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The Pottery Studio glossary of terms and abbreviations

Index

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
Agate ware	Pottery made from clays of two differing colours, not completely mixed. The result is a srtreaked effect resembling agate. Example
Alumina	Aluminium oxide. It is used to bed bone china in the biscuit firing. A fine white powder with a high fusing temperature.
Antimony oxide	Produces a yellow colour in glazes.
Ash glaze	A glaze made with ground ash, usually wood ash and sometimes mixed with other materials. Example
B
Bagwall	The inner wall of the kiln - it protects the pots being fired from the flames.
Ball clay	A sedimentary clay that will withstand high firing temperatures. Plastic in quality.
Ball mill	A grinder for reducing hard materials to powder.
Baluster	The name given to a shape of a vase or other vessel that is slender above and bulging below. Example
Bamboo knife	A piece of bamboo sharpened to a chisel edge. Used in throwing.
Banding Wheel	A turntable used for applying lateral decoration to a pot.
Bat	A flat disk that sits on the wheel. Used for heavy pieces that would be difficult to separate from the wheel.
Bisque (or biscuit)	Pots that have been given a preliminary firing to render them hard enough for further work such as decoration and glazing. The higher the temperature of the bisque firing, the harder will be pot, resulting in reduced reaction between glaze and body in the final firing.
Blunge	Mix water with clay.
Blunger	Machine for mixing water with clay. The clay is fed into a hopper and goes through a system of angled rotating blades to mix it with the water.
Body	The substance from which a pot is made. A mixture of one or more clays, grog, feldspars, etc., to give a material suitable for shaping and firing.
Bone ash	Animal bones that have been baked and ground to a powder, used in the production of bone china.
Bone china	A china made white and translucent by the addition of calcined animal bone to the body.
Borax	Sodium borate, a mineral salt found in alkaline deposits. A form of borax purified by calcination is used as a flux in glazes.
Bottle kiln	A large kiln, wide at the bottom and narrow at the top like a bottle.
Burnish	To smooth the surface of a pot by rubbing with a hard object to give a finish with a polished effect.
C
Calcine	Reduce to calcium carbonate. To purify a substance by subjecting it to high temperatures.
Calcium carbonate	A white insoluble solid. Occurs naturally as chalk, limestone, marble and calcite. It is used as flux in glazes.
Caliper (or Calliper)	A measuring device resembling a compass. Internal calipers measure internal diameters or apertures and external calipers measure outside diameters or overall sizes. External calipers look like a jockey (without his horse) and inside calipers look like a girl in a tight skirt.
Cast	To produce shapes by pouring fluid clay into moulds. The 'negative' moulds are usually of plaster of Paris, and made from a 'positive' so that when they wear out, new ones can be made. Example
Celadon	A grey-green glaze, usually pale in colour, of Chinese origin. Example
Cheese-hard	. . . or leather-hard. Clay that has dried to the point where it is stiff enough to retain its shape but wet enough for further work to be done on it.
China	Porcelain. The first porcelain imported into Europe was from China.
China clay	Kaolin. A white clay made from pegmatite found in Cornwall.
China stone	Pegmatite. A feldspar.
Chrome oxide	Used to produce yellow or green colours in glazes.
Chuck	Tube-like form to hold a pot upside-down on the wheel for trimming the foot.
Chun	A pale blue glaze used on stoneware.
Clay	A mixture of water an powder from decomposed feldspar. Clay is the potter's basic material. When moist it is soft and plastic; when fired becomes permanently hard.
Climbing kiln	A multi-chamber kiln with each successive chamber at a higher level than the last. This type of kiln is of oriental origin and was popularized in Britain by Bernard Leach and his students.
Cobalt oxide	Used to produce a blue colour in glazes. Example
Coiling	Rolled clay in flat form or with a rounded section that welds to itself when fired to make a solid form.
Cone	Cones are test pieces inserted in the kiln to indicate to the potter when a certain temperature has been reached. They are made of various glaze materials of known melting point. Two examples of cones are Seger cones, named after Hermann August Seger, and Orton cones, manufactured by the Orton Ceramic Foundation in the USA.
