Having a glossary of terms on hand is essential when you start a new hobby. It’s also useful to refer back to when you’re unsure of certain processes or techniques. They can be confusing at first, so it helps to have a little reminder around. We put together this guide of common pottery and ceramic terms you might come across when working with clay.
Common Pottery and Ceramic Terms
Absorption – A term used to determine the amount of water a fired/bisque item can absorb to determine its porosity or vitreosity.
Airbrushing – the process of applying paints to an item using an air compressor and a spray gun.
Antiquing – the process of applying a paint and wiping it off, leaving varying amounts of color in the detail or design of an item.
Ball Clay – A very fine plastic clay body that has a high shrinkage rate. Not good by itself, but with other additives and clays makes makes them more plastic and workable. Used also in glazes as a suspending agent.
Banding Wheel – a flat surface that sets on a revolving base used to turn items easily while painting or decorating.
Bisque – aka bisq – a clay item that has been fired to mature hardness which removes all moisture from the piece creating an adequate surface to apply glazes and paints.
Biscuitware – the same as bisque or bisqueware.
Blistering – the formation of bubbles in a glaze that freeze in place when cooled, often popping and creating craters sometimes with sharp edges. Caused when materials in the glaze and/or clay body are still volatilizing at the end of firing. Usually caused by impurities or firing/cooling too fast. Often from greenware not having been fired to full maturity before glazing. Can also happen when the clay or slip has impurities, too much iron or not thoroughly blended especially if mixing different lot batches.
Bloating – trapped gases in the clay body that don’t release during firing creating bubbles in the bisque. Caused when all the organic materials in the clay do not burn off.
Bone China – Soft porcelain that is made with calcined bone ash as a flux. It is harder and more durable than regular porcelain.
Bubbling – See Blistering.
Burnish – To smooth and polish the surface of an object (in ceramics, usually an unfired pot) by rubbing it with a smooth object such as a river rock or the back of a spoon. With this procedure a high shine can be developed without the use of glaze. Burnished objects are fired to a lower temperature (around cone 010) than many other objects, as the surface shine is reduced or lost if fired to higher temperatures.
Candling – Putting ware in kiln and running it with one element on low, often overnight, in order to make sure all the ware is bone dry in order to minimize risk of items blowing up during normal firing.
Casting – aka slip casting – the process of pouring ceramic clay slip into a plaster mold and then draining it to leave a formed item.
Ceramicist – An alternative name for a ceramist.
Ceramics – the art of creating items out of clay. Includes the field of pottery.
Ceramist – any person dabbling in the practice of creating ceramic/clay items.
China Paint – a concentrated paint/color pigment applied to fired, glazed surface or porcelain bisque which is then re-fired to harden and fuse to the item.
Clay Lifting – The process of cutting edges of designs into the surface of wet clay and lifting it giving a raised design.
Clay Puzzling – a technique of using ropes of extruded clay or flattened clay shapes to create a fretted look. Often involves shaping inside a plaster mold or piece of bisque. Can also be solid coverage.
Cleaning – the process of removing seams and flaws from greenware.
Colorants – Oxides and carbonates added to base glazes and slips to give color.
Cone – specially formulated clay rods designed to melt at specific temperatures. Used to control firing temperatures of kilns.
Cone Table – Charting the range of temperatures controlled by cones for firing clay bodies. Usually from about 1050 to about 2400.
Crackle Glaze – A decorative glaze that leaves tiny fine line cracks spidering through the service. Often times, a coloring material is scrubbed in after fire to accentuate the lines. This is not a food safe glaze. Similar to crazing tho intentional and not accidental.
Crawling – a flaw in a fired glaze where the glaze pulls away from the surface of the item leaving an area of bare bisque.
Crazing – a flaw where glazes have a web-like cracking in the surface of the finished piece. Prevalent in vintage ware, though a continuing problem with modern ceramists. Sometimes desired, most often not.
Decals – colored painted designs on a thin film-like base which are applied to fired glaze surfaces and then re-fired to fuse to the surface of the item. The filmy base is fired away just leaving the design.
Deflocculant – a chemical such as sodium silicate or sodium carbonate which reduces the amount of water needed to make slip fluid – consequently reducing shrinkage after it is applied to the clay.
Density – The weight of clay in comparison to water also referred to as gravity.
