This document defines 63 terms related to ceramics and pottery making. It covers materials like clays, glazes, and oxides. It also defines processes such as firing, forming techniques like coil building and pinch pots, and decorating methods like slip trailing and sgraffito. Kiln types, equipment, and firing methods are also explained, such as pit firing, salt firing, and raku firing. The terms describe the various stages of working with clay from its raw form to the finished ceramic item.

1. Vocabulary
1. alumina- one of the refractory (high-melting) materials in glazes
2. bisque-clay that has been fired once but not glazed
3. bone dry-greenware which is thoroughly room dried
4. burnishing- rubbing leather-hard or dry clay with any smooth tool to polish it, tighten
the clay surface, and compress the clay particles
5. ceramist-One who makes ceramic objects or artwork; one who makes pottery
6. coil building-the technique of building ceramic forms by rolling out coils, or ropes, of
clay and joining them together with the fingers or a tool.
7. coloring oxide- combination of an element with oxygen, used in formulating glazes
and for coloring glazes and clays.
8, clay-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.
9. clay body-any blend of clays and non-plastic ceramic materials that is workable and
has certain firing properties. Clay bodies are formulated to serve particular purposes and
to achieve maturity at various firing temperatures.
10. dipping-applying glaze or slip to a pot by immersing it and shaking off the excess
glaze.
11. dunting- Cracking that occurs in ceramic ware that is cooled too quickly. Dunting can
exhibit itself as simple hairline cracks or ware can fracture into pieces. Ware of uneven
cross section, ware with glaze that fits poorly, or large pieces (i.e. large flat plates) are
often subject to dunting. Ware with high amounts of cristobalite or quartz undergoes
sudden volume changes when heated or cooled through the inversion temperatures of
quartz.
12. dry footing-A potters' term for removing all the glaze from the foot of the pot before
firing.
13. earthenware- A clay fired at low temperatures (cone 010-02) where it does not
develop maturity (vitrify). Earthenwares are porous and therefore not as strong as
stonewares and porcelains (sintering is the primary particle bonding mechanism).
Earthenware glazes are usually very bright colored and if the glazes are properly fitted,
earthenware can be quite strong and functional. (Terra Cotta is a special type of
earthenware where red burning clay is used.)

2. 14. engobe- white or colored slip applied to clay as a coating or by slip trailing, usually at
the leather hard stage.
Engobes are formulated with less clay content than slips. A slip shrinks with the ware as
it dries. A engobe formulated for application to dry or bisque ware cannot shrink
excessively. Also, a higher percentage of flux in an engobe helps it to bond to the surface
during firing. A slip, on the other hand, bonds to the surface during drying by the
interlocking of the flat clay particles at the interface between the damp clay and wet slip.
15. extrusion-a process using a mechanical aid for forming moist clay by pressing it
through a dye. This can create a variety of clay forms; forms can be made quickly.
(tubes, tiles, sewerpipes, etc.)
16. filler- elements added to a clay body to alter its properties.(such as reduce shrinkage
or strenghen greenware. Grog is an example of a filler.
17. firing- the process of heating the pottery to a specific temperature in order to bring
about a particular change in the clay or the surface.
18. flux- 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
19. foot- the base of a piece of pottery, usually left unglazed in high fire ware;
occasionally glazed in low-fire, in which case the ware must be put on stilts to keep it
from sticking to the shelf.
20. frit- ceramic glass that has been premixed from raw powdered minerals and then
melted, cooled by quenching in water, and ground into a fine powder.
21. glaze-A glass-like surface coating for ceramics that is used to decorate and seal the
pores of the fired clay
22. greenware-ceramic ware that has not been fired
23. grog- granular material made from crushed brick, refractory rock, or other pre-fired
ceramic product. It is added to bodies to reduce drying and firing shrinkage and thermal
expansion, increase stability during firing, and to add texture
24. hump mold-a mold of plaster or terra-cotta or a found object such as a rounded rock,
an upended bowl, a bag of sand, foam padding, or crumpled news paper over which a
slab of clay can be laid to shape as it stiffens.

