It usually falls into three main classes—porous-bodied pottery, stoneware, and porcelain. Raw clay is transformed into a porous pottery when it is heated to a temperature of about 500°C;. This pottery, unlike sun-dried clay, retains a permanent shape and does not disintegrate in water. Stoneware is produced by raising the temperature, and porcelain is baked at still greater heat. In this process part of the clay becomes vitrified, or glassy, and the strength of the pottery is increased.
Pottery is formed while clay is in its plastic form. Either a long piece of clay is coiled and then smoothed, or the clay is centered upon a potter's wheel (used in Egypt before 4000 B.C.) that spins the clay while it is being shaped by the hand, or thrown. Decoration may be incised, and the piece is allowed to dry to a state of leather hardness before firing it in a kiln. The type of finish, depending on the kind or number of glazes, dictates the total number of firings. When slip and graffito are used, they are applied before the first firing. There are two types of fires—reducing and oxidizing. The former removes oxygen while the latter, a smokeless fire, adds it. Reduction and oxidation change the color of the fired clay and gave early potters their palette of red, buff, and black.
Pottery is one of the most enduring materials known to humankind. In most places it is the oldest and most widespread art; primitive peoples the world over have fashioned pots and bowls of baked clay for their daily use. Prehistoric (sometimes Neolithic) remains of pottery, e.g., in Scandinavia, England, France, Italy, Greece, and North and South America, have proved of great importance in archaeology and have often supplied a means of dating and establishing an early chronology. Some of the oldest pottery has been found in Japan and China, dated to at least 16,000 and 17,500 years old respectively. Pottery has also been of value as historical and literary records; ancient Assyrian and Babylonian writings have been inscribed upon clay tablets. Simple geometric patterns in monochrome, polychrome, or incised work are common to pottery of prehistoric and primitive cultures.Pottery of the Ancient Mediterranean
By 1500 B.C. the use of glazes, such as the famous greens and blues, was known in Egypt. Especially noteworthy is the early Aegean pottery of the Minoan and Mycenaean periods with its curvilinear, painted decoration. In Assyria and Neo-Babylonia, painted and glazed bricks were in common use. The Ishtar gate in Babylon, with its ceramic reliefs, is an early example of the majolica technique.
The Greek vases (800-300 B.C.), famous for symmetry of form and beauty of decoration, include red, black, and varicolored examples. The last were for tombs only, as the colors were painted, unfired, and easily marred. The red ware is decorated with black figures, or the ground is black and the figures shown red. Water, oil, and wine jars were numerous. Of the Greco-Roman wares, the Arretine or Samian, also a red ware, was molded after first being turned on the wheel to the size of the mold, which carried the decoration in intaglio.Pottery of Asia
Painted pottery of the Neolithic period has been found in China. By the 2d cent. B.C. the Early Han period had developed a green glaze which may have come from the Middle East. In the Sui period (A.D. 581-618) and the T'ang period (618-906), porcelain and porcelaneous ware (the envy of the Western world) began to be made and exported to Korea and Japan and to the Islamic world. Technical knowledge, however, was not exchanged, and Islam made no true porcelain.
Islamic pottery making was centered at Baghdad in the 10th cent. Blue and green clear glazes were used, and lusterware was first employed as an overglaze. Lusterware was highly developed under the Fatimites in Egypt (969-1171), and the technique continued in use at major pottery centers over the centuries that followed. During the 13th cent. Mongol domination of Persia brought renewed Chinese influence to Islamic pottery making. Fine examples of Hispano-Moorish pottery date from the 14th cent. Islamic architecture in the 15th cent. utilized ceramic tile in immense quantities, as on the Blue Mosque at Tabriz.Pottery of Europe
In Europe there was little pottery of great aesthetic importance before the 15th cent., except perhaps some German stonewares. Majolica was mainly developed in Italy and from there spread to Spain, France (where it was called faience), and to Holland (where it came to be known as delftware). Majolica and stoneware were the main pottery forms in Europe until the advent (18th cent.) of porcelain.Pottery of the Americas
Prehistoric pottery found in Peru, Mexico, and the SW United States reveals a high degree of skill in color, form, and decorative motifs. Baked-clay work by colonists in North America began in 1612 with the making of bricks and tiles in Virginia and Pennsylvania. In these states and among the Dutch settlers of New York, potteries were soon established. The first whiteware was made in 1684. A stoneware factory was opened in New York in 1735, and c.1750 the Jugtown pottery of North Carolina was first produced. Terra-cotta works were operating in Massachusetts and Pennsylvania after the middle of the 18th cent. Palatinate refugees produced slip-decorated and graffito earthenware, and their product formed the foundation of Shenandoah pottery.