Drape Mold – a mold or convex shape used to lay and press clay over to create a shape. Can also refer to a convex ceramic bisque shape used to form fired glass.
Dry Brushing – The process of using a stiff bristle dry brush and small amounts of paint to gradually add color to a base-coated item through dragging the brush crosswise over the raised details of the design, or by a pouncing to create a softer cloth-like finish.
Dryfoot – the practice of leaving the bottom of a ceramic piece unglazed so that it can be fired standing on the kiln shelf without being stilted. Some molds are specifically designed to produce ware that can be dry footed. Stoneware and porcelain are always dry footed.
Dunting – Cracking of the clay body caused by rapid and/or uneven changes in temperature during heating or cooling. Can also be caused by glaze compression (glaze shrinking too fast).
Engobe – a colored decorating slip, often opaque. Concentrated color is added to liquid slip and then applied to greenware before firing. Many underglazes are Engobes.
Earthenware – a low-fire blend of clay, usually porous, used worldwide for domestic ware.
Embed – the process of painting the crevices of a carved design a contrasting color from the background, not to be confused with antiquing.
Emboss – Similar to slip trailing; however, done with thickened glazes, underglazes and stains (acrylics) – Leaving a raised design.
Extruder – a tool used to press clay into long strings or strips of varying designs.
Fettling – trimming the spare clay from the mold pour gate area before removing the greenware piece from the mold – Usually done with a tool called a fettle knife.
Fettle Knife – a metal or plastic knife like tool use to remove spare from pour gates of molds.
Flashing – In a mold, it is when the mold pieces do not fit tight and slip spreads between the seams. In glaze, it is the coloration from volatile materials that are present.
Flocculant – A thickening agent added to slurry which causes the particles to stay in suspension.
Flux – an oxide which causes ceramic fusion when combined with other oxides and heated. It promotes melting which helps lower the melting point of a glaze.
Fretting – the art of cutting intricate designs in leather hard castings/clay leaving open cuts completely through the thickness of the clay and covering the majority of the item.
Frit – A specific mixture of oxides which are melted together, become glassy and then are ground to a fine powder.
Fuse – To melt together.
Glaze – liquid composed primarily of silica which creates a glassy coating that is fused onto the surface of the clay when fired. Glazes may be matte or glossy, transparent or opaque, depending on their chemical makeup.
Glazing – the process of applying glazes to items and then firing them.
Gravity – The desired weight showing clay and water ratio of slip. One of two necessary steps to creating high quality slip and ware.
Greenware – Pertaining to any unfired clay object.
Grog – Clay that has been fired and then pulverized varying degrees. Sometimes added to clay to reduce shrinkage and makes clay more suitable for sculpting larger items.
Hard Spot aka Hot Spot – An area on a greenware or bisque item that is resistant to accepting paint. Most often caused from the casting process in a mold, or from over rubbing/polishing the greenware when cleaning it. Contaminants from the hands can also create hard spots, such as grease or hand lotions.
Hakeme – The oriental art of applying thickened slip using a coarse brush to a piece of wetware creating a unique texture.
High-Fire – the firing of a clay body to the range of cone 2 up to cone 13. Ware fired at cone 2 and up is usually referred to as Stoneware or Porcelain.
Hydrometer – A device to quickly measure the density/gravity of slip. Not as accurate as weighing.
Incise or Re-incise – the process of cutting into a clay body to create a design or to refine already established details.
Kaolin – A primary clay component of porcelain.
Kickwheel – A large turn table powered by kicking or electric motor, designed to spin while shaping clay into various designs with one’s hands. Similar principle as a lathe.
Kiln – the oven used to fire or bake clay or glass items.
Kiln Sitter – the part of a kiln that holds the firing cones and gauges the temperature then automatically shuts off the kiln.
Kiln Furniture – the shelving, posts and other supports used in a kiln.
Kiln Wash – A mixture of kaolin or flint which, when painted on kiln furniture and saggers, helps to prevent glaze from adhering.
Lace Draping – the process of dipping cotton lace into slip and applying it to an unfired item and then firing it. The lace burns away, leaving the delicate clay design.
Leather Hard – That point when wet clay becomes sufficiently stiff that it is no longer plastic, but is still damp, holds its shape and can be handled.
