Ceramics Final Study Guide

Reduction

(Compare to Oxidation) 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.

Oxidation

(Compare to Reduction) A firing atmosphere with ample oxygen. In electric kiln always gives an oxidizing fire. In a wood or gas firing, the mixture of fuel and air is perfectly adjusted to give a clean burn.

Mishima

(inlaid clay) variation - contrasting colored slip is inlayed into incised lines. This can be done using wax resist - incising then applying slip. OR slip may be applied to incised lines and sanded off the raised body.

Earthenware Maturing Range (Temperature)

1,830 - 2,010 degrees Fahrenheit

Stoneware Maturing Range (Temperature)

2,100 - 2,300 degrees Fahrenheit

Crawling

A bare spot (from the shrinking of a glaze) on a finished piece where oil or grease prevents the glaze from adhering to pottery.

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. Can be colored, opaque, translucent or matte.

Porcelain

A combination of kaolin (a pure white primary clay), silica and feldspar. A unique aspect of it is that it can be worked as clay, but when fired properly reaches a state similar to glass. Primary qualities of this are translucency and whiteness.

Matt Glaze

A dull glaze surface, lusterless and non shiny, not very reflective when fired. It needs a slow cooling period or it may turn shiny.

Bat

A flat disc made out of plaster, wood, or plastic which is affixed to the wheel head with clay or pins. Bats are used to throw pieces on that would be difficult to lift off the wheel head.

Vitrify

A glassy, non-porous state caused by heat or fusion.

Frit

A glaze material which is derived from flux and silica which are melted together and reground into a fine powder.

Satin Glaze

A glaze with medium reflectance, between matt and gloss.

Stoneware

A high fire clay fired between 2,100 and 2,300 degrees. Stoneware is waterproof even without glaze; the resulting ware is sturdier than earthenware.

Majolica

A low fire glazing technique. The process involves applying an opaque tin glaze to earthenware and painting it with different colored oxides.

Earthenware

A low-fire clay fired to a temperature of 1,830 - 2,010 degrees Fahrenheit. Available in red or also white. Porous and not waterproof. To be functional, it must be glazed.

Flux

A melting agent causing silica to change into a glaze.

Wedging

A method of kneading clay to make it homogenous by cutting and rolling.

Clay Body

A mixture of different types of clays and minerals for a specific ceramic purpose.

Wheel Thrown

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 composite pots (a teapot can be constructed from three or four thrown forms).

Coiled Pottery

A piece of clay rolled like a rope which are laid on top of each other and joined through blending, used in making pottery. Coil pieces can be almost any shape or size.

Chuck

A piece used to aid the potter in trimming. A form that can hold a pot upside-down above the wheel head while the potter trims it. They are thrown and bisque fired clay cylinders which are open on both sides.

Slip Cast Mold

A plaster shape designed to pour slip cast into and let dry so the shape comes out as an exact replica of the mold.

Additive

A process in art that involves adding material to the piece.

Cone

A pyramid composed of clay and glaze, made to melt and bend at specific temperatures. It is used in a kiln to determine the end of a firing or in some electric kilns, it shuts off a kiln setter.

Banding Wheel

A revolving wheel head which sits on a pedestal base. It is turned by hand and used for finishing or decorating pottery.

Gloss Glaze

A shiny reflective gloss.

Peephole

A small observation hole in the wall or door of a kiln.

Subtractive

A subtractive process (Carving) involves taking material away from the piece.

Slurry

A thick slip.

Calipers

A tool used to measure the diameter of round forms, for example calipers are used to get lids to fit just right.

Stilt

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

Engobe

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

Sprigging

An embossed decoration on pottery, usually press molded shapes applied to greenware.

Firebrick

An insulation brick used to hold the heat in the kiln and withstand high temperatures.

Foot

Base of a ceramic form. This is the part of the vase that meets the floor.

The enclosed portion of a kiln where pottery pieces are placed for a firing.

Chamber

Clay

Clay = Alumina + silica + water.

Plastic Stage

Clay is easily manipulated and bent in this stage

Firing

Clay is hardened by heating it to a high temperature, fusing the clay particles.

Slip

Clay mixed with water to a mayonnaise consistency. Used in casting and decoration.

Slab Built

Clay slabs are cut to shape and joined together using scoring and slip. Slabs can be draped over or into forms, rolled around cylinders or built up into geometric forms.

Bisque

Clay that has been fired once, usually at a low temperature.

Elements

Coils of high temperature resistance wire that convert electricity to heat.

Engobes

Consist of a mixture of materials, with clay forming about half the total. Because of the low clay content engobes can be applied in a wide range of ways. The great advantage is their ability to be applied on work that is dry or even bisqued; it is also possible to apply them to leatherhard work.

A condition where molten glaze pulls away from portions of the surface to leave areas unglazed.

