Gary Jackson: Fire When Ready Pottery
A Chicago potter’s somewhat slanted view of clay & play

Ball Clay
A fine-grained, plastic, sedimentary, white or near-white firing clay. Used as a glaze ingredient and added to clay bodies to increase plasticity.

Banding Wheel
A hand-operated turntable used to rotate your work during the decoration process… my banding wheel is a Shimpo – and was my first “pottery” Christmas gift from my parents… sold to them by Steven Lee, one of my wheelthrowing teachers at Lillstreet years ago!

A rigid, flat disc placed directly onto the wheelhead and held in place with clay or placed on top of screwheads. When the throwing is finished, the bat is lifted off the wheelhead to avoid damage or warpage created by lifting the piece itself. I prefer to use plastic bats as they are more lightweight and come in a variety of sizes. Most frequently, I use 7″ square bats for mugs, vases, soap dispensers, oil lamps & more.

Extremely plastic clay formed by decomposed volcanic ash and glass. Used to render short clays workable and for glaze suspension. So if your glaze is settling into a hard layer at the bottom of the bucket, a bit of Bentonite might do the trick to keep it liquid longer!

Sadly, it’s not another episode with the Soup Nazi” on “Seinfeld”…
An initial kiln firing in which the clay sinters without vitrifying, and though very porous, will no longer soften in water. The bisque firing makes a pot ready to be glazed.. and then fired again. I bisque most of my work to cone 06.

A glaze defect where the fired glaze surface contains bubbles, which often break open to leave sharp-edged craters in the surface. Which I would consider to be no longer food-safe – as it could trap bacteria in the “craters” or be sharp to the touch. And that would be bad…
Or it could be the blistering that comes after touching a really hot part of the kiln…
and that would be bad too!!!

A firing defect where blisters form within the clay body, raising large lumps to the surface. This is caused by expansion of gases within the clay as a result of excessive early reduction, excessive bisque-firing, or over-firing. Much like the feeling a couple hours after the annual Thanksgiving meal.

Body Reduction
The period of reduction atmosphere induced between cone 012 and 08 to bring out iron color and speckles in the clay body, especially in high-fire stoneware. Maybe I need a little more reduction atmosphere to work on my own “body” reduction?!

Bone Dry
Completely dry and very brittle state that clay must reach before bisque firing. If the clay is fired before becoming bone dry, there is a chance the water will expand during firing and “explode” the pot. This stage of the process is also referred to as “greenware.”

In glazes, the tendency of certain glazes to give different colors in thick or thin areas – where the color appears to “break” from thick to thin. Take temoku glaze for example, where the shiny black glaze “breaks” to a nice brown color on the edges & sharp points. In all other pottery aspects… “breaking” is a very bad thing, but not this time!

Method of achieving a shine by rubbing clay or slip with a hard smooth object. After trimming the bottom of a pot, I always burnish the surface smooth before finishing to avoid sharp edges that might scratch your tabletops. I’ve been using the same wood knife tool since I started throwing, and it is now worn away to half as long as it was when I started. Kinda like rubbing that popsicle stick on the pavement when you were a kid to get a sharp point!

A classic east Asian transparent or translucent glaze with small percentages of iron, or copper, or chrome, giving a range of soft greens, blue-greens, and gray-greens. It’s a very “safe” glaze that is very forgiving – drips & runs all blend together really well.

The first critical step in throwing when the clay is formed into a symmetrical lump prior to opening it up and lifting the walls. If the clay is centered on your wheel, it spins smoothly without any wobble or wiggle. Of course, many people find this the toughest skill to master – and of course, it is also the first!

A very soft, pliable animal skin used wet to smooth the edges of wet clay surfaces. If no chamois is available, a small piece of wet plastic will work in the same way… but don’t let the transparent plastic “disappear” into your reclaim – because it will undoubtedly “reappear” when you least want it to!!!

A reuseable, bisque-fired form upon which leather-hard pots can be inverted for trimming. Most look like a small nuclear reactor with a hole on the top and bottom. That way, the form can be flipped to accommodate a wider range of pot sizes.

Coil Building
A forming method using rope-like coils of clay, assembled in successive layers to build up walls of vessel.

In wheel-throwing, it’s using you finger pressure on the bottom of the pot to reduce the moisture and create a stronger & denser floor. Lack of compression will often result in the dreaded S-crack in the bottom.

