with a porous and permeable body after firing which is waterproofed,
if necessary, by a covering glaze.
Because of its colors and workability, earthenware is used for the
widest range of working methods: throwing, hand building, pressing,
prepared self-glazing clay body that contains water soluble fluxes
that move to the surface as the clay dries. During firing, the fluxes
combine with silica and alumina in the clay to create a thin layer
of glaze on the surface. Egyptian paste has low workability, and ceramists
who use it often employ press mold forming or slip casting techniques.
It was developed in pre-dynastic Egypt for the production of beads
and vessels, and is presently still used almost exclusively for
decorative wares such as beads, small dishes and vessels, and frames.
liquid clay slip which has lower clay content than other slips and
is colored with metallic earth oxides or glaze stains. It is applied
to wet or leather-hard ware for decoration.
Engobes and slips do not flow in the fire, therefore they can be used
for complex, graphic images.
up fired clay particles, used as a filler in making a clay body. Grog
serves to subdue the sticky quality of highly plastic natural clays.
It also helps reduce clay shrinkage, warping, cracks, and heat shock.
In addition, it strengthens the clay body and makes complex construction
bodies are fired at temperatures between 1700-2000 F.
Low-fire clay has good workability and will not shrink, warp, or sag.
They, however, are less durable and can absorb liquids.
Low-fire clay is divided into two types: white and buff firing and
darker-colored bodies. The white bodies are composed of half clay
and half melter (often talc). Dark-colored bodies have a high clay
content; their color derives from the iron-bearing clays used their
clay is white and very hard, and, unless it is very thin, it is the
strongest of all clay bodies. The body can be either translucent or
opaque when fired, depending on the thickness or composition of the
clay. Porcelain bodies are not easy to throw or handle as they have
a critical moisture range and can easily be too soft or too dry. Prepared
porcelain bodies can be bought from a supplier, but many potters mix
hard, strong and vitrified ware, usually fired above 2192 F, in which
the body and glaze mature at the same time and form an integrated
Stoneware clays are especially appropriate for functional ware because
they stand up well to constant use and frequent cleaning.
earthenware that is generally low-fired and unglazed.
The word comes from the Italian and means simply fired earth. Terra
cotta is associated with pottery and architectural work.
extraordinary fine-ground clay suspension in water that shines when
applied as a coating. It is always fired at low temperatures to preserve
Terra sigillata is best applied to greenware. It can be applied by
brushing, spraying, dipping, and pouring. Terra sigillata is often
used with sgraffito imagery on greenware pieces, a technique used
by the ancient Greek vase painters.
wheel thrown piece is often altered after the throwing process to
give it diversity. Thrown forms can have subtle modifications or significant
alterations; for example, parts can be added to or subtracted from
the form, or the shape of the piece can be changed. The resulting
form has characteristics of both throwing and hand building.
process of polishing with a smooth stone or tool on leather-hard clay
or slip to make a surface sheen; the surface will not stay shiny if
fired at temperatures above 2000 F.
is one of the techniques used to create surface imagery. Flat, angled
tools or other implements are used for carving.
of hand-building hollow forms by rolling and attaching ropes of soft
technique of making an image from various materials or objects which
are affixed to a surface.
used to change the shape of clay by forcing it, mechanically or by
hand, through an auger or other form.
that do not use the potter's wheel or molds. These include pinching
clay, coil building, forming, and slab building.
created by pressing into the clay with objects like stamps, coins,
shells, wood, leaves, bone, and textile fabrics.
decoration made by cutting, using a beveled tool to scratch into wet
or leather-hard clay. When the article is glazed, the depth of the
incision gives a subtle quality and variation of color as well as
decoration created by filling a recess or impression in a clay surface
with another plastic clay or slip. When both are leather-hard or bone
dry, the surface is carefully scraped to leave a sharp outline between
the two colored clays.
technique for creating pattern in which holes are cut through the
technique used to create a smooth surface finish on fired ceramics
using abrasive paper.
forming technique in which plastic clay slabs are pressed onto, against,
and into plaster molds or other forms. As the clay stiffens, it retains
the shape of the mold.
of cleaning or treating a piece with a jet of sand driven by compressed
air or steam.
of hand-building forms. Clay is beaten or rolled out into flat slabs,
trimmed into various shapes, and joined together with slip to produce
the desired form. Slab construction is ideal for large scale; it is
a faster method than other hand-building methods like pinching or
coiling. Slabs for large work can be laid over combustible cores or
used to build mold-formed pieces. A clay slurry is poured into a plaster
mold. As the clay next to the mold begins to dry, a clay wall is formed
in the shape of the mold and any excess clay slurry is poured out.
