The States of Clay: Five Conditions, and What Each One Will Let You Do

PLASTIC clay takes a shape and holds it. Throwing, pinching, coiling and slab building all happen here, and so does joining — the clay is wet enough that two pieces scored and slipped together actually knit. LEATHER-HARD is the state people underuse. It is firm enough to pick up and turn over, soft enough to carve, trim and cut cleanly. Handles are attached here, feet are trimmed here, and carved decoration is done here because it does not smear. BONE DRY is pale, cool to the touch, and extremely fragile. Nothing can be done except sponging the sharpest edges and loading the kiln. Clay that still feels COLD against your cheek is not bone dry, however dry it looks — and firing it wet is the other way pots explode.

A pot dries from the outside in and from the rim down, because those parts are most exposed. Thin rims, handles and feet dry first, shrink first, and are held back by the wetter body they are attached to — which is exactly how cracks start. So cover the work loosely with plastic and let it dry SLOWLY and evenly. A day or two under plastic, then a day in the open, beats a morning in a draught every time. Cover the parts that would otherwise race ahead. A strip of plastic over just the rim, or over the handles, lets the thick body catch up — which is the same principle as the thin-bits-burn-first problem in the forge.

Two pieces of clay join properly only when both are the same state and wet enough for their particles to interlock. Score both faces with cross-hatching, wet them with slip made from the SAME clay body, press together and work the seam. Slip from a different body is a common and avoidable mistake: two bodies shrink by different amounts, so the joint is pulling itself apart from the moment it dries. A handle attached to a leather-hard pot is the classic failure. The pot has done most of its drying shrinkage and the handle has not, so the handle shrinks onto a body that cannot move and cracks at the join. Attach at the same state, or bring the handle back to match.