PURPOSE:

Knowing the techniques and terminology of ceramics and sculpture will help you understand how to make interesting work, and the common problems that can happen when you rush or don't pay attention. This vocabulary list is divided into the following sections:

Clay management
Stages of Clay
Clay Building Terms and Techniques
General Clay Terms
Clay Equipment
Decoration Techniques
Firing Terms
Glazing Terms
Studio Health and Safety

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CLAY MANAGEMENT TERMS

To keep clay moist and workable it is necessary to cover it with plastic. This creates a humid environment prolonging the working stages of the clay. Plastic will help keep your work wet for a period of time, but eventually the clay will dry out even when covered. If clay has stiffened more then desired, than spray it or wrap it in wet newspaper and wrap with plastic. Allow the water to penetrate the clay then cover it with plastic to re-moisten the clay.

Managing the stages of clay for your project - A guideline for storing clay projects:

Wrap clay entirely (all the way around then set on board)– clay maintains most moisture and workability.
Wrap clay entirely including board – The board will absorb a slight amount of moisture allowing the clay to set up slightly still maintaining workability.
Wrap the clay on the board (set the piece on a board, wrap plastic snuggly around clay paying close attention to where the plastic meets the board) – The board will absorb a slight amount of moisture. Small amounts of air will seep in underneath the plastic allowing the clay to stiffen up slightly more while maintaining a workable state.
Drape plastic over clay – when the piece is finished or a slower dry is required. Keep piece covered with plastic allowing air underneath. As the clay dries it will start to lighten in color and look chalky. This is the beginning of the Bone Dry stage and the point at which the plastic can be removed entirely.

STAGES OF CLAY

1. Greenware: A piece that has not yet been fired. Clay at this stage can be recycled and returned to a wet stage to build over and over again.

The 3 stages below are considered greenware because you can add water back in and build a different piece:

Wet Clay: Soft and pliable. (Clay is most versatile at this stage allowing many types of building to occur such as coil, soft slab, pinch pots, wheel throwing, extruding, etc.).

Leather Hard Clay: Dried slightly, some shrinkage has taken place, but still slightly flexible. (Sometimes called “cheese-hard”. Hard slab construction is possible at this stage for precise, geometric forms. Also, a good stage for carving, brushing on slip, slip-trailing, and sgraffito.
Bone Dry Clay: Rigid & fragile; clay is light in color; all physical moisture has evaporated from clay; more shrinkage has taken place. No construction or surface decoration involving addition of moisture can be done at this point. The addition of any moisture to bone dry clay will make it crack or disintegrate with too much water! Clay is now ready for bisque firing (see below for bisque-ware).

2. Bisque ware: work that has been fired once in the kiln, undergone the ceramic change– a chemical change where clay becomes ceramic and can never be re-used/returned to the greenware stage. Bisque ware is still porous and therefore ready to accept glaze.

3. Glaze ware: work that has glaze applied to it and is fired to a temperature where the glaze has melted.

CLAY BUILDING TERMINOLOGY AND TECHNIQUES

Basic Building Techniques:

Coil-building: A hand-building technique where clay "snakes" or coils are formed, pushed and pinched to combine them into a pot. Coils can be left as-is to achieve a design or blended together to form a smooth surface.
Pinching: A hand-building technique where a lump of clay is pressed with the thumb into the center of the ball. While turning the ball in one hand, the walls are pressed or “pinched” evenly with the thumb into the inside and the fingers on the outside.
Slab-building: A hand-building method where flat pieces of clay are cut into shapes and joined to form an object. Slabs can be formed using a roller or a piece of equipment called a slab roller.

Wheel-throwing: Making a form using the potter’s wheel, a revolving horizontal disk on which clay is shaped.

Shaping Techniques:

Compressing: Applying pressure to clay to achieve a more dense clay body. Technique used to reinforce vulnerable areas that may crack or cause problems.
Paddling: Shaping a soft or medium leather-hard piece by gently hitting with a wooden paddle to achieve the form you want. Sometimes the paddle is textured to create flat facets or to resolve irregularities in the surface.

