Glossary of Ceramic Terms
Welcome to our Glossary of Ceramic Terms, a practical reference created for anyone learning or working with clay. Pottery and ceramics come with their own language, and many terms can feel confusing at first — especially when you’re new to the studio. This glossary explains common ceramic and pottery terms in clear, plain language, helping you better understand techniques, materials, firing processes, and studio practices. Whether you’re just getting started or refining your skills, this page is designed to be a quick, reliable place to look up ceramic terminology as you learn.
A • B • C • D • E • F • G • H • I • J • K • L • M • N • O • P • Q • R • S • T • U • V • W • X • Y • Z
A
Absorbency
The ability of a porous material to absorb water into its air spaces. In pottery, absorbency is important because bisque-fired clay must absorb glaze evenly before the glaze firing.
b
Bisque
Bisque (also called bisque ware or biscuit ware) refers to pottery that has been fired once without glaze. This initial firing causes physical and chemical changes in the clay, hardening the piece and preparing it to absorb glaze before the final firing.
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Black core
Black core is a defect that occurs when carbon is not fully burned out of the clay body during firing. This trapped carbon weakens the ceramic piece and is more likely to occur when there is insufficient oxygen in the kiln atmosphere, such as during certain firing conditions.
Blackhard
A stage in the drying process when a pottery piece is no longer pliable but not yet completely dry. At this stage, the clay often appears darker due to its remaining moisture content.
Bone china
Bone china is a type of ceramic body developed in 18th-century Britain to replicate the translucency of Chinese porcelain. It is made using bone ash as a key ingredient, which gives it strength, whiteness, and translucency, making it especially popular for fine tableware.
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Burnishing
A technique used to smooth leather-hard or black-hard clay by rubbing the surface with a hard, smooth object such as a stone or spoon. Burnishing creates a polished, lustrous surface and is typically done on unglazed pottery, sometimes with the use of fine slips for decoration.
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c
Casting slip
A liquid mixture of clay and water used in slip casting, where the slip is poured into a porous mold to form ceramic objects. As the mold absorbs water from the slip, a solid clay layer builds up along the inner surface, creating the shape of the piece.
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Ceramic change
Ceramic change refers to the permanent transformation that occurs when clay is heated to high temperatures, typically around 1100°F (600°C) or higher. At this point, chemically bound water is driven out and clay particles fuse together, making the change irreversible and preventing the clay from returning to its original, workable state.
Ceramic
The term ceramic comes from the Greek word keramos, meaning clay. In pottery and ceramics, it refers to objects made from clay that are permanently hardened through the use of heat during firing. This firing process is what distinguishes ceramic materials from unfired or temporary clay forms.
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Cheesehard
Cheesehard describes an early stage in the drying process when clay is still soft and workable but has begun to lose moisture. At this stage, the clay holds its shape more easily than freshly formed clay but is not yet leather-hard.
China
Originally used in Britain to describe ceramic wares imported from China and later European imitations, the term china today generally refers to fine, white, translucent ceramic tableware. It is typically glazed and fired at a lower temperature than the clay body itself, giving it a smooth, finished surface.
That’s concise, accurate, and glossary-appropriate.
Clay
Clay is a naturally occurring inorganic material made up of extremely fine, plate-like particles. When mixed with water, these particles slide past one another, giving clay its plasticity or workability—an essential property that allows it to be shaped and formed in pottery and ceramics.
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Clay body
A clay body is a formulated mixture of different clays and mineral materials designed for specific ceramic uses. By combining clays with varying properties, ceramicists can create a clay body that meets particular needs such as strength, workability, firing temperature, and surface quality. → Read more major page to write supporting pillar
Coiling
A hand-building technique in which long, rope-like coils of clay are stacked and joined to form a ceramic shape. The coils are usually smoothed together to create an even surface, though they may be left visible for decorative effect.
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Cones
Ceramic cones are small, pyramid-shaped indicators made from materials that bend or melt at specific heat levels during firing. They are used to measure heatwork in a kiln, showing how much heat and time a firing has received rather than relying on temperature alone.
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Contraction
Contraction is the temporary reduction in size that occurs when a ceramic material cools. Unlike shrinkage, which is permanent, contraction is reversible and happens as clay and glaze expand and contract with changes in temperature.
