| Abrasives | Hard materials used for grinding,cutting or polishing e.g.alumina |
| Absorption | The amount of water that a body can draw into its surface at any stage of processing |
| Agate ware | Pottery made by incomplete mixing of 2 different coloured bodies. The fired result is a streaked effect resembling agate. |
| Alumina | Aluminium oxide. A hard non fusing powder used to stop ware sticking to the supports in kilns. |
| Amorphous | Non crystalline structure e.g.glass |
| Antimony oxide | Used to produce yellow colours in glaze or pigments. Now considered toxic. |
| Apparent porosity | Relation between the volume of item and the volume of water absorbed on immersion. |
| Ark | Large storage vessel or container e.g slip ark or glaze ark |
| Ash glaze | A glaze using wood ash as the flux . Sometimes mixed with other materials. |
| Autoclave | An air tight container used to heat articles under water pressure . e.g to test the craze resistance of a piece |
| Bagwall | The inner wall of kiln . Sometimes referred to as muffle it protects ware from direct flames on gas firing. |
| Ball clay | A sedimentary clay usually of fine particle size. This clay is usually highly plastic |
| Ball mill | A ceramic lined steel cylinder filled with ceramic balls used to grind glaze or clay body. |
| Baluster | The name given to a vessel that is slender at the top and bulbous at the bottom. |
| Bamboo knife | A piece of bamboo that is sharpened to a chisel edge.Used in throwing. |
| Banding wheel | A turntable, usually made of metal, for applying decorative colour bands to vesssels or plates |
| Batt | A flat disc which attaches to the potters wheeel for throwing large articles. Also a refractory shelf. |
| Batt wash | A coating of refractory powder applied as a slurry to kiln furniture or saggars to stop sticking of ware. |
| Bentonite | A general term for montmorrllinite clay. Often added to glaze to stop sedimentation or to clay body to add plasticity |
| Biscuit | Pottery that has undergone its first firing. This gives the pottery sufficient strength to allow decoration and glazing. |
| Bloating | Deformation of the body on firing . Produced by gas trapped in the partially fused mass. |
| Blunging | Mechanical mixing of clay body with water to produce a slip. |
| Body stain | Ceramic pigment used to colour the body on firing |
| Bone ash | Animal bones that have been processed and calcined to produce a ceramic powder, |
| Bone china | A thin, white translucent pottery made using bone ash as a body component. |
| Borax | Sodium borate-usually as the decahydrate form. Used in the manufacture of frits. |
| Bottle kiln | A huge bottle shaped brick kiln. Originally used in Stoke onTrent for firing of pottery-now museum exhibits exist only. |
| Bullers ring | Special ceramic discs used to assess the firing in kilns. The measured contraction of the disc indicates the heat applied. |
| Burnish | To smooth the surface of a pot or precious metal decration to give a polished or shiny effect. |
| Calcium carbonate | Used a a glaze or frit component-also called limestone |
| Calcination | A high temperature heating process usually employed to change the crystalline form.e.g.flint |
| Caliper | A device for measuring the internal or external diameter of an object. |
| Casting | Forming pottery by pouring a slip into a porous mould |
| Casting slip | A very fluid slip of high solids content made of clay body,deflocculant and water. It is used in the casting process to form pottery shapes. |
| Celadon | A transparent green glaze pale in colour of Chinese origin |
| Ceramic | Derived from the greek word 'Keramos' meaning earthen vessel. Used nowadays to describe many high temperature formed produced using ceramic materials. |
| Cheesehard | Also called leatherhard-a clay body that is dry enough to retain its shape. |
| Chemically combined water | Water that is chemically attached to materials e.g. clay and is only removed by high temperature firing |
| China clay | Also known as kaolin. Made from pegmatite and mined in cornwall and other parts of the world. |
| Chinastone | Pegmatite. A fedspar and in its impure form the source china clayin the UK. |
| Chrome oxide | Used to produce yellow or green pigments or glazes |
| Chuck | Tube like former to hold a pot in position on the wheel while the foot is being trimmed. |
| Chun | A pale blue glaze used on stoneware |
| Clay body | The main pottery body composed of intimately mixed clays,feldspar,silica and other materials |
| Cobalt oxide | Used as a blue colorant in body glaze or decoration. |
| Coefficient of expansion | A measure of the reversible change of volume with temperature. can be quoted as linear or cubic expansion |
| Coiling | Rolled cylinders of clay build up to make a solid pottery form. |
| Colloid | A stable suspension of ultra fine particles. |
| Comminution | Size reduction by breaking, crushing or grinding |
| Compressive strength | The ability of an an article to withstand crushing loads |
| Cones | Sometimes called pyrometric cones, these ceramic pieces change shape and slump on exposure to heat. Used by potters as an indicator of a repeatable firing cycle. |
| Copper oxide | Used to produce green transparent colours in glaze. Under reducing fire can give bright red colours. |