Copper oxide	Used to produce green colours in glazes. When used in a reducing atmosphere it produces a red colour. Example
CPA	The Craft Potters' Association. An organization to promote the work of British potters.
Crackle	Cracks in the glaze formed intentionally as a decorative feature. (See also - Crazing) Example
Crawling	Shrinkage or retraction of the glaze during firing, causing exposed areas of body.
Crazing	A fine network of cracks in the glaze usually caused by uneven contraction and expansion of the body and the glaze during changes of temperature. In some pottery this is a design feature rather than a fault (See - Crackle), but in earthenware pots the cracks can allow moisture to penetrate to the porous body leading to further damage. Example
D
Damper	A crude device - usually a refractory clay brick - used to block the flue of a kiln.
Delft	Opaque lead glazed earthenware with a pattern or design painted in metal oxides on the glaze before firing.
Dunting	Cracking or breaking of pots when cold draghts are allowed to enter the kiln. Can also be caused by the free silica in the body being too fine.
E
Earthenware	Pots that are porous when unglazed. Usually fired at low temperatures. Earthenware is softer and more easily damaged than stoneware. Example
Enamel	Low-fired coloured glazes.
Endless loop	See Loop, Endless.
Engobe	Slip - wet fluid clay used for decoration or for covering a base coloured body. This term is most often used to describe coloured slips.
F
Faience	Tin glazed European earthenware, usually from France. Quimper and Desvres are good examples of faience. Example
Feathering	Effect obtained by trailing a feather through wet slip decoration.
Feldspar	(Also called felspar). A crystalline substance found in granite.
Fettle	The removal of unwanted blemishes, seams and flash from nearly dry pots prior to glazing and firing.
Fire	To heat pots in a kiln to a specific temperature for a specific time.
Firing Range	The temperatures between which a clay or glaze matures or fuses.
Flambé	A flame-like effect produced by a reduced copper oxide glaze.
Flatware	Plates, saucers, trays, etc.
Flint	Calcined and powdered silica. Used in earthenware bodies.
Fluting	Grooves cut into the clay in parallel lines running in any direction. Example
Flux	A substance mixed with a body or glaze to promote fusion. It effectively lowers the melting point.
Foot	The base of a pot.
Frit	A vitreous composition used in glazes and enamels.
Fusibility	The ability of a material to fuse or melt.
G
Galena	An ore of lead sulphide used as a glaze.
Glaze	A vitreous substance used to decorate pottery and render it impermable to moisture.
Glaze firing	The last firing of a pot when the glaze is applied.
Greenhouse	Place where pots are kept to harden before biscuit firing.
Greenware	Pottery that has not been fired.
Grog	Gritty material added to clay to modify its behaviour in firing. It is usually ground clay that has already been fired, and can be course or fine depending on the type of work for which it is being used.
Gypsum	Plaster of Paris.
H
Hakeme	Oriental technique of applying white slip with a brush made from straws. The top ends of the straws are tied in bunch like a small besom allowing the slip to be applied to the pot thickly. Example
Handbuilding	Constructing pots from pre-made parts. The components might be moulded, coiled or fashioned by hand. Example
Hollow ware	Cups, jugs, bowls, etc.
I
Impressed (design)	Stamped into the leather-hard clay with a tool or die. Example
Impressed (mark)	Stamped into the leather-hard clay with a tool or die. Example
Incised (design)	Pattern cut into the clay with a sharp tool. Example
Incised (mark)	Maker's name, monogram or mark cut into the clay with a pointed tool. Example
J
Jigger	Mould or profile used when unform shapes have to be made repetitively on the wheel. See also - Jolley
Jolley	Mould or profile used when unform shapes have to be made repetitively on the wheel. See also - Jigger
K
Kaolin	China clay. A white clay made from pegmatite found in Cornwall.
Kiln	The oven in which pots are fired. Kilns can be fired by wood, coal, oil, gas or electricity.
Kiln Furniture	The various items made of refractory materials that are used in the kiln to support or protect the pots. Shelves, posts, stilts, saggars, etc.
