Pottery fracture results from stress within a ceramic body due to thermal expansion and contraction, shrinkage, and other forces. Poor drying or uneven compression and alignment of particles can result in low strength. Cracking may appear in greenware as well as each stage of the firing including bisqueware and glazed ware. [1]
Fracture in greenware resulting in stresses during the making. To avoid cracks in greenware uniformity should be maintained in the thickness of the pot, the drying of the greenware, as well as consistency of the clay body itself. Cracks can result in uneven drying from thinner to thicker spots within the pot. A lack of compression in the bottom while throwing results in a commonly seen "s" crack on the underneath of the pot.
Fractures caused by thermal shock called dunting occur during the firing process and are witnessed in the bisqueware stage. Dunting is a problem that commonly occurs during the cooling process of the firing cycle. Latent or dormant cracks which went unnoticed in greenware may appear in bisqued ware after firing. [2]
A crack that appears in any stage of firing worsens through multiple firings. Cracks may also go unnoticed until after the glazed firing. In glazed ware the glaze causes stress due to the thermal expansion. The interaction of the glaze and the clay body causes stress on the pot in glaze firing.
A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain, and brick.
Pottery is the process and the products of forming vessels and other objects with clay and other raw materials, which are fired at high temperatures to give them a hard and durable form. The place where such wares are made by a potter is also called a pottery. The definition of pottery, used by the ASTM International, is "all fired ceramic wares that contain clay when formed, except technical, structural, and refractory products". End applications include tableware, decorative ware, sanitary ware, and in technology and industry such as electrical insulators and laboratory ware. In art history and archaeology, especially of ancient and prehistoric periods, pottery often means only vessels, and sculpted figurines of the same material are called terracottas.
Raku ware is a type of Japanese pottery traditionally used in Japanese tea ceremonies, most often in the form of chawan tea bowls. It is traditionally characterised by being hand-shaped rather than thrown, fairly porous vessels, which result from low firing temperatures, lead glazes and the removal of pieces from the kiln while still glowing hot. In the traditional Japanese process, the fired raku piece is removed from the hot kiln and is allowed to cool in the open air.
Earthenware is glazed or unglazed nonvitreous pottery that has normally been fired below 1,200 °C (2,190 °F). Basic earthenware, often called terracotta, absorbs liquids such as water. However, earthenware can be made impervious to liquids by coating it with a ceramic glaze, and such a process is used for the great majority of modern domestic earthenware. The main other important types of pottery are porcelain, bone china, and stoneware, all fired at high enough temperatures to vitrify. End applications include tableware and decorative ware such as figurines.
Celadon is a term for pottery denoting both wares glazed in the jade green celadon color, also known as greenware or "green ware", and a type of transparent glaze, often with small cracks, that was first used on greenware, but later used on other porcelains. Celadon originated in China, though the term is purely European, and notable kilns such as the Longquan kiln in Zhejiang province are renowned for their celadon glazes. Celadon production later spread to other parts of East Asia, such as Japan and Korea, as well as Southeast Asian countries, such as Thailand. Eventually, European potteries produced some pieces, but it was never a major element there. Finer pieces are in porcelain, but both the color and the glaze can be produced in stoneware and earthenware. Most of the earlier Longquan celadon is on the border of stoneware and porcelain, meeting the Chinese but not the European definitions of porcelain.
Donabe are pots made out of a special clay for use over an open flame in Japanese cuisine, and in the case of semi-stoneware Banko ware of high petalite content. Often, the food is cooked at the table on a gas burner for various nabemono dishes such as shabu-shabu and dishes served simmering including nabeyaki udon. They are sized by sun, one of the Japanese units of measurement.
In pottery, a potter's wheel is a machine used in the shaping of clay into round ceramic ware. The wheel may also be used during the process of trimming excess clay from leather-hard dried ware that is stiff but malleable, and for applying incised decoration or rings of colour. Use of the potter's wheel became widespread throughout the Old World but was unknown in the Pre-Columbian New World, where pottery was handmade by methods that included coiling and beating.
