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Glossary
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IFB; insulating firebrick; softbrick
Porous firebrick with insulating values much higher than hardbrick.
IFB; insulating firebrick; softbrick
Porous firebrick with insulating values much higher than hardbrick.
ilmenite
An iron ore with significant titanium—most often used in granular form
to produce dark specks in clay or glaze. Higher iron concentration than
in rutile.
impressing
Decorating technique where textured or patterned material or object is pressed into clay surface.
incising
Decorating technique where design is formed by cutting or carving shallow lines in clay surface.
inclusions
Any particles or bubbles of material that remain suspended within the glaze-melt, affecting the glaze appearance.
interface
Contact face between clay and glaze. On low-fired wares, primarily just
a physical interlocking of glaze into pores in clay. In high-fired
wares, an intimate interaction of clay and glaze, reinforced by mullite
crystals, creating very strong bond.
iron
Most abundant coloring material
on earth, responsible for brown and sometimes black color in natural
rock and fired clays. In oxidation firings, the red ferric oxide
remains very refractory, but in reduction firing and or at high-fire
temperatures it transforms to the black ferrous oxide, a powerful flux.
iron chloride; ferric chloride
FeCl2×6H2O—soluble metallic salt—fuming agent used to produce lusters on glazed surface. Highly toxic in inhalation and ingestion.
iron chromate
FeO×Cr2O3—glaze
colorant producing pink or red with tin, brown with zinc, gray with
alkaline fluxes. Highly toxic in absorption, inhalation, and ingestion.
iron oxide, black ferrous
FeO—reduced form of iron oxide—gives same results as red iron in the firing, dependent on oxidation/reduction.
iron oxide, red, ferric
Fe2O3—powdered
rust—refractory red in oxidation, converts to black iron (flux) in
reduction and/or high-fire. Low quantities in clear glaze produces
celadon-green—high quantities produce temmoku black or saturated iron
red—powerful flux. More than 5% in a glaze significantly increases
fluxing in reduction.
iron oxide, yellow
See yellow ochre.
Jasper ware
Ware developed by Wedgwood in which colored stoneware is decorated with contrasting raised relief slip or clay imagery.
jiggering; jolleying
A partially mechanized vessel-forming process on the potter’s wheel, where a pivoting arm (a jigger or jolley) with a mounted profile rib is brought down against a centered clay ball within or upon a wheel-mounted mold.
jolleying; jiggering
A partially mechanized vessel-forming process on the potter’s wheel, where a pivoting arm (a jigger or jolley) with a mounted profile rib is brought down against a centered clay ball within or upon a wheel-mounted mold.
jug finger; potter’s finger
A long wooden tool with a knob on the end, often covered with chamois, which is inserted in a bottle or jug on the wheel after the top has been necked in and is used to broaden and refine the shape.
kaki
High-fired Japanese saturated iron glaze usually containing at least 10% (of dry-batch weight) iron oxide, which produces iridescent microcrystalline rust red. See tessha.
kanna
Japanese trimming tool, formed of a steel strap bent and sharpened on the ends.
kaolin; china clay
Al2O3×2SiO2×2H2O—Primary clay that fires pure white, very refractory, coarse particle size, low plasticity, high-temperature—major component of porcelain and some whiteware bodies. See EPK, Grolleg, Helmer, Tile-6.
kaolinite
Crystalline clay mineral forming the basis of most clays we use in ceramics.
keramos
Greek term meaning earthenware from which the word ceramics is derived.
keys; registration marks
In plaster slip-casting molds, small rounded depressions carved in each parting face of a mold segment, so that when adjacent segments are cast a corresponding bump will form. In use, the keys allow the mold segments to be aligned and assembled securely after the original prototype is removed.
kiln
A specialized oven or furnace used for firing clay for pottery.
kiln furniture
Refractory shelves, posts, and stilts used in a kiln to support the wares.
kiln sitter
Automatic shutoff device mounted on many electric kilns; accepts a small-size pyrometric cone, and shuts off kiln when cone deforms.
kiln wash
Refractory slip coating applied to top surface of kiln shelf to protect from glaze runs. For all but salt and wood firings, 50-50 kaolin and silica. For salt and wood, 60% alumina, 30% kaolin, 10% ball clay.
kindling temperature
In combustion of fuels, temperature that must be reached before oxidation reaction will produce enough heat to sustain and accelerate. For wood and paper, kindling temperature is 451° F.