Crazing
It’s also known as “crackle” or “spiderwebbing,” and it’s a glaze fault caused by a difference in the degree of shrinkage in the clay and the glaze. It is usually unappealing, but it is occasionally employed as a decorative feature. It should be avoided for dinnerware and kitchenware.
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d
Decorative
In ceramics, decorative refers to work created primarily for artistic or ornamental purposes rather than practical use. Sculptures, wall pieces, and objects that resemble functional forms but are not intended for use are common examples.
Dunting
Stress during the fire and chilling process causes cracking in ceramics. Clay goes through a “silica inversion” at just over 400 degrees Fahrenheit and then again at slightly over 1000 degrees Fahrenheit during the fire process. The clay is put under a lot of strain throughout this process. Another factor might be the difference in clay and glaze contraction. Although all pottery is subjected to this stress, the majority of it is able to tolerate it.
Dunting isn’t usually visible right after the kiln is turned off. It can take up to a month or more for it to appear, but it should not be mistaken with cracks caused by “thermal shock.”
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e
Earthenware
Earthenware is a type of clay body commonly used in low-fired ceramics. It remains more porous than higher-fired clay bodies and often has a rougher texture, making it well suited for decorative work and glazed functional pieces when properly sealed.
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Firing
Firing is the process of heating clay and glaze in a kiln to high temperatures in order to permanently harden ceramic objects. This process causes physical and chemical changes that make the piece durable and stable, transforming it from soft, unfired clay into finished ceramic.
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Flameware
Flameware is a type of ceramic made from specially formulated clay bodies that can withstand extreme and rapid temperature changes. Because of its high firing and thermal shock resistance, flameware is often used as cookware and can be placed directly over an open flame, unlike ovenware which cannot tolerate direct heat.
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Frit
A frit is a pre-melted and ground mixture of glaze materials used in ceramic glaze formulation. The fritting process reduces the solubility and potential toxicity of raw glaze ingredients by binding them together, making glazes safer and more stable to use.
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g
Glaze
A glaze is a glass-like coating formed when a mixture of minerals and colorants is melted onto a ceramic surface during firing. Glazes are used to decorate pottery and to seal the surface, making it less porous and more functional.
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Glaze fit
Glaze fit refers to how well a glaze and clay body are compatible with one another after firing. When glaze fit is poor, defects such as crazing, shivering, or cracking can occur due to differences in how the glaze and clay expand and contract.
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Greenware
Greenware refers to unfired pottery that has dried enough to hold its shape but has not yet been fired. At this stage, the clay is fragile and easily damaged, and it may pass through several drying phases that allow for shaping and decorative work before firing.
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Grog
Grog is fired clay that has been crushed into a granular material and added to a clay body. It improves strength, reduces shrinkage, and increases workability, especially in clay bodies designed to withstand thermal stress.
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h
Hand building
Hand building is a method of forming ceramic objects without using a potter’s wheel, relying instead on shaping clay by hand. Common hand-building techniques include slab building, coiling, and pinching, and are used to create both functional and decorative ceramic forms.
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High-temperature glaze
A high-temperature glaze is a ceramic glaze designed to mature at higher firing temperatures, often identified by its cone rating (such as cone 10). These glazes tend to be more durable and less porous than low-fire glazes, though they are often more subtle in color.
i
Intermediate glaze
An intermediate glaze is a ceramic glaze that matures within a mid-range firing temperature, typically between 1900°F and 2200°F. These glazes offer a wide variety of colors and surfaces and, when properly matched with a compatible clay body, can produce durable functional ware.
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k
Kiln
A kiln is a specialized oven used to heat ceramic objects to high temperatures in order to harden clay and melt glazes. By controlling heat and atmosphere, kilns transform fragile greenware into durable, finished ceramic pieces.
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Lead
Lead is a metal that has historically been used in some ceramic glaze formulations as a flux to help glazes melt at lower temperatures. Because lead can leach from improperly formulated or fired glazes, its use raises important food safety concerns in functional ceramics.
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Leather-hard
Leather-hard is a stage in the drying process when clay has stiffened enough to hold its shape but is still flexible enough to be altered. This stage is ideal for trimming, carving, and adding attachments such as handles to ceramic pieces.
Low-temperature glaze
A low-temperature glaze is a ceramic glaze that matures at lower firing temperatures, typically below 1900°F (cones 06–01). These glazes often produce bright, vivid colors but are generally softer and less durable than mid-range or high-fire glazes.
