Pottery Glossary

The purpose of this resource is to give you quick answers about pottery terms, definitions, details, techniques, tips, history, science, and art so you can more fully enjoy and even perhaps learn as you proceed through the gallery. Many entries offer links to other more authorative online resourses if you want to go deeper.

montefin's Pottery Glossary.

| 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 |

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Albany Slip -- a slip made from clay mined in the vicinity of Albany, New York, USA famous for rich, translucent, chocolaty brown surface decorations. The known, naturally occuring deposits of Albany Slip have almost all been depleted. For a good overview of Albany Slip from the historic, aesthetic and technical viewpoints with some good guidance on Albany substitutes visit http://www.digitalfire.ab.ca/cermat/material/31.html.

Atmosphere -- the chemical make up of the volatilized vapors surrounding the pottery inside a pottery kiln, or within a post firing containment such as is frequently used in raku pottery.

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Barnhard's Clay is a high-fire slip which gives burnt metallic tones to the finished surfaces of pots to which it is applied.

Bats are surfaces on which wet clay or pottery is carried or worked upon. Throwing bats are circular disks that can be fitted to the head of a pottery wheel so that finished pieces, particulary broad bottomed pieces such as plates or platters, can be easily lifted off the wheel. Bats can be made of Plaster of Paris, wood, or bakelite.

Bisque is a fired piece (bisquette) of unglazed clay used to make pottery, figurines, dolls, knickknacks, ornaments etc. This porous, vitreous ceramic can be created using heat, which causes a chemical reaction (dehydroxylation) in clay (e.g. kaolinite) to irreversibly change:

Unearth or procure clay and mold, form, turn, wedge, cast or sculpt into the desired shape. Avoid air pockets.
Wrap the piece in plastic wrap and set in a moist environment for several days. Once air-dried, the clay piece is called greenware.
Apply no glaze. Place the greenware into a kiln similar furnace and fire for about three days, a) dry the piece at a low temperature for about 12 hours, b)then fire the piece to approximately 1800 to 2260F (1000 to 1238C) for another day, c) and allow the bisquette to cool to a safe handling temperature of 150F (65C).

If you've ever noticed that some pots look like living, breathing things, you're not far off the mark. From antiquity, potters have given pots lift and vitality by breathing into them while still wet, then pinching the mouth of the pot shut and letting it dry to the leather-hard stage before trimming away the closure and finishing the pot.

To burnish means to polish clay when it is leather-hard. Typically done with a hard object that has a smooth surface, such as a metal spoon or a well worn river stone.

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Celadon or Longquan Celadon is a type of pottery having a pale green glaze, originally produced in Longquan city, Zhejiang province, China. The first making of Celadon in Longquan begins in the Jin Dynasty (265-376 B.C.). The Northern Song Dynasty (960-1127 B.C), the most important dynasty in Chinese porcelain history, also brought prosperity in celadon production and appreciation. By the Southern Song and Yuan Dynasty (1127-1368 B.C), Longquan Celadon entered a most prosperous period during which the skill of making celadon had reached a new height and gradually formed a comprehensive celadon kiln system centering on Longquan town.

Longquan Celadon has two types, say, Ge Kiln and Di Kiln (Ge means elder brother and Di means younger brother in Chinese). The former together with Ru Kiln, Jun Kiln, Guan Kiln and Ding Kiln are recited as Five Famous Kilns in Song Dynasty. Famous worldwide, Longquan celadon was not only used for every dynasty's royal courts in ancient China, but exported to many other countries and regions of Asia, Africa and Europe early since the Song Dynasty.

Especially in the middle of the Ming Dynasty Longquan Celadon was introduced into Europe while its price was worth gold. Modern Longquan celadon inherits the products feature of traditional Longquan kiln and has been innovating and developing. Recently, many celadon products made by local masters and craftsmen have won the honors and prizes in various pottery-making competitions. A few of those have built up reputations of the Treasures of the Nation and have been collected in many museums.

The term celadon for these pale Jade-green glazes, is distinctly un-Chinese. In fact the term 'celadon' was applied by European connoisseurs to the wares when they appeared in France in the 17th century. In Honoré d'Urfé's (1567-1625) French pastoral romance, L'Astrée (1627), one of the shepherds was named Celadon, and the refined simplicity of Arcadia was applied to the ceramics.