Liner or Long Liner – A very thin brush that is used for detailing and creating thin lines
Low-fire – the firing of a clay body to the range between cone 015 and cone 02. Ware fired at low temperatures is usually referred to as Earthenware.
Majolica – a glaze technique of applying an opaque satin/matte glaze to bisque, then colors are painted on this and fired to fuse the two together and create a bright, colorful and detailed surface.
Maturation Point – the firing point at which a clay body reaches its maximum hardness and non-porosity.
Melt down – When a kiln exceeds desired temperatures often causing items to melt or warp beyond use. They become more glass-like. Ceramist nightmare.
Mochaware – A design that looks like feathers or tree branches/roots on ware that is created by dipping wetware into liquid slip and dripping an acid/oxide mixture onto the surface which then flows into a web-like, one of a kind pattern on the ware.
Mold – a plaster form which is used to shape and model clay.
Opaque – A solid color, not transparent in any way. You cannot see through an opaque color.
Opacifier – Material that makes the glaze non-transparent or opaque such as titanium dioxide, tin oxide or zirconium silicate.
Open Pour Mold – a one piece mold that can be used for casting slip or pressing clay into it.
Overfire – When a kiln does not shut off automatically or manually and exceeds desired temperature.
Overglaze – colored paint-like surface decorations which are applied on top of a previously fired glazed item which is then fired again at very low temperatures. Most common are gold, metals, mother of pearl, decals, and china paint.
Oxidation firing – a firing process which takes place in an atmosphere of ample oxygen in a kiln to produce complete combustion of the contents. This allows the metals in clays and glazes to produce their oxide colors. Bright, clear low-fire colors are associated with glazes and clays fired in an oxidation atmosphere.
Oxide – A substance made when an element combines with oxygen.
Paint or painting – careless term referring to the application of acrylics, stain, glazes, under-glazes, over-glazes or any colorant to ceramic/clay items.
Peephole – the hole/s on the side of a kiln used to view the inside during firing and to allow the exchange of oxygen and gasses during the firing process.
Pinhole – a small pore in a glaze surface which is caused by escaping gases when the molten glaze cools too soon.
Plasticity – the ability of damp clay to readily change shape without cracking.
Polished Underglaze – the process of rubbing damp underglazes to a sheen prior to firing them.
Porcelain – a blend of clay, naturally white, which is fired to a high temperature at which the clay body vitrifies and becomes translucent. The more crushed bone added, the more transparent the ware. Colorants can be added.
Pour gate – the opening of a plaster ceramic mold where the slip is added.
Press mold – an open mold used by pressing clay into it.
Pyrometer – The gauge for measuring temperature in a kiln.
Raku – The process of rapidly heating a clay body to 1800 degrees F, then removing from the red-hot kiln (with long tongs) and placing into combustible materials like straw, wood chips, dried leaves, paper, etc. Can be open (oxidation) or smothered (reduction) in an enclosed container. Once thought to be exclusive to pottery, but can also be done with low-fire earthenware.
Rouging – similar to drybrushing but you use paste translucents and apply with a soft lint free cloth, like T-shirt material.
Reduction firing – a firing process that reduces the proportion of gas to oxygen, forcing the oxygen-starved flame to attack the oxides in the clay and glazes of the ware. Color changes during the process because there isn’t sufficient oxygen in the kiln for complete combustion and carbon dioxide in the kiln combines with the oxygen in the clay body and glaze.
Resist – Wax, tape, or any substance used to prevent glaze from adhering to specified areas during firing.
Reverse Dry-brushing – the same as dry-brushing except color is built from a dark base and each layer is increasingly lighter. The lightest color is the last, top most layer.
Salt Glaze – The vapors caused by adding salt near the end of firing glazes 2350 degrees F. Has the characteristic of orange peel. Can deteriorate the inside of the kiln. See Soda Glaze.
Sculpt or sculpting– the process of working with clay and creating objects without the use of a casting mold or wheel.
Semi-Transparent – the ability to see through color slightly with some distortion. In the case of glazes, color deepens in crevices and details of item and is lighter on the high points. Often referred to as ‘self-antiquing’.
Semi-Opaque – Dense color that has a very slight translucency.
Sgraffito – the method of producing a design on ceramics by incising the outer coating of slip or glaze to reveal the base of a different color. A surface decoration drawing technique in which coats of contrasting underglazes or colored slips are applied to clay, then scratched off with a fine-pointed knife or stylus to reveal layers beneath the surface.
