Ceramics Glossary

Welcome to the Ceramic Materials Workshop ceramics glossary!

Al

Aluminum (aluminium) – Metallic element

Alkali Metal (AM)

Group 1 of the periodic table consisting of elements lithium, sodium, potassium, rubidium, cesium, and fracium

Alkaline Earth Metal (AE)

Group 2 of the peridic table consisting of elements beryllium, magnesium, calcium, strontium, barium, and radium

Alkalines (AE)

Group 2 of the peridic table consisting of elements beryllium, magnesium, calcium, strontium, barium, and radium

Alkalis (AM)

Group 1 of the periodic table consisting of elements lithium, sodium, potassium, rubidium, cesium, and fracium

Alumina

Stable oxide form of aluminum metal, Al2O3

Amorphous

Having no long-range order in crystal structure. Commonly refered to as glass

Ash

Solid by-product of a combustion reaction

Aventurine

Category of crystalline glaze using Iron as the major AE (Alkaline Earth) flux, known for it’s brown color and sparkle

Ball clay

Kaolinitic sedimentary clay

Ball milling

Technique of mixing and crushing powders or slurries

Barium

Alkaline Earth commonly used in glazes

Bentonite

A type of clay used as a suspension agent in glazes

Bisque Firing

Firing strategy used to sinter materials together and remove combustible species without beginning the vitrification process. CMW recommends Cone 08.

Blistering

Glaze defect noted by craters that look like popped bubbles. Commonly caused by the presence of Iron or Copper in oxidation firings

Blushing

Atmospheric contamination of copper on other work or kiln furniture. Generally takes place in reduction firing.

Bone Ash

Ceramic material containing Calcium and Phosphorus that has historically been made by calcining bones.

Bone China

Dinnerware made of a high proportion of Bone Ash, along with kaolin and feldspar. Resulting in a highly translucent ware.

Bone Dry

Completely dry, but unfired clay.

Borax

A water soluble ceramic material containing sodium and borate.

Boron

Glass forming element of the periodic table commonly used in traditional ceramics to lower melting temperature

Bristol Glaze

Glaze formulation that utilizes the chemical reaction between zinc and calcium to lower the melting temperature

Butterscotch

Lightly yellow glazes generally from the presence of high amounts of Rutile

Calcine

To fire materials to a relatively low temperature (generally Cone 015), to purify or remove physical properties. Commonly used for kaolin, rutile, and zinc

Capillary Suction

The behavior of open spaces to absorb water. The process by which clay bodies draw in the water during glaze application. Why glaze application dries quickly

Carbon Trap

The act of capturing atmospheric carbon in a reducing atmosphere. Caused by deposits of soluble sodium on the clay or glaze surface

Carbonates – Alkaline Earths – AE

Ionically bonded pairs of cations with CO3^2- that typically decompose with temperature, forming a metallic oxide and carbon dioxide

Celadon

A Chinese glaze known for its light blue or jade-green color.

Chemical Analysis

Investigation of material composition, including, but not limited to, chemical constituency, chemical formula, and mineral composition.

China (fine)

Dinnerware made with the “China process” which generally involved bisqueing to high temperature and glazing at a relativly low temperature

China Paint

Oil based overlgaze painting

Chrome

Element of the periodic table used in it’s trivalent form to create green color in ceramics

Chun/Jun

A traditionally Chinese glaze most noted for a sky-blue color and phase-seperated effect

Clay

Kaolinitic, naturually occuring mineral

Clay Body

An intentional combination of clay, and commonly silica and feldspar, generally designed to form a vitrifed material when fired to an appropriate temperature

Clear

Transparent or translucent quality, but generally referring to a glaze without colorant or opacifier

Coagulant (Flocculant)

A chemical that draws particles closer together in a suspension, increasing the viscosity of the system

Cobalt

Element of the periodic table used to create blue color in traditional ceramics

Coefficient Thermal Expansion

The proportion in which a material changes in dimensions as a result in a change in temperature

Colemanite

A hydrated calcium borate material. One of the components of Gerstley Borate is used in its place outside the U.S.