Cones, Pyrometric
Small triangular cones made of ceramic materials that are compounded to bend and melt at specific temperatures to determine when a firing is complete. They measure heat work of the firing, both temperature & duration.

A glaze fault where glaze recedes away from an area in firing leaving bare clay to show through. Usually caused by dusty, dirty or oily surface beneath the glaze… or simply too much glaze!

Very fine cracks in the glaze surface. While technically a fault in glazed wares, it is often sought after for its appearance. Typically caused by different stresses between clay body and glaze.

Creative Camouflage
A technique I encourage my students to use… to hide or cover-up a mistake to make it appear as though you intended to do it. If a pot is a little wonky… bend it, twist it, alter it. Make it look like it was intended to look like that.

Crystalline Glazes
Glazes in which significant crystal structures form in the surface of low-alumina glazes seeded with zinc or titanium. Crystalline glazes feature large, visible crystal development during the cooling process.

Low-fired ware, usually still porous after firing. Must be sealed with vitreous glaze to be functional. The most popular form of earthenware is terra cotta.

Slip formulated with less raw clay content in order to reduce drying shrinkage, to allow application to bone-dry or bisque-fired clay. It’s basically halfway between a glaze and a clay. Usually used to harden the surface, change the texture or alter the color of the clay.

Machine that forces clay through a die to produce tubes of extruded clay shapes… think Play-Doh Fuzzy Pumper #9.

Decorative technique involving cutting or paddling flat facets in the clay surface. Extra cool surfaces especially when cut with a wiggly-wire!

Fettling Knife
A long, tapered knife useful for cutting or trimming clay.

Refractory clay used to manufacture bricks, muffles, saggers, etc. Plastic enough to be used as a clay body ingredient.

A decorative result of soda firing where the surface colors transition from one to another based on where the soda affected the surface.

A decorative technique involving carving or forming vertical flutes or grooves in the surface of a piece. You can use a taut section of your wire tool, or a metal rib, or my favorite… an old wired cheese slicer with the roller removed. Or, even better, if you want groovy facets, use a spring that has been stretched out to be a wavy wire!

The low-melting component in clay or glaze that reacts with silica to form glass.

Partial or complete glaze that is melted and reground for the purpose of eliminating toxic effects of lead or the solubility of borax, soda ash and so forth.

Depositing a very thin layer of metal on a glaze. Never done it. Never seen it. Seems kinda dangerous??? Like there’s metal vapors floating around the kiln???

A coating of powdered ceramic materials usually prepared and applied in water-suspension, which melts smooth and bonds to clay surface in glaze firing.

Glaze Firing
The kiln firing in which glazes are melted to form a smooth, glassy surface.

Glaze Fit
The matching of glaze to clay body in terms of composition and coefficient of expansion so that it will adhere permanently.

Glaze Resist
Decorative technique where resist materials are applied to prevent glaze from adhering to certain areas. Wax or latex are frequently used as a glaze resist.

Any dry, unfired piece of clay. You can usually find shelves & shelves of greenware in my studio waiting to be bisque fired.

Filler or tempering grit added to clay bodies to reduce shrinkage and give structure for throwing and handbuilding. It is the scratchy stuff that might rip up the side of your hands when you are first learning to throw on the wheel.

High Fire
High temperature firing range typically cone 8 to cone 12, for firing stoneware or porcelain.

Decorative technique where textured or patterned materials or objects are pressed into the clay surface.

Decorative technique where a design is formed by cutting or carving shallow lines into the clay surface.

A “furnace” for firing ceramics. Made of refractory and insulating materials.

Kiln Furniture
Refractory shelves, posts, and stilts used in a kiln to support the wares. High-fire bricks are most frequently used in high-fire kilns. The bricks and the shelves are stacked and unstacked after every firing.

Kiln Wash
A refractory slip coating applied to the top surface of kiln shelves to protect against glaze runs. It’s typically a white slip formulated to stick to the shelf, but pull off easily if glaze runs off a pot during the firing. The object is that the kiln wash keeps the glaze run from ruining the kiln shelf.

Condition of the clay where it has stiffened… when it is still damp, but not sticky. Still damp enough to be worked further with carving, stamping, burnishing, joining, etc.

Low Fire
Low-temperature firing range typically below cone 02. Used for most bisque-firing and for glaze-firing terra cotta.

Thin metallic coating of glaze that produces iridescence. Usually done with a second glaze firing at a lower temperature.

Matte Glaze
Glaze featuring a dull, non-glossy surface.

