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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. No two pieces of handwork will be exactly the same, so it is not suitable for making precisely matched sets of items such as dinnerware. Doing handwork enables the potters to use their imagination to create one-of-a-kind works of art. These methods are often referred to as "handbuilding". 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 wheel is made to revolve rapidly while the body is pressed, squeezed, and pulled gently into shape. 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 foot) can be taken. Potter's wheels can be used for mass production, although often it is employed to make individual pieces. Wheel work takes a lot of technical ability, but a skilled potter can produce many virtually identical plates, vases, or bowls in a day. Because of its nature, wheel work can only be used to initially create items with radial symmetry on a vertical axis. These pieces can then be altered by impressing, bulging, carving, fluting, faceting, incising, and other methods to make them 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. Pottery that is thrown on the wheel is often finished in a process known as trimming. Jiggering & jolleying These can be seen to be an extension of using a Potters wheel, and in comparison allow increased speed and improved repeatability. 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. The jigger tool shapes one face whilst the mould the other. Jiggering is the term specific to flatware such as plates whilst a similar technique, jolleying, refers to the production of holloware like cups. 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. The rotary tool is in the form of a shallow cone of the same diameter as the ware and shaped to produce the back of the article being made. The ware is completely shaped, by relatively unskilled labour, in one operation at a rate depending on the size of the ware of about 12 pieces per minute. The machine, developed from earlier attempts to improve on the use of a fixed tool, was patented by T. G. Green & Co. and H. J. Smith (Brit. Pat., 621 712, 14/4/49) with subsequent improvements by J. A. Johnson (Brit. Pat., 765 097, 2/1/57; 895 988, 9/5/62). 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; after the pressing operation, air is blown through the porous mould parts to release the shaped ware. Although the process was patented in 1952 by Ram Incorporated, US Pats, 2 584 109 & 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. The granulate is produced by spray drying to give a fine and free flowing material with a low moisture content of around 5-6%. 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
Glazing A glaze is a vitreous coating to a ceramic material whose primary purposes include decoration or protection. Glazes can be considered specialised forms of glass. Glazing is the process of coating the piece with a thin layer of material that during firing forms the glass coating. Compositions are varied but are usually a mixture of minerals which generally, but not always, mature at temperatures lowers than the body itself. Glaze can be important for functional earthenware vessels, which would otherwise be unsuitable for holding liquids due to permeability. Glaze may be applied by dusting it over the clay, spraying, dipping, trailing or brushing on a thin slurry of glaze and water. Brushing tends not to give a very even covering but can be effective as a decorative technique. 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. In their early days (8th century), potters of Samarra and Baghdad employed lead glazes with relief designs, a technique which came down from the Romans who spread it in countries of the Mediterranean basin, including Egypt. The nature of these wares consisted mostly of red earthenware on which the shiny green or yellowish brown glazes were applied. As they became more experienced, these potters introduced another glazing method, which they developed from attempting to imitate the popular white Chinese ceramics. In doing so, the Muslim potters introduced tin oxides to lead glaze, giving it a white finish. 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. Tin oxide was mixed with a modified form of lead glaze, which by the suspended particles was rendered perfectly opaque and white. When applied to a well purified yellow or pinkish clay, this glaze achieved a most deceptive similarity to the T'ang porcelain. But fortunately the Baghdad potters did not rest content as imitators. They were tempted to paint on the fine white surface, using cobalt blue, copper green, manganese purple, and sometimes antimony yellow". (Lane, A. (1947) `Early Islamic Pottery', Faber and Faber, London, p.13). 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. In Surah 76, for example, Allah promises His devotees: "Enter ye the Garden, ye and your wives, in (beauty and) rejoicing. To them will be passed round, dishes and goblets of gold: there will be there all that the souls could desire, all that their eyes could delight in: and ye shall abide therein (for eye). Such will be the Garden of which ye are made heirs for your (good) deeds (in life). Ye shall have therein abundance of fruit, from which ye shall have satisfaction ".(43:71-3). In Surah 43, the Exalted reminds the believers: "And amongst them (the Devotees of Allah) will be passed round vessels of silver and goblets of crystal. Crystal-clear, made of silver: they will determine the measure thereof (according to their wishes). And they will be given to drink there of a Cup (of Wine) mixed with Zanjabil, A fountain there, called Salsabil" (76:15-8). Lustre provided the right ingredients for producing such vessels in a cheaper and acceptable way as Islam prohibits the use of gold and silver vessels. This is not the first time we see Muslim craftsmen try to imitate paradise themes. Similar approach was adopted in architecture, gardening, and even carpet making. The technique involved preparing pigments by mixing silver or copper oxides with an earthy vehicle such as ochre, and then vinegar or grape juice were added as medium. This pigment is then painted onto the glassy surface of the vessel, which has been glazed and fired once. The vessel is then fired for a second time in a reducing kiln, then the ochre is rubbed away. 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. The process is carried out in a kiln. 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. Kilns can either be oxidized by opening a port to allow oxygen into the interior or reduced by closing off the kiln from outside air to attain colors as desired. A number of various firing techniques can be used in addition to normal glaze-firing. Most of these involve heating the kiln to a high temperature and then delivering an amount of dry chemical into the kiln's interior. Sulphur is commonly used, as are various salts or ashes. Such substances will stick to pieces within the kiln and melt onto their surfaces, often resulting in a mottled texture which has a distinctive "orange peel" feel. Colors generally depend on what chemical is added to the kiln. 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 kiln is heated to a low temperature, usually no higher than cone 06, and then ware is pulled out of the kiln while still hot (using tongs, of course) and smothered in ashes, paper, or woodchips. This can be done in an enclosed container, which allows the supply of oxygen to be cut off and reduction to take place. 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. History
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