Crawling

Grog

Fired clay ground to various mesh sizes.

Pyrometer

Instrument used to record the exact temperature of the kiln.

Dry-Foot

Leaving the bottom of ceramic pieces unglazed.

Underglaze

Liquid clay slip that contains coloring oxides and chemicals used to apply color and designs to a ceramic piece.

Stacking

Load a kiln to hold the maximum number of pieces.

Soaking

Maintaining a low steady heat in the early stages of firing to achieve a uniform temperature throughout the kiln.

Mid-Range Clay Maturing Range (Cone)

Matures between cone 4 and cone 7

High Fire Clay Maturing Range

Matures between cone 8 and cone 11

Low Fire Clay Maturing Range (Cone)

Matures between cones 02 and 012

Oxides

Metal oxides 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 stained wood. The most common stain is iron oxide (rust).

Crackle Glaze

Minute decorative cracks in the glaze that are often accentuated by rubbed-in coloring material.

Kiln Wash

Mixture of Kaolin, flint and water. It is painted on one side of the kiln shelves to separate any glaze drips from the shelf.

Bone Dry Stage

No visible moisture - no dampness to touch - Clay is ready to be fired.

Opaque Glaze

Non-transparent glaze, it covers the clay or glaze below it.

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 F.

Stain

Oxide and water, used as a colorant for bisque ware.

Chamois

Pieces of chamois skin (about 2 x 4 inches) are excellent for compressing and smoothing the upper edges of thrown ware. Chamois can also be used to smooth ware that is leather-hard.

Composite Pots

Pots that were thrown or hand built in separate pieces and then assembled.

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.

Cut-Off Wires

Probably the most common ones have two hardwood handles at either end. Fishing line and uncoiled springs can also be used as cut-off wires.

Compress

Pushing the clay down and together, forcing the particles of clay closer.

A manufactured ceramic object enclosed in a kiln during firing that bend at specific temperatures.

Pyrometric Cones

Kiln Furniture

Refractory posts and shelves used for stacking pottery in the kiln for firing.

Slip Trailing

Slip (a liquid clay) is applied to the greenware through a tube or nozzle, much like icing a cake.

Leather Hard

Stage of the clay between plastic and bone dry - firm enough to bend yet soft enough to be carved. Clay is still damp enough to join it to other pieces using slip. For example, this is the stage handles are applied to mugs.

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. Many coil-built pieces are constructed on top of a pinched bottom.

Centering

Technique to move the clay in to a symmetrical rotating axis in the middle of a wheel head so you can throw it.

Neck

The (usually) narrower part that leads from the body of the vase to the mouth.

Burnishing

The ancient rubbing process of polishing the outside skin of a clay pot while greatly reducing its porosity. This finishing is done by hand, using a stone or a metal piece which is usually embedded in a wad of wet clay that perfectly fits the burnisher's hand.

Glaze Firing

The final firing, with glaze.

Crazing

The fine network of small cracks that occurs on glazes. The Japanese encourage crazing and will stain cracks with concentrated more than the clay body in cooling process.

Vitrification

The firing of pottery to the point of glossification - the surface is made shiny and nonporous by fusing a vitreous solution to it; it becomes "glazed pottery"

Kiln

The furnace in which ceramics are fired.

Mouth

The opening at the top of a vase.

Plasticity

The quality of clay which allows it to be manipulated into different shapes without cracking or breaking.

Firing Range

The range of temperature at which a clay becomes mature or a glaze melts.

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

Pyrometric Cones

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

Incised

These decorations are surface designs cut into the clay.

Potter's Needles

These long heavy needles set into wooden, metal, or plastic handles are one of the most versatile tools in pottery. Just a few of their uses are trimming the top edges of ware while on the wheel and for scoring slabs and coils when hand building.

Kiln Posts

Thick posts that support the shelves in a kiln, comes in a variety of heights.

Sgraffito

This comes 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.

Body

This is the main part of the vase. It is usually the largest part.

Mille Fiore

This refers to a method of creating designs by folding different colored clays together into "rods" or bars, then slicing them.

Maturing Point

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

Fire

To heat a clay object in a kiln to a specific temperature.

Ribbon Cutting Tools

Tools derive their name from the thin flat ribbon-like steel that is used to form their cutting heads. These tools provide sharp cutting edges with additional strength in the direction of cut.

Transparent Glaze

Transmits light clearly.

Greenware

Unfired clay ready or nearly ready for firing.

Fettling Knives

Used in pottery to clean ridges left by casting and other trimming chores. These thin-bladed knives come in either a hard temper or soft.

Ribs/Kidney Tools

Used in throwing, these tools can help shape and smooth pots as they are being formed on the wheel.

Lower-Mid Range (Cone)

from cone 01 to cone 3

High Fire Range (Cone)

from cone 8 to cone 14