in the Jiangxi province of China.[42][43]

Other early pottery vessels include those excavated from the Yuchanyan Cave in southern China, dated from 16,000 BC,[40] and those found in the Amur River basin in the Russian Far East, dated from 14,000 BC.[5][44]

The Odai Yamamoto I site, belonging to the Jōmon period, currently has the oldest pottery in Japan. Excavations in 1998 uncovered earthenware fragments which have been dated as early as 14,500 BC.[45] The term "Jōmon" means "cord-marked" in Japanese.

It appears that pottery was independently developed in Sub-Saharan Africa during the 10th millennium BC, with findings dating to at least 9,400 BC from central Mali,[47] and in South America during the 10,000s BC.[48] The Malian finds date to the same period as similar finds from East Asia – the triangle between Siberia, China and Japan – and are associated in both regions to the same climatic changes (at the end of the ice age new grassland develops, enabling hunter-gatherers to expand their habitat), met independently by both cultures with similar developments: the creation of pottery for the storage of wild cereals (pearl millet), and that of small arrowheads for hunting small game typical of grassland.[47] Alternatively, the creation of pottery in the case of the Incipient Jōmon civilisation could be due to the intensive exploitation of freshwater and marine organisms by late glacial foragers, who started developing ceramic containers for their catch.[46]

In Japan, the Jōmon period has a long history of development of Jōmon Pottery which was characterized by impressions of rope on the surface of the pottery created by pressing rope into the clay before firing. Glazed Stoneware was being created as early as the 15th century BC in China. A form of Chinese porcelain became a significant Chinese export from the Tang Dynasty (AD 618–906) onwards.[7] Korean potters produced porcelain as early as the 14th century AD.[49] Koreans brought the art of porcelain to Japan in the 17th century AD.[50]

In contrast to Europe, the Chinese elite used pottery extensively at table, for religious purposes, and for decoration, and the standards of fine pottery were very high.

The arrival of Chinese blue and white porcelain was probably a product of the Mongol Yuan dynasty (1271–1368) dispersing artists and craftsmen across its large empire. Both the cobalt stains used for the blue colour, and the style of painted decoration, usually based on plant shapes, were initially borrowed from the Islamic world, which the Mongols had also conquered. At the same time Jingdezhen porcelain, produced in Imperial factories, took the undisputed leading role in production, which it has retained to the present day. The new elaborately painted style was now favoured at court, and gradually more colours were added.

The secret of making such porcelain was sought in the Islamic world and later in Europe when examples were imported from the East.

Pottery was in use in South Asia dating back to prehistoric times, including areas now forming Pakistan and northwest India, during the Mehrgarh Period II (5,500–4,800 BC) and Merhgarh Period III (4,800–3,500 BC), known as the ceramic Neolithic and chalcolithic. Pottery, including items known as the ed-Dur vessels, originated in regions of the Saraswati River / Indus River and have been found in a number of sites in the Indus Civilization.[52][53]

Despite an extensive prehistoric record of pottery, including painted wares, little "fine" or luxury pottery was made in the subcontinent in historic times.

Around 8000 BC during the Pre-pottery Neolithic period, and before the invention of pottery, several early settlements became experts in crafting beautiful and highly sophisticated containers from stone, using materials such as alabaster or granite, and employing sand to shape and polish. Artisans used the veins in the material to maximum visual effect. Such objects have been found in abundance on the upper Euphrates river, in what is today eastern Syria, especially at the site of Bouqras.[54]

The earliest history of pottery production in the Fertile Crescent starts the Pottery Neolithic and can be divided into four periods, namely: the Hassuna period (7000–6500 BC), the Halaf period (6500–5500 BC), the Ubaid period (5500–4000 BC), and the Uruk period (4000–3100 BC). By about 5000 BC pottery-making was becoming widespread across the region, and spreading out from it to neighbouring areas.

Pottery making began in the 7th millennium BC.

The invention of the potter's wheel in Mesopotamia sometime between 6000 and 4000 BC (Ubaid period) revolutionized pottery production. Newer kiln designs could fire wares to 1,050 °C (1,920 °F) to 1,200 °C (2,190 °F) which enabled new possibilities and new preparation of clays. Production was now carried out by small groups of potters for small cities, rather than individuals making wares for a family. The shapes and range of uses for ceramics and pottery expanded beyond simple vessels to store and carry to specialized cooking utensils, pot stands and rat traps.[55] As the region developed, new organizations and political forms, pottery became more elaborate and varied. Some wares were made using moulds, allowing for increased production for the needs of the growing populations. Glazing was commonly used and pottery was more decorated.[56]

In the Chalcolithic period in Mesopotamia, Halafian pottery achieved a level of technical competence and sophistication, not seen until the later developments of Greek pottery with Corinthian and Attic ware.

