Ceramics Vocab

ideal thickness of clay?

1/4 an inch

how long does it take for clay to be ready for firing?

10 days to 2 weeks

water content

20% water; likewise it shrinks 20% during the drying and firing faces

firing

Clay is hardened by heating it to a high temperature of 1700-2100 degrees, fusing the clay particles. 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.

porcelain

Made in Korea and China around 960 AD; a combination of kaolin, silica, and feldspar. it can be worked as clay but when fired properly reaches a state similar to glass. this is translucent and white. potters in the 17th century invented bone china to compete with this

Ceramics

Objects made of clay fired sufficiently high in temperature for a chemical change to take place in the clay body, usually over 1550 degrees.

terra cotta

a brownish-orange earthenware clay body commonly used for ceramic sculpture

glaze

a coating of material applied to ceramics before firing that forms a glass like surface. glazes can be colored, opaque, translucent, or matte.

leatherhard

a damp condition of clay when it is too firm to bend yet soft enough to be carved

oxidation

a firing atmosphere with ample oxygen, an electric kiln always gives an oxidizing fire. in a wood or gas firing, the mixture of fuel and air perfectly adjusted to give a clean burn. acoma whiteware is fired in oxidation

reduction

a firing atmosphere with inadequate oxygen and large amounts of carbon. what would have been copper oxide in an oxidation atmosphere will be pure copper in reduction. reduction allowed the chinese to develop the sangue de beouf red glazes and the same piece in oxidation would be terra cotta color

vitrify

a glassy, non-porous state caused by heat or fusion, mature

stoneware

a high fire clay; this is usually waterproof even without glaze; buff (beige in color)

earthenware

a low-fire clay, porous and not waterproof. To be functional it must be glazed

kiln wash

a mixture of china clay and flint in water solution used to coat kiln shelves to protect them from dripping glaze

stilt

a triangular support for clay pieces that helps prevent glaze from melting on the shelves during a firing

engobe

a white of colored thin layer of clay used to decorate a bisque pot. it may or may not be glazed over

plastic stage

clay is easily manipulated and bent

slab built

clay slabs are cut to shape and joined together using scoring and wet clay called slip. slabs can be draped over or into forms, rolled around cylinders or built up into geometric forms. large forms are difficult because of stresses on the seams because the slab around this by working fibers into the clay body. the fibers burn out during firing, leaving a network on tiny holes. MUST BE LEATHER HARD TO JOIN

bisque

clay that has been fired once, usually at a low temperature, the first firing

elements

coils of high temperature resistance wire that convert electricity to heat

sgraffito

comes from the italian word meaning "scratched through" and is done by incising or cutting a design through a colored slip coating to reveal the clay body

support systems

due to the high content of water, clay must be supported by these with lightly crumpled newspaper; small boxes, or the like for it retain its form

matte glaze

dull surfaced glazes, lusterless and non shiny

describe the molecules of clay

flat

malleable

foldable

dry footing

glaze is removed from the bottom of a piece before firing, making stilting unnecessary

pyrometer

instrument used to record the exact temperature of the kiln

underglazes

liquid clay slip that contains coloring oxides and chemicals used to apply designs to a ceramic piece, no glossy, most of a stain

crackle glaze

minute decorative cracks in the glaze that are often accentuated by rubbed in coloring

bone dry stage

no visible moisture, no dampness to touch, clay is ready to be fired

Coiled Pottery

one of the oldest ways of forming pottery; long strands of clay which are laid on top of each other and joined through blending coil to coil. Coil pieces can be almost any shape or size.

raku

pottery is fired normally but removed when it is red hot and the glaze is molten. it is then usually placed in a bed of combustible materials and covered, creating intense reduction resulting in irregular surfaces and colors.

pinch pots

starting with a ball of clay, the potter opens a hole into the ball and forms a bowl shape through a combination of stroking and pinching the clay.

wheel thrown

term throw comes from the Old English word meaning spin. A piece of clay is placed on a potter's wheel head which spins. the clay is shaped by compression while it is in motion. often the potter will use several thrown shapes together to form one piece.

crazing

the fine network of small cracks that occurs on glazes. the japanese encourage crazing and will stain cracks with concentrated tea

kiln

the furnace in which ceramics are fired. they can be electric, natural gas, wood, coal, fuel oil, or propane. materials used to heat the kiln can affect the word. s

silica

the main chemical compound in sand; also a important element in glass, glaze, and ceramic bodies

wedging

the process of freeing the clay of air and working it to uniform consistency; the method of pushing, lifting, turning 1/4 of a turn is repeated till clay shows no air bubbles. dry clay can be added now if the clay is too wet.

kiln shelves

the shelves inside a kiln that ceramic greenware is stacked on in the kiln. the shelves must be coated with kiln wash to prevent glazed pottery from sticking to the shelf.

incised

these are decorations that are surface designs cut into clay

pyrometric cones

these are slender pyramids of ceramic material made in a graded series to melt and indicate when a firing is nearly completed. In an automatic cutoff kiln, they trip a switch when they melt to cute the kiln off.

oxides

these can be mixed with water and applied to the surface of clay. by varying the amount of material applied and rubbed off, the potter can achieve effects similar to stained wood. the most common stain is iron oxide.

shelf supports

thick posts used to hold shelves in a kiln

slip

this fills in pores and gives a uniform color; also attaches leather hard pieces of clay together after being scored

maturing point

time and temperature needed to completely fire a glaze or clay object to the "vitrified" state

greenware

unfired clay ready or nearly ready for firing

scoring

use to join clay pieces. a process of scratching the surfaces of wet clay with needle tool

riverbeds

where clay is found in it's natural state, formed through erosive effect of water on rock