How to Throw a Plate That Doesn't Warp in the Kiln

A flat plate that comes out of the kiln with a gentle saddle or a raised rim is one of the most common frustrations in studio pottery. Hours of centering, opening, and pulling end in a piece that rocks on the table or refuses to sit flush. Warping happens when one part of the clay dries or shrinks faster than another, and the kiln then locks that imbalance into stoneware. The good news is that most warping can be prevented long before the bisque firing, with a combination of clay choice, throwing method, and patient drying.

Australia's varied climate actually makes this topic especially relevant. A potter working from a backyard shed in Brisbane deals with summer humidity that can keep a plate leather-hard for days, while someone in a Melbourne garage during a cold winter may see the same plate bone-dry in twelve hours. Studios along the coast in Sydney or Perth experience salt air that affects drying, and inland makers in places like Castlemaine or Adelaide must guard against the hot, dry winds that wick moisture from the rims first. Building a routine that responds to your local conditions is more reliable than following any single rigid timetable.

Before diving into technique, it helps to remember that a plate is essentially a very wide, shallow bowl with a thin floor. The wider and thinner the piece, the more any imbalance gets amplified during firing. Treat every step from wedging to the final glaze fire as part of one continuous process, and warped rims will slowly become the exception rather than the rule.

Choosing a Clay Body Suited to Wide Forms

Not every clay behaves well as a dinner plate. Highly grogged or heavily grogged stoneware can be forgiving in sculpture but tends to drag when you try to open a wide, smooth surface. A finer, slightly plastic body with moderate grog - usually labelled as a "throwing" or "tableware" stoneware - gives the best balance of workability and strength. If you are buying in Australia, suppliers such as Walkers Ceramics in Adelaide, Northcote Pottery Supply in Melbourne, and Pottery Supplies Queensland in Brisbane all stock blends specifically blended for flatware.

A practical approach is to keep a small log of which bodies warp and which hold flat. Note the batch number, the screen mesh size, and any additives like paper clay or molochite. Paper clay can dramatically reduce warping in wide forms because the burnout paper fibres leave a network of micro-channels that allow even drying. Local studio swaps and community colleges in places like the CAE in Melbourne or the Sydney Community College often host clay trials where you can test small amounts before committing to a full bag.

Clay bodies worth trialling for wide plates:

A fine porcelain blended with 5 percent paper fibre for very thin dinner plates
A mid-range white stoneware with 15-20 percent fine grog for durability
A recycled grogged body made from your own trimmings, soaked and re-wedged
A local terracotta from a regional supplier, suited to lower firings

Throwing Technique for Even Thickness

The single biggest cause of kiln warp is uneven wall thickness. A plate that measures six millimetres at the centre and four at the rim will dry and shrink unevenly, and the rim will curl upward during the bisque. To avoid this, open the clay deliberately from the start rather than letting it balloon. Use a flat wooden rib pressed gently against the floor as you widen the base, checking the thickness by feel and by sliding a needle tool under the rim.

When pulling the rim, keep your hands level and avoid lifting too high. A plate wall should rise only a few centimetres above the foot ring; any taller and you begin throwing a bowl. Trim the foot only after the piece has set up to a firm leather-hard, ideally the next morning if your studio runs cool. Many Australian makers leave their plates on batt boards covered with thin plastic overnight before trimming, which keeps the rim and floor at a similar moisture level. If you want to explore a related project, the guide on building a functional watering can covers similar principles of even wall thickness applied to a different form.

Drying Tricks That Prevent Warping

Drying is where most warping is won or lost. The goal is to remove moisture evenly from the rim, floor, and foot at roughly the same rate. A plate that dries from the outside in will develop a skin that traps moisture in the centre, and that trapped moisture later escapes through the floor, pulling the piece into a saddle. Conversely, a plate that dries from the centre out will curl at the rim.

The most reliable method is to slow the early drying and then equalise the moisture before the piece goes bone-dry. Place freshly thrown plates on wooden batt boards in a closed cabinet or under a plastic tent for the first twelve to twenty-four hours. Then flip them onto their rims on a soft towel so air reaches the floor. Cover the top with a single sheet of thin plastic, leaving the edges open. This trick, used widely in studios from Fremantle to Fitzroy, lets the floor catch up with the rim without shocking the clay.

If you live in a humid coastal city like Sydney or Cairns, you may need to run a small dehumidifier in your drying cabinet. In drier regions such as parts of South Australia or inland Victoria, a spray bottle of water misted lightly under the plastic can buy you extra time. Whatever your climate, never dry a plate on a wire rack or directly on plaster, because one face will dry too quickly.

Drying stages to monitor over several days:

Stage one - plastic covered, rim and floor both saturated
Stage two - flipped, floor exposed, rim still covered
Stage three - uncovered, turned twice daily to even out
Stage four - bone-dry, stored flat with airflow underneath

Loading the Kiln and Firing Schedules

Even a perfectly dried plate can warp if the kiln loads it unevenly. Place plates on the middle shelves where heat distribution is most stable, and never stack them directly on top of each other. Use kiln wash on the shelves so the piece can shrink slightly as it fires. If you fire with a witness cone pack, set a self-supporting cone three next to the plates to confirm the kiln reaches full maturity.

A slow bisque is essential for wide forms. Ramp at no more than 80 degrees Celsius per hour up to 600 degrees, then slow to 50 degrees through quartz inversion at 573 degrees. Many Australian studio kilns, whether electric in a suburban garage or gas-fired at a community space like the JamFactory in Adelaide, benefit from a hold of fifteen to thirty minutes around 1000 degrees to equalise heat before the final climb. This pause helps thick and thin areas mature together.

Glazing and Final Firing Considerations

Glaze can hide a multitude of sins, but it cannot fix a warped plate. Apply glaze evenly, and avoid pooling near the foot where extra weight can pull the piece out of shape. Some makers leave the foot ring completely unglazed and instead rub it with a bit of beeswax or alumina after firing. If you sell functional ware, remember that Australia follows the Australia New Zealand Food Standards Code for items that contact food, so choose glazes labelled as food safe and lead free.

A slow cooling cycle through quartz inversion on the way down is just as important as the climb up. Crack the kiln a centimetre or two at 500 degrees and let it cool naturally for several hours. Rapid cooling is one of the silent culprits behind plates that come out flat on the rim but twisted in the centre. Pairing patient cooling with the drying tricks above will give you plates that ring true, sit flat on the table, and last for decades.

To keep your ideas flowing between firings, sketching habits can be just as valuable as studio routines, and the reflections in this sketchbook of clay ideas from nature walks show how observation feeds form. Browse the gallery of finished plates and tableware, sign up for the mailing list to receive studio updates, and reserve a place in an upcoming workshop to throw your own flat, kiln-ready plate.