Some definitions of common pottery and ceramics terms.
Used to add color or texture to the clay, prior to working. Sands and other grogs will give the final product texture, and contrasting colored clays and grogs can be used to create patterns. Combustible particles can be mixed with clay or pressed into the surface, to give textures.
Pottery that is made with a mixture of different colored clays. The name comes from agate rock, which shows bands of different colors. Two or more different colored clays are lightly kneaded together, before being formed into a shape. The clays used need to be matched in terms of shrinkage rates during drying and expansion in firing. It is common to use a light colorless clay and add colorants to different portions of it.
One of the basic building blocks of clay and glaze (along with silica). It doesn’t melt at temperatures used for ceramics and glazes, reduces flow in glazes, and helps with strength.
The process of heating a glaze and then slowly cooling it to toughen it and reduce brittleness.
The technique of applying a stain gently rubbing it off, to accentuate the detail of the piece.
A container used for the storage of clay or glaze slips. It is mechanically stirred continuously, to prevent the contents from settling.
A term used for many clays. This is usually light in color and highly plastic. By itself, it is too slippery and fine for use, and so needs to be combined with sand, grog or coarser less plastic clays before use.
A grinder used for reducing hard materials to powder.
A decorative technique where a band decorative area or glaze is applied which encircles a pottery vessel.
A hand-operated revolving wheel (is a turntable on a pedestal base) used to apply banding to a piece.
A decorative technique where a slip thick slip is applied to a leather hard pottery piece by piping using a fine nozzle.
A type of stoneware that is black and unglazed. A high proportion of the clay is vitrified and colored by iron and manganese oxides.
A decorative technique in which figures or shapes protrude just slightly from the surrounding surface. Figures are not undercut to become three-dimensional.
A pottery bat is a flat disc that attaches to the head of a potter’s wheel to make throwing and lifting larger pieces easier. Wedging and drying clay is done with square or rectangular bats. Normally bats are made from wood, plaster of Paris, or plastic.
A mixture of flint and water used to clean kiln shelves after they become sticky from glaze droppings, to prevent other pieces from sticking to the shelves during firing.
The phenomenon where the glaze rolls back in on itself and forms odd shaped raised globs on a piece of pottery.
Volcanic ash clay that can absorb a large amount of water and swells to many times its dry volume.
Biscuit / Bisque
Bisqueware or biscuit pottery has been fired only once without a glaze to a temperature preceding vitrification. It is soft and porous. Glaze sticks more easily to pottery in this state due to its porosity. The temperature for biscuit firing is lower than the glaze firing temperature.
The appearance of broken bubbles on glazed surfaces of fired ceramics and pottery.
A swelling, or an increase in diameter of a piece of pottery.
To mix water with clay.
Used for mixing water with clay. The clay is fed into a hopper and is mixed with water by a system of angled rotating blades.
The color and composition of the clay.
A fine red clay used as a pigment.
Animal bones that have been baked and ground to a powder, used in the production of bone china.
Placing pottery bowls or cups rim-to-rim during drying and firing to prevent warping.
Firing pottery at a temperature of at least 1112 F (600 C)
The technique of rubbing leather hard clay pottery with a smooth hard object such as the back of a spoon or a polished stone, to create a polished appearance.
A type of glaze crawl where the glaze folds back on itself leaving double thickness and a bald patch on a piece of pottery.
Casting (aka slip casting)
A slip is poured into plaster molds which draw the moisture out of the clay to create a piece of greenware.
The slow process of clay becoming ceramic. Clay which is exposed to heat loses its chemically bound water molecules, meaning it can no longer be broken down by water. Once this change has occurred it cannot be reversed.
The craft of making decorative and/or functional objects from fire-hardened clay, or to the objects themselves. Ceramics is a broader term than pottery, as it also refers to porcelain and other objects made from materials that permanently change when heated.
Extremely smooth and soft leather. Used to soften sharp edges on wet to leather-hard clay pottery.
A rippling effect that appears when on turned clay on a kick-wheel that is too hard or soft, if a blunt or hard tool is used. Chattering can be used as a decorative technique.
A stage of clay where it can be carefully handled without deformation. It is drier than its plastic state, but not yet leather hard. It is the softest stage at which pottery can be shaved, or turned on a lathe, or kickwheel.
A very pure natural clay.
A translucent white body covered with a glaze fired lower in temperature than the body.
A hollow cylinder of clay used to hold a pot upside-down on the wheel while trimming the foot.
The clay mixture that the potter works with. Usually created by blending different types of clays or by adding other materials to the clay to produce a particular workability, texture, maturing temperature, or finished result.
A colorant that creates a dark dense royal blue in most cases. Used in China as a painting pigment on blue and white wares.
A hand building technique used to make pottery. Long round coils of clay are hand manipulated, pinched and squashed together to form a pot.
A substance that can be used to color something else (a clay or a glaze).
Pyrometric cones are composed of clay and glaze material, and designed to melt and bend at specific temperatures. The conditions inside the kiln can be determined by observing them (through a small peep-hole) during firing. Cones are a better indicator than temperature alone as the degree of glaze melt is determined by a combination of time and temperature.