Clay is a by-product of the earth’s crust, resulting from the decomposition of aging rocks exposed to the natural elements. Formed from small crystal compounds it is made up of the mineral kaolin, which consists of silica (SiO2) and alumina (Al2O3). These elements, silicon, oxygen and aluminum are the most abundant in the earth’s crust. There are three main groups of clays: Kaolinite-Serpentine, Illite, and Smectite. Altogether, there are about thirty different types of "pure" clays in these categories, but most natural clays are mixtures of these different types, as well as other weathered minerals. For more info visit en.wikipedia.org/wiki/Clay

Ceramics is the craft of creating useful and/or decorative objects from clay. For more info visit www.fact-index.com/c/ce/ceramics.html

Chamois -- extremely smooth and soft leather that, when wet, can be used to soften sharp edges on wet to leather-hard clay pots.

Crackle, also called crazing, is tiny, virtually invisible cracks on the surface of glazed pots. Basically, this happens because the glaze and clay fuse, individually and to each other, at the height of the firing temperature. As the kiln and the pottery cool, the clay body and the glaze shrink together, though at slightly different rates and degrees. If the glaze and clay body have been properly matched, all that happens is that the glaze accomodates the clay by developing this widespread crackle.

If you have ever seen the tiny dark lines in the well of a much loved tea cup that has been used for generations, you've seen crackle made visible by warm tea repeatedly seeping into the minute cracks. Now much loved, much used tea, yea even coffee, vessels have much wabi and much sabi. No wonder that the raku pottery process is steeped in crackle.

But, hey, say you've got a nice stoneware pot that's got a great shape and a great smooth, glistening glaze, and all it needs is for you to bring out that naturally occuring crackle to make it perfect? Got a century or two? Don't dispair, Chinese potters have been burying celadon pots in super strong tea and achieving respectable crackle in a year or two. But, if you're impatiant like me, try this. Get a bottle of plain old India Ink, heat the pot in a warm over, say 200 degrees - just enough to open up that old crackle then smear good old India Ink all over. It dries in moments and you vcan wipe the surface ink off with a damp paper towel exposing a deep, dark permanent crackle. For a good example of India Ink crackle click here page.

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Decorative and finishing techniques

Clay additives can be used to give colour to the clay, prior to working. Various coarse additives can also be added. Sands and other grogs give the final product texture, and contrasting coloured clays and grogs result in patterns. Combustible particles can be mixed with clay or pressed into the surface, to give textures.

Agateware refers to techniques that give a mixture of coloured clays. The name is derived from agates, which show band of colours, although it can be made with any sort of clay. Two different colours of clay are lightly kneaded together, before being formed into a shape. Although, in principle, any clays can be used, differing rates of drying and expansion in firing mean that it is usual to use a light colorless clay, and add a colorant to part of it. An analogue of marquetry can also be made, by pressing small blocks of coloured clays together.

Burnishing, like the metalwork technique of the same name, involves rubbing the surface of the piece with a polished surface (typically steel or stone), to smooth and polish the clay. Finer clays give a smoother and shinier surface than coarser clays, as will allowing the pot to dry more before burnishing, although that risks breakages.

To give a finer surface, or a coloured surface, a thin slurry of clay called slip can be coated on to the dry clay. This can be painted on, or the piece can be dipped for a uniform coating. Sgraffito involves scratching through the clay or a layer of slip, glaze, or stain to create texture or reveal a different colour underneath. One colour of slip can be fired, before a second is applied prior to scratching, if the base clay is not of the desired colour or texture.

Glazing is the process of coating the piece with a thin layer of a glassy material (often a mix of dolomite, frit, flint, feldspar, sodium borate, clay and whiting). This is important for functional earthenware vessels, which would otherwise be unsuitable for holding liquids due to porosity. Glaze may be applied by dusting it over the clay, or dipping or brushing on a thin slurry of glaze and water. Brushing tends not to give very even covering, but can be effective with a second coating of a coloured glaze as a decorative technique. With all glazed items, a small part of the item (usually on the base of the piece) must be left unglazed, else it will stick to the kiln during firing.

Some of the strongest colorants used are the oxides of cobalt (blue), iron (red or green depending on kiln atmosphere), and rutile, a.k.a. titanium (tan to blue breaking into red like tongues of flame (see Rutile Bowl)).

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Earthenware is a ceramic made from potash, sand, feldspar and clay, typically fired at a temperature of around 500 degrees Celsius (900 degrees Fahrenheit). Earthenware is typically fired at a temperature of around 500 degrees Celsius (900 degrees Fahrenheit). It is one of the oldest materials used in pottery. Classically, most earthenware has a red coloring, due to the use of iron rich clays. However, this is not always the case, and for the modern potter, white and buff colored earthenware clays are commercially available.

Earthenware may sometimes be as thin as bone china and other porcelains, though it is not translucent and is more easily chipped. Earthernware is also less strong, less tough, and more porous than stoneware - but its low cost and easier working compensate for these deficiencies. Due to it's higher porosity, earthenware must usually be glazed in order to be watertight.

