A pug mill leaves the clay de-aired but still laminated, and every laminate becomes a crack once the wall is pulled thin. Spiral wedging (the Japanese method, sometimes called the ram's-head because of the shape the mass takes) is the technique that scales past the 3 kg ceiling of rams-horn wedging. Half an hour of work gets a whole bag of stoneware to an even, plastic, genuinely air-free state — and the wire-cut test proves it instead of assuming it.

Cross-section of a 13 cm form: rim 11 cm, belly 12.5 cm, foot 6.5 cm. — **Vessel cross-section** — Section drawn to the rim, belly, foot and height recorded for this entry.
H 13 · Ø11 / Ø12.5 / Ø6.5 cm

What wedging actually has to fix

Two defects matter. The first is trapped air: a void 3 mm across becomes a bubble that blows a pinholed crater in the glaze or, worse, an S-crack radiating from the base of a pot. The second is moisture and particle alignment — clay straight from the bag is softer on the outside of the block than in the middle, and it carries the directional structure of whatever extruder pushed it out.

Spiral wedging addresses both at once. Each turn folds the mass over itself in a different orientation, so no two layers run parallel and any air pocket is sheared open and re-absorbed instead of compressed into a larger bubble.

The movement, in detail

Stand or sit with the wheel head or wedging board at hip height. Slap the 5 kg block down so it is roughly a cone, apex toward you. Your left hand stays low on the near face and pushes down and slightly away; your right hand comes over the top of the mass and pulls the apex forward and down toward you. The lump rolls a quarter turn with each pass.

The mistake almost everyone makes is pushing with the arms. The power comes from a straight left forearm and a pivot at the shoulder, not from the wrists. Once you are using the wrists you fatigue in 10 minutes and the batch gets uneven — the outside stays hard while the inside turns to paste.

How long, and when to stop

For 5 kg of stoneware at a working moisture of 18 to 20 percent, expect 45 to 60 complete passes, about 25 to 30 minutes. The clay is ready when it feels uniform: push a thumb in and the resistance should be the same at the centre as at the edge, and the surface should pull back at the thumb hole instead of tearing around it.

Dry stoneware stiffens as you work because water leaves the mass into the air and your hands. Once you are past 30 minutes, stop and wrap the batch in a plastic bag overnight rather than adding water. Water added at the end sits in pockets and produces the same blisters that wedging was supposed to remove. Rewetting is a slope you only have to step onto once to lose a batch.

The wire-cut test

Cut the wedged mass in half with a taut cutting wire, right through the middle, and look at both faces. You are looking for a face with no visible holes, uniform colour, and no streaks of lighter or darker clay. Any hole bigger than about 1 mm means another 15 passes; visible lamination lines mean the folds are running in one direction and you have been working in a circle instead of alternating.

Photograph the cut face and keep the picture with the batch. It is the only record you get — after the pot is fired, a crack in the base tells you something went wrong, but not whether it was the wedging.

Steps

Weigh the batch. Spiral wedging is reliable up to about 8 kg; above that divide it into two lots and wedge them separately, then join with a full weld.
Slap the block into a cone on a plaster or canvas-covered board, apex tilted roughly 20 degrees toward your body.
Left forearm straight and braced, push down and away on the near face while the right hand draws the apex forward and over.
Let the mass roll a quarter turn per pass. Count passes out loud if you need to — 50 is the target for 5 kg.
Keep the working surface free of loose slip. Wipe the board with a damp sponge every 10 passes so the mass grips and rolls rather than sliding.
After 50 passes, wire-cut the block, inspect both faces, and add 15 more passes if you see voids.
Wrap in two layers of plastic, folding the open edge under. Store at 20 degrees Celsius, away from a concrete floor that will wick moisture out of the bottom.

Where it goes wrong

Wetting your hands to make the clay feel smoother. The moisture goes into the surface only and creates a slip layer that will separate in the wall.
Working on a wet board. The mass slides instead of rolling, so the folds never fully invert and lamination survives.
Wedging reclaimed or very wet clay straight from a slaking bucket. Let it dry on plaster to the plastic state first, or you will be pushing water around for an hour.
Mixing two bodies into one batch to use up scraps. Under 10 percent of a body within one cone of the main clay is safe; more than that and the shrinkage mismatch opens cracks at the rim.

Symptom and cause
Symptom	Cause
S-cracks radiating from the base of a thrown pot	trapped air or a lamination in the wedged batch; cut the next batch to check.
Pinholes clustered in one area of a fired glaze	a single air pocket that reached the surface during firing.
Walls that tear in a horizontal line while pulling	moisture gradient left over from insufficient wedging, so the inner and outer layers move at different rates.
A rim that cracks in a spiral	the fold direction was never reversed, so the whole pot shares one plane of weakness.

Recipe and schedule numbers here were recorded on the workshop’s own kiln. A different kiln, a different thermocouple position or a different clay batch will move the result, so treat every firing schedule as a starting point and keep your own log beside it.

Same cone — Cone 6

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Spiral wedging a 5 kg batch without trapping air

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