Lusters
Lusters are metallic decorative finishes applied to glazed ceramic surfaces. Made from metal compounds suspended in a medium, they are fired at very low temperatures to leave a thin metallic layer on the glaze, often used as accents or highlights rather than full surface coverage.
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n
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Ovenware
Ovenware refers to ceramic objects designed for use in an oven and made from clay bodies that can withstand gradual temperature changes. Unlike flameware, ovenware is not intended for direct contact with open flames or stovetop heat.
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Oxidation
Oxidation refers to a firing atmosphere in which sufficient oxygen is present in the kiln during firing. In oxidation firings, oxygen allows materials in the clay and glaze to react fully, influencing color development and helping burn off impurities such as carbon.
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p
Pinching
Pinching is a hand-building technique used to form ceramic vessels without a wheel, coils, or slabs. The pot is shaped by pressing a finger into a ball of clay and gradually thinning and forming the walls by pinching.
Porcelain
Porcelain is a high-fired ceramic material known for its whiteness, strength, and translucency when thin. Fired at very high temperatures, the clay body and glaze partially fuse, creating a dense, durable ceramic commonly used for fine tableware and decorative objects.
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Porosity
Porosity refers to a ceramic material’s ability to absorb water through tiny internal pores. In pottery, porosity affects strength and durability and is influenced by firing temperature and glaze coverage, with higher-fired ceramics generally being less porous.
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Potter’s wheel
A potter’s wheel is a rotating device used to shape clay into symmetrical ceramic forms such as bowls, cups, and vessels. Clay is centered on the wheel and formed as it spins, a process known as throwing.
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Pottery
Pottery refers specifically to ceramic objects formed from clay that are intended to function as containers or vessels. While the term ceramics includes all clay objects made using heat, pottery commonly describes items such as bowls, cups, vases, teapots, and planters.
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r
Raku
Raku refers to a low-fire ceramic process in which pottery is removed from the kiln while still hot and placed into combustible materials. This rapid cooling and reduction create unpredictable surface effects, making each raku piece visually unique.
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s
Salt glaze
Salt glaze is a ceramic firing technique in which salt is introduced into a hot kiln, causing sodium vapor to react with the silica and alumina in the clay body. This process produces a distinctive, durable, orange-peel textured surface on the pottery.
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Shrinkage
Shrinkage refers to the permanent reduction in size that occurs as clay dries and is fired. Unlike expansion and contraction, which are caused by temperature changes and are reversible, shrinkage happens only during drying and firing and cannot be reversed.
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Slab
A slab is a hand-building method in which clay is rolled or pressed into flat sheets that are then cut and assembled to form ceramic objects. Pieces made using this method are often referred to as slab-built.
Slip
Slip is a liquid mixture of clay and water, sometimes colored with oxides or stains, used for decorating ceramic surfaces or joining clay parts. It is commonly applied during the greenware stage, and variations of slip are also used in slip casting.
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Stoneware
Stoneware is a type of high-fired pottery known for its strength, durability, and low porosity. Fired at high temperatures, stoneware clay bodies mature into dense, hard ceramics that are commonly used for functional items such as tableware and cookware.
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t
Temperature
Temperature in ceramics refers to the level of heat applied during firing, which directly affects the clay body and glaze. Firing temperature influences color development, glaze behavior, strength, and overall durability of a ceramic piece.
Throwing (wheel-thrown)
Throwing, also called wheel-thrown, is a pottery-making process in which clay is shaped on a rotating potter’s wheel. The clay is centered on the wheel and formed into symmetrical vessels, which are later trimmed and refined after partial drying.
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Vitrification
Vitrification is the process by which clay becomes dense, hard, and glass-like when fired at high temperatures. During this stage, the clay particles fuse together, greatly reducing porosity and producing a strong, durable ceramic body.
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Ware
Ware is a general term used to describe ceramic objects, often grouped by their intended use. Common examples include kitchenware, ovenware, and dinnerware.
Wedging
Wedging is a clay preparation process similar to kneading dough, used to remove air pockets, evenly distribute moisture, and homogenize the clay. Proper wedging improves strength and makes the clay easier to work with, especially for wheel throwing.
Whitehard
Whitehard is the final stage of drying before pottery is fired in the kiln. At this stage, the clay appears pale and contains no remaining free moisture. Proper drying to whitehard is essential, as trapped water can turn to steam during firing and cause the piece to crack or explode.