Kingman feldspar
Potash spar no longer mined. Substitute Custer or G-200.
Kona F-4 feldspar
Na2O×Al2O3×6SiO2—a common soda feldspar—powerful HT alkaline flux. Toxic in inhalation.
kyanite
3Al2O3×2SiO2—aluminum silicate used in place of alumina and silica to promote formation of mullite crystals, increase thermal shock resistance. Coarse-ground used as grog in refractory bodies for kiln furniture.
L.O.I.; loss on ignition
The fraction of any material that volatizes and outgases during firing—includes carbonates, sulfates, nitrates, organic contamination, and chemically combined water.
lead carbonate; white lead
2(PbCO3)×Pb(OH)2—former source of lead for glazes. Highly toxic in absorption, inhalation, and ingestion. Remove from studio and dispose of in a responsible fashion.
lead oxide; red lead
Pb3O4—Former source of lead for glazes. Highly toxic in absorption, inhalation, and ingestion. Remove from studio and dispose of in a responsible fashion.
lead silicate
3PbO×2SiO2—fritted lead compounds—LT flux, but resulting glazes may be toxic and should not be used on functional wares. Most powerful of all fluxes, promotes smooth-flowing, self-healing glazes. Highly toxic in inhalation and ingestion.
leather-hard
Condition of clay in which it has stiffened but is still damp. Point at which pieces are joined and most surface modification and trimming are done. Soft leather-hard ideal for forming, joining, thick slip-decorating. Medium leather-hard good for thin slip- decorating, joining, incising, carving, piercing. Hard leather-hard good for thin slip- decorating, carving, scraping.
lepidolite
Lithium feldspar—HT alkaline flux—used for thermal shock bodies and matching glazes. Contains fluorine, with associated problems. Toxic in inhalation.
limestone; marble; chalk; whiting; calcium carbonate
CaCO3—alkaline earth, contributing calcium oxide to glaze—powerful AT flux—major HT flux for glazes—gives strong durable glass. Sometimes used in low-fire claybodies to extend firing range and give greater fired strength.
limit formulas
A set of formulas giving ideal ranges of glaze oxides that can be present in glaze unity formulas at different firing temperatures. Used in conjunction with glaze calculation to predict or evaluate glaze performance. See unity formulas.
line blend graph
Method for testing glaze materials, where proportional amounts vary through a series of samples between two limits. May involve change in a glaze material, or addition of a colorant or modifier. See triaxial blend.
lithium carbonate
Li2CO3—powerful AT alkaline flux, especially with soda or potash feldspars. Promotes hardness and recrystallization in LT glazes. Forms low-temperature eutectic with silica. Toxic in inhalation.
Lizella clay
High-iron (4%) orange-red stoneware clay—substitute for Ocmulgee, which is no longer being mined.
loss on ignition; L.O.I.
The fraction of any material that volatizes and outgases during firing—includes carbonates, sulfates, nitrates, organic contamination, and chemically combined water.
low-fire
Low-temperature firing range, usually below cone 02 (2048° F), used for most bisque-firing and for glaze-firing terracotta and whiteware.
low mid-range
Firing range usually including cone 01 to cone 3, underused in studio ceramics, useful for functional earthenware, refractory sculpture bodies, and outdoor terracotta work.
luster
Metallic overglaze finish created either by painting prepared luster (metallic salt in organic binder) over previously fired glaze and firing to cone 018 or by spraying metallic salt dissolved in water into kiln and/or on to wares at low red heat, either during cooling cycle of a glaze-firing, or in a separate firing heated to [...]
luting
English word for attaching clay forms with slurry.
lye
Potassium hydroxide or sodium hydroxide. Caustic alkaline soluble that leaches out of wood ashes when they are soaked in water. Occasionally used as a flux additive in terra sigillata, as in the black slip on Classical Greek wares. Toxic in liquid state, and may cause burns.