Kiln Wash	Kaolin solution applied to kiln furniture to facilitate the easy removal of glaze drips.
L
Lead-glaze	A clear glaze containing a lead component. Nowadays lead must be used in its non-poisonous bisilicate form.
Leather-hard	. . . or cheese-hard. Clay that has dried to the point where it is stiff enough to retain its shape but wet enough for further work to be done on it.
Limestone	Chalk. Used in lime glazes.
Loop, Endless	See Endless Loop.
Lustre	Metallic oxide film applied to pots after glazing and firing to produce pearly finish after a further firing in a reducing atmosphere.
Lute	To join two pottery surfaces together with slip.
M
Majolica	The technique of applying low fired tin-glazes with different oxides to produce multi-coloured effect. Example
Manganese oxide	Used to produce a purple or brown colour in glazes.
Maturing temperature	The temperature at which a body reaches its optimum strength or a glaze is fully fused.
Mould	A concave shape made from plaster of Paris for slip casting. Also the die used for press-moulding.
N
Nickel oxide	Produces a brown, green or violet colours in glazes.
O
On-glaze decoration	Decoration applied after the pot has been glazed.
Overglaze decoration	A decoration applied over an already glazed finish.
Oxidation	Firing with a good supply of oxygen so that combustion is complete.
P
Peephole	Small hole in the kiln for the potter to see what is going on inside.
Pin dust	The term applied to the metal filings, a by-product in the manufacture of brass pins, which were added to clay to produce a green finish. The technique was used at Rye around the turn of the nineteenth century, and they devised a mark (known as the pin dust mark) to distinguish pots made from clay with brass filings from those made with undoctored clay. Before firing there was no other way of telling one from the other.
Pinching	Indenting a pot with the fingers and thumbs before it is hard. Example
Plaster of Paris	Gypsum. Calcium sulphate. Used for making moulds for slip-casting.
Plastic (adj)	Capable of being formed into a shape or moulded.
Porcelain	Hard, fine, high-fired material made from china clay, feldspar and silica. It is white and translucent. Also known as hard paste. Example
Potarama	Our silly name for pot photographs processed using the Apple QuickTime Virtual Reality technology. Click on the items marked as Potarama pictures and you can see them in a 360 degree view. If you do not have the QuickTime plugin for your browser you will need to download it. A link is provided with each Potarama picture. Example
Pug	To mix body clay. See - Wedging and Pugmill
Pugmill	A machine to take the hard work out of 'wedging'. It is similar in operation to a domestic food mincer, The clay is put in at the top and comes out of the mouth at the bottom in the form of slices or wedges.
Pulling	Shaping a handle. Example
Pyrometer	A thermometer able to measure the very high temperatures found in kilns.
Q
Quill	Pointed instrument - a porcupine quill, a thin piece of bamboo, a knitting needle, whatever - used in throwing.
R
Raku	Low-fired Japanese lead-glazed earthenware. Raku is Japanese for 'enjoyment' and this type of pottery is traditionally used in Japan for the tea ceremony.
Reduction	Firing in a reducing atmosphere. This is when there is insufficient air for the flame to burn off its carbon content. The result is a smoky atmoshere that causes metallic content in the glaze and clay to change colour.
Refractory	Capable of withstanding very high temperatures. The kiln furniture has to be able to remain stable at temperatures in excess of the normal firing temperature an must be made of refractory materials.
Rib	A shaped tool to facilitate the forming of pots.
S
Saggar	A fireclay box used to protect pottery while it is being fired.
Salt-glaze	Thin glaze produced by throwing salt into the kiln. The salt vapourizes and produces a fine 'orange peel' texture to the surface of the pot. Example
Sand	Coarsely ground pebbles (silica).
Sang-de-boeuf	Ox-blood. Used to describe deep red colours in glazes.
Sedimentary clay	Clay formed by the decomposition of igneous rock.
Sgraffito	The technique of scratching through a coating of slip to reveal the contrasting colour beneath. Example
Slabbing	A building technique where flat sheets of clay are formed and jointed. Used to good effect by Troika and by Bernard Rooke. Example
Slip	Fluid clay in a creamy texture used for decorating, joining and as a material for casting.
