Why a slab tray deserves proper attention

A tray is one of the most useful things you can make in a home studio. It holds your tools, carries biscuits to the table, corrals keys and coins by the door, and looks good on a shelf when it is empty. It is also a shape that punishes laziness. Slabs that are rolled unevenly warp in the kiln, seams that are not properly joined split open, and rims left knife-sharp make the finished piece feel like a piece of scrap.

The good news is that none of these problems are difficult to solve. They just need a bit of method. Get your slabs consistent, join your seams with real care, and spend a few minutes softening every edge — and you will have trays that look professional and feel lovely to hold.

Rolling slabs you can actually trust

Consistency is everything. A slab that varies between 6 mm and 12 mm will dry at different rates and pull itself out of shape, so set your thickness before the rolling pin touches the clay.

• Place two wooden battens or strips of MDF either side of your clay, around 8–10 mm thick for a tray. Roll across them so the pin rests on the battens at each end and compresses the clay to a uniform depth.
• Roll from the centre outwards, never back and forth over the same spot. Push the clay away from you rather than pressing down, which thins it unevenly.
• Rotate the slab a quarter turn every few passes, or turn it over onto a fresh piece of cloth. Clay that sticks to the board stretches, and stretched clay remembers.
• Finish by running a stiff rib across the whole surface in overlapping strokes. This compresses the particles, closes small tears, and gives you a surface that will not crack when it bends.

If your clay is very soft, let the rolled slab rest on a board for twenty minutes. It will firm up just enough to handle without distorting.

Shaping the tray and easing the corners

The simplest and most reliable tray is a flat base with four walls, or a shallow curved dish pressed over a hump mould. Whatever route you take, do your corner work while the clay is still soft. Sharp internal corners are stress points and awkward to clean; a rounded corner is stronger and easier to wipe out.

To form a box-style tray, cut the base slightly oversized, then cut the four wall strips to the same height. Before joining anything, take a damp sponge and gently press the inside of each corner of the base where the walls will sit. Now round that corner slightly with your thumb, easing the clay rather than squashing it. When you attach the walls, the clay will follow that soft curve instead of creasing into a tight fold.

For a curved tray, drape the slab over a plaster hump or even an upturned bowl lined with cloth. Let it settle under its own weight, then press the rim gently into shape with a damp sponge. Do not force it — if the clay fights you, it is too dry and needs a light misting and a rest.

Seams that will not split

Seams fail for one reason: they were never really joined in the first place. Slip painted onto a smooth surface sits on top of the clay rather than fusing with it.

• Score both surfaces thoroughly with a fork, a needle tool or a toothed rib. Make real scratches, not decoration.
• Apply a thick slip — the consistency of double cream — or a drop of vinegar-and-clay slurry. Press the pieces together and wiggle them slightly so the slip squeezes out at the edges.
• Blend the joint inside and out with a rib or your fingertip, pulling clay across the seam rather than wiping it away.
• Add a small coil of soft clay along the inside of each join and blend it in. This fillet does more for strength than anything else you can do.

Once the seam is blended, compress it with a rubber or wooden rib. Compressed clay is denser, drier and far less likely to open up during firing.

Softening the edges at leather hard

This is the stage that makes all the difference, and it happens when the clay has firmed up enough to handle without denting — usually a few hours after building, or the next morning if you cover the tray with plastic overnight.

Run a damp sponge around the rim with a light, rolling motion, letting the sponge round the edge rather than flattening it. Work along the whole rim in one continuous pass so you do not create flat spots. Then, with a piece of chamois leather or a barely damp fingertip, polish the rounded edge smooth. The clay is still slightly plastic at this point, so you can gently press out any wobble in the rim line.

Do the same for the outer corners of the tray, easing them into a soft radius. A tray with rounded corners is noticeably kinder to pick up and much less likely to chip if it is knocked.

Drying flat and firing without tears

Dry your tray slowly and evenly. Cover it loosely with a plastic bag for the first day or two, then lift the cover a little more each day. Rushing this stage is what causes warping and corner cracks.

Place the tray on a flat board and, once it is firm enough to move, turn it over so the base can dry as well as the top. A light weight — a board with a small book on top — on the flat base while it dries will keep it from curling at the edges. When it is bone dry, smooth any roughness on the rim with a fine abrasive pad or a little silicon carbide paper.

Fire slowly through the early stages of the bisque, and resist the temptation to fill the kiln too tightly. A tray that has been rolled evenly, joined properly and softened at every edge will come out of the kiln flat, strong and quietly beautiful — and you will find yourself making them in sets.