Cistercian Ware - deep red clay that is thinly potted, it has a glaze that is dark and shiny, which contains iron and manganese oxides.
Clair-de-lune Flush - term used in the 19th century to describe pale blue stripes. This can be found in Chinese stoneware glazes.
Clay - a natural material of earth, that becomes plastic when moistened and hard when fired. Composition is hydrous aluminum, silicates and other minerals.
Clay Body - a clay designed for a special purpose. It is created by blending different clays or by adding to clays other materials, such as feldspar and flint in order to produce a desired workability, maturing temperature, or finished result.
Clay Carbon - carbonless paper used to transfer designs onto greenware.
Clobbering - when people add decoration to someone else’s already finished pottery, in the hopes of giving the item an added boost to increase the value of the piece.
Cobalt - cobalt creates a dark dense royal blue in most cases. The strongest colorants used are the oxides of cobalt (blue), iron (red or green depending on kiln atmosphere and titanium (tan to blue breaking into red like tongues of flame. Used in China as a painting pigment on blue and white wares.
Coiling - a hand building technique used to make pottery. Long round strips of clay are used. They can vary from a thin strip to a large sausage like strip. It is hand manipulated, pinched and squashed together to form a pot without the coil like look from how it was started, though in some cases the clay can be left snakelike for the decorative look. It is started at the base of the pot and built upwards.
Colorant - any substance that will color something else.
Cones - pyrometric cones are composed of clay and glaze material, designed to melt and bend at specific temperatures. By observing them through a small peep hole in the kiln it is possible to ascertain the exact conditions in the kiln. Cones are a better indicator than temperature alone as the degree of glaze melt is a combination of time and temperature heat work. A fast firing needs to go to a higher temperature to get the same results as a slow firing to a lower temperature.
Cone Numbers - cones are numbered from cone 022 up to cone 42. Cone 022 is the lowest melting cone and requires the least amount of heat to deform or bend. During firing, a cone softens and melts as it is heated. Cones used on the kiln shelf bend due to the effects of gravity pulling the tip down. This bending indicates the cone and the piece of pottery has received a specific amount of heat. It typically takes 15 to 22 minutes for cones to bend fully once they start bending. Each higher cone number requires more heat to bend. A cone 01 needs less heat treatment than cone 1 and cone 020 needs less than 019. Although cones do not actually measure temperature, cone bending behavior and temperature are related. The faster the firing, the higher the temperature required to bend the cone and the slower the firing, the lower the temperature required to bend the cone. The 6 oclock position, 90 angular degrees, is considered the end point of cone bending.
Cornish Stone - the usage of this feldspathoid is that of a flux in bodies but is also a major element in glazes. Contents include quartz, feldspar, mica, kaolinite with a small percentage of fluorspar. Upon melting at 2102 F to 2372 F (1150 C to 1300 C) this becomes a stiff glass which is opaque in appearance with suspended fine bubbles.
Costrel Bottle - this is a pottery bottle that was made in many shapes and sizes that had handles near the top or neck.
Crackle - raku ware often has this feature. It is a glaze that intentionally has minute cracks in the surface finish which are caused by the uneven contraction of glaze and body. It gives the piece of pottery an interesting finished texture.
Cratering - moon-like craters that appear on a glazed surface.
Crawling - when a glaze pulls apart from a continuous surface into many nearby sections with voids in between, a bit like spots on a leopard. This is sometimes done intentionally to give the surface of the piece of pottery increased texture and interest.
Crazing - this is caused by the glaze shrinking during cooling to a greater extent than the clay underneath shrinks. The outside glaze is too small for the clay which it covers. Because the glaze covering over shrinks, it cracks. This is also described as the glaze not fitting the clay. This is often used to create an interesting surface texture on pieces of pottery.
Creamwear - this is the forerunner of English white earthenware today. It was developed in the 18th century, by the Astburys, and later Whieldon and Wedgwood perfected it. The recipe is made up of 25% china clay, 25% ball clay, 35% flint and 15% Cornish stone.
Crystalline Glazes - most glazes have no easily visible crystal structure, but crystalline glazes have large and dramatic crystals up to about three inches across. A high alkaline low alummina glaze is vital for crystals to develop. Additions of zinc and titanium also help seed the crystals. An extremely slow cool of the kiln is necessary, to allow the crystals to grow. Because of the low alumina content in crystalline glazes they are very runny and often pottery is supported in the kiln on stilts to avoid them adhering to the kiln shelves, the stilts can be broken off after the firing.
Damper - a crude device, usually a refractory clay brick, used to block the flue of a kiln.
Decals - picture or pattern applied, after soaking in water to release backing, to a piece of glazed pottery or ceramic. All bubbles have to be removed or there will be cracks in the decal after the lo-temp firing needed to adhere the decal to the ceramic.
Deflocculant - with the addition of very little water, this substance will act chemically on plastic clay giving it liquid characteristics. Sodium silicate and sodium carbonate will have this effect.
