Glossary of pottery terms

This is a list of pottery and ceramic terms.

Definitions in Wiktionary are noted as "(W)".

A

• Absorbency. The ability of a material to soak up water.

• Alumina. A major component of the chemical composition of clays, clay bodies and most glazes.

B

• Ball clay. A secondary clay moved from the parent rock, ball clay is often mixed with other clays and minerals, organic matter are frequently present. Ball clays commonly exhibit high plasticity and high dry strength.(W)

• Band. are lines marked around circular ceramic utensils, plates, jars or lids using any method of decoration which can be applied at all stages of manufacture. Banding is the action of marking a band.

• Bat. or "batt." Less commonly also known as a "batterboard", thin slab of wood, plaster, or plastic used to support pottery forms during throwing, attached to the head of the potter's wheel by clay body or "bat pins".

• Bentonite. An extremely plastic clay which can be added in small quantities to short clay to make it more plastic.

• Biscuit or occasionally Bisque. Pottery that has been fired but not yet glazed. (W)

• Biscuit fire. Preliminary firing prior to glazing and subsequent firing again.

• Bloating. The permanent swelling of a ceramic article during firing caused by the evolution of gases.

• Blunging. suspending ceramic raw materials in liquid by agitation.

• Body. The structural portion of a ceramic article, or the material or mixture from which it is made.

• Bone ash. Calcined animal bone used in the production of bone china. (W)

• Bone china. Vitreous, translucent pottery made from a body of the following approximate composition: 45-50% calcined bone, 20-25% kaolin & 25-30% china stone. (W)

• Bone-dry The final stage of greenware dried to a completely dry state and ready to be fired. In this stage, the clay is very fragile, non-plastic and porous.

C

• Candling. The lower temperature stage of some firing cycles used to complete the drying of the ware.

• Carbonizing The permanent staining of a ceramic material by the introduction of carbon particles during firing.

• Casting, slip casting

• Celadon Stoneware glazes containing iron which produce green, grey and grey-blue colours in reduction firing.

• Ceramic (W)

• China Clay synonym for kaolin, which is the primary clay used for producing porcelain.

• Chamotte (Grog) A ceramic material formed by the high temperature firing of a refractory clay, after which it is crushed and graded to size. Used as the a non-plastic component of some clay bodies. (W)

• Clay A group of hydrous aluminium phyllosilicate minerals. Often also used to refer to the clay body, which sometimes may only contain small amounts of clay minerals. (W)

• Clay body The material used to form the body of a piece of pottery. Thus a potter might order such an amount of earthenware body, stoneware body or porcelain body from a supplier of ceramic materials.

• Coiling A hand method of forming pottery by building up the walls with coils of rope-like rolls of clay.

• Cone, See pyrometric cone.

• Crackle glaze A glaze intentionally containing minute cracks in the surface.

• Crawling. A parting and contraction of the glaze on the surface of ceramic ware during drying or firing, resulting in unglazed areas bordered by coalesced glaze. (W)

• Crazing. A glaze fault characterised by the cracking of fired glazes and due to high tensile stresses. (W)

• Crock. synonym of pot. (W)

• Crocker. synonym of a potter, one who creates pottery (archaic). (W)

• Crockery. synonym of pottery. (W)

• Crystal glaze Glazes characterised by crystalline clusters of various shapes and colours embedded in a more uniform and opaque glaze

• china clay See Kaolin

D

• Deairing. The removal of entrapped air from a mass or slurry, often by the application of a vacuum. (W)

• Deflocculate. To separate agglomerates in a slurry by chemical means, and so decrease viscosity. (W)

• Delftware. A light-coloured pottery body covered with a tin glaze with overglaze decorations in cobalt on the unfired glaze. Developed in Holland to imitate Chinese blue and white porcelain.

• Dipping. Glazing pottery by immersion in a glaze suspension.

• Dunt. A crack caused by thermal shock, especially if ware cooled too rapidly after it has been fired. (W)

E

• Earthenware. A pottery created by low temperature firing. (W)

• Enamel (W) Coloured, glass-like decoration applied to ceramic wares. Also called on-glaze decoration. Often made by mixing metal oxides with a flux. Enamels are usually fired to temperatures in the range of about 700 to 800 degrees Celsius.

