A device operated with an air compressor
used for spraying on colors, either in
overall coverage or decorative
A method of applying color and wiping it
back to accentuate the detailed
A turntable operated by hand, used for
an all over coat of color on bisque on top
of which detailed decorating is
A plaster disk or slab for clay
Clay that has been fired but not glazed.
Sometimes referred to as "biscuit."
Cadmium: Heavy metal used in producing red
glazes and underglazes.
A Technique where the leather hard clay is polished with a hard instrument to force the smallest clay particals to the surface creating a soft sheen, this surface remains after the pot is fired.
To purify a material through the action of heating to red heat 1292-1382 °F.
A clay form made from a mold. May also
refer to plaster castings.
A liquid clay used in the process of
forming objects with molds. Also referred
to as "slip."
The inside section of a mold where the
casting is formed. Ceramics: Clay forms
which are fired in a kiln.
The slow process of clay becoming ceramic. Clay which is exposed to heat 1112 °F, loses its chemically bound water molecules and can no lnoger be broken down by water. Once this change has occured it cannot be reversed.
A term which usually refers to the bone
china of England, but also is associated
with vitreous white wares and
The Decomposition of Granite through the process of Kaolinization creates clay ( See Kaolinization). Clay is a minteral with a plate ( Platelet) like structure; it is these plates, (about 0.5 microns across) when lubricated with water, slide against each other to form the plastic mass we know as clay (see Water). 'Primary' clays are those found close to the area of Kaolinization and hence the purest (Kaolin or Chins Clays). Secondary clays are those moved by water away from the site of Kaolinization and get progressively more plastic and less pure (Ball Clays, Fire Clays, Earthenware's and Marls).
A clay designed for a special purpose. It is created by blending different clays or by adding other materials to clay, such as feldspar and flint in order to produce a desired workability, maturing temperature, or finished result. A clay body is the result of technology.
process by which mold seam lines and
surface imperfections are removed from
unfired clay objects.
of ceramic color by brush, sponge, and
spray which cover an entire area or a
specific area of a piece.
One of the strongest coloring oxides used by the potter. Cobalt creates a dark dense royal blue in most cases. Historically used in China as a painting pigment on blue and white wares.
A meathod of handbuilding a form using long rolled out, or extruded, snake-like lengths of clay. Each coil of clay is integrated with the previous one to build the work up. The coils may be completely obliterated in the construction process or retained for their decorative qualities.
A brush lightly coated or dampened with a
fluid to prepare it for the application of
a specific type of color or
Coat (glaze or underglaze):
thin coat of color that will soak into the
greenware or bisque well.
(See Pyrometric Cones).
small clay cone holder used when cones are
placed on the shelf of the
mixture of time and temperature at which
the cone will bend.
Decorative craze lines in a glaze.
Bubbles in the glaze finish which
The fine network of small cracks that occurs on glazes. The Japanese encourage crazing and will stain cracks with concentrated tea.
Glaze which pulls together and beads up,
leaving bare spots of bisque. Also
referred to as "separation."
Mosr glazes have no easily visable crystal structure. Crystalline Glazes have large and dramatic crystals up about three inches across. A high alkaline low alummina glaze is vital for crystals to develpoe. Additions of zinc and titanium also help seed the crystals. An extremely slow cool of the kiln is necessary to allow the crystals to grow. Because of the low alummina content in crystalline glazes they are very runny, often pots are supported in the iln on stilts to avoid them adhering to the kiln shelves, the stilts can be broken off after the firing.
alkaline substance which is added in
extremely small amounts to slip to make it
more fluid without adding excessive
amounts of water.
process of dipping ware into
technique of applying color which produces
a feather-like effect using a dry brush
and liquid colors.
process by which glaze is removed from the
bottom or foot of a clay object so it may
be fired without stilting.
Cracks, which occur on pottery during the heating or coolinf cycle of the firing. They are usually caused by the silica inversion at 1063°F (Alpha to Beta phase) or the Crystobalite (one of the 'phases' os silica) inversion at 428 °F in both cases there is an expansion and contraction, of around 2-3%, in the heating and cooling cycles.
A low-fire porous
clay bodies which are fired to maturity at
approx. 2000°F. They are not waterproof and must be glazed to be used.
heating coils of an electric kiln. (Tired
or burned-out elements refer to elements
which carry too little or no electrical
current for producing heat).
A form of low temperature glaze that is applied on top of an already fired higher temperature glaze. Enamels are often lead based, as it is a flux, which works at a low temperature.
