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| earthenwares are normally fired at temperatures in the range of about 1,000°C (1,830 °F) to 1,200 °C (2,190 °F); |
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| stonewares at between about 1,100 °C (2,010 °F) to 1,300 °C (2,370 °F); |
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| porcelains at between about 1,200 °C (2,190 °F) to 1,400 °C (2,550 °F). |
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| the way that ceramics mature in the kiln is influenced not only by the peak temperature achieved but also by the duration of the period of firing. 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. |
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| 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. |
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| 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.[ |
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| a popular method for shaping irregular shaped articles. It was first practised, to a limited extent, in China as early as the T'ang dynasty |
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| a glassy coating on pottery, the primary purposes of which are decoration and protection. One important use of glaze is to render porous pottery vessels impermeable to water and other liquids. Glaze may be applied by dusting the unfired composition over the ware or by spraying, dipping, trailing or brushing on a thin slurry composed of the unfired glaze and water. 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. |
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| 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. |
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| 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.[23] 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. |
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| is the final stage of some pottery making. A glaze may be applied to the biscuit form and the object can be decorated in several ways. After this the object is "glost fired", which causes the glaze material to melt, then adhere to the object. The glaze firing may also harden the body still more as chemical processes can continue to occur in the body. |
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| the malleability of the body; porosity, the degree to which the fired pottery will absorb water; and shrinkage, the degree of reduction in size of a body as water is removed. |
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| The two essential components of clay are Silica and Alumina which combine to form Aluminium silicate, also known as Kaolinite. Other mineral compounds in the clay may act as Fluxes to lower the melting point of the silica during firing. |
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| is sometimes referred to as China clay because it was first identified in China. |
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| An extremely plastic, fine grained sedimentary clay, which may contain some organic matter. It is usually added to porcelain to increase plasticity. |
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| A clay having a slightly higher 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. |
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| substance that promotes fusion in a given mixture of raw materials |
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| Suitable for creating Stoneware. This clay has many of the characteristics between fire clay and ball clay, having finer grain, like ball clay but more heat resistant like fire clays. |
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| common red clay and shale clay |
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Definition
| 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 |
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| An extremely plastic clay which can be added in small quantities to short clay to make it more plastic. |
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| granulate pressing/dust pressing |
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| 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 5 and 6 per cent. Granulate pressing, also known as dust pressing, is widely used in the manufacture of ceramic tiles and, increasingly, of plates. |
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| 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. |
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| 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. remain dominate method for producing flateware |
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| 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 coloured clays and grogs are sometimes used to produce patterns in the finished wares. Colourants, 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. |
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| Grog is used in pottery and sculpture to add a gritty, rustic texture called "tooth"; it also reduces shrinkage and aids even drying. This prevents defects such as cracking, crow feet patterning, and lamination. The coarse particles open the green clay body to allow gases to escape. It also adds structural strength to hand-built and thrown pottery during shaping although it can diminish fired strength. |
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| 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. |
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| 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. |
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| 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, |
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| 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 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. |
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| A form of pottery called Plainware is found throughout sites of Oceania. |
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| The lower temperature stage of some firing cycles used to complete the drying of the ware. |
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| The permanent staining of a ceramic material by the introduction of carbon particles during firing. |
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| used to gauge heatwork during the firing of ceramic materials. The cones, often used in sets of three as shown in the illustration, are positioned in a kiln with the wares to be fired and provide a visual indication of when the wares have reached a required state of maturity, a combination of time and temperature. Thus, pyrometric cones give a temperature equivalent, they are not simple temperature-measuring devices. |
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| A crack caused by thermal shock, especially if ware cooled too rapidly after it has been fired. |
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| Coloured, glass-like decoration applied to ceramic wares. Also called on-glaze decoration. Often made by mixing metal oxides with a lead-based flux. Enamels are usually fired to temperatures in the range of about 700 to 800 degrees Celsius. |
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| A form of tin-glazed earthenware |
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| A very plastic form of clay such as ball clay |
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| The removal, in the unfired state of excess body left in the shaping of pottery-ware at such places as seams and edge |
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| A product made by quenching and breaking up a glass of a specific composition. Common uses include as components of a glaze or enamel |
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| A tool used to ensure that thrown pots are of uniform size or shape. |
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| Natural gums used as binders to enable the glaze to adhere better to the body. |