| Crackle | Intentionally produced decorative crazing of the glaze. |
| Crawling | Shrinkage of the glaze leaving exposed body or pinholes after glaze firing-has many causes. |
| Crazing | Cracking of the glaze after firing. Caused by mismatch of body and glaze expansion. |
| Cryptocrystalline | Possessing crystals so small that they cannot be distinguished by optical microscope |
| Cut glaze | Bare areas on glazed ware caused by mechanical damage of the glaze prior to firing. |
| Damper | A crude device or small hinged refractory door to control the flow of gases from the kiln. |
| De-airing | Removal of air from clay either by wedging by hand or using a special chamber in the pug mill. |
| Deflocculation | The dispersion of clay slip or glaze by the addition of an electrolyte e.g.sodium silicate or soda ash |
| Delft | Opaque lead glazed eathenware often decorated by metal oxides prior to firing |
| Devitrification | Crystallisation of a vitreous glaze after firing. Often at the surface of the glaze. |
| Dilatancy | The property of a suspension whereby it gets thicker as it is stirred and thinner as it stands. |
| Dipping | The application of glaze or decoration slip by immersion and ten allowing excess to drain off. |
| Dispersion | The separation of the clusters of fine particles in water into individual particles. |
| Draw | Absorption of glaze by an unglazed surface during firing. |
| Dropper | Globules of glaze that are found on glazed pieces after firing. These are caused by drops from the kiln roof. |
| Dunting | Cracking pottery on cooling. Often caused by silica inversions in the body or too fast firing. |
| Earthenware | Originally a moderately porous pottery formed by firing a mixture of ball clay, flint , china clay and feldspar. |
| Edge runner mill | At ype of mill for mixing or grinding materials using 2 large stone rollers and a stone pan. |
| Efforescence | A growth on the surface of bricks or other articles due to the the presence of soluble salts. |
| Electrical porcelain | Type of porcelain used for producing elelectrical insulators. Typical formula 28 ball clay,22 china clay.quartz25,feldspar 25 |
| Elutriation | The separation of particles according to their size or density by a controlled velocity water stream. |
| Enamel | A fusible low temperature coating for metal or decoration for pottery. |
| Engobe |
A white or coloured coating of clay slip applied to the body prior to glazing. Often used for technical or decorative reasons. |
| Eutectic | A set mixture of 2 components having a lowest melting point of any ratio of the individual components. |
| Extrusion | The process of forcing a clay body thro an aperture or die to achieve a specific cross section or size. |
| Faience | Style of tin glazed earthenware produced in Europe. |
| Feathering | Effect obtained by trailing a feather thro still wet slip decoration |
| Feldspar | A crystalline mineral caused by weathering of granite. Used as a high temperature flux in many bodies. |
| Fettling | The removal of the seams edges and blemishes from dried pots prior to glazing |
| Fillers | Minerals added to a body to give it rigidity or strength. Quartz and flint are termed as fillers. |
| Filter cloth | Used to filter press clay slip to produce solid filter cake |
| Filter pressing | Process used to change slip into solid clay. Clay slip is forced thro a special cloth to remove water. |
| Fireclay | Clay that is uesd for refractory items. some fireclays contain naturalgrogs to improve shock resistance. |
| Firing | The increase in temperature used to produce a ceramic item. |
| Flocculation | The aggregation of ceramic particles in a suspension. A divalent electroltye such as CaCl2 is commonly used to create a thickening effect. |
| Flambe | A stronge red glaze produced by a reduced copper glaze. |
| Flatware | Plates,saucers,trays etc |
| Flint | Calcined powdered silica often used in earthenware bodies. |
| Fluting | Grooves cut into clay in parallel lines |
| Flux | A material added to a glaze body or colour to improve its melting properties |
| Foot | The base of the pot on which the piece stands. |
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Frit |
A special glass ground to a powder and used to reduce the melting point of a glaze. |
| Frizzling | A decorating fault where the decoration curls or moves on firing. There are many causes. |
| Fusibility | The melting behaviour of a ceramic glaze,frit,flux or decoration with increase in temperature. |
| Glaze | a thin glaze coating formed on the surface of pottery to render it impermeable and provide decoration. |
| Glaze-body fit | The relationship between the thermal expansion of rhe body and glaze. Ideally the glaze should have a lower expansion than the body. |
| Glaze stain | A colouring pigmant added to a glaze to produce a coloured glaze. |
| Glost | A glazed and fired piece is referred to as 'glost'. |
| Greenware | Clay pieces that have been formed but not fired. |
| Grog | Ceramic material that is relatively coarse compared to the rest of body components. Generally used to give texture or improved thermal shock properties. |
| Gypsum | Plaster of paris used to make moulds |
| Hakeme | Oriental technique of applying white slip with a brush made of straw-allows slip to be applied thickly. |