Trimming: Removal of excess clay at leather hard stage. You can trim something that’s been wheel-thrown or a hand-built piece.
Slipping and Scoring: two terms used together to describe how to join two pieces of clay together.
- Slip = A fluid suspension of clay and other materials in water used in combination with scoring to attach moist clay together.
- Score = Scratching the clay surface in a cross-hatched method. Used in combination with slip to join 2 pieces of clay together securely.

A Note on slipping and scoring: the more even the two pieces of clay are (in thickness and water content) the better, because they’ll shrink at the same rate. But it’s sometimes necessary to slip and score clay together that ISN’T exactly the same - like when you’re building a tall piece and need the bottom half to harden to support the top half, or attaching a handle to a cup. You can put plastic over the piece after you’ve joined the pieces together so they will have time to dry at the same rate.

Wedging: The process of working the air pockets out of the clay. Wedging also aligns and rearranges clay particles to help build work.

GENERAL CLAY TERMINOLOGY

Clay: A fine-grained mineral that contains aluminum silicate - formed when igneous rocks break down.)
Earthenware: A clay-body that is made to be fired at a low temperature. Its structure is is more porous (more space between the particles), permeable and fragile than stoneware or porcelain clay bodies.

Grog: Ground up bisque added to a clay body to decrease shrinkage and add strength & workability.
Plasticity: The property of clay that allows it to be shaped and to hold its shape. This is what makes clay different than plan dirt or soil.
Porcelain: A clay body high in kaolin that can be fired to extremely high temperatures to vitrify. Originated in China.
Shrinkage: Contraction of clay during the drying process caused by loss of water, also causing the clay to become more dense.
Stoneware: A grogged clay body requiring a high firing to vitrify.

CLAY EQUIPMENT

Banding wheel: A revolving wheel-head which sits on a pedestal base. It is turned by hand and used for finishing or decorating pottery
Bat: a flat circular piece of wood, plaster or particle board that you can attach to the wheel-head to throw clay on. Useful for throwing plates or bowls where it’s hard to remove the piece from the wheel-head without distorting the form.
Extruder: A tubular device for making shapes by forcing soft clay through dies. Useful for making coils.

Pugmill: A machine used to mix clay into a moist workable consistency.
Slab roller: A device for rolling out flat, uniform sheets of clay.
Slurry Barrel: Generally a trash can where used clay is deposited for the purpose of recycling.
Wedging table: a table made of plaster to wedge clay on. Useful for taking water out of clay if it’s too wet to work with.
Toolkit: a toolkit usually comes with the following tools:
- needle tool - for scoring clay
- wood knife - for compressing and carving into clay, sometimes used for trimming extra clay
- feddling knife - good for cutting slabs of clay
- wire tool - for faceting or cutting clay
- metal or wood rib - for smoothing clay
- sponge - for wetting or smoothing clay
- trimming tools - good for fluting and trimming leather hard clay to create designs or thin a piece.

DECORATION TERMINOLOGY

Darting: cutting pieces of clay out of the side of a form and rejoining the sides together to create a different shape.
Decorative Slip: Liquid clay with a stain or oxide added for decorating.

Faceting: A method of altering the shape of a round pot by cutting or shaving the wall (with a cheese cutter-like tool) to create a multisided form. This should be done when the pot is soft but firm and the form should be thicker than usual since you will be extracting clay from the surface.
Fluting: Using a carving tool to extract ribbons of clay leaving a trough-like appearance on the surface of the piece. This should be done when the pot is soft but firm.
Mishima: A technique of inlaying slip, underglaze, or even clay into a contrasting clay body, the main clay body of the pottery piece.
Paddling: Shaping a soft or medium leather-hard piece by gently hitting with a wooden paddle to achieve the form you want. Sometimes the paddle is textured to create flat facets or to resolve irregularities in the surface.
Sgraffito: Scratching through a layer of slip to reveal another clay body beneath.