Colorant

Material category used to color ceramics

Cone 04

1063C or 1945F

Cone 10

1285C or 2345F

Cone 6

1222C or 2232F

Cone 8

1249C or 2280F.

Copper

Element of the periodic table used in traditional ceramics to create green, blue and in reduction, red

Crackle

A synonym for the appearance of a crazed glaze. Generally used in a positive description, but it has exactly the same effect as crazing.

Crater

Glaze defect created by the popping of a bubble in the glaze

Crawling

Glaze defect created by glaze shrinkage during the drying process and high surface tension in the melting glaze

Crazing

A mismatch in glaze and clay body coefficient of thermal expansion that causes the glaze to crack, but stay adhered to the clay body

Crystalline

Glazes that form independant crystals within the glass matrix that are observable with the naked eye

Crystallization

The formation of a long-range crystal structure

Darvan

Common name for polymer based deflocculant. Dispex in an international equivalent.

Dispersant (Deflocculant)

A chemical that pushes particles farther apart in a suspension, decreasing the viscosity of the system

Dolomite

A carbonate mineral and sedimentary rock that contains calcium and magnesium

Dunting

Firing defect where the work cracks. Often caused by thermal expansion mismatches between glazes and clay bodies. This causes vitrified ceramics to lose their ringing “ping”

Durability

The ability to withstand wear. Generally referring to a glaze’s resistance to chemical reaction in traditional ceramics.

Earthenware

Pottery made of clay fired to a porous state

Engobe

A colored or white semi-vitrified slip that is applied for decoration or surface texture

EPK

Edgar’s Plastic Kaolin – Brand name for a Florida, USA based kaolin product

Eutectic

A homogenous mixture of two or more substances that has a lower melting point than any of its individual components

Fake Wood Ash

A glaze type composed of extremely low silica and alumina levels and often with exclusively AE (Alkaline Earth) fluxes.

Feldspar

A family of aluminosilicate minerals containing varying amounts of potassium and sodium

Feldspathoid

Materials that share all of the chemical parts and behavior, but do not fall under the literal geologic definition of a feldspar. a group of alkali aluminosilicate minerals similar to feldspars, but with a low silica level

Flashing

Depositing of soluble sodium on a glaze or clay body resulting in an orange discoloration

Flaws

Unintended defects

Flint

Synonym for silica or quartz usually referring a powder consistency

Floating Blue

A phase separation glaze effect

Flocculant

A chemical used to clump or aggregate particles in a suspended slurry

Flux

Materials whose role is to lower the high melting temperatures of other materials, generally the glass formers

Food Safe

A generally useless term. Actual food safety in the U.S. only references the release of lead and/or cadmium and no other materials into food from glazes.

Formula

Generally referring to a combination of specific materials.

Frit

Pre-manufactured glass composition crushed into fine particles and used as a substitute for naturally occurring materials.

Fuming

Atmospheric contamination of chrome on other work or kiln furniture. Worse in barium-containing glazes

Gerstley Borate

Specific borate product mined in California with a unique naturally occurring combination of coleminite, ulexite, & bentonite

Glass-Formers

Materials that literally form the glass in glazes and clay bodies

Glaze

A combination of ceramic materials used to form a glass on the surface of a clay object for decoration and function.

Glomax

Brand name of a calcined kaolin

Gloop

Colored feldspar applied to the surface of work

Glossy

A word used to describe glazes with high reflectivity

Green

Term referring to unfired ceramics

Grolleg

Brand name of primary kaolin originating in the UK

Guan/Fish Scale/Snowflake/Crackle

A glaze effect caused by deep crazing in a thick glaze application

Hand-Building

Additive clay forming technique, typically utilizing one’s hands and a hand-powered forming tool.

Hard Panning

When a liquid glaze settles to the bottom of the bucket, creating a solid, unsuspended layer.

Heating Rate

The speed at which the kiln gains temperature.

Igneous Rock

Rock formation though a volcanic process

Iron

An element of the periodic table, commonly utilized in ceramics to produce a brown color.

Kalium Feldspar

See Potash feldspar

Kaolin

A hydrated aluminosilicate mineral commonly referred to as clay.

Lava Glaze

Glazes that foam, generally from the addition of silicon carbide.