Once dry, the remaining clay is removed from the mold and finished
Slip-casting is economical and allows for easy duplication of complex
forms and decoration from the same mold.
is a process used to apply complex surface imagery with slips and
of forming pieces from solid lumps of clay into hollow forms on a
revolving potter's wheel.
slip glaze made from Albany clay which produces rich yellows, blacks
and browns over a wide range of temperatures. Albany clay is mined
in the vicinity of Albany, New York, and is natural clay containing
sufficient fluxes to melt and function as a glaze. It was first developed
when the early American potters followed the European practice of
refining the clay to make a glaze.
pigments photo-screened or pattern-screened onto flexible decal paper
for transfer to bisque or over glaze. Decals can be bought or made.
glazes produce a wide range of colors and bright, shiny surfaces.
They are reliable, easy to control, colorful and durable enough for
most purposes. However, lead is toxic and should not be used on vessels
that hold or serve food. Lead's toxicity can be controlled somewhat
but not eliminated.
The invention of lead glazes around 1000 B.C. was a milestone in ceramics
history because practical glazed ware became possible for the first
time. Since then, most of the glazed earthenware in all parts of the
world has been glazed with lead.
low-fire glazes can be divided into two distinct groups--alkaline
or lead. Both result in smooth, glossy surfaces and are often characterized
by bright, shiny colors.
with a brilliant, iridescent metallic film on glaze, formed from certain
metallic salts at a specific temperature in a reduced atmosphere,
usually on the cooling side of the firing cycle.
opaque glaze with a smooth, glossy surface, and generally white in
color produced by its significant tin content. This serves as a base
for colored stain or overglaze decoration which is applied to the
unfired base coat.
Historically, majolica refers to the decorated tin-glazed earthenware
from the island of Majorca which was imported to Italy in the 15th
metallic oxides and scientifically prepared stains or enamels can
be used to give color to ceramics. They will vary in strength and
homogenous mixture of clay and water. Slips are used for coating clays
to give color and a smooth textured surface. There is also a process
for forming pots from slip.
technique using dung (animal excrement) as a fuel.
Dung can also be used as insulation during pit firing.
temperature range of 2232 F to 2400 F. High-fire produces durable
clay bodies with rich, stable glazes. However, as the temperature
rises, the color range becomes more limited.
temperature of 1940 F to 2014 F. Low-fire produces vivid colors and
graphic glaze imagery though low-fire clay bodies are less durable
and can absorb liquids.
presence or lack of oxygen in a kiln chamber during firing has a significant
effect on the appearance of the ware. A piece which has been oxidation
fired has been fired in a kiln chamber that retained an ample supply
of oxygen therefore allowing the oxygen to combine completely with
the glaze and metals in the clay.
wares in a pit that has been laced with combustible materials such
as straw, paper, rags, sawdust, or twigs. The pit could be a pit in
the ground, a formed pit using bricks or other materials, or some
type of container.
is a quick-firing technique that produces wares with brilliant, crackled
glazed surfaces and dark bodies. Raku firing requires a special low-fire
kiln, and can be used only on wares and glazes specifically designed
to withstand abrupt heating followed by rapid cooling.
presence or lack of oxygen in a kiln chamber during firing has a significant
effect on the appearance of the ware. A piece which has been reduction
fired has been fired in a kiln chamber with a restricted supply of
oxygen. This restriction of oxygen causes the kiln fuel to give off
carbon monoxide which in turn produces significant color changes.
Copper in reduction is oxblood red, in oxidation firing green; iron
in reduction firing is celadon, in oxidation amber yellow, or brown.
salt is thrown into the fire at the maturing temperature of the clay
until an "orange-peel" clear glaze appears on the ware.
simple system of firing in which pots are set in sawdust within a
brick or metal lidded box. Pockets of oxidation and reduction firing
are caused which produce interesting decoration especially on burnished
red clays. Many potters now use this process to produce interesting
coloration and also some reduction to lustre of copper and silver
salts on previously biscuited pieces.
fired is similar to salt fired except that soda can be added to the
fire at any temperature. Soda encourages bright colors and does not
produce the pockmarked surface of salt glazing.
using wood as the fuel for bisquing and glazing. The advantage of
wood-burning kilns is the unique effects that wood and its ashes
have on the surfaces of both unglazed and glazed wares.
The wood must be absolutely dry, and must be prepared and stored
at least a year in advance.
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