In Philadelphia fine china was made (1769) for the first time in America. The potteries of Bennington, Vt., which opened in 1793, were known especially for their stoneware jugs; a variety of stoneware was also produced in several locations in New York state. East Liverpool, Ohio, since 1839 one of the foremost centers of the industry, produced the first American Rockingham ware. Also widely produced in the United States were redware, ironstone, and yellowware. Another center, begun in 1852 at Trenton, N.J., made fine Belleek or eggshell china. The Centennial Exposition of 1876 in Philadelphia and the World's Columbian Exposition of 1893 in Chicago did much to awaken native consciousness of pottery as a form of art.Modern Pottery
American art pottery flourished in the first half of the 20th cent., with works created by a variety of artisans, many of whom were employed by companies such as the Rookwood Pottery and Cincinnati Art Pottery. Much collected in the decades that followed, this art pottery was created in such styles as art nouveau, arts and crafts, and art deco. In addition, many of the major artists of the 20th cent. created exquisite ceramic works. Especially notable are those by Picasso, Matisse, and Miró. In spite of the continuing development of mass-production techniques and synthetic materials, the demand for hand-crafted ware of fine quality has not diminished. A variety of artisans make utilitarian objects as well as works of art using many methods of pottery production. Moreover, indigenous peoples, notably native Americans, continue to create a number of vessels adapted from traditional forms.
See L. A. Boger, The Dictionary of World Pottery and Porcelain (1970); W. E. Cox, Book of Pottery and Porcelain (2 vol., rev. ed. 1970); E. Cooper, A History of Pottery (1973); G. Savage and H. Newman, An Illustrated Dictionary of Ceramics (1974); R. Fournier, The Illustrated Dictionary of Pottery Decoration (1986).
Prior to most shaping processes, air trapped within the clay body needs to be removed. This is called de-airing and can be accomplished by a machine called a vacuum pug, or manually by wedging. Wedging can also help to ensure an even moisture content throughout the body. Once clay body has been de-aired or wedged, it is shaped by a variety of techniques. After shaping it is dried before firing. There are a number of stages in the drying process. Leather-hard refers to the stage when the clay object is approximately 75-85% dry. Trimming and handle attachment often occurs at the leather-hard state. A clay object is said to be "bone-dry" when it reaches a moisture content at or near 0%. Unfired objects are often termed greenware.
The potter's most basic tools are the hand, but many additional tools have been developed over the long history of pottery manufacture, including the potter's wheel and turntable, shaping tools (paddles, anvils, ribs), rolling tools (roulettes, slab rollers, rolling pins), cutting/piercing tools (knives, fluting tools, wires) and finishing tools (burnishing stones, rasps, chamois).
Pottery can be shaped by a range of methods that include:
Handwork or handbuilding. This is the earliest and the most individualized and direct forming method. Wares can be constructed by hand from coils of clay, from flat slabs of clay, from solid balls of clay — or some combination of these. Parts of hand-built vessels are often joined together with the aid of slurry or slip, a runny mixture of clay and water. Handbuilding is slower and more gradual than wheel-throwing, but it offers the potter a high degree of control over the size and shape of wares. While it isn't difficult for an experienced potter to make identical pieces of hand-built pottery, the speed and repetitiveness of wheel-throwing is more suitable for making precisely matched sets of wares such as table wares. Some potters find handbuilding more conducive to fully using the imagination to create one-of-a-kind works of art, while other potters find the spontaneity and immediacy of wheel-thrown pottery as their source of inspiration.
The potter's wheel. A ball of clay is placed in the center of a turntable, called the wheel-head, which the potter rotates with a stick, or with foot power (a kick wheel or treadle wheel) or with a variable speed electric motor. (Often, a disk of plastic, wood or plaster — called a bat — is first set on the wheel-head, and the ball of clay is thrown on the bat rather than the wheel-head so that the finished piece can be removed intact with its bat, without distortion.)
During the process of throwing the wheel rotates rapidly while the solid ball of soft clay is pressed, squeezed, and pulled gently upwards and outwards into a hollow shape. The first step, of pressing the rough ball of clay downward and inward into perfect rotational symmetry, is called centering the clay, a most important (and often most difficult) skill to master before the next steps: opening (making a centered hollow into the solid ball of clay), flooring (making the flat or rounded bottom inside the pot), throwing or pulling (drawing up and shaping the walls to an even thickness), and trimming or turning (removing excess clay to refine the shape or to create a foot).
The potter's wheel can be used for mass production, although it is often employed to make individual pieces. Wheel-work makes great demands on the skill of the potter, but an accomplished operator can make many near-identical plates, vases, or bowls in the course of a day's work. Because of its inherent limitations, wheel-work can only be used to create wares with radial symmetry on a vertical axis. These can then be altered by impressing, bulging, carving, flute, faceting, incising, and by other methods making the wares more visually interesting. Often, thrown pieces are further modified by having handles, lids, feet, spouts, and other functional aspects added using the techniques of handworking.
Jiggering and jolleying: These operations are carried out on the potter's wheel and allow the time taken to bring wares to a standardised 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 whilst 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.
