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Creative Glazes
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Ceramics 101
Glossary of Ceramic
Terms
Alumina ~ An extremely hard mineral which is added to
glazes to harden them. The addition of this mineral helps to prevent excessive
running of glazes on the surface of the clay during firing.
Banding
wheel ~ A revolving stand used to slowly turn the ceramic piece while applying
glazes or decorations.
Bisque firing ~ A preliminary firing of greenware
which removes all moisture from the piece and provides a more stable form to
which glazes and paints are applied.
Ceramics ~ The art of making
objects out of clay derived from the Greek word "keramos" which indiated a
large Athenian depository of clay.
Cone ~ Elongated, three sided
pyramids specially formulated to bend at a specific temperature giving an
accurate measurement of the temperature inside your kiln. Visit the Orton
Foundation Web Site for more information.
http://www.ortonceramic.com/
Crawling ~ A glaze flaw which is characterized by the glaze peeling off
the surface of the ware or pulling back to leave an area of bare
bisque.
Crazing ~ A glaze flaw that resembles a spider's web of cracks
over the surface of the ware.
Deflocculant ~ A material such as sodium
silicate or sodium carbonate which reduces the amount of water needed to make
slip fluid - consequently reducing shrinkage after it is applied to the
clay.
Dryfoot ~ Leaving the bottom of a ceramic piece unglazed so that
it can be fired standing on the kiln shelf without being stilted. Some molds
are specifically designed to produce ware that can be dryfooted. Stoneware and
porcelain are always dry footed.
Earthenware ~ A low-fire blend of clay,
usually red and porous, used worldwide for domestic ware.
Engobe ~ A
colored decorating slip, often opaque. Concentrated color is added to liquid
slip and then applied to greenware before firing. Many underglazes are
Engobes.
Fettling ~ Trimming the spare clay from the mold pour area
before removing the greenware piece from the mold.
Glaze ~ A substance
composed primarily of silica which creates a glassy coating that is fused onto
the surface of the clay when fired. Glazes may be matte or glossy, depending on
their chemical makeup.
Greenware ~ Any unfired clay
object.
High-fire ~ The range of firing from cone 2 up to cone 10 or 13.
Ware fired at cone 2 and up is usually referred to as
Stoneware.
Low-fire ~ The range of firing ware that is usually between
cone 015 and cone 1. Ware fired at low temperatures is usually referred to as
Earthenware.
Majolica ~ (Maiolica) An earthenware technique made popular
in Italy after being introduced by the Spanish. Majolica is created by applying
an opaque satin glaze to bisque, then colors are painted on this and fired to
fuse the two together and create a bright, colorful surface.
Maturation
Point ~ The firing point at which a clay body reaches its maximum hardness and
non-porosity.
Mold ~ A plaster form which is used to shape and model
liquid clay (slip). The plaster absorbs water from the slip leaving a coating
of clay next to the mold surface which takes the shape of the mold.
Opaque ~ Solid color, not transparent in any way. (You cannot see
through an opaque color!)
Overglaze enamels and China paints ~ Colored
paint-like surface decorations which are applied on top of a previously fired
glazed piece which is then fired again at low temperatures, sometimes this
takes many applications and firings to complete.
Oxidation firing ~ A
firing process which takes place in an atmosphere of ample oxygen in a kiln to
produce complete combustion of the contents. This allows the metals in clays
and glazes to produce their oxide colors. Bright, clear low-fire colors are
associated with glazes and clays fired in an oxidation
atmosphere.
Pinholes ~ A small pore in a glaze surface which is caused
by escaping glazes.
Plasticity ~ The ability of damp clay to readily
change shape without cracking.
Porcelain ~ A blend of clay, usually
white, which is fired to a high temperature at which the clay body vitiries and
becomes translucent.
Reduction firing ~ A firing process that reduces
the proportion of gas to oxygen, forcing the oxygen-starved flame to attack the
oxides in the clay and glazes of the ware. Color changes during the process
because there isn't sufficient oxygen in the kiln for complete combustion and
carbon dioxide in the kiln combines with the oxygen in the clay body and
glaze.
Sgraffito ~ A method of producing a design on ceramics, murals,
etc. by incising the outer coating of slip or glaze to reveal the ground of a
different color. A surface decoration drawing technique in which coats of
contrasting underglazes or colored slips are applied to clay, then scratched
off with a fine-pointed tool to reveal layers beneath the surface.
Slip
~ A finely sieved mixture of clay and water, either white or colored, which can
be applied to clay surfaces in one or more layers. Slip is also poured into
molds to cast ceramic pieces.
Slip Trailing ~ A method of decorating
ware by squeezing slip from a bottle or nozzle onto the surface of the pottery
to create raised lines.
Spare ~ The portion of clay waste which is
trimmed from the mold before the greenware is removed from the
mold.
Stoneware ~ A blend of clays, usually brownish in color, which is
characteristically fired to a high temperature at which the clay body becomes
vitrified and non-porous, but not translucent.
Terra sigillata ~ A
variety of slip made by mixing clay and water and allowing it to settle.
Characteristically thinner than other slips, terra sig dries to a soft, silky
sheen.
Terra cotta ~ A type of clay whose name translates as 'baked
earth'.
Transparent ~ See through color. Transparent glazes generally
'settle' into detailed areas, making them darker and bringing the detail to
view.
Underglazes ~ Colored agents, such as slips and commercial
underglazes, which are used under a glaze. Most commonly indicates colors used
to decorate greenware and bisque before a protective clear glaze is applied.
Vitrification ~ The point at which a clay body or glaze reaches a
glassy, dense, hard and non-absorbent condition.
Wax resist ~ A wax
emulsion especially created to repel underglazes and glazes applied over them.
Apply one good coat of Wax Resist over the glaze and allow it to dry thoroughly
before proceeding with your technique. Fire your glazed piece to Cone 06. The
wax is burned off during firing, revealing the designs you protected from other
paints applied around them.
General Paint Descriptions - Ceramics 101
Simple, Secure, Convenient - Creative Glazes.
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