Basic
Ceramic Vocabulary
Clay
Particles of decomposed rock combined with water to create a
plastic, malleable body which is then fired in a kiln to fuse the particles
back into a stone-like state.
STAGES OF CLAY
Slip
A thick and creamy mixture of clay and water used to join
clay parts together or to decorate the surface. It is applied before firing,
when the clay is still wet. See Engobe.
Plastic
Clay that is soft, pliable and easy to work with.
Bone Dry
Clay that is dry and ready to be fired in the kiln.
Leather-hard
Clay that has been allowed to dry slightly, making it
stiffer and able to support its weight, but can still be worked on and have
parts attached.
Bisque
The first firing for the clay, removes all of the water,
(both actual and chemical) and carbon, The fusing of the particles has begun,
yet the clay is still porous to allow for glaze absorption. It can no longer be
slaked down and recycled.
Glazeware
The second firing of the clay with a coating of glaze upon
its surface, it is fired to a higher temperature than bisque and therefore
fuses the particles into a solid, non-porous state..
CERAMIC DECORATION
Glaze
It is a mixture of powdered ceramic materials, such as clay,
glass, fluxes and colorants in water. It is applied to bisque ware and then
re-fired. Glaze is used to decorate, protect and make the ware food-safe. Do
not apply glaze to the bottom surface of the work or the any part that may rest
upon or touch the kiln shelf.
Engobe
A mixture between slip and glaze, it is applied to wet clay
for decoration like slip.
Underglaze
A commercially prepared mixture of "ceramic paint"
that can applied to wet, dry or bisque clay.. The pre-fired color of the
"paint" stays true through the firing, but is not shiny so it needs
to be sealed with a clear glaze on top.
Washes
A thin solution of the same metallic oxides that is used to
color glazes, it can be applied under or over a glaze. Applied first, it can be
rubbed into the carving and textures, picking up details, applied over a glaze-
it can fuse and flow as the glaze melts given a softer result.
Room-temperature Glaze
Materials such as paint, crayon, pencil, gold-leaf, or
tool-dip that are applied on the surface and does not require further firing.
Stamp
It is any device that can be pressed or rolled into clay to
create an imprinted design. It can be made of clay, plaster, wood or a found
object.
Sprigging
The technique of adding an appendage or decorative element
to the surface of the work using coils, stamps, molds or free-form design.
HAND FORMING TECHNIQUES
Coil
A building technique utilizing long "ropes" of
clay stacked in layers upon one another to create a vessel or form.
Pinch
The process of starting with a ball of clay, inserting your
thumb and "pinching" the clay between your thumb and fingers,
gradually expanding and shaping the wall into a bowl-like form.
Slab
Using thin sheets of clay to build a structure, the sheets
can be either rolled or stretched out. They can be manipulated while plastic
and formed around molds (Soft Slab) or when used leather-hard and have the form
constructed from shapes cut from the sheet (Hard slab).
Mold
A form used for support and shaping of the clay, usually
made of paper, clay or plaster. Soft slabs are draped on top or slumped inside
and allowed to get leatherhard and then built upon or cut and shaped further.
Clay can be pressed into plaster molds with a design carved or cast into a
negative space and then popped out and attached.
KILNS AND FIRING
TECHNIQUES
Kiln
A furnace made of refractory (non-melting) materials
constructed to fire clay. They are usually fueled by electricity, gas or wood,
but may also be fired using coal, oil, manure or even old tires.
Cone
A pyrometric cone is a triangular shaped piece of ceramic
materials carefully formulated to melt at a specific temperature. They are
placed in the kiln t monitor and determine kiln temperature.
Oxidation
A kiln atmosphere which contains oxygen; electric kilns are
always an oxidation firing.
Reduction
A kiln atmosphere which is deprived of the oxygen needed to
burn, causing oxygen to be taken fro the glazes and clay resulting in a desired
color effect. i.e. copper reds. Gas, wood and raku have reductive atmospheres.
Raku
A firing process in which glazed, red-hot pots are taken out
of the kiln and placed in a combustible material, choking off the oxygen and
resulting in a smoky black, crackled, metallic or iridescent surface.
CLAY BODIES
Raku
A low temperature body specifically developed to withstand
the thermal shock of the severe firing process. It is usually under-fired at
bisque to protect it from the expansion of heating and rapid cooling.
Earthenware/Terra Cotta
It is a low-fire porous clay body, usually red or orange-tan
in color due to the impurities and presence of iron. It is the most widely
available type worldwide. There is also a term of "white
earthenware", which is not a true earthenware, but created by man to fire
at low temperatures.
Stoneware
It is a high temperature, strong, vitreous clay body,
usually gray-brown in color. It is the most popular clay for utilitarian wares.
Porcelain
It is the highest temperature clay body and most difficult
to work with. It is the purest form of clay possible. It is white and has
translucent capabilities.
MISCELLANEOUS TERMS
Wedging
It is the kneading of plastic clay in a rocking, spiral
motion in order to remove air bubbles and create a uniform consistency. This
can be achieved also by repeatedly slamming a ball of clay onto the table on
alternating sides to force the air out.
Grog
Ground up bits of fired clay used to temper a clay body,
reduce shrinking and cracking or add texture or "tooth". It comes in
grades from very fine to extra coarse.
Slip and Score
The method for joining pieces of clay where the two surfaces
are scratched up and slip (or water) is added like a "glue" to create
a strong, melded bond. It is an essential step in ceramic construction, because
clay will stick to itself when wet, but when dry, will fall apart, especially
after bisque when all the water is removed. Texturing the surface gives the
clay some grip, almost like Velcro.
CONE TEMPERATURES
Bisque 08-04
Low-Fire 06-04 Mid-Range 4-6 High-Fire 9-11
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