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. The roller-head machine is now used in factories world-wide.
RAM pressing: A factory process for shaping table wares and decorative 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.
Granulate pressing: As the name suggests, this is the operation of shaping pottery by pressing clay in a semi-dry and granulated condition in a mould. The clay is pressed into the mould by a porous die through which water is pumped at high pressure. The granulated clay is prepared by spray-drying to produce a fine and free flowing material having a moisture content of between about five and six per cent. Granulate pressing, also known as dust pressing, is widely used in the manufacture of ceramic tiles and, increasingly, of plates.
Slipcasting: is often used in the mass-production of ceramics and is ideally suited to the making of wares that cannot be formed by other methods of shaping. A 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. Slipcasting is widely used in the production of sanitary wares and is also used for making smaller articles, such as intricately-detailed figurines.
Pottery may be decorated in a number of ways, including:
Additives can be worked into the clay body prior to forming, to produce desired effects in the fired wares. Coarse additives, such as sand and grog (fired clay which has been finely ground) are sometimes used to give the final product a required texture. Contrasting colored clays and grogs are sometimes used to produce patterns in the finished wares. Colorants, usually metal oxides and carbonates, are added singly or in combination to achieve a desired colour. Combustible particles can be mixed with the body or pressed into the surface to produce texture.
Agateware: So-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.
Banding: This 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.
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.
engobe: This is a clay slip, often white or cream in colour, 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.
Litho: This is a commonly used abbreviation for lithography, 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 covercoat, 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
Gold: Decoration with gold is used on some high quality ware. Different methods exist for its application, including:
The atmosphere within a kiln during firing can affect the appearance of the finished wares. An oxidising atmosphere, produced by allowing air to enter the kiln, can cause the oxidation of clays and glazes. A reducing atmosphere, produced by limiting the flow of air into the kiln, can strip oxygen from the surface of clays and glazes. This can affect the appearance of the wares being fired and, for example, some glazes containing iron fire brown in an oxidising atmosphere, but green in a reducing atmosphere. The atmosphere within a kiln can be adjusted to produce complex effects in glaze.
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; lidded 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.
It is believed that the earliest pottery wares were hand-built and fired in bonfires. Firing times were short but the peak-temperatures achieved in the fire could be high, perhaps in the region of 900 degrees Celsius, and were reached very quickly. Clays tempered with sand, grit, crushed shell or crushed pottery were often used to make bonfire-fired ceramics, because they provided an open body texture that allows water and other volatile components of the clay to escape freely. The coarser particles in the clay also acted to restrain shrinkage within the bodies of the wares during cooling, which was carried out slowly to reduce the risk of thermal stress and cracking. In the main, early bonfire-fired wares were made with rounded bottoms, to avoid sharp angles that might be susceptible to cracking. The earliest intentionally constructed kilns 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.
The earliest known ceramic objects are Gravettian figurines such as those discovered at Dolni Vestonice in the modern-day Czech Republic. The Venus of Dolní Věstonice (Věstonická Venuše in Czech) is a Venus figurine, a statuette of a nude female figure dated to 29,000–25,000 BCE (Gravettian industry). The earliest known pottery vessels may be those made by the Incipient Jōmon people of Japan around 10,500 BCE . The term "Jōmon" means "cord-marked" in Japanese. This refers to the markings made on clay vessels and figures using sticks with cords wrapped around them. Pottery which dates back to 10,000 BCE have also been excavated in China. It appears that pottery was independently developed in North Africa during the tenth millennium b.p. and in South America during the seventh millennium b.p.
The invention of the potter's wheel in Mesopotamia sometime between 6,000 and 4,000 BCE (Ubaid period) revolutionized pottery production. Specialized potters were then able to meet the expanding needs of the world's first cities. Pottery was in use in ancient India during the Mehrgarh Period II (5500 - 4800 BCE) and Merhgarh Period III (4800 - 3500 BCE), known as the ceramic Neolithic and chalcolithic. Pottery, including items known as the ed-Dur vessels, originated in regions of the Indus valley and has been found in a number of sites in the Indus valley civilization.
In the Mediterranean, during the Greek Dark Ages (1100–800 BCE), artists used geometric designs such as squares, circles and lines to decorate amphoras and other pottery. The period between 1500-300 BCE in ancient Korea is known as the Mumun Pottery Period.
The quality of pottery has varied historically, in part dependent upon the repute in which the potter's craft was held by the community. For example, 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 distinctive Red Samian ware of the Early Roman Empire was copied by regional potters throughout the Empire. The Dark Age period saw a collapse in the quality of European pottery which did not recover in status and quality until the European Renaissance.
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. Trace element analysis, mostly by neutron activation, allows the sources of clay to be accurately identified and the thermoluminescence test can be used to provide an estimate of the date of last firing. Examining fired pottery shards from prehistory, scientists learned that during high-temperature firing, iron materials in clay record the exact state of Earth's magnetic field at that exact moment.