Slip trailing: The application of lines of decorative slip using a fine-pointed dispenser. Decorative slips are generally applied to leather-hard work.
Sprigging: A relief decoration added to the clay surface. Sprigs are usually thin slabs formed in a mold.
Stamping: Design made by impressing an object into (set up, but not sticky) clay.
Stenciling: A traditional method for applying stencils is to cut or tear paper shapes, adhere them to leather-hard clay and then apply slip over the entire clay surface to create a design.
Stain: A manmade ceramic colorant produced by fusing a variety of ceramic ingredients to obtain colors not found naturally. Stains can be used for coloring decorative slips.

Oxides: A combination of an element found in nature with oxygen in powder form. Oxides are used for coloring decorative slips.
Underglaze: A commercially formulated liquid color used under a glaze. They are stable and keep their shape/design under a glaze, unlike stains that can sometimes shift in a glaze-fire.

FIRING TERMS

Bisque fire: the first firing clay goes through. This firing turns clay into ceramic (through the ceramic change — see above).
Ceramic change: the slow process of clay becoming ceramic. Clay which is exposed to heat 600°C / 1112°F, losses its chemically bound water molecules and can no longer be broken down by water. Once this change has occurred it cannot be reversed.
Cone (or pyrometric cone): small ceramic pyramids that are made to melt at specific temperatures. They are used to measure kiln heat - and also describe different clay and glaze types (for example, we use cone 6 clay in this class. Do not bring cone 04 clay as it will melt when fired to cone 6 temperature and ruin our kilns!)
Glaze fire: The firing to the temperature at which glaze materials will melt to form a glasslike surface coating.
Kiln: A heating chamber for hardening and maturing the clay and glaze.

Kiln wash: A coating for kiln shelves to protect them from glaze drippings
Maturity: The temperature & time in a firing at which the clay reached the desired condition of hardness & density. (for example: “The piece reached maturity.”)

GLAZING TERMS

Crawling: Term used to identify a glaze defect in which glaze pulls away or crawls from the bisque. Usually caused because of dust or applying glaze too thick.

Dry foot: The place where your work comes in contact with the kiln shelf that has been cleared of all glaze.
Glaze: Any vitreous coating made of fine ground minerals that has been melted onto the clay surface in the kiln.
Glossy: A glaze with a shiny and smooth, bright high gloss and a highly reflective surface
Matt (or matte): A glaze surface that is dull/soft, reflecting little shine. The opposite of glossy.

Opacity: How transparent or opaque a glaze is. Knowing this will help you get the effect you want for the surface of your piece. Examples of opacity are:
- Opaque: A glaze that covers the surface underneath, where most colors (underglazes or stains) will not show through. (think frosting on a cake).
- Transparent: The ability to see through a glaze to the surface, texture, or color underneath. The color underneath might slightly tinted by the overlying glaze color that changes the appearance only a little. (for example you can objects see through a colored stained-glass window).

Thermal Shock: Cracks in a ceramic body caused by sudden heating or cooling.

Vitreous: Impervious (waterproof) surface of the clay - usually a surface that’s been burnished or fired. Vitreous clay cannot accept glaze.
Wax resist: Liquid wax that is painted onto the clay surface or onto the glaze so that anything on top of it is “resisted” or won’t stick. Once you paint wax resist onto the surface of your piece, anything underneath it is protected or “frozen” until the wax is burned off in the kiln. Wax is used to create a dry foot on the bottom of a piece, or to protect an area of glaze so you can layer over it and create patterns.

STUDIO TERMINOLOGY:

Clay dust: A very fine dust that can linger in the air for days. Prolonged exposure to clay dust can cause silicosis or lung disease. To prevent clay dust from accumulating in the studio, we clean up clay using water, a wet mop or wet sponge. Never sweep in the clay studio!

4 Bucket Glaze System: The system we use to rinse off tools that have glaze on them, so these chemicals don’t get into our waterways and injure wildlife. We use the glaze collected to make paver bricks for the garden/outdoor use.
Paver Brick: A brick made from sink scrap & glaze waste in an effort to render chemicals in the glaze inert by firing it in the kiln. Technique used to prevent glaze chemicals from going into our landfills and waterways.
Sink Trap: the system we use to rinse off tools that have clay on them, so the clay doesn’t get into the sinks and water supply.