Shivering – A glaze that is not compatible and shrinks less than the clay, causing the glaze to fall off or pop off in sheets that can be razor sharp. Best to discard the piece.
Shrinkage – Reduction in size of the clay item during drying and firing. A clay item can shrink anywhere from 4 to 15 percent from original size depending on the clay recipe.
Silica – the primary ingredient in glaze aka flint, quartz and silicon dioxide.
Slip – liquefied clay used for casting ceramic molds. A finely sieved mixture of clay and water, either white or colored, which can be applied to clay surfaces in one or more layers.
Slip Cast – Slip that has been poured into a plaster mold and then drained after a sufficient ‘shell’ has formed. When reaching a solid, but still damp state, the item is removed from the mold.
Slip Trailing – the method of decorating ware by squeezing thickened slip from a bottle or nozzle onto the surface of the pottery to create raised lines.
Slump Mold – A plaster or bisque mold with concave shape to lay or press clay into to create a bowl-like shape. Also can be a ceramic bisque item used to fire/melt glass creating a concave shape.
Slurry – A mixture of plastic clay and water similar to slip but not always with the same properties.
Soak or Soaking – A process most commonly used by potters where firing temperatures are held at a specific point for a period ranging from one half to one and a half hours. Often makes glaze colors more vivid.
Soda Glaze – Adding soda carbonate or sodium bicarbonate as an alternative to salt glazing. Similar result, less kiln damage. See Salt Glaze.
Sodium Silicate – aka Waterglass – a compound used in ceramic clay casting slip to help liquefy the slip and reduce shrinkage rate.
Soft Bristle brush – brushes that are made of soft material like sable or taklon which give least resistance when used to apply colorants, glazes, etc.
Spare – the clay waste which is trimmed from the pour gate of a mold before the greenware is removed from the mold.
Spray Fix or fixative – a clear spray used to give a protective finish to stained, non-fired items.
Stain – In the field of ceramics, it most commonly is referring to non-fired painting
products/techniques. May also be used when referring to colorants.
Stiff-bristle brush – brushes with stiff bristles which are used for dry-brushing, acrylic paints, or special techniques, most common are white, but can be other material/colors
Stilts – high fired ceramic supports with nichrome pins on the top surface to use under glazed items so they do not stick to the kiln shelf.
Stoneware – a blend of clays, usually brownish in color, which is characteristically fired to a high temperature at which the clay body becomes vitrified and non-porous, but not translucent.
Terra cotta – a type of clay whose name translates as ‘baked earth’ ranging in color from yellow to orange to red. Can be simulated by adding colorant to slip.
Thixotrophy – When the bond between the clay particles and water become out of balance and become weaker. Often evident when slip becomes gelatinous, but will reliquify upon mixing. Creates weak slip
Throw or Thrown – To make pottery by hand on a potter’s wheel or kick wheel.
Tiny Bubbles – Tiny bubbles trapped in a fired glaze are most usually caused by too thick of glaze application. Most often found in recessed areas and inside container bottoms. Similar to pinholes, but they do not break surface. Glaze is too thick for the gases to escape.
Toxicity – The point where a material is considered to be dangerous/poisonous.
Transparent – clear or color you can see through. Transparent glazes generally ‘settle’ into detailed areas, making them slightly darker and bringing the detail to view.
Under Fire – When firing does not reach maturity.
Underglazes – a liquid containing a clay or chemical base with colored agents which are used under a glaze. Most commonly indicates colors used to decorate greenware and bisque before a protective clear glaze is applied.
Viscosity/viscous – the fluidity of ceramic slip.
Vitreous Vitrification – the point at which a clay body or glaze reaches a glassy, dense, hard and nonabsorbent condition.
Wax resist – a wax emulsion especially created to repel underglazes and glazes applied over them. The wax is burned off during firing, revealing the designs protected from other paints applied around them.
Wet-brushing – similar to dry brushing only using slightly larger amounts of paint on a dampened brush, thereby enhancing the color at a faster rate sometimes resulting in filling in the design details somewhat more than the dry brushing technique.
Wetware – any clay item that is freshly removed from a casting mold or still wet. Also includes sculptured pieces and things thrown on a kickwheel.
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Why not take a look at our other pottery info articles for more tips and tricks.
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