Engobes are liquid clays slips typically applied to pots at the leather-hard or greenware stage to add color, texture, or improve the surface quality for later decoration. For a good overview of engobes visit http://www.ceramicstoday.com/articles/engobes1.htm.

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In pottery, glazing is the process of coating the piece with a thin layer of material that becomes not only glassy during firing, but actually glass. This can be achieved by brushing, pouring or dipping on liquid glazes prepared according to usually very precise recipes, or it can be achieved by manipulating the atmosphere within the kiln with additions of substances like ash or salt which in effect actually turns the skin of the clay pottery into glass.

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Hump Mold is the process of laying a slab of clay over a shape, the hump, or slapping, paddling or pounding an amount of clay over such a form.

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The Jomon period - 10,000 B.C. to 300 B.C. Some of the most fascinating pottery ever made in Japan dates back to the Jomon. The open-pit fired large vessels had the most amazing decorative features and continue to inspire potters today. For more information and photographs visit http://www.e-yakimono.net/html/jomon-dogu.html.

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A kiln, (the 'n' is silent among aficionados, but I've noticed there's little disgrace in pronouncing it) is an oven that is used for hardening, burning, or drying anything. Kilns have been used for converting wood into charcoal and are used to heat dried clay objects in order to make them hard and durable in a process referred to as firing.

Kilns have been made for as long as there has been pottery and items made of clay. The technology is thus very old. Most likely the first kilns where campfires or open bonfires. Early examples of kilns found in the United Kingdom, include those made for the making of roof-tiles during the Roman occupation. These kilns were built up the side of a slope, such that a fire could be lit at the bottom, and the heat would rise up into the kiln.

There are many kinds of kiln types, but the major division is between fuel burning kilms and electric kilns.

Fuel burning kilns are usually known by the name of their fuel: such as wood fired kiln, gas kiln, etc. Kilns can also be known by the particular type of pottery they're designed or dedicated for, such as a raku kiln or a salt kiln. Kilns can be permanent, re-usable fixtures or one time kilns, for example, kilns built, fired and torn down, or kilns tailored to fit a specific monumental pieces of pottery, or a primitive sheep or cow dung dome kiln in which the fuel itself is the structure of the kiln and does not survive the firing.

There's even talk of a solar kiln for ceramics.

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Lead Glaze -- Long before chronic lead poisoning became a public health issue. lead was a popular constituent of ceramic glazes. Some vibrant colors, particularly red and green, can only be achieved with lead glazes. Knowing what we now know, great care must be taken in the application and use of any lead glazed pottery to be used for eating or drinking or food storage, particularly of acidic foodstuffs, i.e. tomato sauces, vinagar, wine, etc.

Great care must also be taken when disposing of lead glazed pottery or shards of all types to assure against contamination of human and wildlife food or water resources.

Leather-hard - describes the stage during drying when a pot can be trimmed, and other, equally leather-hard pieces of clay can be affixed to it by sprigging.

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Majolica is named for the Spanish island of Majorca where the production of this functional ceramic earthenware, characterized by ornate decorations over a base of white tin or lead glaze, and under a lustrous clear glaze, reached its pinnacle of quality and beauty. And, yes, you do prounounce the "j" as in "jolly". There's an excellent article on The Art and History of Majolica at http://www.rencentral.com/GSS/lesson11-maiolica.shtml

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Overglaze is a partial or complete coating of one or more glazes, often clear or translucent, applied over previous layers of glaze or glazes, called an underglaze, which may or may not be previously fired.

oxidizing atmosphere is an atmosphere rich in oxygen, the major effect of which is to limit the range of colors possible, particularly at high temperatures.

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Pinch pots are pots made by forming a ball of clay with just the potter's hands pushing one thumb down into the center of the ball and pinching up the wall while rotating the pot. Simple, but some of the world's most treasured pieces of raku artistry are plain old pich pots.

Plaster of Paris, or simply plaster, is a type of building material based on calcium sulfate hemihydrate, nominally (CaSO4)2. H2O. A large gypsum deposit at Montmartre in Paris is the source of the name. When the dry plaster powder is mixed with water, it re-forms into gypsum, initially as a paste but eventually drying into a solid.

Plaster of Paris is absorbent. This feature is put to good use in pottery as working surfaces on which overly wet clay can be wedged to bring it to a more workable condition. Plaster of Paris is easy to shape and makes a great mold in which or over which (as in hump molding) clay can be shaped into desired forms. For more info visit en.wikipedia.org/wiki/Plaster_of_paris it keeps you interested;

Porcelain is a type of hard pottery. It is white, but mildly translucent, i.e. light shines through in thin sections and can be decorated to provide colour. For more info visit www.fact-index.com/p/po/porcelain.html

Production stages

All pottery items go through a series of stages during construction.

