Ceramics Glossary of Terms

Ceramics Glossary of Terms

A

Abrasive – Hard substances (such as fused alumina) that are used for polishing, cutting or grinding. 

Absorbency – The ability and capability of a material to soak up a liquid. In pottery and ceramics this would relate to a glaze prior to firing.

Alumina – Alumina is a technical ceramic commonly used in engineering owing to its outstanding electrical insulation properties combined with rigidity and resistance to corrosion.

Advanced Ceramics – These types of ceramics are known as technical ceramics, high-tech ceramics, and high-performance ceramics. They are for industrial and commercial applications demanding high mechanical strength, abrasion and chemical resistance, electrical insulation or resistance to high temperatures.

B

Ball Mill – Comprised of a hollow cylindrical shell that rotates about its axis. A ball mill is used to grind and blem materials for use in ceramics. 

Batt – Depending upon its use a batt is either a type of tray to enable the movement of ceramic ware without it being handled directly. Or it can mean a kiln batt which acts as a kiln shelf support element upon which ware is positioned during firing.

Batt Wash – A type of kiln wash which is coated onto kiln shelves and furniture to stop the adhesion of ware during the firing process.

Bisque / Biscuit – This is the term given to ware which has been fired initially but has not yet been glazed.

Biscuit Firing – Is an initial firing process which dries and changes the composition of clay prior to glazing and/ or secondary firing. The term originates from the French ‘bis-cuite’, which means ‘twice baked’.

Bone Ash – Calcinated animal bone used as an ingredient in bone china.

Bone China – A type of pale thin porcelain with a translucent quality made with a clay composite containing a minimum of 30% of phosphate derived from animal bone.

C

Casting – A method where slip is poured into a mould to create more complex ceramic forms. Examples include sanitary ware, figurines, and teapots.

Ceramics – This is a term which covers a broad range of clay based products from bricks to tableware. The name originates from the Greek ‘Keramos’ which relates to potter, pottery or earthen vessel.

Ceramic Change – When clay reaches 1100 fahrenheit / 593 centigrade the material is changed by its particles being fused together.

Cheesehard – A stage of drying where clay is hard enough to be moved without deforming but can still be worked on by adding elements like handles and decorating techniques.

China – The term in relation to porcelain is derived from 17th century Britain to describe ceramics imported from China. It could not be manufactured in Europe making it very expensive. Eventually a substitute was found, and animal bone ash was added to make the delicate fine porcelain we know today.

Chittering – The result of incorrect fettling, chittering is a collection of small irregularities that form on the outer rim of pottery ware. 

Coiling – Building up ceramic forms and walls of an object by layering and coiling thin rolls of clay.

Cones – These small pyramid items are designed to melt at an equal temperature to a specific glaze. They act as a visual indicator within a kiln and are positioned to be viewed from a peephole.

Crazing – This is a form of random cracking pattern to the glaze caused by shrinkage of the ceramic item. This is considered either an intended decorative effect or an unwanted defect depending upon the type of ware upon which it occurs.

Clay – Clay is dug up from underground and is a fine grained material usually found in areas where prehistoric rivers once flowed. Over time this sedimentary rock is formed from ancient flora and fauna as a result of water pressure and the microscopic grains settle into clay beds. The three most common types of clay are earthenware, stone ware and kaolin. It can be moulded and manipulated when wet, before being dried and kiln fired to make bricks, pottery, and ceramics.

D

Decal – a design set on special paper or as a transfer to enable the decorative reproduction on to the surface of porcelain. This is an abbreviation of decalcomania and the decoration, once attached to the glazes ware is fired again at a lower temperature to complete the process.

Decorative – this is ceramic ware which is purely for decoration without any practical application.

Deflocculation – a process of making casting slip where clay is made more fluid with the addition of sodium carbonate and sodium silicate.

Dunting – cracking and breaking of pottery, usually during the firing process. This is usually caused by uneven heating and cooling.

Dryfooting – leaving the base or footring of a pot without glaze so that it can stand on a kiln shelf during the firing process.

Dipping – the method of applying glaze through immersion.

De-airing – the removal of air from clay, usually in a pug mill.

E

Earthenware – a type of ware which is fired at a relatively low temperature (1000c-1100c) to produce a porous form.

Extrusion – the clay is forced through an aperture, to reform it or extract air.

