Wedging Clay Properly to Avoid Air Pockets

Why Air Pockets Ruin Pots

Trapped air is one of the most common reasons a piece cracks, bloats or explodes in the kiln. When clay is fired, any moisture inside a pocket turns to steam, and that steam expands with enormous force. At 1000°C and above, a pocket the size of a pea can blow a pot apart or leave a disfiguring split. Even smaller voids cause hairline cracks that only appear after glaze firing. Wedging is not just about mixing clay; it is about removing those voids and making the whole body consistent. Spiral wedging and ram’s head wedging are the two traditional methods that do this reliably. They also even out moisture, soften hard spots and align clay particles so the clay throws, coils and slab-builds without fighting you. If you have ever lost a favourite piece in the kiln, the culprit is often a pocket of air that was never properly pressed out.

Setting Up Before You Wedge

Good wedging starts with the right consistency. Clay that is too wet will stick to your hands and the board, trapping air as you fold. Clay that is too dry will crack and resist folding. Aim for a firm but pliable feel, like chilled butter. If you are reclaiming clay, spread it on a plaster batt for a few hours to firm up, turning it once. Work on a plaster batt or a canvas-covered board, not bare wood that grips and tears the clay. Stand at a comfortable height, ideally with the board at waist level, so you can use your body weight rather than just your arms. Cut your clay into manageable blocks – around 1–2 kg for spiral wedging, larger for ram’s head – using a wire cutter. Keep unused clay covered with plastic so it does not crust over while you work. A damp cloth over the block helps too.

Spiral Wedging: The Everyday Method

Spiral wedging, sometimes called kneading, is ideal for most stoneware and earthenware bodies. Place your block on the board. Press the heel of your right hand into the clay, pushing down and slightly forward. Use your left hand to guide the clay as it stretches. Then fold the far edge back over towards you, give the block a quarter turn, and repeat. The motion creates a spiral pattern through the clay, which is where the name comes from. Work rhythmically, pushing and folding, turning, pushing and folding. For a 2 kg block, aim for 60–80 repetitions. You will feel the clay become smoother and more even. Do not fold loosely – press firmly enough that each fold merges into the mass without trapping a layer of air. If you feel a soft spot or a hard lump, keep wedging. The clay is ready when it feels consistent all the way through and a wire-cut slice shows no holes.

Ram’s Head Wedging for Stiff or Large Batches

Ram’s head wedging is a more forceful method, excellent for stiff clay, reclaimed scraps or large amounts you plan to divide later. Shape your clay into a rough cone or dome. Lift it and throw it down onto the board with a firm, flat motion, then press down with both hands as if ramming. Fold the mass over, give it a quarter turn, and repeat. The action compresses the clay and drives out air pockets through sheer pressure and impact. Use your body weight, not just your shoulders. Twenty to thirty good repetitions are usually enough for a 3–4 kg batch. This method also helps align particles, which reduces warping during drying and firing. Keep the clay moving so you do not create a flat, over-compressed base. If the clay starts to crack at the edges, it is too dry – sprinkle a little water on your hands, not directly on the clay, and continue.

Testing and Troubleshooting

How do you know when wedging is done? Cut the block in half with a wire cutter and look at the cut faces. You want a smooth, even texture with no visible holes, soft patches or streaks. Pinch off a small piece and roll it between your palms – it should feel uniform, not crumbly in places. If you see voids, re-wedge. Common mistakes include under-wedging (especially with reclaimed clay), over-wedging until the clay becomes stiff and tired, and wedging wet clay that smears instead of folding. Remember that wedging is not a one-off job: if you store clay for weeks, it can settle and trap new air. Give it a quick spiral wedge before use. For throwing, coning up and down on the wheel also removes air, but it is no substitute for proper wedging. Consistency is key – a well-wedged clay body will reward you with fewer cracks, better glaze fit and pieces that survive the kiln. Make wedging a calm, regular part of your making routine, and your pots will thank you.