The raw clay is wedged to make its moisture and other particle distribution homogeneous and to remove air bubbles. It is then shaped either by hand or using tools such as a potter's wheel, an extruder, or a slab roller. Water is used to keep the clay flexible during construction and to keep it from cracking.
Work that is thrown on the wheel often needs to be trimmed or turned to make its thickness uniform and/or to form a foot on the piece. This process is done when the piece has dried enough to survive this manipulation. This is known as the leather-hard stage.
The piece is allowed to air dry until it is hard and dry to the touch. At this stage it is known as greenware. Items of greenware are very brittle but they can be handled with care. Greenware items are often sanded with fine grade sandpaper to ensure a smooth finish in the completed item.

The greenware is often given a preliminary firing in a kiln. Once it has been fired once it is known as 'biscuit' ware or bisque.

Biscuit ware is normally a plain red, white or brown colour depending on which type of clay is used. This is decorated with glaze and then fired again to a higher temperature.

Some pieces are not bisque-fired before being glazed. These pieces are called once-fired.

There are three basic techniques used in pottery - handwork, wheelwork, and slipcasting. Handwork is the most primitive and individual technique, where pieces are constructed from hand-rolled coils, slabs, ropes and pinched balls of clay, often joined with a liquid clay slurry. No two pieces of handwork will be exactly the same, so it is not suitable for making matched sets of items e.g..dinnerware. Doing handwork enables the potter to use their imagination to create one-of-a-kind works of art. The potter's wheel can be used for mass production, although often it is employed to make individual pieces. A ball of clay is placed in the center of a turntable, called the wheel head, which is turned chiefly using foot power (a kick wheel or treadle wheel) or a variable speed electric motor. The wheel revolves rapidly while the clay is pressed, squeezed and pulled gently into shape. Wheel work takes a lot of technical ability, but a skilled potter can produce many virtually identical plates, vases or bowls in a day. Because of its nature, wheel work can only be used to initially create items with radial symmetry on a vertical axis. These pieces can then be altered by impressing, bulging, carving, fluting, faceting, slicing, and other methods to make them more visually interesting. Often, thrown pieces are further modified by having handles, lids, feet, spouts, and other functional aspects added. Slipcasting is probably the easiest technique for mass-production. A liquid clay slip is poured into plaster moulds and allowed to harden slightly. Once the plaster has absorbed most of the liquid from the outside layer of clay the remaining slip is poured back into the storage tub, and the item is left to dry. Finally the finished item is removed from the mould, trimmed neatly and allowed to air-dry.

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Raku loosely translates as enjoyment, contentment, pleasure and happiness and these are meant to be embodied in the forms called Raku. Originally, Raku items were utensils for use in the highly ritualized Japanese Tea Ceremony. Now, it is spread around the globe and comes to life in many functional and artistic embodiments.

Raku is said to possess more or less of two characteristics wabi and sabi. For more information visit www.fact-index.com/r/ra/raku.html

A reducing atmosphere (or reduction atmosphere) is a condition created in a kiln in order to produce specific effects on the ceramic wares being fired. A reduction atmosphere is produced in a fuel fired kiln by reducing the draft and depriving the kiln of oxygen. This reduced level of oxygen causes incomplete combustion of the fuel and raises the level of carbon inside the kiln. At high temperatures the carbon will bond with and remove the oxygen in the metal oxides used as colorants

Sabi adds seeming history and age to wabi also incorporating serenity, melancholy, loneliness, and imperfection - a chip, a crack, an uninetended consequence of process - so that fresh from the fire the pot seems to have lived and maybe lived a very long time ago.

Wabi is a tough nut, particularly among westerners. It's to pottery what umami is to gastronomy: it emanates the natural world; has quiet, understated earthy elegance, it is a coming out or returning into nature but not in a harsh way; like the lotus it keeps you interested;

Wabi-sabi - Some commentators so closely identify sabi with wabi that they talk of wabi-sabi as a one concept.

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Sgraffito (as in graffiti), is a surface decoration technique that involves scratching through the wet, damp, leather hard, or even dried clay or a layer of applied slip, glaze, or stain to create texture, imagery, designs, or reveal a different colour underneath. One colour of slip can be fired, before a second is applied prior to scratching, if the base clay is not of the desired colour or texture.

Slabs are flat, thin ( 1/8" to 1/4") sections of clay which are produced by hand or with a mechanical device called a slab roller. Slab built pottery is pottery constructed wholely or mostly from sections of clay slabs.

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Underglaze is 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.If there are multiple glaze firings, each subsequent glaze firing is done at a lower and lower temperature so that each underlying designs is not affected. For an example of underglaze click Majolica Moroccan Bowls.

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