That point in a firing where the clay has reached its maximum non-porosity and hardness and when a glaze has flowed and formed a strong bond with the clay. It has nothing to do with acting silly or pulling practical jokes!!!

An east Asian method of creating an inlaid effect by applying contrasting slip into a design incised in leather-hard clay. When the slip stiffens, the excess is scraped off to reveal the incised & filled pattern.

Oxide Stain
A mixture of coloring oxide and water, sometimes including a little flux, used as an overall patina or for overglaze brushwork.

Oxidation Firing
Any kiln atmosphere with an abundance of oxygen to combust the fuel and ozidize the ceramic materials. Includes all electric firings and any gas firing with adequate air to insure complete combustion of the fuel close to the burner.

Technique of shaping soft or medium leather-hard clay by gently hitting it with a wooden paddle (sometimes textured) to create flat facets or to resolve irregularities in the surface.

Paper Clay
Utilizing a clay body or slip containing paper pulp, which reduces shrinkage in the drying stage, and encourages extremely strong joints, allowing for unconventional attachments such as wet to dry. See my Link to ceramic artist Cory McCrory for beautiful examples of what can be done with paper clay.

Paper Resist
Decoration technique where strips of moist or adhesive paper are adhered to the surface to resist application of slip or glaze. Once covered with slip, the paper is carefully removed to reveal the masked design.

An overall thin wash of glaze or oxide stain, allowing the color and texture of the clay body to show through.

Glaze defect characterized by fine pinholes in the surface; often caused by pinholes already present in dry unfired glaze coating. Can also be caused by burst bubbles in glaze surface that are not given opportunity to “heal” at the end of the firing.

A quality of clay that allows it to be manipulated and still maintain its shape without cracking.

High-fired vitreous clay body – usually pure white or “eggshell” in color. Some porcelains may fire translucent where thin.

Refractory columns used in kiln furniture to support kiln shelves. Some call them bricks. But no matter what you call them, they are used to support the shelves in the kiln. As you load a kiln, you layer shelves with pots, raise the next shelf with posts to a height just above the height of the pots below. You stack the posts directly above each other so they can support the weight through the entire height of the stacked kiln.

Press Mold
A mold, usually plaster, into which moist clay is pressd to create multiples.

A machine similar to an oversized meat grinder, used to homogenize plastic clay bodies. De-airing pugmills have a vacuum attachment which effectively removes all air from the clay. Think “Play-Doh Fuzzy Pumper No. 9.”

Pyrometric Cones
Small, slender pyramidal-shaped indicators made of ceramic material formulated to bend at a specific temperature – standard method for determining maturing temperature of firing. Like clay and glazes, cones respond to temperature, duration and atmosphere of firing far more accurately than mechanical measurement.

Quartz Inversion
Abrupt expansion in heating an corresponding contraction in cooling that occurs in silica crystals in all clay and glazes around 1063-degrees, Greatest risk is in cooling high-fired wares and in re-firing previously high-fired wares.

A low-fire process originating in Japan. Involves placing glazed bisque ware into a kiln that is already up to temperature and removing the pieces with long handled tongs when it is red hot and the glaze has sufficiently melted. It is then sometimes placed in a carbon-rich atmosphere. Like a garbage can full of straw, newspaper, and other fun things that burn!!!

Profile of the firing of a kiln, including speed, duration, soaking periods, etc. of both heating and cooling cycle, as in firing ramp and cooling ramp.

Chemical reaction in which oxygen atoms are removed from a compound. Very scientific, huh? Think of it as reducing the amount of air in relation to the amount of gas. The flame is now unstable and looking for more air to make it more efficient. So the flame is searching for air anywhere it can find it – in this case, from the porous pots! They won’t be porous after the reduction firing because all of the air has been pulled out!

Reduction Firing
In fuel-burning kilns, it is the firing atmosphere with insufficient oxygen to completely combust the fuel, introducing abundance of unoxidized carbon and hydrogen, which extract oxygen molecules from surface of wares, altering appearances of clay and glaze. Still confused?… read the explanation above.

The quality of resisting the melting effects at high temperatures.

Material used in glazing an decorating that can be applied to surface to prevent adhesion of slip or glaze. Most frequently, a liquid wax is used on the bottom  of each piece to make it easier to wipe the glaze off the bottom before firing. The downside… wherever the wax may accidentally touch, the glaze will never adhere to… so wax carefully!