Leather Hard

Stiff but not dry clay.

Line Blend

Proportional mixing of two separate glaze or clay recipes, usually presented as a gradient.

Lithium

An Alkali Metal flux.

Lithium Carb(onate)

The carbonate form of Lithium. Commonly used in glazes, even though water soluble.

Macro-Crystalline

Crystals that are observable with the naked eye.

Magnesium

Alkaline Earth Metal. Commonly used in glazes.

Mahavir

Brand name of a potassium feldspar that is mined in India.

Majolica

A decorating style from Italy where glaze was used to make paintings on a white base glaze

Manganese

An element in the periodic table that is used for obtaining brown or specialty metallic-looking glazes.

Map (Stull’s Map)

A graphical tool used in ceramics to predict the behavior of glazes based on their chemical composition.

Material

The matter from which a thing is or can be made.

Matte

Glazes that crystallize microcrystals based on chemical definitions laid out by Stull’s Map.

Mesh

A value representing the fineness of the grind of a material, with larger numbers being finer. The value refers to the number of holes in 1 square inch of the screening material.

Metal Marking

When metal utensils leave a mark on ceramic ware.

Metallic

Metal like

Micro-Crystalline

Crystals that are not distinguishable with the naked eye and require a microscope to observe.

Minspar

Brand name for a sodium feldspar native to the U.S.

Mullite

An aluminosilicate mineral formed when firing clay-based ceramics to mid or high temperatures.

Natrium Feldspar

See Sodium Feldspar

NCECA

National Council on Education for the Ceramic Arts. Mainly in reference to its yearly conference.

Nepheline Seyenite (Neph Sy)

A Feldspathic material high in sodium.

Neutral Firing

Firing environment in which the amount of oxygen gas available for combustion is equal to that which is needed to combust all fuel.

Nickel

A transition metal element in the periodic table, commonly used as a colorant in glazes, producing browns and greens.

Nuka

A Japanese phase separation effect.

Oil Spot Glaze

Glaze effect seen as spots in the glaze, caused by the decomposition and subsequent bubbling of iron in an oxidation atmosphere.

Opacifier

A material added to glazes to increase opacity (i.e., decrease translucency).

Opaque

The characteristic of a material in which light does not pass through the material.

Oribe

A style of Japanese pottery that originated in the 16th century. Recognized by its green color.

Overglaze

A glaze that is applied over an already fired glaze and then fired again, typically at a lower temperature than the original firing.

Oxidation Firing

A firing environment in which the amount of oxygen gas available for combustion is in excess of the amount of fuel provided for combustion.

Periodic Table

A table of the chemical elements arranged in order of atomic number, usually in rows, so that the elements with similar atomic structure appear in vertical columns.

Petalite

A Lithium aluminum phyllosilicate mineral that is utilized in ceramics as a lithium source.

Phase Separation

A glaze effect seen as a streaky or completely opaque haze inside a glaze.

Pinholing

A glaze defect identified by a small circular hole in the glaze that exposes the clay body.

Pitting

A bubble-based glaze defect, caused by the presence of Titanium.

Plucking

When an unglazed foot sticks to the kiln shelf after firing. Often causing the foot to chip when removed. Generally caused by soluble sodium interacting with silicon carbide shelves.

Porcelain

The category of clay body noted by a white, fine-grained body that is usually translucent.

Potash Feldspar

Feldspar material that is high in potassium content, AKA Kalium Feldspar.

Potassium

An alkali Metal element of the periodic table utilized as a flux in ceramics.

Pyrometric Cone (“Cone(s)”)

A physical way of measuring temperature in a kiln.

Quartz

A geologist’s reference name for naturally occurring Silica/Flint.

Raku

A Japanese firing style where glazes are removed from the kiln while molten and placed in combustible materials to induce localized reduction.

Recipe

In ceramics, a specific combination of materials.

Reduction Firing

A firing environment in which the amount of oxygen gas available for combustion is less than the amount of fuel provided for combustion, forcing chemical changes in certain molecules.

