Already Registered? Please sign in.
Glossary
Search Glossary
earthenware
Low-fired ware, usually still porous after firing—must be sealed with vitreous glaze to be functional.
earthenware clay
Natural low-fire secondary clay—fluxed with iron, fires porous. Often called “common” clay, found almost everywhere, matures below 2000°F.
effloresce, efflorescence
Formation of crystalline deposits on surface of clay or concrete as soluble compounds migrate to surface during drying. See Egyptian paste.
Egyptian paste
A self-glazing clay body in which soluble alkaline fluxes effloresce to the surface as the piece dries, and subsequently form a thin glassy coating in the firing.
element
Any of a group of slightly over 100 substances on earth that may exist as individual atoms, and from which all materials on earth are composed. See periodic table of the elements. In electric kilns, the heating coils.
enamels; china paints
Very low temperature (cone 018) glaze colors applied over a previously fired higher-temperature glaze. Allow greater detail, brighter colors than other ceramic glaze effects, but are vulnerable to surface abrasion.
engobe; underglaze
Colored slips formulated to have low drying shrinkage, allowing application to bone-dry or bisque-fired surface before glazing.Commercial underglazes are available in a wide palette of colors primarily for low-fire, but many will survive high-fire.
entrained air
Primary air drawn into an atmospheric burner, or mechanically injected into a power burner.
envelope kiln
A kiln in which the firing platform is stationary, but the body of the kiln rolls out of the way horizontally on tracks. Often equipped with two firing platforms to be fired alternately.
EPK, calcined
Al2O3×2SiO2—used in place of regular kaolin to adjust raw fit (reduce glaze drying-shrinkage) in glazes and engobes.
EPK; Edgar Plastic Kaolin
Al2O3×2SiO2×2H2O—pure white kaolin, less plastic than Tile-6 kaolin, frequently used in glazes.
epsom salts; magnesium sulfate
MgSO4—water soluble, rarely used as magnesium source in glazes. Most often used as flocculant for slips and glazes. Often added to porcelain and porcelaineous stoneware bodies (1/2 of 1% of dry materials weight) to counteract deflocculating alkalinity released by kaolins or fluxes.
ergonomics
The science of comfortable and effective utility, determining how well a functional object or device works with the human body.
eutectic
Chemical phenomenon where two materials in combination melt at lower temperature than either material by itself. For example, lithium carbonate and silica each melt at cone 32 (3100°F) but mixture of 55% silica and 45% lithium develops a eutectic and melts at cone 06—1830°.
extruder, extrude, extruding
Machine that forces plastic clay through a die to produce extruded clay shapes.
faceting
Decorating technique involving cutting or paddling flat facets in the clay surface.
faience
Widely used (and misused) term referring to any earthenware pottery glazed with an opaque glaze (usually white) and overglaze decoration.
feathering; feather-combing
Decorating technique where a soft, fine pointed tool is drawn through adjacent contrasting-colored bands of liquid slip applied to a damp clay surface.
feldspar
HT alkaline fluxes—insoluble aluminum silicates of potassium, sodium, calcium, and/or lithium—inexpensive flux for clay and glaze. Substitution of soda spar for potash spar can lower vitrification by 100 degrees. Toxic in inhalation. See Custer feldspar, G-200, Kona F-4 feldspar, nepheline syenite, spodumene.
feldspar
HT alkaline fluxes—insoluble aluminum silicates of potassium, sodium, calcium, and/or lithium—inexpensive flux for clay and glaze.Substitution of soda spar for potash spar can lower vitrification by 100 degrees. Toxic in inhalation. See Custer feldspar, G-200, Kona F-4 feldspar, nepheline syenite, spodumene.
ferric chloride; iron chloride
FeCl2×6H2O—soluble metallic salt—fuming agent used to produce lusters on glazed surface. Highly toxic in inhalation and ingestion.
fettling knife
Long tapered knife useful for trimming cast or pressed pieces, and for separating mold components.
figure-ground
The fundamental design relationship between foreground imagery and background or surrounding area. Foreground shapes subdivide background, creating additional important shapes.
fillers; tempering materials; temper
Gritty materials like sand, grog, volcanic ash, crushed seashells, etc., added to clay to open up body, give physical structure in wet-working and increase thermal shock resistance.
fire-eye
Ultraviolet sensor used on industrial burner systems to monitor burner flame. See flame-rectification system.
firebox
The part of a fuel-burning kiln where fuel gases combust before contacting wares. Gas kilns need little if any firebox, whereas wood and oil kilns produce long hot flames whereas require a large firebox unless flame-flashing and ash-slagging (with wood) effects are sought.