| Handbuilding | Constructing pottery from premade components. These components might be made by moulding,coiling or by hand. |
| Hardening on | A firing process normally 650-700C to remove organic components of underglaze decoration. |
| Hot pressing | Densification of a ceramic by simultaneous application of heat and pressure. |
| Holloware | cups,jugs,bowls etc |
| Impressed | A design stamped into the leatherhard clay using a die or tool |
| Incised | Pattern cut into the clay with a sharp tool |
| Jiggering | Machine process using a mould to form the inside of the plate and the tool the outside |
| Jolleying | Machine process using a mould to form the outside of the pot and the tool the outside |
| Kaolin | Also called china clay. White firing clay used in many bodies. |
| Kiln | High temperature oven or furnace used for firing of pottery. |
| Kiln furniture | General term used to describe refractory pieces used to separate or support items during firing |
| Kiln wash | Refractory slurry applied to kiln furniture to stop sticking during firing |
| Lamination | A fault structure in clay before or after firing where the clay is aligned in layered clusters. |
| Lawn | A sieve |
| Lead solubility | The solubility of lead containng glaze or colour powders when exposed to aqueous hydrochloric acid |
| Leatherhard | Or cheesehard. Clay that has dried to a point where it retains its shape. |
| Limestone | Calcium carbonate-often used as a glaze component |
| Lithograph | A method of decoration involving transfers.Allows fine detailed printing. |
| Loss on ignition | The loss in weight of a clay body when fired to a high temperature (usually 1000C) expressed as a % |
| Lustres | A metallic thin film applied to pottery either as a glaze or decorative effect |
| Lute | To join 2 pottery surfaces together with slip |
| Majolica | The technique of applying low fired tin glazes with colours to produce a multi coloured effect. |
| Manganese oxide | Colouring oxide used in glaze or decoration to give brown to purple colours. |
| Model | The original or prototype article |
| Modulus of elasticity | The term used to define the extent a material can be distorted under stress withot fracture. |
| Modulus of rupture | The term is used to define the strength of unfired clay body or the fired ceramic. |
| Moisture expansion | The extent to which a porous ceramic expands when it absorbs moisture or water vapour. |
| Mould | The shape usually made of plaster used to form the article either by casting or pressing. |
| Muffle kiln | A type of kiln where the ware is protected from the flame by an inner refractory box. |
| Nickel oxide | Used to produce brown,green or violet colours in glaze. Now considered toxic. |
| Onglaze | Decoration applied on top of the fired glaze. Overglaze or enamel terms are sometimes used. |
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Opacifier |
An additive to the glaze to give opacity e.g. zircon or tin oxide |
| Particle size | The distribution of particle sizes either as a powder or a slurry. Important measure in manufacture of glaze or colour. |
| Peeling | A defect in glazed and fired ware.The glaze flakes off in pieces particularly on edges. |
| Peephole | Small hole in a kiln door for the potter to observe the progress of firing. |
| Pinching | Indenting a pot with fingers or thumb before it is hard. |
| Pinholes | A common fault in the body or glaze. Small holes appear in the glaze or body as gases erupt thro the surface. |
| Pitchers | Fired or broken scrap pottery (of course also a large jug) |
| Plaster of paris | Gypsum. Used to make moulds. |
| Plasticity | The property of clay which allows it to be moulded and retain its shape after the force is removed. |
| Plucked ware | A fault caused by the ware sticking to the refractory support during firing |
| Porcelain | A vitrified and white translucent ware made predominantly in Europe and Asia.Usually strong in use. |
| Porosity | The amount of pore space in a ceramic body-consists of closed and open pores. |
| Pouncing | The ancient technique known as pouncing is when 'pounce', powder graphite or charcoal, is rubbed through a series of small holes punched in a paper pattern to transfer a design to an item to be decorated. |
| Pugging | The intimate mixing and extrusion of plastic clay body. Also the machine used to carry out this process. |
| Pulling | Shaping a handle by hand to the correct size and shape. |
| Pyrometer | High temperature measuring device |
| Pyrometric cones | Special refractory cones placed next to the ware to confirm repeatable firing. |
| Quenching | Method of making a frit where the molten glass is poured into cold water to produce small granules of frit |
| Raku | Low fired glazed earthenware produced normally by rapid firing. Raku is japanese for'enjoyment' and this type of pottery is used in the Japanese tea ceremony. |
| Raw glaze | A glaze in which no frit is present-normally a high fire glaze over 1100C |
| Reducing atmosphere | A kiln atmosphere which is deficient in free oxygen(more gas less air)-used to produce specific glaze colours or effects |
| Refractory | Ceramics that are able to withstand high temperatures without distortion. |
| Rib | A shaped tool to facilitate forming of a pot on a wheel. |
