Pottery Dictionary

Absorption

A numeric representation of a fired ware’s ability to absorb water. (2)

Agateware

A piece made by combining more than one color of clay. (3)

Atmosphere

The environment in the kiln; either oxidation, neutral, or reduction. (2)

Ball Clay

A plastic, fine-grained secondary clay colored by organic matter. (3)

Banding Wheel

A turntable that revolves which allows a piece to be turned easily as it is made or decorated. (3)

Base Recipe

The essential ingredients in a glaze recipe, without colorants, opacifiers, or suspenders. (2)

Bat

A slab of plaster, fired clay, (wood, plastic, etc) used for drying out clay or as a platform for work in clay. (1)

Bisque

1. Ware which has had one firing unglazed and is durable yet porous. (1, 2)

2. The preliminary firing to harden clay prior to glazing. (3)

Blistering

Bubbles and craters caused by gases escaping from a glaze during firing. (3)

Bloating

Blistering of the clay body caused by trapped gasses. (2)

Blowhole

An opening at the top of a kiln to let out heat and facilitate cooling, or to let out steam during the early part of firing. (1)

Blunge

To mix a slip. (1)

Blunger

A piece of equipment with a revolving blade used to prepare casting slip or clay bodies from dry materials. (3)

Bone Ash

The ashes of calcined bones, usually cattle bones, which are high in calcium and phosphorous oxides. (2)

Calcine

To heat to red heat (around 1292°F) or more to remove chemically combined water and volatile matter. (1, 3)

Carbonate

A substance produced when carbon dioxide combines with an oxide. (2)

Chuck

A solid lump of clay (or other similar device) used to hold a leatherhard piece on the wheel as it turns. (3)

CMC

Carboxymethelycellulose, a glaze binder and suspending agent. (2)

Coil

v. To make clay objects by building with ropes of clay. (1)

Colloid

Tiny insoluble particles that are suspended in another substance; halfway between a solutions and a suspension. (2)

Colloidal

Jelly-like, without grain structure. (1)

Colorants

Oxides added to a base glaze recipe to give color. (2)

Contraction

A reversible physical contraction of a material during cooling. (2)

Crackle

Decorative craze lines in a glaze produced deliberately. (1, 3)

Crawling

A condition where glaze pulls away from areas of a pot caused by grease or dust repelling the glaze or glaze shrinkage before it is fired, leaving areas of bare clay body. (2, 3)

Crazing

The formation of a network of cracks in a glaze caused by the glaze contracting more than the clay body. (1, 2, 3)

Cristobalite

Crystalline form of silica that has a high expansion and contraction rate. (2)

Crystalline Glaze

A glaze that contains crystals formed when the kiln firing is held at a specific temperature as it is cooled. (3)

De-air

To remove the air from clay, as in a de-airing pug mill, which removes the air from the clay by passing it through a vacuum chamber. (1)

Decant

To remove the water that has collected at the top when a material settles in a liquid. (1)

Deflocculant

A soluble base that is added to a glaze slurry causing the particles to repel one another. This can keep particles in suspension for a time and makes it possible to use less water to achieve the same fluidity but can cause the glaze to settle into a hard layer at the bottom of the container. (2, 3)

Deflocculate

To disperse the particles in a slip so that less water is required for fluidity. (1)

Dehydration

The loss of water from a clay during firing. (1)

Density

The weight of a material in comparison to water, also called specific gravity. (2)

Dissociation point

The temperature at which a substance breaks down into its constituent parts. (1)

Dunting

Cracking of the clay body which can happen during cooling or heating and can be caused by a weak form, stress from glaze that doesn’t fit, or irregular firing or cooling. (2, 3)

Dry foot

The foot of a pot which has been cleared of glaze. (1)

Earthenware

Pottery or other objects made from fired clay which is porous and permeable. Objects may be glazed or unglazed and often buff, red, or brown in color. (1)

A type of clay…

Engobe

A layer of slip applied to ware to change the color of the body which has a proportion of flux between the fired properties of a slip and a glaze. (1, 3)

Eutectic

1. n. The lowest-melting mixture when two or more substances are combined in certain proportions. (1, 2)

2. adj. Describing the temperature of lowest melting. (1)

Expansion

A reversible physical expansion of a material as it’s heated. (2)

Extruder

Equipment that forces clay through a die. (3)

Extrusion

The process of making shapes by forcing clay through dies. (1)

Fat clay

A clay body that is highly plastic. (1)