fire clay
Highly refractory secondary clays with minimal fluxes and usually fairly coarse particle size—low shrinkage, buff-color, often nonplastic.
firing down
Maintaining some heat input after maturation, to slow down the cooling process, or to maintain reduction atmosphere during cooling. See reduction cooling.
firing ramp
The profile or schedule for temperature change in a kiln-firing, often including both the heating and cooling ramps.
flame-flashing
Surface effects caused by direct flame contact on wares.
flame-off; blow-off
In burners, when speed of air/fuel mixture exiting tip of burner is greater than combustion rate—flame jumps off tip of burner and often blows out.
flame-rectification system
A burner system with automated reignition feature that immediate restores flame should it become extinguished. Usually incorporates a fire-eye ultraviolet sensor to monitor burner flame.
flame-retention tip
Gas burner tip that causes turbulence in moving stream of gas and air, intermixing them, speeding combustion, holding flame at burner tip, and preventing both flame-off and back-burning
flameware
Wares made to stand stove-top heat. Explosions from trapped moisture, and resulting lawsuits have caused studio flameware to disappear from the domestic market.
flashing
Color change in fired clay or slip due to direct flame contact and residual ash deposition in wood firing, or due to variable currents of vapor deposition in salt and soda firing. Flashing can occur on almost any light-colored claybody, but is most dramatic on porcelain bodies and slips.
flashing slip
Slip that is painted or dipped onto wares in order to promote flashing effects in the firing.
flint; quartz; silica; silicon dioxide
SiO2 —The primary glass-former in clay and glazes—vitrification, fluidity, transparency/opacity controlled by adding fluxes and/or refractories. Highly toxic in inhalation.
flocculation; flocculate
The process of adding an acidic (usually) substance (flocculant) that gives particles in suspension opposite electrical charges, causing them to attract one another (to flock together)—a disadvantage in a casting slip but a great advantage in a claybody or a decorating slip. Usually only claybodies high in kaolin need to be flocculated by adding 1/2 [...]
flocs
Commercial flocculant used in glazes—1/4 tsp. per gallon of glaze.
flue
Passages in kiln for flames or exhaust gases.
fluorspar
CaF2—limited use as flux. As with Cryolite, fluorine reacts w/silica at high temperatures, can cause pinholing, blisters. Useful in special-effect crater-glazes. Highly toxic in inhalation and ingestion.
fluting
Decorating technique involving carving or forming vertical flutes or grooves in surface of a piece.
flux
Low-melting component in clay or glaze that reacts with silica to form glass.
fly-ash
Airborne ash in a wood-kiln.
foot
Base of a ceramic piece.
forced-air
Firing system in a fuel-burning kiln that uses power-driven blowers or other pressurized air source to entrain primary air.
forced-draft
Direct-connected exhaust system equipped with suction fan, used on commercial furnaces, but never on studio ceramic kilns. Term often mistakenly used to refer to forced-air system.
fracture plane
Fracture zone that results when clay components are pressed straight together without disrupting the surface (by scoring and adding slurry or by smearing together) to intermix the platelates. Parts hold together while wet and tacky, but will separate easily when dry or fired.
frit
Combinations of ceramic materials that have been melted to a glass and crushed/ground back to a powder, in order to give greater chemical stability and to eliminate toxicity resulting from water solubility of raw material. All frits are ground glass and are toxic in inhalation. FERRO 3124—high-alumina calcium-borate frit, gives greater strength in LT claybodies. [...]
fritting; fritted
The process of melting particular ceramic materials to a glass and then crushing and grinding to form a frit.
fuming
Process of introducing metallic salts into kiln or onto wares at about cone 018, producing thin layer of metallic surface iridescence.
fusion; fused
In the glaze-melt, the point where dissolution of sintered structure is complete, and all refractory particles are dissolved into the glaze melt, forming a fused material—one that has melted to liquid.
G-200
K2O×Al2O3×6SiO2—common potash feldspar, HT alkaline flux—close match to Custer. Toxic in inhalation.
geometric style
In ancient Greek ceramics, early pre-Classical (Archaic) style featuring intricate geometric slip decoration.