Wide, flat handheld tool used to shape, smooth and/or scrape clay surfaces. Typically made of wood, plastic or rubber and either rigid or flexible, with straight, curved or profiled edges.

S-shaped cracks that occasionally appear in the bottom of wheel-thrown pots, resulting  from inadequate compression of the bottom or excessive water left in the bottom. Occurs most often in fine-grain, gritless clay bodies, especially when thrown off the hump.

To rough up the surfaces of two pieces of clay prior to joining. After scoring, the pieces are attached with a bit of slip in between two scored areas. With the kids, we refer to it as “scratch & attach.”

Decorating technique achieved by scratching or carving through a layer of slip or glaze before firing to expose contrasting clay body beneath.

A classic Japanese glaze ranging from gray to white to orange, often containing spodumene or other sources of lithium or nepheline syenite. The orange color is achieved with thinner glaze coating when fluxes within the glaze activate the iron content in the clay body.

Serious and dangerous glaze defect where excessive glaze compression causes small razor-sharp chips of glaze to pop off along outer edges, corners and rims. All wares showing shivering should be thrown away. Cure is to slightly increase the flux, or decrease the silica, in the glaze.

Clay with insufficient plasticity – tends to fragment during forming.

Permanent contraction of the clay in both drying and firing stages. Stoneware has an average shrinkage rate of 12-15%.  Much like a swim in a cold pool… ha.

In heating clays and glazes, a solid-state reaction where particles stick together permanently and the mass can be considered “fired.”

Slab Roller
A mechanized, but usually manually operated, device for rolling out large uniform slabs of clay.

Clay suspended in water, usually the consistency of thick cream. May be colored and used to decorate surfaces, or may be cast into plaster molds to create ceramic forms repeatedly.

Slip Trailing
Application of decoration to wet or leather-hard clay by flowing on lines of slip with a fine-pointed dispenser, such as a rubber syringe or squeeze bottle.

I tell my beginning wheelthrowing class frequently not to worry about making perfect pots.
It’s a beginning class and they shouldn’t be too focused on perfection as they are making handmade objects. So the slogan goes like this… “If you want perfect pots, go to Pottery Barn.”

Slump Mold
A mold over which a moist slab of clay is slumped in order to create a vessel form.

Very thick clay slip, often used for joining clay pieces after scoring surfaces.

Soda Firing
An atmospheric firing technique where the final glaze effects are created by adding soda ash & soda bicarbonate into the kiln when it is close to its top temperature. The soda mixture vaporizes instantly, travels on the flames and leaves a “glaze” residue on the pots where the flames have touched it.

Surface decoration technique in which small, decorative coils or balls of clay are affixed to the damp or leather-hard surface, usually with a layer of slip. See my Link to ceramic artist Amy Higgason for beautiful examples of what effects can be created with sprigging.

Mixture of ceramic stains or pure coloring oxides (sometimes with a little flux) in water suspension, which can be used for overglaze brishwork, or as a patina on unglazed clay.

Decorative technique of pressing textured items into the clay to leave a decorative impression. I make my own stamps out of clay and bisque fire them before using them. Apparently… stamping is one of my favorite techniques, huh?

High-fired vitreous ware (above cone 8), literally as hard and durable as a stone, with slight or no absorbency.

Terra Sigillata
Ultra-refined clay slip that can give a soft sheen when applied to bone-dry wares and if polished or burnished while still damp may give a high gloss.

At the leather-hard stage, it is the removal of excess clay from a piece using any of a variety of sharp cutting tools. Most frequently, the pot is flipped over, centered and re-attached to the wheel. Then, while spinning rapidly, a sharp trimming tool is pressed against the piece to trim away the excess and create a refined “foot” on the bottom of the pot. I really enjoy trimming… I think it fits right in there with my “control issues.”

Colored slips formulated to have low drying shrinkage, allowing application to bone-dry or bisque-fired surface before glazing.

Reference to a material’s resistance to flowing. A viscous glaze flows less.

Fired clay that has fused together completely, so that the pores between particles are filled with glass and the body is impervious to water.

A soda-resistant clay mixture used to lift the pots off the kiln shelf during the soda firing process. Small balls of wadding are placed under every piece in the kiln so that the soda glaze does not adhere the pot to the shelf. Which also includes each & every single tile I place in the soda kiln… one by one… tile after tile… wad after wad.

Freeing the clay of air, and working the clay to a state of textural and moisture uniformity by an action of the heels of the hands and/or cutting & pounding.