Slip decoration	The application of slip to a pot. This can take the form of an all-over or partial coating, or a trailed, feathered, combed or brushed design. Example
Slip trailing	Method of decoration where slip is trailed onto a pot through a fine nozzle.
Slipware	Slip decorated earthenware pottery. Example
Slurry	Slip with a thick consistency.
Soaking	Keeping a steady temperature in the kiln.
Sprig	Decorative pieces, usually press-moulded, applied to pot when it is leather hard. Example
Spur marks	The marks left by the stilts used to support pottery in the kiln. Usually seen as three dots in the form of an equilateral triangle. Example
Stacking	Loading a kiln with pots. Large and small items are carefully positioned to use the space most efficiently. Example
Stoneware	Pottery fired at high temperature which is inherently non-porous. The clay vitrifies during firing and the surface will not absorb moisture. Stoneware can be left unglazed and still be usable for holding water, but it is more usual to glaze the inside of the vessel, at least. Stoneware is more durable than earthenware, and capable of resolving finer detail. Example
T
Tenmoku	A Japanese name for a Chinese glaze containing iron oxide. Tenmoku glazes are characterized by their black to reddish brown colour which is lighter in colour where the glaze is thinner and darker where it is thicker. Example
Terracotta	Red earthenware, usually unglazed.
Thread	Twisted cord sometimes used instead of the thrower's wire for cutting pots off the wheel. It leaves an attractive pattern on the base of the pot. Example
Throw	To make a pot on a potters' wheel. The wheel revolves and maintains a fairly constant speed as would a flywheel. The clay is thrown onto the centre of the wheel and the potter shapes it by hand to the desired form.
Tin-glaze	White opaque glaze containing tin oxide. Example
Titanium	A metallic element found naturally in many clays. It is used in glazes to produce a crystalline effect.
Transfer printing	Method of decoration where a pattern or picture is printed onto the gelatin coating of paper and then, when wet, is slid onto the surface of a pot. The gelatin can be sensitized with silver halide allowing the same process to be used photographically. Example
Tube-lining	A decorating technique where soft clay is piped from a bag via a fine tube onto the body of a pot. This creates an outline for a design that can later be enhanced by further painted decoration. Example
Tunnel kiln	A kiln made in the form of a tunnel, with the highest temperature in the middle. The pots move slowly through on trucks, and the effect is similar firing in a normal kiln with a heating and a cooling period. Tunnel kilns burn all the time, allowing greater throughput.
U
Underglaze decoration	A decoration applied to a biscuit or once-fired pot for subsequent covering with a transparent glaze.
Unpacking	Unloading a kiln after firing. The most traumatic time for the potter. "The kiln is the potter's gamble; he doesn't need the pools or the lottery." - David Leach.
V
Vitrification	To change to a glassy state.
Volatilize	To cause to evaporate. Volatilized oxides can migrate from one part of the kiln to another.
W
Wall pocket	A vase, usually with a flat back, that has a hole or holes for fixing to a wall. Example
Wax-resist	Wax applied to a pot to prevent adhesion of slip or glaze and produce a decorative effect.
Wedging	The cutting of clay into wedges in the process of mixing and kneading it to an even consistency. See also - Pugmill
Wheel	A heavy horizontal wheel onto which clay is thrown and shaped. The weight of the wheel gives momentum to preserve continuity of speed. Potters' wheels can be powered by the potter's foot, an assistant, electricity or in the factory environment from mid-19C to mid-20C a belt from a shaft driven by a steam engine. Example
Wire	Length of wire with a handle at each end for cutting clay. Used in throwing and wedging.
X
Xenocryst	A unexpected mineral present within a rock or a crystal of another mineral. A 'foreigner'.
Y
Yunomi	A drinking vessel on a raised foot of smaller diameter than the body. Usually of a basically cylindrical shape. Sometimes seen spelt 'unomi'. Example
Z
Zettlitz kaolin	A pure kaolin found near Carlsbad in Germany used for making high temperature Seger cones.