3. 25. kiln- a furnace or an oven of heat-resistant materials for firing pottery or sculpture,
sometimes referred to as a kil.
26. kiln wash- refractory powder that can be mixed with water and painted on kiln
shelves to prevent ware and accidental glaze drips from sticking
27. kiln sitter- a control that uses small pyrometric cones that slump when the desired
temperature is reached and turn off the power to an electric kiln my tripping a switch or
to a gas kiln by shutting off the gas sollinoid valve.
28. kiln furniture- heat-resistant shelved, posts, and slabsthat support the wear in the kiln
during firing. Kiln shelves may warp in firing if hey are not well supported.
29. leather-hard- The condition of clay body when much of the moisture has evaporated
an d shrinkage has just ended but the clay is not totally dry. Carving burnishing or
joining slabs are often done at this stage.
30. majolica-
type of faience usually associated with wares produced in Spain, Italy, and Mexico. The
process of making majolica consists of first firing a piece of earthenware, then applying a
tin enamel that upon drying forms a white opaque porous surface. A design is then
painted on and a transparent glaze applied. Finally the piece is fired again. This type of
ware was produced in the ancient Middle East by the Babylonians, and the method
remained continuously in use. It was extensively employed by the Hispano-Moresque
potters of the 14th cent. By the mid-15th cent. majolica was popular in Italy, where it
became justly famous through the decorations of the Della Robbia family. The method is
still widely used in folk art.
low fired pottery employing a red-burning clay covered with a soft opaque white glaze.
Most majolica also has colored brushwork designs which are painted over the dried glaze.
The Majolica process is exacting and requires careful technique and good technical
understanding to make it successful. Metallic colors are brightest at low temperatures and
stiff-melt white glazes provide an ideal canvas for them.
31. mature (maturity)- term referring to the degree to which a clay or glaze has vitrified
or melted in the kiln. A 'mature' stoneware or porcelain clay is normally one that is dense
and strong, a 'mature' glaze flows well and heals imperfections to provide a good
covering. Like the term 'vitrification' mature needs to be taken in context. A mature
sintered refractory, for example is quite porous and would be considered immature for
other uses
32. mishima- Carve a design on soft leather hard clay, cover with engobe, and when
leather hard scrape the surface to reveal the inlaid design

4. 33. opacifier-material that causes a glaze to become opaque by producing minute crystals.
tin, zirconium, and titanium oxides are used as opacifiers in combination with various
oxides
34. oxides- combination of an element with oxygen, used in formulating glazes and for
coloring glazes and clays.
35. oxidation- firing of a kiln or open fire with complete combustion so that the firing
atmosphere contains enough oxygen to allow the metals in clays and glazes to produce
their oxide colors.
36. peephole- hole in the door or wall of a kiln through which the ceramist can watch the
pyro-metric cones, the color of heat in the kiln, and the process of firing [wear proper
shade goggles]
37. plasticity- ability of damp clay body to yield under pressure without cracking and to
retain the formed shape after the pressure is released
38. pinch pot-a method of shaping clay by inserting the thumb of one hand into a ball of
clay and lightly pinching with the thumb and fingers while slowly rotating the ball in the
palm of the other hand
39. pit firing-refers to a process of firing clay ware under primitive conditions, usually in
a fire or a fire pit. It requires a clay that will handle thermal shock well (normally well-grogged).
If you burnish your pots you will need to consider whether the grog will mar
the finish so it might be better to slip the ware and burnish that. One challenge is
generating enough heat to sinter the pots well. In a typical open wood fire it is difficult to
achieve temperatures more than a few hundred degrees above red heat. Use of sawdust,
hard wood, and various schemes to contain the heat are all common. Firings may double
as a social occasion and take only a few minutes or they may be quite elaborate insulated
hole-in-the ground affairs that span several days.
40. primary clay- Clay found in nature that was formed in place rather than transported
by the action of water. Also called residual clay. Kaolin is a primary clay.
41. porcelain-clay body which, when fired, becomes very mature and usually translucent.
Porcelain is normally quite white and fires to a very smooth pleasant surface. Porcelain
clays lack iron impurities and are ground to very fine particle sizes. Plastic porcelain
clays tend to be shorter than their stoneware or earthenware counterparts. Porcelain
casting slips achieve the whitest and most translucent results.
42. pottery- Originally a term for earthenware, now loosely used to refer to any type of
ceramic wear, as well as to the workshop where it is made.
43. press mold- Any mold made from plaster, fired wood, wood, or a found object into
which damp clay can be pressed to reproduce the shape of the mold.

5. 44. pyrometer-A simple probe made from two kinds of wire (i.e. platinum, rhodium)
welded together. This probe is wired to a sensitive electronic meter that displays a
reading of the voltage it generates when heated.
However the world of high temperature measurement and thermocouples is a complex
one. There are many kinds of thermocouples. Some generate a nice smooth voltage
increase that bears a direct relationship to temperature increase, others require complex
software to make the translation. There are also different manufacturing processes,
calibration techniques, response to different atmospheres, abilities to measure different
temperature ranges, different types decay in their accuracy in different ways, variations in
frequency of need for recalibration, etc.
Maintaining accurate pyrometers can be expensive and typical inexpensive type K
devices used in potters kilns are not accurate at higher temperatures (most potters won't
pay for the platinum/ 10% platinum-rhodium (type S) thermocouples and control systems
that really should be used, and the more expensive plated switches and contacts).
However the type K are more resistant to oxidation than types E, J, and T at temperatures
over 500C.
45. pyrometeric cones- small pyramids of ceramic materials formulated to bend over and
melt at designated temperatures.
46. quartz inversion- The point at which the silica crystals in the clay change in structure
and volume during the rise and fall of the temperature in the kiln. This development
influences the fit of a glaze to the clay body.
47. raku-literally “pleasure” a method of firing pottery that takes a ceramic piece in its
raw state, greenware, and quickly (in 45 minutes to an hour rather than 8 to 18 hours)
takes the temperature up to almost 2000 degrees; A soft, lead-glazed, low-fired type of
pottery used most often in "chado" or "Tea Ceremony" started in Kyoto during the
second half of the 16th century by a tilemaker named Chojiro. characterized by a rough,
hand made appearance with subtle, often transparent, lead glazes and exposed patches
48. reduction-A kiln firing in which there is insufficient oxygen to consume the free
carbon emanating from the heated glaze and clay, resulting in the formation of carbon
monoxide. Oxygen-starved carbon monoxide pulls oxygen from the clay body and glaze,
forming color changes in the coloring oxides.
49. refractory-The ability of a material to withstand heat without deforming or melting;
kiln atmosphere which is deficient in free oxygen
50. sagger firing- a firing where pottery is placed in local reducing material such as
leaves, seaweed, cow dung, or the organic material in a refractory container.
51. salt firing-a process where unglazed ware is fired to high temperatures and salt fumes
are introduced into the kiln chamber (normally by a spray in the burner ports). The
sodium in the salt combines with the silica and alumina in the clay to form a glaze. Salt