Feldspar

A group of minerals containing alumina, silica, potassium, sodium and calcium. (3)

Fettle

To finish or smooth the surface of leatherhard clay. To trim off spare clay at a seam from cast or jiggered pieces. (1, 3)

Filler

A material of little or no plasticity which helps to promote drying and control shrinkage in clay bodies or engobes. (1)

Fit

How well the expansion and contraction rate of a clay body and glaze match each other. (2)

Flashing

The impingement of flame on a pot in the kiln which often causes discoloration of the body or glaze due to volatile materials being present. (1, 2)

Flocculate

To thicken. (1)

Flux

An oxide which causes or promotes melting or ceramic fusion when combined with other oxides and heated. (1, 2, 3)

Footring

The base of a piece of pottery which is often left unglazed for mid-fired or high-fired pieces. (3)

Formula

An expression of the chemical composition of a glaze. (2)

Frit

A precise mixture of ceramic oxides which are melted together into a glassy state, quickly cooled, and then finely ground; Usually used in glaze recipes as generally insoluble sources of oxides. (2)

Gallery

The shelf on a pot rim that secures a lid and prevents it from falling out when the pot is tilted. (3)

Glass Former

An acidic oxide that retains its amorphous structure when cooled to a solid state instead of re-forming into a crystalline structure. (2)

Glaze

A glass layer that fuses to a clay piece during firing. (2)

Glaze Fault

An unwanted feature in a glaze including pinholing, crawling, or crazing. (2)

Greenware

Unfired pottery or clay piece that is finished but not dry enough to fire. (1, 2, 3)

Grog

Clay which has been fired and then ground into particles of various sizes and when added to a clay body provide texture and workable strength and reduce shrinkage. (1, 3)

Heat Work

The temperature that a ceramic piece has been heated to along with the time it has to absorb the heat. (2, 3)

Hydrometer

A device for quickly measuring density or specific gravity. (2)

Jiggering

Forming a pot between a revolving mold which shapes the inside and a template which shapes the outside and foot. (1)

Jollying

Forming a pot between a revolving mold which shapes the outside and a template which shapes the inside. (1)

Kaolin

A clay with few impurities, pure white in color, highly heat resistant and low plasticity. (3)

Kaolinization

The formation in nature of kaolin from feldspar. (1)

Kiln Wash

A mixture resistant to heat, usually kaolin or flint, which is applied to kiln shelves and saggers to prevent glaze from adhering. (1)

Leather hard

Clay dried enough to be stiff and nonplastic, but still damp enough to be joined to other pieces with slip, cut and burnish. Cool and damp to the touch. (1, 2, 3)

Line Blend

A glaze test that uses proportional variations of one or more materials. (2)

Lustre

Metallic surfaces on glazes derived from precious metals. (3)

Luting

Joining leather hard clay by slip. (1)

Maiolica

Decorated tin-glazed ware traditionally low fired with lead glaze made opaque by adding tin. Color decoration is added on top of the unfired glaze. (3)

Mature

Fired to a tight, hard, serviceable structure. (1)

Melting Point

The point at which a material changes from a solid to a liquid state. (2)

Neutral Atmosphere

The atmosphere in a kiln that has a perfect balance of oxygen and fuel for complete combustion, not oxidation or reductions. (1, 2)

Opacifier

A material that makes a glaze opaque. (2, 3)

Open

To make a clay more open or porous in structure by adding fillers or grog. (1)

Oxidation

A chemical reaction caused by heat in which oxygen atoms combine with other molecules or atoms. (2)

Oxidation Atmosphere

An atmosphere in a kiln where there is more oxygen present than is needed to burn the fuel. (2)

Oxide

Any element combined with oxygen. (1)

Oxygen Probe

A device placed in the kiln during firing to indicate the atmospheric conditions. (2)

Pinholing

Small bubbles in a glaze caused by gasses released from the clay body or glaze. (2, 3)

Plasticity

The workability of a material allowing it to be shaped without cracking and ability to hold the shape and can be adjusted by increasing water content, weathering, ageing, or adjusting the proportion of ingredients. (1, 2, 3)

Porcelain

Pottery or other objects made from a white, vitrified, and translucent body. (1)

Porous

The capacity to absorb water. (3)

Pottery

Objects, and especially vessels, which are made from fired clay. Including earthenware, stoneware, and porcelain. (1)

Pug Mill

Equipment that compresses and mixes plastic clay to a homogeneous state. (3)