| Saggars | A fireclay or other refractory box used originally to protect the ware during firing |
| Salt glaze | Thin orange peel glaze produced onthe surface of pottery-originally produced by throwing salt into the kiln and allowing it to vapourise. |
| Sang-de- Boeuf | Ox-blood colour used to describe deep red colour of some glazes |
| Sedimentation | The settling out over time of any clay or glaze slip. More noticeable in glazes low in clay content. |
| Sgraffito | The technique of scratching through an applied slip layer to reveal the cour of the body beneath. |
| Shelling | Same as peeling: A defect in glazed and fired ware.The glaze flakes off in pieces particularly on edges. |
| Shivering | Same as peeling: A defect in glazed and fired ware.The glaze flakes off in pieces particularly on edges. |
| Sintering | The adhesion and densificationof particles on heating |
| Slip | Suspension of body or glaze in water. |
| Slip decoration | Application of contrasting coloured slip to a body as a form of decoration. |
| Slabbing | A buliding technique where slabs of clay are joined at edges to form an article. |
| Silk screen | A form of decoration where the colour paste is forced thro a decorative patterned screen either directly onto the ware or a transfer paper. |
| Soak | Allowing the pottery to remain at the peak temperature for a time period. This allows all positions in the kiln to reach approx the same temperature |
| Spalling | Flaking.cracking or disintegration of ceramics when subjected to rapid temperature changes. |
| Specific surface area | The total surface area of a all particles per unit weght of material |
| Spitout | Rapid desorption of moisture during the onglaze firing process causing a severe fault of small craters or pinholes. |
| Spray drying | A means of drying clay slips or other ceramic slurries by spraying the slurry into a large chamber of hot air |
| Sprig | Decorative pieces applied to leather hard pots |
| Spur marks | The marks left on pottery from refractory supports used to fire the piece. |
| Stoneware | A vitreous opaque pottery containing naturally vitrifying clay. Favoured by many studio potters |
| Surface tension | The tendency of a fluid to wet a surface.E.g. low surface tension= high wetting |
| Tailings | The portion of a material which does not pass thro a sieve or is returned for further processing |
| Tenmoku | A stoneware glaze deeply coloured by iron oxide. Colours can vary from yellow,green.red.blue or black |
| Tensile strength | The resistance of a materal to being stretched by tension or pulling |
| Terracotta | Red eathenware body usually made with naturally red clays |
| Thermal conductivity | The rate at which heat passes through a material as measured by its rise in temperature. |
| Thermal shock | The failure of a ceramic article due to stresses created by rapid temperature change. -either hot to cold or cold to hot |
| Thermocouple | A device for measurement of temperature in a kiln. Usually in the form of a special metallic wires encased in a ceramic sheath. |
| Thread | Twisted wire sometimes used by potters for curting pots of a wheel |
| Throwing | Making a pot on a potters wheel |
| Tin glaze | White opaque glaze produced with tin oxide in the glaze recipe. |
| Titanium oxide | Used in glazes to produce decorative crystalline effects |
| Towing | The smoothing of the outer edge of flatware in its green state. |
| Transfer printing | The method of applying a decoration to a pot. Slide off transfers using ceramic colours are applied to the glost ware and the refired to bond the decoration to the glaze. |
| True porosity | The sum of open and closed pores in a ceramic body. |
| Tube lining | A decorating technique where coloured slips are piped thro a small nozzle onto clay ware. This is often used as a border for further decoration. |
| Tunnel kiln | A kiln where the pottery moves progressively thro a heated zone to fire the pottery. |
| Underglaze | A decoration applied either directly to the clay or biscuit prior to glaze application and firing |
| Viscosity | The resistance of a fluid to flow. the reciprocal of fluidity |
| Vitreous | Glassy-having very low or zero porosity |
| Vitrification | The change from a porous to vitreous state of a ceramic |
| Volatility | The process of evaporation of materials on firing |
| Wall pocket | A vase usually with a flat back for attachment to a wall |
| Water absorption | A measure of the open porosity of a ceramic-determined by soaking the item in water for a set time |
| Wax resist | Wax applied to a pot to stop glaze or decoration sticking to these areas during application. |
| Wedging | A method of de-airing and dispersing moisture evenly in clay. The clay is worked by hand by repeated throwing of the clay onto the bench and folding over. |
| Wetting agent | A chemical used to help the application of glaze or colour to allow it to better cover uneven areas. |
| Wheel | Also potters wheel- a horizontal disc on a foot operated or motor driven shaft. Used for throwing of pots. |
| Wreathing | Ripples or waves on the inside of a cast pot after draining. Caused by variation in casting rate at different parts of the pot. |
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Recommended reading |
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