Refractory

In ceramics, the characteristic of a material to be resistant to heat

Rutile

A mineral made of 90% titanium dioxide and 10% iron oxide. Can be sold as Light, which is calcined and more concentrated, or dark, which is less concentrated

Satin

In ceramics, it generally refers to a matte surface finish that has more reflectivity and gloss.

Sculpture

A ceramic art form in which materials are worked into three-dimensional forms.

Semi-Matte

In ceramics, it generally refers to a matte surface finish that has more reflectivity and gloss.

Semi-Opaque

Partially see-through, or translucent.

Shino

A Japanese glaze style utilizing primarily only AM (Alkali Metal) fluxes, resulting in a fleshy surface.

Shivering

In ceramics, when there is a mismatch in the thermal expansions of the glaze and clay body, where the glaze experiences compression and may break or chip off of the clay body.

Si

Chemical abbreviation for the element Silicon

Silica

Oxidized form of silicon.

Silicon Carbide

A very high temperature material that, when added to a glaze, can create extreme bubbling or a possible reduction reaction.

Sinter

The act of physically bonding material together through heat. Commonly, what takes place in a bisque firing

Slip

The general term for liquid glaze, either for casting or surface decoration.

Slipcasting

The act of utilizing ceramic slurries and plaster molds to form ceramics.

Soda Ash

A sodium carbonate material historically obtained from the ashes of plants.

Soda Feldspar

A sodium rich feldspar mineral AKA Natrium Feldspar.

Sodium Silicate

A simple dispersant

Soluble (Water Soluble)

Materials that dissolve in water (like sugar). Not ideal for ceramics as water-soluble materials do not stay in the glaze application and travel into the body with water upon application.

Solution

A liquid mixture in which solid materials are dissolved by a liquid. Not ideal for glazes.

Spodumene

A feldspathic mineral that is utilized in ceramics for its high lithium content.

Stain

Ceramic material with a specific color used as a colorant for glazes and clays.

Stoneware

A broad term for mid-to-high fired ceramics that lack the translucency of porcelain and more tan/grey colors.

Strontium

An Alkaline Earth metal of the periodic table utilized as a flux in glazes.

Stull

The originator of the Stull Map.

Suspension

A liquid in which solid particles are suspended. Most glazes are a suspension.

Talc

Magnesium silicate

Tare

A term used for calibrating, or “zeroing,” a mass measurement scale.

Tea Dust

A style of glaze known for small crystal formations that appear as specs of dust within the glaze.

Tenmoku

A 12th-century Chinese glazing style that is known for its dark brown colors.

Terra Sigillata

A type of highly refined clay slip used to create a semi-impermeable, smooth surface.

Theramal Decompostion

A behavior where certain molecules (generally Iron and Copper) will release oxygen from their structure, generally at 1150 °C – Cone 4, resulting in bubbling/blistering in the glaze or body.

Thermal Contraction/Expansion

The tendency for a material to change in dimensions with a change in temperature.

Throwing

A term used to describe the act of using a potter’s wheel to create clay pottery.

Titanium

An element of the periodic table utilized in it’s oxide form in ceramics

Tomato Red

AKA Kaki, Persimmon. Tessha, Red achieved with Iron, generally using bone ash, magnesium & calcium.

Translucent

Allows some light through, or is partially see-through.

Transparent

Allows all light through, or is completely see-through

Ulexite

A sodium borate material and one of the components of Gerstley Borate.

UMF

The acronym for “Unity Molecular Formula”

UMF Charts

A chart that displays the molecular content of alumina on one axis and the molecular content of silica on the other axis.

Underfired

A term used to describe a clay body or glaze that has not reached the necessary temperature and thermal exposure to complete its reaction.

Underglaze

A highly colored vitrified slip.

Valance

Relating to or denoting electrons involved in or available for chemical bond formation.

Viscosity

The resistance of a fluid to a change in shape or movement of neighbouring portions relative to one another. Commonly used to describe the “thickness” of a liquid.

Vitrification

The act of becoming glass by firing.

Whiting

Calcium Carbonate. The most common form of calcium used in glazes.

Wollastonite

A Calcium Silicate mineral utlized as a source of calcium in ceramics.

Zinc

An element of the periodic table utilized in its oxide form in ceramics. Used as an Alkaline Earth flux in glazes