Pyrometer

A mechanical device for measuring the temperature in a kiln. (1)

Pyrometric cone

A pyramid shaped device that melts when specific conditions of temperature, time period, and rate of rise are met; used to measure heat work. (1, 2)

Quartz Inversion

Approximately 1% expansion or contraction of quartz at 1063°F. (2)

Raku

A low-fire technique where fired work is removed from a red-hot kiln and reduced in combustible material. (3)

Recipe

The list of ingredients in a glaze or clay body. (2)

Reduction

A chemical reaction where oxygen is removed from oxide molecules. (2)

Reduction Atmosphere

The atmosphere in a kiln during firing where there is less oxygen than needed for complete combustion of the fuel. (1, 2)

Refractory

Resistant to heat, a material that can withstand high temperatures. (1, 3)

Respirator

A breathing device used to prevent the inhalation of harmfu materials. (2)

Rib

A smooth wooden, plastic, (metal) tool used to apply even pressure when throwing. (3)

Sagger / Saggar

A refractory box or container which protects ware from flames and ashes or creates a local atmosphere for the ware during firing. (1, 2)

Salt glaze

Glazing by the vapors from salt in the kiln. (1)

Sgraffito

The decorative process which employs a scratched line through a layer of slip to expose the clay body beneath. (1, 3)

Shards

Pieces of broken pottery. (1)

Shivering

When a glaze contracts less than the clay body which causes the glaze to fall or pop off the piece. (2)

Short

Nonplastic, poor in working properties. (1)

Shrinkage

Reduction in the size of a clay body as it is dried or fired. (2)

Sieve

1. v. To remove impurities or large particles by putting a glaze through a metal screen which comes in various mesh sizes. (2)

2. n. The device used to complete this task which has a specific mesh size.

Silica

The primary glass former in glazes. (2)

Sinter

1. To fire to the point, around 1112°F, where cohesion of materials begins.(1, 3)

2. Particles that hold together through partial melting or mutual adhesion. (2)

Slake

To moisten dry clay or dry glaze materials by submerging in water. (1, 2)

Slip

A fluid suspension of clay or other materials in water. (1)

Slurry

A mixture of glaze ingredients or clay and water. (1, 2)

Soak

To hold the kiln at one temperature for a period of time. (1)

Soluble

Capable of being dissolved in water. (1)

Specific Gravity

In ceramics, a number that represents how much heavier a liquid is than water. (2)

Sprig

A relief decoration added to a clay surface, usually thin slabs formed in a mold. (1)

Stabilizer

An oxide that keeps a glaze from running down the pot when combined in proper proportion to a glass former and a flux. (2)

Stable Glaze

A glaze that does not exhibit glaze faults or a glaze that does not leach toxic components. (2)

Stain

A coloring pigment, often referring to a commercially prepared coloring stain in which oxides have been fritted together and ground. (2)

Stilt

A three-pointed, heat resistant support used to lift low-fired ware off the kiln shelf during firing.

Stoneware

Pottery or other objects made from fired clay which is dense and vitrified, opaque and fired to at least 2200°F. (1)

Surface Tension

The attractive force on the surface of a liquid or molten glaze. (2)

Terra Sigillata

A decorating slip which has very fine particles. (3)

Throw

To make pottery by hand on a wheel. (1)

Tooth

Toughness in a clay body; course grain structure. (1)

Toxicity

How poisonous a material is considered. (2)

Triaxial Blend

A systematic method of testing three variables in a glaze at once. (2)

Underglaze

Decorated color applied under a transparent glaze. (3)

Unity Molecular Formula

A theoretical method of considering on a molecular level the oxides that make up a glaze and their relationships to each other. (2)

Viscosity

The relative resistance of a liquid to stirring or movement often describing glaze when it is fired. (1, 3)

Vitrify

To fire to the point of glassification (or vitrification). (1, 3)

Volatile

Materials that change from a liquid to a gas during firing. (2)

Wash

A mixture of oxide or stain and water that is applied to a ceramic piece or glaze coat to color it and sometimes includes a flux to help it fuse to the clay or glaze during firing. (2)

Wedge

To knead or mix plastic clay by cutting or rolling. (1)

Wood Ash

Ashes produced from burning wood. (2)

References

1. Clay and Glazes for the Potter Third ed. by Daniel Rhodes
2. The Complete Guide to High-Fire Glazes by John Britt
3. The Practical Potter by Josie Warshaw