Ceramics and Pottery: General Information

Ceramics

An inorganic, non-metallic solid made up of either metal or non-metal compounds that have been shaped and hardened by heating to high temperatures. Generally hard, corrosion-resistant, and brittle.

Keramicos

Ceramics come from this Greek word which means pottery.

Keramos

Greek word which means potter's clay.

Pottery

The process of forming vessels and other artifacts with clay and other ceramic materials which are fired at high temperatures to give them a hard, durable form.

Jomon culture

A settled Paleolithic culture of prehistoric Japan, characterized by seaside villages and the creation of some of the world's earliest fired earth vessels.

Clay State

Also known as Greenware. This is the stage wherein the ware is formed but hasn't gone under firing. They are very brittle and fragile but they can be handled with care. Often sanded with fine-grained sandpaper to ensure a smooth finish in the completed item.

Leather hard

This refers to a specific stage during the drying of the object. At this stage, the clay is still visibly damp but has dried enough to be able to be handled without deformation. This is a damp condition of the clay when it is too firm to bend yet soft enough to be carved.

Bone dry

A term used to identify Greenware pottery that has dried as much as possible before it has gone through its first firing. When held, it feels to be at room temperature. It is very brittle at this stage.

Biscuit Stage

It is also known as Bisque, which is a term literally meaning "half-baked" when ware has undergone preliminary low range firing through an oven or a kiln. All underglaze colors and printing are applied at this stage.

Bisque porcelain

Also known as biscuit porcelain; is unglazed white porcelain that is treated as a final product with a matte appearance and texture to the touch. Mainly used for decorative purposes.

The Glazed State

The stage after the ware had been covered with the glaze and had undergone a second firing. It is done to make wares sanitary - if enamel or other decorations is applied over the glaze, a second firing is done, but at a comparatively lower heat in the enamel kiln.

Glaze

A mixture of chemicals, mostly silica, the major component of glass, clay, a melting agent, water, colorants, and a suspension agent allowing the chemicals to stick together and not separate like oil and water.

Salt Glaze

A traditional form of glaze, high-firing and usually used on stoneware. This is where common salt is introduced to the kiln during the firing process. It results to a textured, high granular surface.

Ash Glaze

A type of glaze wherein ash from the combustion of plant matter has been used as the flux. The source is generally the combustion waste from the fueling of kilns.

Alkaline Glaze

This glaze is low-high firing depending on the alkaline flux, such as borax, potash, or soda ash. Frequently transparent but can produce brilliant colors such as Egyptian blue.

Lead Glaze

Another traditional type of glaze, used for low-firing on earthenware. It is shiny and transparent after firing and gives a smooth glasslike finish that allows bright colors and patterns to shine through.

Tin Glaze

This is basically a lead glaze but with added tin oxide, making it white, shiny and opaque. It is used for earthenware. Its whiteness provides a good background for brightly painted decoration.

Feldspathic Glaze

A high-firing glaze which uses feldspars as base, more often than not, Petuntse. It is a good base for glazes as it contains the right proportion for 'glass' materials, flux, and agents.

Tin oxide

Oxide which gives off white

Cobalt oxide

Oxide used to create grayish blue to pure sapphire, widely used in East Asia and Europe for blue and white porcelain wares.

Cupric oxide

Oxide used in glazes that give off a distinctive series of blues, and with excess carbon monoxide, yields bluish red known as reduced copper.

Cuprous oxide

Oxide which creates series of greens.

Ferric Iron Oxide

Yellow to black, with the most important being slightly orange known as Iron red.

Ferrous Iron Oxide

This oxide yields a type of green best seen on Chinese Celadon wares.

Manganese oxide

Yields varying colors from bright red purple to a dark purplish brown, almost black. Aubergine purple of Chinese wares was derived from this oxide.

Antimony oxide

Oxide used in glazing which gives off yellows.

Earthenware

A soft pottery, probably the oldest and also the most universal. These are natural clays fired at temperatures from 900°-1200° C/1652°-2192° F. It has not been fired to vitrification thus it is porous and permeable to liquids. It is opaque and its color ranges from pale tan to red and brown

Stoneware

Clays containing a higher percentage of sand when fired from 1200°-1280°C/2191°-2336°F. The body is extremely hard, usually vitrified and impermeable to water. It is naturally non-porous and may or may not be glazed. Can come in dull or glazed forms.

Porcelain

It is the aristocrat of the potter's wheel; a Chinese invention that appeared when feldspathic material in a fusible state was incorporated in a stoneware composition. It contains a kaolin base with decayed granite and fired at 1280°-1400°C/2336°-2552°F.

China

Common name for porcelain; named so because it originated in the country, made by Chinese potters toward the end of the Han Period.

Hard porcelain

Fired between 2390 to 2570°F. Considered the best kind of porcelain. Also known as true porcelain.

Soft-paste

A lower temperature porcelain-like clay body; the type of fine pottery made in Europe before the discovery of Hard or True Porcelain.

Soft porcelain

Type of porcelain fired below 2300°F. It is imitation porcelain. It is more translucent and is not as white in color and does not have the clear ringing tone of true porcelain. It is a mixture of white clay and a ground glassy substance.

Bone china

A white hard translucent ceramic ware, usually glazed. Invented by English potters in the mid-18th C., it gained hardness, whiteness, translucency and stability through the addition of calcium phosphate in the form of calcined. It is first fired at 2760°F and then 2475°F. It lies somewhere between soft-paste and hard-paste in whiteness and tone.

Slip

A thick semi-solid fluid composed of clay, water, and other minerals such as quartz, feldspar, and mica, into which the ware is dipped when it is dry enough to be fired.

Slipware

Ware that has been dipped in slip.

Slip ware

Ware where the slip creates patterns or images.

Terra Sigillata

It means 'sealed earth'. It comes form the name of a type of Roman pottery that was mass produced around the 1st Century AD. It has glossy surface slips ranging from a soft luster to a brilliant glaze shine. It is decorated with impressed or stamped forms.

Decalomania

The art of transferring designs from specially prepared paper to a wood, glass, or metal surface. It is similar to transfer printing in fabrics.

Lithographed

This is a printing process based on the principle that oil and water do not mix. This process systematically treat the surface so that the image areas will accept the oily ink, while the non-image or blank areas are treated to repel the ink.

Sgraffito

The term comes from the Italian graffiare which means to scratch. Designs are drawn with a pointed tool that scratches through the slip to reveal the body.

Overglaze

Colored decoration is applied over a fired transparent glaze. Then the object is fired a third time to set the decoration. Third firing is at a lower temperature than glost firing for a greater range of pigments.

In-glaze

Commonly used in tin-glazed earthenware. Colored decoration is applied over a dried but unfired opaque glaze. During glost firing, the color and the glaze fuse together this creating a uniform surface.

Underglaze

Glazing wherein colored decoration is applied to an unglazed body, and then covered with a transparent glaze. The glaze then seals the decoration during the glost firing. Colors used are limited, as certain pigments, known as grand feu colors, can withstand the high heat of glost firing.

Glost firing

Another term for glaze firing.