One of the predominant naturally occurring fluxes used primarily in stoneware glazes. Feldspars can be the only flux present in a stoneware glaze although this is uncommon and additions of calcium usually supplement it.
The ridges created on a casting where the
mold comes together. They are usually
removed during the cleaning
Gentle rubbing of the glazed surface to
Clay is hardened by heating it to a high temperature, fusing the clay particals. Primitive pottery is usually fired on the ground or in pits with whatever flammable material is available. Kilns allow a more efficient use of materials and more control over the atmosphere during a firing. The two basic atmospheres, oxidation and reduction, affect the color of the final piece.
A finish that must be fired to produce
proper color and surface finish. Fired
Products (fired color products): Products
which must be fired.
The interior of a kiln in which the
ceramic ware is fired (also referred to as
a fire box).
A system of gradually raising and lowering
the temperature of a kiln to properly fire
An application of glaze applied with a
fully-loaded brush so the color flows onto
the surface of the ware.
A substance which causes or promotes melting.
product that has been tested and
determined to be safe for use on surfaces
which come in contact with food or
base or the part of the piece of ceramic
on which it rests. Glaze: A fired glassy
coating on a piece of ceramic.
A combination of materials that have been melted into a glass, cooled, and reground into a powder prior to being added to a glaze recipe.
A shiny, glass-like finish. Greenware:
Unfired clay forms or shapes.
rough scrubbing material used in the
process of cleaning greenware.
Clay that has been fired and then ground into granules of more or less fineness. Grog is considered a filler, and is added to clay bodies for several reasons; it helps open a tight or dense body, promotes even drying, which reduces warping and cracking, and reduces overall shrinkage. Grog also adds tooth and texture to a clay body aiding in the ability of the body to maintain its form during construction.
A coating of material applied to ceramics before firing, that forms a glass-like surface. Glazes can be colored, opaque, translucant or matte.
An area on greenware or bisque surface
that resists color application.
section of a kiln that fires to a hotter
temperature than the rest of the
The process of carving a design into a
A decorative technique where a pattern is carved into the clay at the leather hard stage and contrastingly colored soft clay is forced into the decoration. When the clay is a little drier the excess is scraped off to reveal the pattern.
One of a potters favorite colorants, when combined with the right glaze and firing, iron oxide can produce greens, browns, blacks, yellows, oranges, subtle blues and grays. Most of the best color responses for iron in a glaze need a reduction firing. Iron is also a useful colorant in clay bodies and is best introduced by adding high iron clays to the clay recipe.
A china clay in its purest form, primary clay.
The natural formation of kaolin from the decomposition of feldspar.
(of a mold):
series of notches and bumps carved in the
excess plaster around the cavity of the
mold to !nsure a proper fit.
Basically and insulated box, which is heated to fire clay. They can be either, cross draft, down draft, or up draft. The draft refers to the direction the combustion gasses have to travel from input to exit flues, since no combustion takes place in an electric kiln there are no input or exit flues and they are genuinely heated boxes. The fuels used to heat a kiln are gas, oil, wood, coal (now almost obsolete) and electricity. Each fuel sorce used to fire a kiln offers different possible outcomes for the clay fired in them. The maximum operating temperature for most pottery kilns is about 2372°F, although many woodfired kilns may be fired up to 2462°F.
The series of posts, stilts, and shelves
on which the ceramic ware rests in order
to take full advantage of the interior
space of the kiln.
A device used with a pyrometric cone to
shut off the kiln when conditions inside
the kiln cause the cone to
The refractory coating applied to the top
of the kiln shelves to protect them from
amount of lead that is dissolved from the
surface of a glaze which has been in
contact with acid solutions.
A stage in the drying process of clay, when the clay is pliable but strong enough to handle. It is ideal for trimming and the addition of appendages such as handles and spouts. Relatively wet clay can be attached to the piece durring this stage and the resulting bond will not form cracks.
A soft finish with little or no
bisque that has been fired at the proper
rate of heating and cooling to produce an
even state of hardness
Pyrometric cones used to measure the
firing temperature of a kiln. They are
shaped like bars rather than
Strap (mold bands):
made of cloth, rubber, or metal used to
tightly secure parts of a mold together
during the pouring process.
The procedure of stacking greenware in a
kiln during the bisque firing.
A color that is applied to bisque. These
colors are never fired in a
product that when applied and fired
according to label directions is safe for
use on surfaces that come in contact with
which does not allow other colors to show
A clay piece that has undergone a single glaze firing. The glaze is applied directly on to the dry or leather hard piece thus avaoiding the bisque firing. This approach, although offering certain economic and aesthetic advantages, can create technical problems for the potter.
