Pinch pots with a 4 mm wall, and how to join two into a closed form

Pinching is the oldest pottery technique and the one most often taught badly. The version taught in schools — press a thumb into a ball and rotate — produces walls of 10 mm at the base and 3 mm at the rim. The version that works keeps the wall at 4 to 5 mm throughout by alternating the direction of the pinch, and it makes a form that survives firing instead of one that cracks at the rim two days later.

Starting mass and the alternating pinch

Use 300 g of clay for a 10 cm pinch pot. Anything larger and the wall has to be thinner than 4 mm to reach the height, which is where pinching stops working. Roll the ball smooth, then press the thumb of the dominant hand into the centre, stopping 8 mm from the bottom.

Pinch outward between thumb inside and fingers outside, working in a spiral from the base to the rim. The key is to turn the ball a quarter turn after each pinch and to alternate which hand does the pinching every two spirals. Working one direction only drags the clay into a spiral and thins one side of the wall consistently.

Keeping the wall even

Every three or four pinches, stop and feel the wall between finger and thumb at four points around the circumference. Any point that feels noticeably thinner gets skipped on the next pass. This sounds fussy; it takes ten seconds and it is the difference between a pot that fires clean and one that cracks at a thin spot.

The rim thickens naturally as you pinch outward, because the wall compresses at the top. Let it, then roll it inward between finger and thumb at the end and give it a final pinch to 5 mm. A pinched rim left at 6 to 7 mm looks heavy and chips less, so do not thin it for appearance.

Joining two pinch pots into a closed form

Pinch two bowls of the same diameter — check by holding them rim to rim; a 3 mm difference will show as a step after joining. Let both stiffen for 30 minutes to leather-hard. Score both rims in a crosshatch, apply slip, and press them together with a slight rotation so the two rims key into each other.

Then roll a coil of the same clay 8 mm thick and press it around the inside of the seam with a wooden tool, exactly as with a slab corner. The inner coil is doing the structural work. Outside, blend the seam smooth with a rib so the join does not show through the glaze as a line.

Cutting the opening and drying

For a closed form, cut the opening after the seam has set: with the pot resting on a foam pad, cut a 3 cm circle with a needle tool, then smooth the cut edge with a damp finger and compress it with a rib. A cut edge that is not compressed is a crack waiting for the bisque firing.

Dry pinch pots upside down on a board for 24 hours. They are small and their walls are thin; a pinch pot in a draught will be bone dry in six hours and will have cracked at the rim by then. Then bisque to cone 03 and glaze as normal.

Steps

1. Roll 300 g of clay into a smooth ball and press the thumb of the dominant hand into the centre, stopping 8 mm from the bottom.
2. Pinch outward between thumb and fingers in a spiral from base to rim, turning a quarter turn after each pinch.
3. Alternate the pinching hand every two spirals to keep the wall from spiralling.
4. Feel the wall at four points every three or four pinches and skip the thin points on the next pass.
5. Roll the rim inward and give it a final pinch to 5 mm — do not thin it below that.
6. For a closed form, pinch two equal bowls, stiffen both 30 minutes, then score, slip and press the rims together with a rotation.
7. Press an 8 mm coil around the inside of the seam, blend the outside smooth, then cut a 3 cm opening and compress the cut edge.
8. Dry upside down on a board for 24 hours, away from draughts.

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.

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