Electrical Porcelain – a type of technical ceramic used as an electrical insulating material made from clay, quartz or alumina and feldspar, and glazed to shed water.

Element – the component which carries electrical current for heating a kiln.

Enamel – the decorative and protective coating applied to ceramics which is made by heated and fused glass particles.

F

Faience – The term for earthenware which is decoratively tin glazed over an opaque white glaze.

Flatware – This refers to plates and dishes instead of jugs, mugs and pots which is known as holloware.

Fettling – Removing any excess clay using a fettling knife from the casting ware especially where it has gathered in the seams and joins of moulds.

Firing – The process of heating pottery and ceramics in a kiln to harden and change its composition to become a completed product.

Firing Down – The process of controlling and slowing down the cooling process by maintaining heat in the kiln once the ware has reached maturity. This can be used to create effects in the glaze or reduce the risk of problems like dunting or pin holing.

Floculation – this is the opposite result of deflocculation where a glaze becomes thicker either by the deliberate introduction of ingredients or by storage.

Flux – Fluxes are materials, which are often oxides, used to aid the liquefaction of glaze ingredients like silica and alumina. They also help with the process of fusion.

Frizzling – A decorating fault caused by high temperatures at the start of firing, which causes organic media to erupt or boil off.

Fusion – Combining constituent parts so that they bond together. These could be glaze ingredients or the surfaces of clay and glaze.

Fittings – Fittings can be used at both ends of a prop to help to spread the weight load of the ware which can be considerable on multi-level kiln cars.

Fixed Props – These are supports which enable the construction of multi layered structure for kiln firing.

G

Gauge – A potters gauge is a device which ensures the uniformity of ware.

Glaze – the liquid costing which hardens during firing to protect and/or decorate ceramics and pottery.

Glost Firing – otherwise known as glaze firing, this is the process where the glaze is fired to form a smooth glass like surface.

Greenware – This refers to unfired clay items.

Grog – Otherwise known as chamotte. This is where clay material is fired to remove moisture and then crushed into a grain to be used as an additive.

H

Holloware – shaped and formed ware such as jugs, bowls and containers. The opposite of flatware.

Hardbrick – Also known as kiln bricks, fire bricks, or refractory bricks. These are used to build supports and structures within a kiln and to line furnaces because of their dense structure and capacity to withstand extremely high temperatures.

Heat Work – The process of firing which results in the transfer of energy to wares combining temperature and duration. This can be measured with Pyrometric cones.

Hire Fire – The high-temperature firing range which includes cone 8 to cone 12 in the creation of stoneware or porcelain.

Hot Face – The internal refractory surface area of the kiln.

K

Kiln – A pottery oven in which ceramic ware is fired.

Kiln Furniture – A broad term for shelves and posts used within a kiln to support the ware inside.

L

Loss of Ignition – The percentage of weight lost in clay when it is heated under certain conditions 

Lustres – Made by coating ceramics with metallic substances which are then fired on to the glaze. These are usually iridescent in appearance. 

M

Model – The first cast, or prototype, of a piece. Models are usually made in clay, or sometimes plaster. 

Moisture Expansion – How much a porous ceramic material will expand when it absorbs water. 

Muffle Kiln – A box within a furnace that is used to move pieces out of reach of flames or other combustible materials. 

P

Peeling – A defect that occurs in glazed ware, peeling occurs when the glaze flakes away from the body. 

Porcelain – Traditional ware created from china clay, ball clay, quartz and feldspar. 

Pyrometric Cones – Usually made from ceramic materials, they are used to show accurate firing temperatures and heat work. 

R

Refractory – Used to describe how capable a material is of withstanding high temperatures. This is usually related to kiln shelves, cones, or stilts. 

S

Saggars – Clay boxes that are used to protect ware from contamination during firing. 

Spalling – Used to describe the disintegration of ware when it is subjected to sudden or unexpected temperature changes. 

Stoneware – Ceramics that contain clay which is naturally vitrified. 

T

Tensile Strength – How strong, or resistant, a material is against being torn apart by tension. 

Thermal Conductivity – How effective a material is at letting heat pass through it. 

Thermal Shock – How prone to damage a material is when exposed to changes in temperature.

Throwing – A technique used in the creation of pottery. Clay is often thrown on to a potter’s wheel and shaped by hand. 

V

Vitrification – The way in which materials fuse during firing.