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| Porcelain which had been fired to 1400°C in a reducing atmosphere. |
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| A common oxide in glazes and some clays that generally gives a redish colour. |
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| Supports, often in the shape of a tripod, used to maintain the shape and separate pieces of ceramic during the firing process. |
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| A type of decoration originally developed in Persia which leaves a thin layer of metal on the decorated portions of pottery. |
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| A method of joining together two pieces of dry or leather-hard clay with a slip. |
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| The temperature at which a glaze exhibits it best qualities. |
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| The combined effects of firing time and firing temperature on ceramic wares in a kiln. Within limits, wares fired at low temperatures for extended periods may develop a degree of maturity similar to that achieved by applying higher firing temperatures for shorter periods |
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| The maximum transverse breaking stress applied under specified conditions, that a material will withstand before fracture. It is used as a common quality control test used for both ceramic rawmaterials and ceramic bodies. |
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| Adding reconstituted paper pulp to ordinary plastic clay in proportions up to 50% of the total mass. The added paper gives an unfired material great strength, giving an advantage to hand builders and sculptors. |
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| Also pug mill. A machine for consolidating plastic clay or body into a firm column. It consists of a barrel which tapers at one end to a die, through which the clay or body is forced by knives mounted on a shaft which rotates centrally to the barrel. A vacuum system may be installed to de-ier the clay or clay body. |
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| a temperatue indicator linked to a kiln via a thermocoupler. |
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| refers to applying a glaze to an unfired ware and firing both in a "Once-firing". |
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| refers to heat resistant or clay that is fired at a high tempereture. |
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| This is a decorating technique where a slip is applied to a leather-hard piece of clay and left to dry. Once the slip is dry a host of different tools are used to carve into the clay to remove the slip and leave an embedded decoration behind. |
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| s the process caused by kiln firing which solidifies the clay but does not lead to vitrification. This occurs at low temperatures as in low-fired earthenware. |
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| The mass of water absorbed by a porous ceramic material, under specified conditions, expressed as a percentage of the mass of the dry material. It is used as a common quality control test used for both ceramic raw materials and ceramic bodies. |
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| fine plaster used for coating wall surfaces or molding into architectural decorations. |
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| most commonly a metal block which has one or more small holes through which plastic, metal, or other ductile metal is extruded. |
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| are steel tools that are used by sculptors for the purpose of retouching and attention to small details. |
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| Potters use this type of caliper to measure the inner and outer dimensions of pots where they will meet with other parts of a working set. For example, they are especially useful when measuring lids for jars, measuring the base of a cup to match with the depression in the center of a saucer, or to measure the base of a pitcher that is matched withCalipers can be made of metal, wood, or plastic. Lid Master calipers do not have to be reversed and adjusted the way regular potter's calipers do. |
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| potter's rib- a wide, flat handheld tool used to shape, smooth, and/or scrape clay surfaces; usually wood, rubber, plastic, or metal, either rigid or flexible, with straight, curved, or profiled edge |
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help shape and smooth pots as they are being formed on the wheel. They are also used in the Rib and Hand method of working with coiled pots.
Ribs come in a many different shapes and usually are made from hardwood or rubber.
Scrappers look a lot like ribs, but are lighter and used to smooth wet and soft leather-hard greenware. They come in a myriad of shapes and can be made of steel, rubber, or wood. Some potters use scrappers and ribs interchangeably for tasks. |
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| Wooden modeling tools come in an astounding variety of shapes, useful in all sorts of handbuilding. Although called modeling tools, the triangular-headed varieties are also excellent trimming tools while throwing on the wheel. |
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A large looped ribbon tool made of iron that can be used for trimming as well as carving
handy for trimming greenware and for use in handbuilding. Wire and ribbon varieties are not recommended for use during throwing; they are too fragile. |
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| These long heavy needles set into wooden, metal, or plastic handles are one of the most versatile tools in pottery. Just a few of their uses are trimming the top edges of ware while on the wheel and for scoring slabs and coils when hand building. |
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Probably the most common ones have two hardwood handles at either end. Fishing line and uncoiled springs can also be used as cut-off wires.
These tools are useful in cutting large lumps of clay and also in removing thrown ware from the potter's wheel. When throwing off the mound, fishing line or other very flexible cut-off lines are preferred. |
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These thin-bladed knives come in either a hard temper or soft. The hard ones are inflexible, while the soft fettling knives are flexible and can be bent into desired angles and curves. They were first developed to remove the fettle (the ridge of material left where pieces of the mold join when a piece has been cast). They are also very useful for trimming slabs and thrown pots.
If you have both kinds of fettling knives, it is useful to add a band of paint or indelible marker on one of them so you can easily tell them apart. |
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| Largish natural or special synthetic sponges are used to absorb or distribute water during throwing. Many potters also use elephant ear sponges (a specific type of natural sponge) during the throwing process. |
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| Brushes are used to carry water and slip to specific areas when you are working the clay, as well as used to paint and design with slips, underglazes, and overglazes. The best brushes for ceramics and pottery are sumi, or bamboo, brushes. They can be loaded with a tremendous amount of fluid and still come to a nicely pointed end. |
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| Pieces of chamois skin (about 2 inches x 4 inches) are excellent for compressing and smoothing the upper edges of thrown ware. Chamois can also be used to smooth ware that is leather-hard. |
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