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The process of firing ware at a low
temperature, usually from cone 010 (1661 degrees) to cone 05
(1915) degrees, to produce bisque ware. |
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Unglazed ceramic ware that has been fired
at a low temperature to remove all moisture from the clay body
and to make handling easier during glazing. |
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Rubbing leather hard or dry clay with any
smooth tool to polish it, tighten the clay surface, and compress
clay particles. |
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The act of forcing a lump of clay by hand
into a symmetrical form at the center of a spinning potters
wheel in preparation for throwing pottery. |
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An opaque overglaze paint that is fired
onto already fired glazed ware at various low-range
temperatures. Because of the low temperatures used, colors like
red or orange do not burn out. Sometimes called overglaze
enamel. |
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A variety of earthy materials formed by
the decomposition of granite. In the process,these may have been
combined with a variety of other materials, forming clay bodies
with differing maturing points. |
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Any blend of clays and nonplastic ceramic
materials that is workable and that has certain firing
properties. Clay bodies are formulated to serve particular
purposes and to achieve maturity at various firing temperatures.
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Pyramid shaped temperature cones are used
to measure the amount of heat during kiln firing. Also called
witness cones and pyrometric cones, these devices are made of
different mineral mixtures and numbered accordingly. They are
set near the ware and manually viewed during firing. When the
firing has reached the cone value necessary to properly mature
the ware, firing is terminated. A Three Cone System is often
used to monitor a kiln firing session. |
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Pottery that has been fired at low
temperature (below cone 02, 2048 degrees) and is porous and
relatively soft. Usually red or brown in color. Used worldwide
for domestic ware, glazed or unglazed. |
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Originally, the term referred to slip
that is applied over the entire surface of a piece of pottery or
sculpture to change the color and/or texture of the clay body.
The term now often refers to slip used for decoration. |
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Heating pottery or sculpture in a kiln or
open fire to bring the clay or glaze to maturity. The
temperature needed to mature a specific clay or glaze varies.
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A substance that lowers the melting or
softening temperature of the mix or compound in which it is
present. The degree of melting that occurs depends on the
particle size of the powders present and the melting temperature
of the individual particles. It also depends on whether material
particles present are premelted and whether they soften or melt
suddenly. Fluxing oxides are those of the RO group and include
ones like K2O, Na2O, CaO, Li2O, MgO. B2O3 is actually considered
a glass former but it is also regarded as a flux by virtue of
its low melting temperature.
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A ceramic glass used in glazes that is
made from raw powdered minerals, melted, cooled, and ground into
a fine powder. This is an expensive process reduces the toxicity
of glazes by driving off undesirable and unsafe compounds such
as lead or barium. Glasses are also less volatile. Over and
underglaze colors work better with frits than raw materials
because they are cleaner, less reactive, melt evenly, and have a
more closely controlled chemistry. This means colors are
brighter with better glaze clarity. |
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Gerstley Borate is a consistent plastic
borate containing the minerals Colemanite (Ca2B6O11 : 5H2O),
Ulexite (NaCaB5)9 : 8H2O) and Hectorite. This tan power mixes
with water to produce a creamy slurry that gels and is very slow
to settle out. It is used to make vitrified stoneware at
temperatures lower than typical bisque firings. A thick layer
will produce a glossy completely transparent glaze. |
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Any vitreous coating that has been melted
onto a clay surface by the use of heat. Made of fine ground
materials that, when fired to a certain temperature, fuse into a
glassy coating. Glazes may be matt or glossy, depending on their
components. |
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A furnace or oven built of heat-resistant
materials for firing pottery or sculpture, sometimes pronounced
as kil.
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The condition of a clay body when much of
the moisture has evaporated and shrinkage has just ended, but
the clay is not totally dry. Carving, burnishing, or joining
slabs are often done at this stage. |
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The range of firing clays and glazes in
which the kiln temperature reached is usually in the cone 015 to
cone 1 (1479 degrees to 2109 degrees) range. |
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A thin film of metallic salts usually,
although not always, applied to a glazed surface, then refired
at a low temperature in reduction. |
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The firing of a kiln or open fire with
complete combustion so that the firing atmosphere contains
enough oxygen to have a clean burning flame and allow the metals
in clays and glazes to produce their oxide colors. Electric
kilns always produce oxidizing firings unless reducing materials
are added. Bright and clear low-fire colors are often associated
with glazes and clays fired in an oxidation atmosphere.
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A combination of an element with oxygen.
In ceramics, oxides are used in formulating glazes and for
coloring glazes and clays. They are also used for decorating
ware. |
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An outer coat of glaze or painted/printed
decoration applied over a glaze. |
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The ability of a damp clay body to be
shaped or formed.
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A translucent, nonabsorbent body fired at
high temperature. White and hard, it was first developed in
China. Traditionally fired in the 2370 degree to 2670 degree
range. |
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A revolving horizontal disk on which clay
is shaped manually. |
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Originally a name used by a Japanese
family that has made tea ceremony ware since the seventeenth
century. Now refers to both the process of raku firing and to
ware glazed in such a firing. Soft and porous, traditional raku
ware was lead-glazed, placed in a red-hot kiln, and quickly
withdrawn when the glaze melted. In the West, lead is now rarely
used in raku glazes. Leadless frits and Gerstley borate are now
commonly used fluxes in place of lead. Raku ware is often
reduced after firing by burying it in straw, sawdust, paper, or
other combustible material, then covering it with an airtight
lid to create a reducing atmosphere that aids in producing
luster or opalescent colors.
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(reducing firing, reduction atmosphere)
A firing in which insufficient air is supplied to the kiln for
complete combustion. Under these conditions, the carbon monoxide
in the kiln combines with the oxygen in the oxides of the clay
body and glaze, causing the oxides to change color. Commonly
associated with high-fire stoneware, porcelain, raku and
lusters. |
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A slip or slurry is a suspension of clay
and mineral particles in a water medium. It typically consists
of clay ingredients and is used to aid in the bonding of clay
pieces. |
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A type of clay body fired to a
temperature at which the body becomes vitrified, dense, and
nonabsorptive, but not translucent. Natural stoneware clay is
usually brownish in color because of the presence of iron, but
there are formulated white stoneware bodies. Usually matures at
temperatures above 2192 degrees. |
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The three cone system is achieved by
placing three cones near the ceramic ware during firing. Choose
consecutively numbered cones as follows:
- Firing Cone - cone number recommended by manufacturer
- Guide Cone - one cone number cooler
- Guard Cone - one cone number hotter
Use the three cone system to:
- determine temperature uniformity in the kiln
- check the performance of the KilnSitter or electronic
controller
- manually shut off the kiln by direct observation of the
cones bending
- evaluate heatwork that ware receives during firing.
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Forming objects on the potters wheel
using a clay body with plastic qualities. |
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Pertaining to or having the nature of
glass. In ceramics, a vitreous glaze or clay body has been fired
to a dense, hard and nonabsorbent condition. High-fire glazes
vitrify and combine with the glassy particles that form in the
high-fire clay body as it approaches vitrification is results in
a glaze that is united with the clay body as compared to a
low-fire glaze that merely coats the surface of the fired clay.
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