• Eutectic. An invariant point on an equilibrium diagram. A mixture of two substances which has the lowest melting point in the whole series of possible compositions. (W)

• Engobe. A slip coating applied to a ceramic body for imparting colour, opacity or other characteristics. It may subsequently be covered with a glaze. (W)

F

• Faience A form of tin-glazed earthenware (W)

• Fat clay A very plastic form of clay such as ball clay

• Fettling. The removal, in the unfired state of excess body left in the shaping of pottery-ware at such places as seams and edges. (W)

• Fire clay A highly heat resistant form of clay which can be combined with other clays to increase the firing temperature.

• firing. The process of heating pottery in a kiln to bring the glaze or clay body to maturity'

• Flatware (W)

• flux. substance that promotes fusion in a given mixture of raw materials. (W)

• Frit. A product made by quenching and breaking up a glass of a specific composition. Common uses include as components of a glaze or enamel. (W)
• Fusion. A process in which the joining surfaces of clay and glaze interact during firing ending in a thin combined layer of the two. (W)

G

• Potter's gauge. A tool used to ensure that thrown pots are of uniform size or shape.

• Glaze. A coating that has been matured to the glassy state on a formed ceramic article, or the material or mixture from which the coating is made. (W)

• Glaze firing A firing cycle in a kiln to the temperature at which the glaze materials will melt to form a glasslike surface coating.

• Glost fire. The firing used to form the glaze over the ware.

• Greenware. Unfired clay articles.

• Grog. See chamotte, above. (W)

• Gum arabic Natural gums used as binders to enable the glaze to adhere better to the body.

H

• Hard-paste porcelain, Porcelain which had been fired to 1400°C in a reducing atmosphere.

• Hollowware. (W)

I

• Iron oxide. A common oxide in glazes and some clays that generally gives a reddish colour.

J

• Jigger. A machine for the shaping of clay body into flatware by the differential rotation of a profile tool and mould. Also the process. (W)

• Jolley. To shape hollowware by the same process as jigger. (W)

K

• Kaolin. Also known as china clay, white or off-white firing kaolinitic. Used to make porcelain(W)

• Kidney A kidney-shaped tool made of flexible steel for finishing thrown pots, or made of stiff rubber for pressing and smoothing clay in a mould.

• Kiln A furnace for the firing of ceramics.

• Kiln furniture Refractory shelves and posts upon which ceramic ware is placed while being fired in the kiln.

• Kiln spurs. Supports, often in the shape of a tripod, used to maintain the shape and separate pieces of ceramic during the firing process.

• Kneading is a step in preparing clay for shaping. It involves manipulating the clay in a fashion somewhat like kneading dough for bread. It ensures the even distribution of moisture in the body.

L

• Leather-hard The condition of a clay or clay body when it has been partially dried to the point where all shrinkage has been completed. (W)

• Lustre A type of decoration originally developed in Persia which leaves a thin layer of metal on the decorated portions of pottery.

• Luting A method of joining together two pieces of dry or leather-hard clay with a slip.

M

• Majolica or maiolica Earthenware developed in Majorca which is Tin-glazed and overpainted with oxides. Similar pottery is known in France as Faience and the UK as Deftware.

• Matte glaze A dull-surfaced glaze with no gloss.

• Maturing temperature The temperature at which a glaze exhibits it best qualities.

• Maturity. 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. (W)

• Modulus of Rupture. 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 raw materials and ceramic bodies. (W)

• Muffle kiln. A kiln used for firing enamelled decoration, constructed so as to protect wares from direct flame and from smoke, soot, ash and other contaminants.

• Mullite Interlocking needlelike crystals of aluminium silicate responsible for toughness and hardness of porcelain which form in high-temperature bodies.

O

• Once-fired, green-fired (W)

• Opacifier An ingredient used in glazes to cause it to be opaque, and hence mask the colour of the underlying body.

• Orton cones See pyrometric cone.

