Vessels made out of fired clay, produced by mankind since the earliest civilizations. They can be hand-built, moulded, or in more sophisticated societies thrown on a wheel. Pottery tends to be soft and rather porous, and is therefore normally protected by a glaze, which also gives a shiny decorative appearance. Glaze is applied after the first firing, when the pot is placed in the kiln for the second time at a lower temperature.
Pottery is a type of ceramic material, which the American Society for Testing and Materials (ASTM) has defined as "(a)ll fired ceramic wares that contain clay when formed, except technical, structural, and refractory products." The term pottery is also used for a technique involving ceramic, where clay is mixed with other minerals and is formed into objects, including vessels generally designed for utilitarian purposes.
A Pottery is a facility of any size, from a modest studio to an industrialized factory, where pottery is made.
Pottery production is a process by which a clay body, clay mixed with other minerals, is shaped and allowed to dry. The shaped clay body, or piece, ware or article, may be "bisque or biscuit fired" in a kiln to induce permanent changes that result in increased mechanical strength, and then fired a second time after adding a glaze or a piece may be once fired by applying appropriate glaze to the dry unfired body and firing in one cycle.
With mass production techniques having replaced the traditional role studio potters have focused more on the aesthetic than the utilitarian
Traditionally, different regions of the world have used produced different types of clay, sometimes mixed with other minerals, to produce regionally distinctive pottery. It is common for different clays and minerals to be mixed to produce clay bodies suited to specific purposes. Pottery that is fired at temperatures in the 800 to 1200 °C range, which does not vitrify in the kiln but remains slightly porous is often called earthenware or terra cotta. Clay bodies formulated to be fired at higher temperatures, which is partially vitrified is called stoneware. Porcelain is a very refined, smooth, white body that, when fired to vitrification, can have translucent qualities
Techniques
A person who makes pottery is traditionally known as a potter. The potter's most basic tool is his or her hands, however many additional tools have been created over the long history of pottery manufacture, including the potter's wheel, various paddles, shaping tools (or ribs), slab rollers, and cutting tools.
Forming techniques
Pottery can be shaped by a range techniques, including:
Handwork can be considered both the most primitive and the most individualized techniques, where pieces are constructed from hand-rolled coils, slabs, ropes, and balls of clay body, often joined with a slurry of clay body, known as slip.
The potter's wheel. A ball of clay body is placed in the center of a turntable, called the wheel head, which is turned either using foot power (a kick wheel or treadle wheel) or a variable speed electric motor. Oftentimes, a bat (a disk of plastic, wood, or plaster) is affixed to the wheel head, and the ball of clay body is attached to the bat rather than the wheel head so that the finished piece can be removed easily without distorting the piece. The process of pressuring the body into a rotational symmetry, so that it does not move from side to side as the wheel head rotates is referred to as "centering" the body — a most important skill to master before the next steps, "throwing" (forming and raising the walls of the piece) and "trimming" or "turning" (removing excess clay to refine the shape or create a bottom or foot can be taken.
Potter's wheels can be used for mass production, although often it is employed to make individual pieces.
Jiggering & Jiggering is the technique where a shaped tool is slowly brought down onto plastic clay body that has been placed on top of a rotating plaster mould. These techniques have been in use since at least the 18th century Partial automation of the jiggering and jolleying processes have long been used to increased production rates and de-skill the operation
Roller-head Machine A machine for the shaping of pottery flatware on a rotating mould, as in a jigger, but with a rotary shaping tool instead of a fixed profile. It is now widely used across the world
Ram Pressing A process for the plastic shaping of tableware and sanitaryware by pressing a bat of the prepared body between two porous plates or mould units; 10, the term is often used for similar type shaping processes
Granulate pressing This involves the shaping of ware by compressing semi-dry and granulated body in a die, one side of which is a solid surface and the other a flexible membrane through which fluid pressure, of up to 100 MN.m-2, is transferred. Also known as dust pressing the technique is widely used in manufacture of wall and floor tiles, and increasingly of plates
Turning is similar to that used for the shaping of metal and wood articles. A blank of clay body, with low water content in a condition known as leatherhard, is mounted on a lathe whilst a cutting tool follows a profile to removes excess material and hence leave a shaped article
Slipcasting is a technique often used for mass-production, and ideally suits shapes that can not be made by other methods. Liquid clay body slip is poured into plaster moulds, the permeability of the mould drawing water from the slip to leave a layer the clay body of the internal shape of the mould. This method is almost universally used for sanitaryware, toilets and wash basins, as well being widely used for smaller pieces such as figurines which have many intricate details
Decorative and finishing techniques
For aesthetic reasons articles can be decorated by a large variety of techniques , including the application of colours and designs. Decoration can be:
In the body On the surface of the body but beneath the glaze, underglaze decoration In the glaze On the surface of the glaze, on-glaze decorationAdditives can be worked into moist clay body, prior to forming, to produce desired characteristics to the finished ware. Various coarse additives, such as sand and grog (fired clay which has been finely ground) to give the final product texture, and contrasting colored clays and grogs result in patterns.
