Pottery

Pottery — Wheel Throwing, Trimming, and Glazing

Overview

Pottery is the process of forming clay into objects by hand, drying them, and firing them in a kiln at temperatures between 1,800°F and 2,400°F to permanently harden the material. Of all the craft disciplines, wheel throwing is among the most dependent on tactile feedback — the pressure of the clay against your hands, the resistance as the wall thins, the subtle wobble that tells you the form is going off-center. The instructions below describe what to do. Developing the feel for how to do it requires 20–50 hours of practice at minimum.

Prerequisites

• Potter's wheel (electric kick wheel, 1/2 HP minimum). Set it at a comfortable height — your elbows should be roughly level with the wheel head when seated.
• Clay body appropriate to your firing temperature. For beginners, a mid-fire stoneware (cone 5–6) with some grog (ground fired clay particles mixed into the body for strength and texture) is forgiving and versatile. A 25-lb bag is enough for a dozen small forms.
• Bat pins and bats (round boards that attach to the wheel head for easy removal of finished pieces)
• Wire clay cutter (a twisted wire with two toggles)
• Wooden rib, metal rib, and a rubber kidney
• Needle tool, trimming tools, and a sponge
• Bucket of water (for keeping hands wet) and a bucket of slip (for recycling)
• Kiln access for bisque firing (cone 04–06, approximately 1,830–1,940°F) and glaze firing (cone 5–6 for mid-fire, approximately 2,160–2,230°F). See references/CONE-CHART.md for the full cone temperature chart, kiln ramp schedules, and glaze defect troubleshooting.
• Glazes, either commercial or studio-mixed. Always test glazes on sample tiles before committing to a finished piece.
• Patience of a kind that is different from other crafts. In woodworking, a mistake can sometimes be sanded out. In pottery, a mistake while throwing usually means starting over. The clay does not care about your feelings.

Wedging

Before throwing, the clay must be wedged to create a uniform consistency and remove air pockets. Air trapped in the clay expands during firing and can blow holes in the wall of a piece or cause it to explode in the kiln, potentially damaging other work.

Cut a 1.5–2 lb piece from the block with a wire. Shape it into a rough ball. Place it on a plaster or canvas surface (not wood — the clay will stick). Push the heel of your dominant hand into the clay at a slight downward angle, compressing it forward. Pull the far edge back toward you and rotate the mass about 30 degrees. Push again. Repeat this ram's head motion 30–40 times, maintaining a consistent rhythm. The clay should develop a spiral pattern in cross-section.

Alternatively, use the spiral wedging technique: press with both palms, rotating the clay in a cone shape with one hand while the other applies pressure. This is more efficient for larger amounts but harder to learn.

When finished, the clay should be smooth, uniform, and free of visible air pockets when cut in half with a wire.

Centering

Centering is the foundational skill of wheel throwing. An off-center lump of clay produces an off-center pot, and an off-center pot cannot be thrown thin or evenly. Centering is the step that takes beginners the longest to learn, typically several sessions of dedicated practice before it becomes reliable.

Throw the ball of clay firmly onto the center of the bat. The clay should stick on impact. Wet your hands and the clay. Start the wheel at medium-high speed (for a right-handed thrower, the wheel turns counter-clockwise).

Brace your elbows against your body or your thighs. This is critical — your arms must be anchored. If your arms are floating free, every slight variation in the clay pushes your hands around and you cannot apply consistent force.

Place both hands on the clay. With your left hand on the left side and your right hand on top, push inward and downward simultaneously. The goal is to force the clay into a smooth dome centered on the wheel head. You are not shaping the clay at this stage — you are eliminating wobble.

The clay is centered when, with the wheel spinning, your hands resting lightly on the surface feel no lateral movement. The surface should be smooth and the form should appear to be perfectly still even though the wheel is turning.

If the clay continues to wobble, the most common cause is inconsistent hand pressure. You are unconsciously adjusting to the wobble instead of overriding it. Lock your elbows, maintain steady pressure, and let the wheel do the work of bringing the clay to your hands.

Opening

With the clay centered and the wheel at medium speed, wet your hands. Place both thumbs on top of the dome and press downward into the center, leaving at least 3/8" of clay at the bottom (this will become the floor of the pot). Go straight down, not at an angle.

Open the floor by pressing your thumbs outward from center toward the 8 o'clock position (for a right-handed thrower), drawing the clay outward to establish the diameter of the interior. The exterior should not move — only the inside is opening. Use a fingertip or a wooden rib to flatten and compress the floor. An uncompressed floor is prone to cracking as it dries.

Pulling Walls

This is where the pot takes shape. The wall of clay between the interior and exterior of the form must be thinned and raised by pulling upward with even pressure.

Slow the wheel to medium or medium-low speed. Place the fingers of your inside hand (typically the left) against the interior wall near the floor. Place the fingers or knuckle of your outside hand directly opposite on the exterior. Squeeze gently — the clay between your hands should be slightly compressed but not pinched thin in one spot.

Pull upward slowly. Your hands should move from the base to the rim in a single smooth motion taking about 3–5 seconds. The upward pull thins the wall and raises the height of the form. Each pull should thin the wall by about 1–2mm.