• Overglaze (W) See Enamel, above.

• Oxidation (W)

• Oxidizing firing A firing in a kiln that retains an oxygen environment.

P

• Paper Clay 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.

• Pinholes. Faults in the surface of a ceramic body or glaze which resemble pin pricks. (W)

• Plasticity is the quality of clay that allows it to be manipulated and still maintain its shape without cracking.

• Porcelain. A vitreous ceramic material. Traditionally considered to be white and if, of thin section, translucent. (W)

• Potsherd. (W)

• Potter. A person who makes pots or other ceramic art and wares. (W)

• Potter's clay. The clay used by the potter (W)

• (Potter's) Wheel.

• Pottery. All fired ceramic wares or materials which, when shaped, contain a significant amount of clay. Exceptions are those used for technical, structural or refractory applications. Pottery is also: (1) the art and wares made by potters; (2) a ceramic material (3) a place where pottery wares are made; and (4) the business of the potter. (W)

Published definitions of Pottery include:

-- "All fired ceramic wares that contain clay when formed, except technical, structural, and refractory products."

-- "China, earthenware and any article made from clay or from a mixture containing clay and other materials."

-- "A class of ceramic artifacts in which clay is formed into containers by hand or in molds or with a potter's wheel, often decorated, and fired"

-- "The term pottery includes many varieties of ware from the crudest vessels of prehistoric times to the most beautiful decorated porcelains, stoneware and earthenware; it also includes many articles such as large grain-jars used in ancient times for storing corn and other dry materials, wine-jars and modern sanitaryware and the large tanks for containing corrosive acids. Many kinds of earthenware, stoneware and porcelains are used for scientific and experimental purposes as well as electrical apparatus, insulators, switch-bases, sparking plugs and bases or frames for electrical heating appliances."

• Pug. 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. (W)

• Pyrometer a temperature indicator linked to a kiln via a thermocoupler.

• Pyrometric cones. (W)

Q

• Quartz

• Quartz inversion

R

• Roller-head machine(W) Used in mass production of pottery, a rotary shaping tool that replaces jigger and jolley to shape wares.

• Raw, is unfired clay

• Raw glazing. refers to applying a glaze to an unfired ware and firing both in a "Once-firing".

• Reduction. Firing in a low oxygen environment.

• Refractory refers to heat resistant or clay that is fired at a high temperature.

S

• Saggar. A lidded or covered ceramic box used to protect wares from direct flame, smoke, fuel-ash or cinders during firing.(W)

• Sgraffito. 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.

• Single-fired see once-fired

• Sintering is the process caused by kiln firing which solidifies the clay but does not lead to vitrification. This occurs in bodies with a low flux content or at low temperatures, such as in earthenware.

• Slip A suspension of clay, clay body or glaze in water.(W)

• Soaking is a period during a firing cycle when a constant temperature is maintained.

• Stoneware. A vitreous or semivitreous ceramic material. Traditionally made primarily from nonrefractory fire clay.(W)

• Seger cone see Pyrometric cone

• Slurry is an aqueous suspension of clay and water

T

• Terracotta (W)

• Throwing The term used when referring to forming or shaping on a potter's wheel. (W)

U

• Underglaze Decoration applied to biscuit pottery and covered with a glaze. (W)

V

• Vitreous. Pertaining to the hard finish of a fired glaze, or the nonabsorbency of a fired body.

• Vitrification Process by which clay materials bond to become dense and nonabsorbent after firing.

W

• Water Absorption. 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 a common quality control test used for both ceramic raw materials and ceramic bodies. (W)

• Wedging. A procedure for preparing clay or a clay body by hand: the lump of clay is repeatedly thrown down on a work bench; between each operation the lump is turned and sometimes cut through and rejoined in a different orientation. The object is to disperse the water more uniformly, to remove lamination and to remove air. (W)

Further reading

• ASTM Standard C242-00. Standard Terminology of Ceramic Whitewares and Related Products.
• Dictionary of Ceramics 3rd edition. Dodd A., Murfin D. The Instiutue of Materials. 1994.