Crater-like flaws that appear on a glazed surface.
The (intentional or unintentional) forming of very fine cracks in the surface glaze of a fired pot. This is caused by the uneven contraction of glaze and body. It can be done intentionally to create a decorative piece, but also can happen unintentionally if the glaze does not fit the clay. Raku ware often has this texture.
Pottery that has been designed to be attractive (it may or may not also be functional).
The practice of not glazing the bottom of a piece of pottery so it won’t have to be stilted.
One of the two main kinds of pottery (stoneware being the other). Earthenware fires at a low temperature and is porous and relatively light. Earthenware is a good clay for beginners to learn with as it is inexpensive and easier to work with than finer clays.
Electric kilns are powered by electricity rather than by burning fuel like a traditional kiln. They are easy and safe to operate, and they offer uniform firing results.
A decorative technique where the pottery has a raised or molded decoration (applied either in the mold or formed separately) before the first firing.
The application of a hard and glossy decorative or protective coating, usually translucent glass, that fuses with its substrate when fired in an enameling kiln.
A colored clay slip applied to greenware or leather-hard clay bodies. An engobe is used to add texture, color, or to prepare the surface for additional decorating. A white engobe can be used to overlay colored clays to the pottery appears to be made of white clay.
A finishing technique, the trimming or removal of excess clay, unwanted blemishes, seams and flash from nearly dry pots prior to glazing and firing.
The process of heating clay in a ceramics kiln. This transforms the clay into a very hard piece of pottery or ceramic, giving it a permanent shape. Different types of clay mature at different temperature ranges and are thus known as low-fire or high-fire clays. Sometimes firing is done twice, once without glaze (bisque firing) and once with glaze (glaze firing).
The appearance of a glossy sheen on pottery produced by when high fired glazed and unglazed ware are fired together.
The bottom of a pottery or ceramic piece.
The process of making of a piece of clay into a piece of pottery.
Pottery that has been designed for a functional (useful) purpose rather than solely for decorative purposes.
To melt together.
A functional or decorative coating applied to the surface of pottery that becomes glass during firing. Glazing can be done to waterproof pottery or to add color or texture. It can be applied by dusting, dipping or brushing a thin slurry on the surface of a pottery or ceramic piece, used to seal the piece, decorate it, or both.
When clay is fired in a pottery kiln after the application of a glaze. This is usually the second firing, and takes place after bisque firing.
A glaze with a smooth, shiny surface.
Unfired pottery. The stages of the greenware drying process are wet, damp, soft leather hard, leather hard, stiff leather hard, dry, and bone dry. Greenware must be air dried until it is bone dry before firing.
Ground up pieces of fired clay. It is used considered a filler and can be added to clay bodies for a number of reasons, such as increasing the strength of a clay, reducing warping and cracking, and reducing overall shrinkage.
A forming technique for making plates and other relatively flat pieces. The clay is placed on a mold that represents the top of the piece, pressed down and spun. A template representing the outline of the underside of the piece is placed against the clay and finishes the shaping.
A china clay in its purest form. Primary clay.
A pottery wheel put in motion by kicking a round flat weighted disc that the pottery worker rests a foot on, thus spinning the disc (wheel head) where the clay is being worked.
A pottery tool made of flexible steel or stiff rubber, used for finishing thrown pots as well as smoothing and pressing clay in a mold.
A pottery kiln is an insulated furnace or oven in which clay, glass, and other materials are baked or “fired” in order to harden them or give them permanent shape. Most pottery kilns use electricity or natural gas as a fuel source. Specialty kilns are designed for applying enamel, creating glassware, or creating Raku ware.
A clay preparation technique, where a lump of clay is rolled in upon itself, while stretching, pulling and pounding to get out the air bubbles.
Historically many glazes contained lead as this as this allowed vibrant colors to be achieved. Now that the health effects of lead are known, most glazes no not contain lead. However it is important to confirm this before using a glaze to glaze any pottery that may be used for food or drink.
A stage in the clay drying process that is midway between wet and bone dry clay. The clay will be stiff enough to be handled, but still damp enough for trimming and finishing.
The process of joining two pottery surfaces together with slip.
A glaze with a non-shiny surface. Matte glazes may have some sheen.
A hollow two piece block of plaster of Paris held together with bindings. Used with slip to create a cast of the design (see slipcasting).
The process of applying pressure to a softened clay object to create a thin neck.
A piece of pottery that has undergone a single glaze firing. The glaze is applied directly on to the dry or leather hard pottery avoiding the bisque firing.
Clay can be made more open (more porous) in structure by the addition of fillers or grog.
A firing where there is either no combustion occurring (as in an electric kiln) or where there is sufficient oxygen in the kiln to allow the fuel to burn cleanly. The atmosphere of the kiln (oxidation, or reduction) dramatically affects the resulting clay and glaze colors, for example, copper in oxidation is green (as is copper oxide) in reduction it becomes red (more like copper metal).