Gerstley borate; colemanite; calcium borate
CaO×3B2O3—traditional important LT alkaline flux, but is no longer being mined. Replace with Ferro 3134 for LT glazes, commercial Gerstley borate substitutes for HT glazes. Test all substitutes.
glass
Super-cooled liquid, which softens and hardens over broad range of temperature and cools to form an amorphous, noncrystalline solid. Level and rate of hardness (viscosity) controlled by temperature and by addition of fluxes and refractories, making possible the wide temperature range of ceramic clays/glazes.
glass-former
The primary material that, in combination with fluxes, forms the glass essential to all fired ceramics. Primary glass-former at all temperatures is silica.
glassy-phase
In heating ceramic materials, point where glass-formers and fluxes combine and soften to begin forming a glass. See sintering, dissolution.
glaze, glazes, reduction-fired glazes, celadon, temmoku, chun, crystalline glazes, macrocrystalline glazes
Coating of powdered ceramic materials, usually prepared and applied in water suspension, which melts smooth and bonds to clay surface in glaze firing. See interface.
glaze-firing
Kiln firing in which glazes are melted to form a smooth glassy surface.
glaze-fit
The matching of glaze to claybody in terms of composition and coefficient of expansion so that it will adhere permanently . See glaze compression, interface.
glaze-melt
The chemically active state of the melted glaze.
glaze-resist
Decorating technique where resist materials are applied to prevent glaze from adhering to certain areas.
glaze compression
In high-fired wares, ideal state when claybody shrinks slightly more than glaze, putting glaze under slight compression, giving greater strength, resiliency. See crazing and shivering.
Glomax
Calcined kaolin. See EPK, calcined.
glycerin; glycerol
An organic gum derived from fats and oils, sometimes used as brushing medium for engobes or for reglazing fired wares. Also used as a lubricant in burnishing. For applying glazes to glaze-fired or vitrified surfaces, add one teaspoon glycerin to 100 grams dry glaze.
Goldart
Buff stoneware clay, produced by Cedar Heights Clay Company.
graniteware
Ware with mottled slip or glaze treatment to create appearance of granite.
grate kiln
An early form of kiln originating in the Middle East, with a below-ground firebox, a grate supporting the wares within a cylindrical enclosure, and a piled shard roof.
green; greenware
Any dry, unfired clay form.
green firing; single-firing
Process of glaze-firing glazed greenware without a bisque-firing.
green glazing; raw glazing
Glazing leather-hard or bone-dry wares for single-firing.
grog
Crushed high-fired clay graded in sizes from 15-mesh (very coarse) to 150M (extra fine) added as a source of filler or tempering grit to claybodies to reduce shrinkage and give structure for throwing or handbuilding. Does not shrink in firing, so in medium and coarse grades will show texture through thin to medium glaze. Toxic [...]
Grolleg kaolin
Al2O3×2SiO2×2H2O—English kaolin, more costly than other choices in the United States, but gives whiter porcelain. Less plastic than TILE-6. Best kaolin for translucent bone china.
groundhog kiln
A long, low horizontal sprung-arch or barrel-arch wood-fired kiln, often banked with earth, traditionally used by potters on the eastern slope of the Appalachian Mountains.
gum additives
CMC Gum, Veegum Cer—water soluble organic thickeners often added to glazes or slips as a suspension and/or brushing agent. Also used to allow glaze adhesion to vitrified or previously glaze-fired surfaces. Most commercial low-fire glazes and underglazes contain gum additives.
handbuilding
Forming plastic clay by hand without the wheel, using pinching, coiling, and/or slab construction.
hard-paste
Traditional European term for high-fired porcelain.
hardbrick
Hard, dense firebrick generally used only in high-stress areas of kiln (floor, burner ports, flues, bag wall) and for corrosive firing processes (salt, soda, wood).
Hawthorn Bond
Refractory stoneware clay or fireclay, used in stoneware claybodies.
heatwork
Work done by effective heat transfer to wares, resulting from ramp rate, temperature and duration of firing.
HEPA
High Efficiency Particulate Arrestor—industrial designation that indicates that a filter or dust mask is capable of blocking microscopic particulates such as silica dust.
high-fire
High-temperature firing range usually including cone 8 to cone 12, for firing stoneware or porcelain.
Hispano-Moresque
Decorative style originating in Moorish Spain, characterized by extremely elaborate patterning and curvilinear plant motifs; major influence on Italian maiolica.
hobs
Steps constructed in walls of wood-kiln firebox in place of grates. Wood cut to proper length catches on hobs and remains suspended above coal bed, insuring quick and complete combustion.
hot face
The interior refractory surface of a kiln.
hydrocarbons
Combustible gases containing hydrogen and carbon, present in fuel gases and produced when carbon-based liquid or solid fuels are heated above kindling temperature.
hydrometer
Laboratory device for measuring specific gravity in slips and glazes. Does not give absolute measurement, and should be used only for comparing and reproducing results. Must be an appropriate glaze hydrometer for measuring suspensions heavier than water. Does not work well in thick glazes.