Apply more pressure at the base (where the wall is thickest) and less as you approach the rim (where the wall is thinnest and most vulnerable to collapse). The base always stays thicker than the top — you can trim excess from the base later, but you cannot add clay to a rim that has gotten too thin.

Repeat the pull 3–5 times, wetting your hands between each pull. A beginner's instinct is to try to achieve the final wall thickness in one or two aggressive pulls. This usually results in the wall tearing, the rim going off-center, or the form collapsing outward. Gradual, consistent pulls produce a better result.

The target wall thickness for a functional mug or bowl is approximately 1/4" (6mm). For thinner, more refined work, 3/16" (5mm). Below that, the piece becomes fragile to handle while wet and difficult to trim.

Shaping

Once the walls are pulled to height, shape the form by adjusting the profile. To belly a form outward, apply gentle pressure from the inside with no opposing pressure on the outside. To collar a form inward (narrow the opening), cup both hands around the exterior and squeeze gently while the wheel turns, moving upward from the belly to the rim.

Use a wooden rib held against the exterior to smooth the surface and refine the curve. A metal rib gives a sharper, more defined profile.

Define the rim by placing a wet chamois leather strip or your wet fingers over the rim edge and gently compressing while the wheel turns. A clean, even rim signals a well-made piece.

Cutting Off and Drying

Stop the wheel. Hold a wire cutter taut against the bat surface and draw it under the base of the pot from back to front in one smooth motion. Do not lift the pot — it is still soft and will deform. Remove the entire bat from the wheel and set it aside.

Allow the pot to dry on the bat until it is firm enough to handle without distorting — typically overnight in a temperate studio, longer in humid conditions. This stage is called leather-hard: the clay holds its shape but can still be carved, trimmed, and attached to. A fingernail pressed into the surface will leave a mark but not a deep gouge.

Trimming

Invert the leather-hard pot on the wheel and center it. Secure it with small coils of clay pressed against the rim to hold it in place, or use a chuck (a bisqued cylinder that the pot nests in).

Using a trimming tool (a looped ribbon of steel on a handle), trim the excess clay from the base and foot. Spin the wheel at medium speed and hold the tool against the rotating form, shaving off thin curls of clay. Create a foot ring — a raised rim on the bottom — by trimming the area inside the foot lower than the ring. The foot ring serves two purposes: it provides a stable base, and it keeps the bottom of the pot off the kiln shelf during glaze firing (glaze that touches the shelf fuses to it permanently).

The foot ring should be about 1/4" wide and the floor should be an even thickness. Tap the base with your knuckle — it should sound consistent. A thick spot sounds dull; a thin spot sounds hollow.

Handles

For a mug handle, roll a thick coil of clay (about 3/4" diameter) and pull it into a strap: hold the coil vertically in one hand, wet the other hand, and stroke downward repeatedly with gentle pressure, rotating the coil slightly between strokes. The coil thins into a strap with a comfortable cross-section — slightly wider than it is thick, with a subtle curve from your fingers.

When the strap is the right thickness and length, cut it free and lay it on a board to stiffen slightly. Attach it to the leather-hard mug by scoring both the mug surface and the handle ends with a needle tool, applying slip (liquid clay) to both scored surfaces, and pressing firmly. Smooth the join with a fingertip or a small wooden tool.

Support the handle's curve with a finger while it sets. If the handle sags, it was attached too wet. If it cracks at the join, the mug was too dry. The mug body and the handle should be at the same moisture level when joined.

Firing and Glazing

Bisque fire to cone 04 (approximately 1,940°F). The ramp should be slow — no more than 200°F per hour through the water-smoking phase (212°F) to allow absorbed and chemical water to escape without generating steam pressure inside the clay walls. A kiln ramped too fast through this phase will produce cracked or exploded work.

After bisque firing, the clay is porous, hard, and permanent but not yet vitrified. Apply glaze by dipping, pouring, or brushing. Wax the foot ring and 1/4" above it before glazing to prevent glaze from reaching the kiln shelf. Any glaze on the foot must be cleaned off completely.

Glaze fire to the temperature specified by the glaze (cone 5–6 for mid-fire stoneware). Do not open the kiln until it has cooled below 200°F. Opening early exposes the glaze to thermal shock, which causes crazing (a network of fine cracks in the glaze surface).

Common Mistakes

• Fighting the wheel. If the clay is off-center, applying more force in a random direction makes it worse. Stop, recenter deliberately with anchored elbows and steady pressure, then continue. The wheel is stronger than you are — work with the rotation, not against it.
• Throwing with dry hands. Friction between dry skin and spinning clay tears the surface and pulls the form off-center. Keep your hands wet. Not dripping — a thin film of water is sufficient. Too much water weakens the clay.
• Pulling too fast. The instinct is to yank the wall up quickly. Fast pulls tear the clay or create thin spots. A slow, steady pull with even pressure does more work and produces a more uniform wall.
• Neglecting compression. Every joint, every floor, every rim needs to be compressed. Uncompressed clay dries unevenly and cracks. Press the floor flat with a rib after opening. Compress the rim after every pull.
• Drying unevenly. If the rim of a pot dries faster than the base (common in dry studios), the rim shrinks first and cracks. Cover pots loosely with plastic and dry slowly. A pot that takes three days to reach leather-hard will crack less than one that dries in six hours.