Clay which has had paper pulp added up to proportions of 50%. It gives greater plasticity, a reduced shrinkage and improved bonding when joining pieces together.
A thin layer of antiquing stain that is applied and wiped back leaving it only in the lines of the design on the piece of pottery or ceramic.
A small hole in each section of the kiln (with a removable ceramic plug) that can be used to check progress of firing by looking at cones.
Pottery pots made the pinching hand building technique. A ball of clay is formed by hand and then pinched and worked to create a pot.
Indenting a pot with the fingers and thumbs before it is hard.
Tiny holes formed in a glazed surface caused by escaping gasses.
Plaster of Paris (aka plaster)
Plaster of Paris is absorbent and can be used formed into surfaces where overly wet clay can be wedged to bring it to a more workable condition. Plaster of Paris is also used to make molds in which to pour slip (see slip casting).
The more commonly used pottery term for malleability or flexibility. It refers to the ease with which a particular type of clay or clay body can be formed into different shapes without breaking or cracking.
A high-fire clay notable for its hard, white, smooth, and sometimes translucent finish. Of the three primary clay types (the other two are earthenware and stoneware), porcelain is the most difficult to work with on pottery wheels.
Anything which absorbs or leaks water. In pottery and ceramics this usually refers to a clay that has been dried but not fired or fired but not to a high enough temperature to glassify it, which makes it vitreous, so that it would be non-porous.
Potter’s Wheel (aka Potter’s Lathe)
A machine with a rotating wheel on which a potter shapes or “throws” clay. Pottery wheels can be driven by electricity or by hand power or foot power (‘kickwheels’).
A method of low-fire surface change produced commonly by putting a red-hot piece of pottery into a bucket called a sagger, which contains combustible material (such as sawdust, newspaper or leaves). The temperature of the piece ignites the materials and they begin to smoke. A lid is then placed on the sagger, which produces a reduction atmosphere, along with the effects of the smoke of the burning materials.
A firing technique using a reduction atmosphere within a pottery kiln. This is caused when there isn’t enough oxygen to fully consume the fuel. Reduction firing results in pottery with unique color characteristics and subtler, earthier, richer colors.
A decorative technique where wax is painted onto pottery that area will resist any coloring or glaze.
A decorative technique achieved by throwing salt into a kiln during the glaze firing. This causes a shiny gloss to occur as the salt vaporizes and combines with the silica in the body of the pottery. Once a kiln has been used for salt glazing it can only be used for that type of firing after that.
A handbuilding technique using slabs or flat sections of clay to built forms.
Flat, thin 1/8″ to 1/4″ sections of clay which are produced by hand or with a mechanical device called a slab roller.
Clay that has been thinned by the adding water to the clay. Slips are often used for decorative purposes, but they are also used for casting clay in plaster molds.
A method of using plaster molds to create forms. The molds are filled with a slip, the plaster absorbs water from the clay in contact with its surface. The excess slip is drained off and the cast can be removed from the mold soon after.
A decorative technique where slip is applied to the greenware through a tube or nozzle (similar to piping icing onto a cake).
A thick slip. Commonly used to adhere handles or other clay pieces in place.
The addition of embossed decorations or low-relief ornamentation to leather-hard or bisque-fired pottery.
Loading a kiln with pots.
A suspension of metallic oxides, clays and other materials in water. Used to add color to the surface of clay and glaze.
A non-porous, high-fire clay that’s harder and stronger than earthenware. Stoneware does not require glazing in order to be waterproof. Stoneware contains more clay than porcelain and is opaque rather than translucent.
Stoneware glaze that is stained by iron oxide to a black or dark brown color.
A hard, semi-fired and absorbent clay used for both decorative and construction products. The colors can range from grayish to dark reddish-orange, light to medium reddish-brown, or strong brown to brownish or deep orange
To make pottery by hand on a wheel.
Circular disks that can be fitted to the head of a pottery wheel so that finished pottery pieces, particularly broad bottomed pieces such as plates or platters, can be easily lifted off the wheel. Bats are commonly made from plaster of Paris or wood.
Trimming (aka Turning)
A finishing technique. The pottery is inverted on the wheel and a metal cutting tool is applied to the bottom or sides of the pottery to trim away excess clay. Can be used to create a foot.
A decorative technique in which one or more colored glazes are applied to pottery then an overglaze of one or more clear or translucent glazes are applied over them either before or after the first glaze firing.
A piece of pottery that has been fired but no finish is fired on the outside.
Pottery designed for use rather than beauty.
The fusion of a clay body or glaze during firing. At a given temperature, the pottery surface will become vitreous, i.e. glossy or glass-like. After vitrification the clay can no longer be recycled although it may be used as grog.
A wax emulsion used to resist glazes, under glaze, stains to mask part of the pottery (e.g. foot rings). Once applied, wax cannot be removed except by firing off in the kiln.
The process of kneading, cutting, and rolling clay by hand so that it is free of air bubbles and has a uniform texture and consistency, making it workable.