Delftware - made in Delft, Holland this English term is used to describe blue tin-glazed earthenware. Often this term is used to describe all blue tin-glazed pottery made in England.
Diatom - a rock, mined in coastal California, composed of the shells of dead microscopic organisms, called diatoms.
Diatomaceous - consisting of diatoms or their skeletons.
Dipping - is a process of covering a bisque body with a glaze by immersion in the liquid, either by hand or machine.
Dolomite - a magnesia rich sedimentary rock resembling limestone.
- practice of not glazing the bottom of a piece of pottery so it won't have to be stilted.
Dunting - the breaking or cracking of clay, from quick cooling, faults in the structure of the piece of pottery, effects of a glaze etc. causing a stress on the pottery great enough to break it.
Dusting - throwing a layer of dry ceramic or glass on a piece of pottery and firing it.
Earthenware - this is one of the two main kinds of pottery, the other being stoneware, earthenware is porous, and not very dense or heavy. Its glazes are usually shiny and bright. Earthenware is opaque, somewhat porous, non-vitrified pottery.
Eflocculate - to disperse the particles in a slip so that less water is required to make the slip fluid.
Elutriation - this is the division of course clay and fine clay, by putting the clay in water. The fine clay will remain suspended in the water where as the larger particles such as stones and sand will sink. A mechanical device is used in this process to move the slurry upwards against gravity.
Embossed - pottery that has a raised or molded decoration produced either in the mold or formed separately and applied before the first firing.
Enamel - a form of low temperature glaze that is applied on top of an already fired higher temperature glaze. Enamels are often lead based and are a flux which works at a low temperature.
Encaustic - decoration where the use of different colored clays are inlaid into the body of the pottery. These inlaid pieces are actually put into cut out portions of the body, though sometimes they are just rolled onto the body.
Engobe - a surface coating usually used for decoration, but not usually considered a glaze. It is made from clay and may contain glaze or glaze components. Depending upon how the piece of pottery is fired, even though it is not a glaze, it may become glaze like or glasslike, even more so than the clay body it covers. It is a white or colored slip used as an intermediate layer between the body of the pottery and the glaze. Sometimes a white engobe is used over colored clays so that the pottery appears to be made of white clay.
Eosine - this rainbow-hued finish is named after the Greek goddess Eos (same as the Roman Aurora), the goddess of dawn. Not the same as Eosin, the organic dye. Eosine is the finish found on Zsolnay pottery from world-famous Zsolnay Factory in Pécs, Hungary.
Faience - this term describes colorfully decorated earthenware or glazes. Today the style that is considered faience is the covering of pottery with matt and shiny glazes that are often blended together.
Fat Clay - highly plastic clay, long clay, that is often added to other clays to improve workability.
Feathering Effect - obtained by trailing a feather through wet slip decoration.
Feldspar - a naturally occurring mineral, aluminosicilate, formed by the decomposition of granite or igneous rocks. Composed of alumina and silicon oxides plus soda (sodium carbonate), potassium or calcium. Feldspars melt around 2150 F (1177 C) and tend not to run due to their high alumina content. It is one of the predominant naturally occurring fluxes used primarily in stoneware glazes. The three most commonly used feldspars are Potash, Soda, and Lithium. Feldspars can be the only flux present in a stoneware glaze although this is uncommon and additions of calcium usually supplement it.
Feldspathoids - though “feldspathoids” have similar perties to feldspar, they are not true feldspars at all. They can be useful in glazes, but cannot be considered as true minerals due to the fact that they do not conform to unified chemical formula.
Fettling - the removal or trimming away of excess clay, unwanted blemishes, seams and flash from nearly dry pots prior to glazing and firing.
Fireclay - this is a clay that can withstand high temperatures. These are typically refractory clays and often used for firebricks. Pale buff or almost white is the color that appears when fired.
Firing - the transformation of clay into a very hard piece of pottery or ceramic. The involvement of heat at least 1112 F (600 C) is required to make this alteration. It is a process of heat treatment of clay based products for the purpose of securing resistance and permanency of product, it is also called burning.
First Red - when the temperature in a kiln reaches 1112 F (600 C) the pottery that has been fired gives off an incandescent glow. This tells you that the point of dunting has been passed and the ceramic change is almost complete.
Fit - the act of clay and surface componets shrinking at about the same rate.
Flambé - means to flame or appears to flame.
Flash - undesirable transfurence of a soft glossy sheen onto unglazed ware when high fired glazed and unglazed ware are fired together.
Flashing - shiny edges on pottery produced by overfiring.
Flint - pure silica which contains less than 5% impurity. Its native color is black which turns to white when heated. It is usually bought in the form of powder, which is added to clay and glazes. When added to clay it gives a whiteness and hardness to pottery and also adds a resistance to crazing.
Flocculate - to thicken.
Fluorspar - used as a flux in ceramics and glass.
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