Salt-glaze or salt glaze pottery is pottery, usually stoneware, with a ceramic glaze of glossy, translucent and slightly orange-peel-like texture which was formed by throwing common salt into the kiln during the higher temperature part of the firing process. Sodium from the salt reacts with silica in the clay body to form a glassy coating of sodium silicate. The glaze may be colourless or may be coloured various shades of brown, blue, or purple.
Pit firing is the oldest known method for the firing of pottery. Examples have been dated as early as 29,000–25,000 BCE, while the earliest known kiln dates to around 6000 BCE, and was found at the Yarim Tepe site in modern Iraq. Kilns allow higher temperatures to be reached, use fuel more efficiently, and have long replaced pit firing as the most widespread method of firing pottery, although the technique still finds limited use amongst certain studio potters and in Africa.
Slipware is pottery identified by its primary decorating process where slip is placed onto the leather-hard (semi-hardened) clay body surface before firing by dipping, painting or splashing. Slip is an aqueous suspension of a clay body, which is a mixture of clays and other minerals such as quartz, feldspar and mica. The slip placed onto a wet or leather-hard clay body surface by a variety of techniques including dipping, painting, piping or splashing. Slipware is the pottery on which slip has been applied either for glazing or decoration. Slip is liquified clay or clay slurry, with no fixed ratio of water and clay, which is used either for joining pottery pieces together by slip casting with mould, glazing or decorating the pottery by painting or dipping the pottery with slip.
Creamware is a cream-coloured refined earthenware with a lead glaze over a pale body, known in France as faïence fine, in the Netherlands as Engels porselein, and in Italy as terraglia inglese. It was created about 1750 by the potters of Staffordshire, England, who refined the materials and techniques of salt-glazed earthenware towards a finer, thinner, whiter body with a brilliant glassy lead glaze, which proved so ideal for domestic ware that it supplanted white salt-glaze wares by about 1780. It was popular until the 1840s.
Architectural terracotta refers to a fired mixture of clay and water that can be used in a non-structural, semi-structural, or structural capacity on the exterior or interior of a building. Terracotta is an ancient building material that translates from Latin as "baked earth". Some architectural terracotta is stronger than stoneware. It can be unglazed, painted, slip glazed, or glazed.
Paper clay is any clay body to which processed cellulose fiber has been added.
Ceramic glaze, or simply glaze, is a glassy coating on ceramics. It is used for decoration, to ensure the item is impermeable to liquids and to minimise the adherence of pollutants.
Glaze defects are any flaws in the surface quality of a ceramic glaze, its physical structure or its interaction with the body.
Dunting is a fault that can occur during the firing of ceramic articles. It is the "cracking that occurs in fired ceramic bodies as a result of a thermally induced stress" and is caused by a "ware cooled too quickly after it has been fired".
A slip is a clay slurry used to produce pottery and other ceramic wares. Liquified clay, in which there is no fixed ratio of water and clay, is called slip or clay slurry which is used either for joining leather-hard (semi-hardened) clay body together by slipcasting with mould, glazing or decorating the pottery by painting or dipping the pottery with slip. Pottery on which slip has been applied either for glazing or decoration is called slipware.
This is a list of pottery and ceramic terms.
In pottery, leather-hard is the condition of a clay or clay body when it has been partially dried to a consistency similar to leather of the same thickness as the clay. At this stage, the clay object has approximately 15% moisture content. The clay is still visibly damp but has dried enough to be able to be handled without deformation. The body is able to be gouged or incised without breaking.
Ceramic art is art made from ceramic materials, including clay. It may take varied forms, including artistic pottery, including tableware, tiles, figurines and other sculpture. As one of the plastic arts, ceramic art is a visual art. While some ceramics are considered fine art, such as pottery or sculpture, most are considered to be decorative, industrial or applied art objects. Ceramic art can be created by one person or by a group, in a pottery or a ceramic factory with a group designing and manufacturing the artware.