The early inhabitants of Europe developed pottery in the Linear Pottery culture slightly later than the Near East, circa 5500–4500 BC. In the ancient Western Mediterranean elaborately painted earthenware reached very high levels of artistic achievement in the Greek world; there are large numbers of survivals from tombs. Minoan pottery was characterized by complex painted decoration with natural themes.[57] The classical Greek culture began to emerge around 1000 BC featuring a variety of well crafted pottery which now included the human form as a decorating motif. The pottery wheel was now in regular use. Although glazing was known to these potters, it was not widely used. Instead, a more porous clay slip was used for decoration. A wide range of shapes for different uses developed early and remained essentially unchanged during Greek history.[58]

Fine Etruscan pottery was heavily influenced by Greek pottery and often imported Greek potters and painters. Ancient Roman pottery made much less use of painting, but used moulded decoration, allowing industrialized production on a huge scale. Much of the so-called red Samian ware of the Early Roman Empire was in fact produced in modern Germany and France, where entrepreneurs established large potteries.

Pottery was hardly seen on the tables of elites from Hellenistic times until the Renaissance, and most medieval wares were coarse and utilitarian, as the elites ate off metal vessels. Imports from Asia revived interest in fine pottery, which European manufacturers eventually learned to make, and from the 18th century European porcelain and other wares from a great number of producers became extremely popular.

Early Islamic pottery followed the forms of the regions which the Muslims conquered. Eventually, however, there was cross-fertilization between the regions. This was most notable in the Chinese influences on Islamic pottery. Trade between China and Islam took place via the system of trading posts over the lengthy Silk Road. Islamic nations imported stoneware and later porcelain from China. China imported the minerals for Cobalt blue from the Islamic ruled Persia to decorate their blue and white porcelain, which they then exported to the Islamic world.

Likewise, Islamic art contributed to a lasting pottery form identified as Hispano-Moresque in Andalucia (Islamic Spain). Unique Islamic forms were also developed, including fritware, lusterware and specialized glazes like tin-glazing, which led to the development of the popular maiolica.[59]

One major emphasis in ceramic development in the Muslim world was the use of tile and decorative tilework.

Most evidence points to an independent development of pottery in the Native American cultures, starting with their Archaic Era (3500–2000 BC), and into their Formative period (2000 BC – AD 200). These cultures did not develop the stoneware, porcelain or glazes found in the Old World. Maya ceramics include finely painted vessels, usually beakers, with elaborate scenes with several figures and texts. Several cultures, beginning with the Olmec, made terracotta sculpture, and sculptural pieces of humans or animals that are also vessels are produced in many places, with Moche portrait vessels among the finest.

In 2007, Swiss archaeologists discovered pieces of the oldest pottery in Africa at Ounjougou in Central Mali, dating back to at least 9,500 BC.[47] The relationship of the introduction of pot-making in many parts of Sub-Saharan Africa with the spread of Bantu languages has been long recognized, although the details remain controversial and awaiting further research, and no consensus has been reached.[60]

Ancient Egyptian pottery begins after 5,000 BC, having spread from the Levant. There were many distinct phases of development in pottery, with very sophisticated wares being produced by the Naqada III period, c. 3,200 to 3,000 BC. During the early Mediterranean civilizations of the fertile crescent, Egypt developed a non-clay-based ceramic which has come to be called Egyptian faience.[1] A similar type of body is still made in Jaipur in India. During the Umayyad Caliphate of Islam, Egypt was a link between early centre of Islam in the Near East and Iberia which led to the impressive style of pottery.

It is, however, still valuable to look into pottery as an archaeological record of potential interaction between peoples, especially in areas where little or no written history exists.

The methods used to produce pottery in early Sub-Saharan Africa are divisible into three categories: techniques visible to the eye (decoration, firing and post-firing techniques), techniques related to the materials (selection or processing of clay, etc.), and techniques of molding or fashioning the clay.[61] These three categories can be used to consider the implications of the reoccurrence of a particular sort of pottery in different areas.

Pottery has been found in archaeological sites across the islands of Oceania.

The Indigenous Australians never developed pottery.[62] After Europeans came to Australia and settled, they found deposits of clay which were analysed by English potters as excellent for making pottery. Less than 20 years later, Europeans came to Australia and began creating pottery. Since then, ceramic manufacturing, mass-produced pottery and studio pottery have flourished in Australia.[63]

Archaeology


The study of pottery can help to provide an insight into past cultures.

Chronologies based on pottery are often essential for dating non-literate cultures and are often of help in the dating of historic cultures as well.

Environmental issues in production


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.

Historically, "plumbism" (lead poisoning) was a significant health concern to those glazing pottery. This was recognised at least as early as the nineteenth century, and the first legislation in the United Kingdom to limit pottery workers' exposure was introduced in 1899.[64] While the risk to those working in ceramics is now much reduced, it can still not be ignored. With respect to indoor air quality, workers can be exposed to fine particulate matter, carbon monoxide and certain heavy metals. The greatest health risk is the potential to develop silicosis from the long-term exposure to crystalline silica. Proper ventilation can reduce the risks, and the first legislation in the United Kingdom to govern ventilation was introduced in 1899.[64] A more recent study at Laney College, Oakland, California suggests that all these factors can be controlled in a well-designed workshop environment.[65]

Other usages


The English city of Stoke-on-Trent is widely known as "The Potteries" because of the large number of pottery factories or, colloquially, "Pot Banks." It was one of the first industrial cities of the modern era where, as early as 1785, two hundred pottery manufacturers employed 20,000 workers.[66] For the same reason, the largest football club in the city is known as "The Potters."[67]

See also


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