A mold that is made up of only one section
or piece of plaster. Also referred to as
an one piece mold because of the lack of a
Any element combined with oxygen.
A firing where there is either no combustion occurring (electric kiln) or where there is sufficient oxygen in the kiln to allow the fuel to burn cleanly. The atmosphere of the kiln (oxidation, or reduction) dramatically affects the resulting clay and glaze colors, for example; copper in oxidation is green (as is copper oxide) in reduction it becomes red (more like copper metal).
Small holes in the side of a kiln used for
viewing shelf cones and ventilating the
kiln during the firing process.
Tiny holes in the final surface finish of
a glaze or underglaze. Plasticity: Refers
to the ability of clay to be formed into a
shape and retain it.
A method of forming clay into a shape by pinching it with your fingers or between objects.
An invaluable mold-making tool. It can be poured or carved into virtually any shape. When it is dry it can be used to press clay into or to slipcast with, forming a specific shape.
The properties of a material that allow it to be shaped and to retain its shape. The plastic properties of clay are principally determined by the size of the platelets. The smaller the platelets the more plastic the clay is. Aging or souring is also relevent to a clays plasticity; with time bacterial action creates a colloidal gel, which aids the lubrication of the platelets.
A white highly virtified clay body that is translucent where thin (often fired up to 2462°F). The translucency is a result of silica glass fused into the fired clay. To achieve this, a high amount of flux is added to a kaolin based clay body. The flux to clay ratio is often flux > clay, indeed some of the original Chinese porcelains had as lillte as 20% clay like minerals. The low clay content makes porcelain very difficult to throw and trimming wares is almost unavoidable. The plasticity of porcelain can be improved by small additions (2%) of white bentonite.
Articles made of refractory material which
support kiln shelves during
The excess clay formed at the pouring
hole of a mold during the casting
Hole (pour gate):
section at the opening of the mold used
for pouring the slip into the mold
) A device of clay or refractory material
used for supporting greenware (usually
porcelain) during the firing process. (2)
Term applied to the slight opening of the
kiln cover during the first stages of the
firing process, kiln prop. (3) Another
word for kiln posts.
small piece of clay compound that reacts
to time and temperature used to indicate
maturity of ceramic clays and
Raku:Origianally a Japanese seal given to a prominent family of potters (1598) who developed the technique. The term describes a low fire form of pottery where the pieces are removed from the kiln as soon as the glaze has melted and then left to cool or doused with water. In the mid 20th century Paul Soldner introduced the now popular process of post-firing rediction. In this case the red hot piece is placed in a lidded bin filled with staw or sawdust. The glazes are dramatically altered by the reduction particularly noteworthy are the colors achieved with Copper.
Reduction:A firing atmosphere with inadequate oxygen and large amounts of carbon (smoke or unburned fuel). What would have been Copper Oxide in an oxidation atmosphere will be pure copper in reduction. Reduction allowed the Chinese to develope the sangue de beouf red glazes and gives Raku its metalic finishes. In Indian pottery, Maria's black pieces are the result of heavy reduction; the same piece in oxidation would be terra cotta color.
Substances that have a resistance to high
lines on greenware produced where two
sections of a mold are locked together
during the pouring process. Also referred
to as fettlings.
A satin-like surface which has a slight
sheen to it.
which generally allow only dark colors to
Slightly colored and/or speckled colors
which allow most colors to show through
with only slight distortions.
cone temperature that is fired on the
shelf of a kiln. The amount of heating the
ware actually receives.
A short cycle at the end of the regular
firing cycle which maintains the level of
heating in the kiln, and enhances many
Usually refers to a natural sponge used
for cleaning and decorating greenware.
There are also synthetic sponges available
colors used for decorating.
Small shapes of bisque with metal or wire
spurs used for supporting glazed greenware
A combination of clays which form a
stone-like vitreous body during
See cone plaque.
mold that has three pieces.
expansion that occurs in glazes and clays
when heated in a kiln.
Sudden changes which occur in a clay or
glaze which causes damage, usually through
sudden heating or cooling.
base colors which are free from cloudiness
A mold that has two parts.
A color which is usually applied to
greenware and in most cases is covered
with a glaze.
firing hot enough or long enough, or
Usually refers to porcelain and stoneware
that are fired at a high temperature. The
clay begins to become glass-like in
nature, although not necessarily
Small holes made by puncturing the wet
greenware with a needle tool when two
pieces of ware have been attached. These
small holes allow the air and gases to
escape during firing. Also refers to the
peep holes in the side of the