Agateware A long established technqiue is to partially mix different coloured clay bodies to give a distinctive 'mottled' decoration. In Great Britain, these techniques are known as agateware, after agate stone which shows similar colour banding, whilst in Japan a similar technqiue is called "neriage. An analogue of marquetry can also be made, by pressing small blocks of coloured clays together, and using the resulting mosaic to create distinctive patterns. To ensure the final articles are unfaulted care is needed with selection to choice different bodies of compatible shrinkage and thermal expansion
Burnishing, like the metalwork technique of the same name, involves rubbing the surface of the unfired article with a suitable tool, typically of wood, steel or stone, to give a smooth, polished surface which remains even after firing. Finer clays give a smoother, shinier surface than coarser clays, as will allowing the pot to dry more before burnishing although that risks breakage
Engobe, to give a finer surface, or a coloured surface, slip can be coated onto the leather-dry body. Slip produced to a specific recipe is sometimes called an engobe. Slips or engobes can be applied by painting techniques, or the piece can be dipped for a uniform coating. Many pre-historic and historic cultures used slip as the primary decorating material on their ware. Sgraffito involves scratching through a layer of coloured slip to reveal a different colour or the base clay underneath. Often slips/engobes used in this process have a higher silica content, sometimes approaching a glaze recipe. This is particularly useful if the base clay is not of the desired colour or texture.
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
Litho, is a commonly used abbreviation for lithography although alternatives names of transfer or decal or used. 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. From the kiln the decoration is dull and requires burnishing is reveal the full colour Acid Gold – a form of gold decoration developed in the early 1860s at Mintons Ltd., Stoke-on-Trent, UK. The process demands great skill and is used for the decoration only of ware of the highest class. It was made by rubbing together gold leaf, sugar and salt, followed by washing to remove solubles
Glazing
A glaze is a vitreous coating to a ceramic material whose primary purposes include decoration or protection. Glazing is the process of coating the piece with a thin layer of material that during firing forms the glass coating. Glaze may be applied by dusting it over the clay, spraying, dipping, trailing or brushing on a thin slurry of glaze and water. To prevent the glazed article sticking to the kiln during firing either a small part of the item is left unglazed or special refractory supports, spurs, are used as supports which are removed and discarded after the firing.
Evolution of Glazing technique
The glazing technique was greatly developed by Muslim potters who first used and improved this old tradition.
As they became more experienced, these potters introduced another glazing method, which they developed from attempting to imitate the popular white Chinese ceramics. Lane explained how and why these potters achieved this: "It was impossible to reproduce the beautiful surface texture of these (Chinese ware) by using an ordinary clear lead glaze over a white slip, and the Mesopotamian potters therefore hit on a device used long before them by the Egyptians. When applied to a well purified yellow or pinkish clay, this glaze achieved a most deceptive similarity to the T'ang porcelain.
In a third stage, the Muslim potter attempted to produce a closer version of the golden and silver vessels of paradise described numerous times in the Quran.
Firing
Firing is an essential stage in the manufacture of pottery, during which chemical and physical reactions occur which causes the material to be permanently altered.
Some clays and glazes are oxygen-sensitive, most notably those containing iron and copper, and will change colour depending on the presence of oxygen during the firing.
A number of various firing techniques can be used in addition to normal glaze-firing. These techniques can have very unusual and frequently unexpected results whether used on an unglazed piece or in combination with normal glazing.
Wood firing is another type of firing which involves using wood, rather than gas or electricity as in most modern kilns, to heat the kiln's interior. An example of a wood fired kiln is the Chinese Anagama, also adopted and used by Korean and Japanese potters. Wood firing is frequently time-consuming, as the kiln must be stoked for days, but the pieces which emerge often have characteristic patches of orange color on the clay itself, known as "blushing".
The Western adaptation of Raku firing, a traditional Japanese technique, has enjoyed a great deal of popularity due to its relative ease. The finished products of this process are not suitable for functional use, as the clay remains porous and may have some toxic chemicals held within it as a result of burning the surrounding woodchips or paper used to smother it. However, because of the low temperature, it is an extremely quick and easy technique to do, and the clay has a distinctive black color.
Production stages
All pottery items go through a series of stages during construction.
Initially the clay body is mixed to homogenise the moisture content, and any entrapped air needs to be removed. This can be achieved either manually by a technique called wedging, or by using machines: dedicated mixers are used to homogenise the moisture whilst de-airing pugs, sometimes called pug mills, are used to remove the air. Examples include the potter's wheel, extruders, rollers, jigger / jolley, RAM press and rollerhead Work that is thrown on the wheel often needs to be trimmed or turned to make its thickness uniform and/or to form a foot on the piece. Sometimes the greenware is given a coating of a clay slip. This is most often done to give a coloured base for decoration, other than the colour of the main body. Depending on historic tradition the biscuit firing can be higher or lower in temperature than the final firing Biscuit ware is normally a plain red, white, or brown colour depending on which type of initial raw materials used.History
The development of pottery was a milestone in human history.
Since pottery is a durable, man-made artifact which was utilized by various cultures around the world, it has proven to be a boon for archaeologists.
While ceramics had been developed in Europe also, pottery was first developed by the Jomon in Japan around 10,500 BCE.
The invention of the potter's wheel in Mesopotamia sometime between 6,000 and 2,400 BCE revolutionized pottery production.
While artistic value of Classical Greek and Roman pottery largely consisted of the surface decoration, the pottery itself was an important art form in China, where efficient kilns allowed high temperature ware to be fired with wood, long before the use of coal.
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