6. glazed ware often has marbled and variegated surface effects and has a very distinctive
look. Salt glazed ware is suitable for functional use.
52. scoring- a method of joining two pieces of clay together. make scratches in the
surfaces that will be sticking together
53. secondary clay- Natural clay that has been moved by water or wind from its source
and settled elsewhere in deposits.
54. sgraffito-a decorating technique developed centuries ago. In its simplest embodiment,
leather-hard clay is coated with an engobe or slip of contrasting color and then a pattern
or picture is added by carving through or scraping off the slip to reveal the clay
underneath.
55. silica- An oxide of silicon; SiO2. Found in nature as quartz or flint sand, it is the most
common of all ceramic materials.
56. silicosis- A disease of the lungs caused by continued inhalation of the dust of
siliceous minerals and characterized by progressive fibrosis and a chronic shortness of
breath.
57. slab- A broad, flat, thick piece of clay. Can be made by using a variety of methods
such as a slab roller, by cutting through a large lump of clay—like you would slice bread
of cheese, hand throwing, wheel throwing, rolling or pressing.
58. slip-slip or slurry is a suspension of clay and mineral particles in a water medium. It
is typically either: a.)
A glaze consisting primarily of clay ingredients. It is applied to once-fire ware. Slip
glazes can be glossy or matte and any color or texture. or b.) A clay slurry poured into
molds to be cast into shapes. The slip is usually deflocculated to minimize water content
and fine tune viscosity. The deflocculation process involves using special chemicals that
enable you to create a fluid clay-water slurry with a very low water content.
slip can also be used in joining clay pieces together.
59. slump mold- A support which a clay slab is draped to shape as it stiffens.
60. spiral wedging- a methed of wedging in which you “spiral” or turn the clay. Creates a
conch shell form.
61. stain- Commercially processed and redefined raw chemicals offered in a wide range
of shades for coloring clays and glazes. They are generally more color stable than
oxides.
62. stoneware-high fired ceramic that is vitreous or semi-vitreous, not translucent, and
often made of clays that are not highly refined. Stonewares can be brown, buff or white.

7. Stonewares commonly have some speck and some particulate material such as sand or
fine grog.
63. terra sigillata- A fine slip used by greeks, Etruscans, and romans to coat their pottery.
It fired black or red according to the kiln atmosphere. Now used in a wide variety of
colors to surface pottery wear or sculpture.
64. thermal shock-Stresses imposed on a ceramic by the volume changes associated with
sudden shifts in temperature. Ceramic materials with good thermal shock resistance are
able to withstand sudden temperature changes without cracking. Cracking usually occurs
when one part of an item is a different temperature than another part and therefore
expanding or contracting at a different rate. Fired ceramic does not withstand thermal
shock nearly as well as other materials like steel, plastic, wood, etc. Ceramic is hard and
resistant to abrasion but it is brittle and propagates cracks much more readily.
65. underglaze-Oxide color mixtures which are applied to bisque or green ware and over
which a transparent glaze is applied. To prevent excessive feathering of edges,
underglazes are usually a mix of metallic oxides and a fritted stable glaze.
66. Vitreous, vitrification-is a process. As clay is fired hotter and hotter, it reaches a point
where, if cooled, it will produce ware of sufficient density and strength as to be useful for
the intended purpose. The intended purpose may well require some porosity to gain
another more important advantage (i.e. stability in the kiln, resistance to blistering).
However 'vitreous' ware is usually functional, water proof, sanitary, hard, and strong.
Ware that has fired dense and strong is said to be 'mature'.
67. wax resist-decorative technique, patterns or designs are created by brushing a wax
medium over an area of clay, slip, or glaze to resist the final glaze application when the
wax is dry.
68. wedging- Any one of various methods of kneading a mass of clay to de-air it, get rid
of lumps, and prepare a homogenous material.
Sources:
Class Text: Hands in Clay 5th ed.
http://pottery.netfirms.com/assignments/assign/terms/glossary.htm Accessed: 10/25/03
http://www.thejapaneseconnection.com/Glossary/raku_ware.htm Accessed: 10/25/03
http://www.digitalfire.ab.ca/cermat/glossary/index.php Accessed: 10/25/03
http://smccd.net/accounts/rodriguezj/terms/list/list.htm Accessed: 11/16/03