Terms and Definitions
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- ALUMINA- Al203: A major constituent in glazes, it controls viscosity of glazes
and is often called the "bones" of a glaze. It is highly refractory
and melts alone at 3450-3630 degrees F.It is constituent of clays and feldspars.
It is rarely used by itself except in kiln wash.
- FLUX- A material which, when added to a glaze, lowers the melting point of that
glaze. Feldspars, Frits, Gerstley Borate, Whiting, and Zinc Oxide are amoung
the fluxes.
- KAOLIN- Al203-2Si02: Used as a source of Alumina in glazes and to improve the
application of glazes. Kaolin melts alone at 3245 degrees F.
- SILICA-Si02, Silicon Dioxide: A material that forms glass. Common forms are
Flint, Quartz. Silica melts alone at 3119 degrees F. Silica is a constituent
of clay, feldspar, mica, wollastonite, as well as other ceramic materials.
- OXIDATION- A condition in firing when there is a significant amount of oxygen
left over after all the fuel in the kiln is burnt.
- REDUCTION- A condition in firing when there is insufficient oxygen to burn the
fuel; the carbon monoxide produced in reduction combines with oxygen from the
clay and glaze to form carbon dioxide, which results in changes in the color
of clay body and glazes (an incomplete but useful description of the process).
- CRAZING- a crackle pattern in a glaze- it is happens when the glaze shrinks
as it cools more than the clay body does. It can also happen with porous, non
vitreous pots when moisture expansion of the body occurs.
- CRAWLING- a curdled looking condition, when the glaze pulls away from the body,
leaving bare patches. It can be caused by dusty or greasy bisque, glaze applied
too thickly, or glazes containing ingredients that promote high surface tension.
- SHIVERING- The flaking off of fired glazes, caused by a glaze coat that does
not shrink as much as the body. In severe cases this can cause cracking of the
clay.
- DUNTING- Cracks in fired glaze ware caused by rapid cooling or very poor glaze
fit.
- MAJOLICA- A low to middle temperature White glaze with colorants applied over
the glaze. Traditionally all Majolica was opacified with tin oxide. Now most
Majolica is opacified with zirconium silicates such as Opax or Zircopax.
- SHINO-(and Carbon Trap), a traditional kiln site in Japan. Shino is also used
to describe the type of pots and glazes produced there. We use the term in the
US to describe a family of fatty glazes that range in color from orange to peach
to white. Some glazes, called carbon traps, are also part of the shino family-
in some firings these glazes show blackened or silvery areas of trapped carbon.
Shino glazes can be used in combination with other glazes, but cause bubbling
if applied on top of another glaze. Remember: "Shino first or fear the
worst" and that goes for carbon traps, too. Traditional Japanese Shinos
are made of hand ground feldspar. The US versions are made from Feldpars, spodumene
and soda ash and are significantly different in appearance from thier Japanese
counterparts.
- TANG Style glazes. The Tang Dynasty(China) is famous for multi colored lead
glazes. The glazes have biright colors pigmented by iron, cobalt, manganese,
and copper. The lead versions are generally not safe.
- CELADON- a large category of translucent or transparent glazes pigmented by
small amounts of iron to a light shade of blue or green.
- TENMOKU-A type of Japanese glaze that is black or brown because of a high iron
content. Historically they were made from high iron clays and wood ash. Tenmoku
glazes break to a rust color on edges and high points.
- ORIBE- A copper pigmented Japanese glaze, normally used as a witha clear glaze
on a white or tan ground with iron oxide decoration. Name for Oribe Fujuita.
Copper greatly increases solubility of glazes. MAny Oribe glazesdiscolor from
lemon juice and should not be used for food surfaces.
- Kaki, Japanese term for persimmon. Used to describe an iron red glaze type.
Tomato Red is a "very" bright Kaki, Fake Mashiko is named for Mashiko slip a silt from Mashiko Japan.
- ia: wo letter suffix for oxide
- RIO: Fe2O3
- cobalt carbonate: stable blue pigment, purple in hi magnesia glazes. Possible to get pinks in some extreme formulations
- copper: red in reduction: green in oxidation: turquoise in
some alkali glazes.
- rutile: iron bearing titanium mineral know for textural effects.
- illmenite: titanium bearing iron mineral, much darker than rutile
- titanium: when pure a white opacifier that also makes textured
glazes. Very small amounts of iron tint it heavily.
- zinc: Zinc oxide is a flux in mid range glazes. It evaporates above cone 6. It can produce beautiful matts. In large quantities it can result in crawling.
- barium carbonate: reduces some scumming from Calcium sulphate. It is a flux that increases gloss in small percentages in some glazes but best know for matts and copper colors in larger percentages. Like lead it can be hazardous in fired glazes.
- calcia: quicklime, oxide limestone, molecular half of
dolomite. Calcium oxide reacts violently with water forming slaked lime or calcium hydroxide. It is the most common stoneware flux and present in nearly all high temperature glazes. It is not very active a lower glazes.
- whiting: calcium carbonate: a source of calcium oxide in glazes, common stoneware flux.
- dolomite: magnesium and calcium carbonate in nearly even molar quantities
- magnesium carbonate : usually a precipitated carbonate often causes crawling,
- magnesia: oxide that in high amounts creates matts and cobalt
purples. It can increase the surface tension and viscosity(?) of glazes.
- silica: flint is a form of it: quartz is a form of it, makes a
high melting glass. main glassformer of ceramics
- silicon: metal element from silica
- silicone: a silicon containing organic chemical "More precisely called polymerized siloxanes or polysiloxanes, silicones are mixed inorganic-organic polymers with the chemical formula [R2SiO]n" from Wikipedia
- zircon: semiprecious stone that is also an opacifier
- zirconia: oxide of zirconium
- zirconium: metal of modern opacification
- opax: zinconium opacifier
- ultrox: zirconium opacifier
- superpax: zirconium opacifier
- magzirsil: magnesium zirconium silicate
- tin: metal of historic opacifier
- antimony: metal of naples yellow
- lead:historic flux. Tang three color glaze flux. metal of
galena
- manganesedioxide : purple in some lead glazes