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 porcelain

Unglazed porcelain as a final product, with a matt surface resembling marble.

Biscuit firing

For twice fired ware the first 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 (or not) 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. Approximately 45-65% of moisture is retained within the clay body.

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-based glazes containing iron which produce green, grey and grey-blue colours in reduction firing. When used on porcelain, translucency is achieved after thickness of (at most) 1'8 of in.

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. Oftentimes caused by uneven glazing or three or more glaze coats. (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

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. Sometimes distinguished from slip by the addition of non-clay materials, and sometimes not. 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) Plates and dishes, as opposed to holloware vessels such as jugs

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, or for the body of fritware. (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. Consists of a Flux, Silica and Colorant/Oxide(W)

Glost firing

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

Greenware

Unfired clay articles. (Ranging from Slip to Bone Dry)

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) Vessels of any shape, as opposed to flatware such as plates

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

devices and implements inside furnaces used during the heating of manufactures individual pieces, such as pottery.

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. Similar to using gold leaf, it comes as a liquid and is a third firing completed after glaze. Common varieties are Pearl, Copper, Gold, Silver, and Platinum.

Luting

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

M[]

Maiolica

or majolica (W) Earthenware developed in Majorca, Spain and Italy which is tin-glazed and overpainted with oxides. Similar pottery is known in France as Faience and in UK and Netherlands as Deftware.

Majolica

(W) or maiolica Earthenware developed in France and England, which is made by applying temperature compatible coloured lead glazes simultaneously to the biscuit body, then firing.

Matte glaze

A dull-surfaced glaze with no gloss. Can also be achieved by Sand Blasting.

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) Pottery that has been through one kiln cycle and is no longer greenware.

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)

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."^[1]

-- "China, earthenware and any article made from clay or from a mixture containing clay and other materials."^[2]

-- "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"^[3]

-- "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."^[4]

Production pottery

sometimes known as standardware, refers to systematic, large-scale production of identical wheel thrown pottery vessels.

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-air 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. Copper red/Blue glazes can only be manufactured in Reduction. (in comparison to oxidation)

Refractory

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

Rib tool

is 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.

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)

Slip casting

technique for forming the body of a piece by using slip in a mould

Slipware

pottery where decoration in slip is a main feature. Includes slip-painting, slip-trailing, and many other techniques

Soaking

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

Soft-paste porcelain

made with little kaolin or china clay, mostly in Europe 1720-1820

Stilt

small supports used to prevent glazes from fusing the pot with the kiln when fired.

Stoneware

A relatively highly fired 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

Stages

the process of the clay for when which it dries

T[]

Terracotta

(W)

Tin-glazed

(W)

Throwing

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

Tile crank

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)

References[]

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.