Throwing a 24 cm cylinder from 1.5 kg: the proportions that keep it standing

A cylinder is the test piece every throwing class uses because it exposes everything: wall consistency, water control, and whether you understand that height comes from removing material, not stretching it. This is the arithmetic of a 24 cm cylinder from 1.5 kg of stoneware, and the sequence that gets it there without the top third going oval.

The numbers first

1.5 kg of stoneware at 20 percent moisture occupies about 1.2 litres. A cylinder 24 cm tall and 10 cm in diameter with a 6 mm wall and 8 mm floor has a volume of roughly 0.75 litres — so you have a comfortable margin and can throw to the full height without running out of material. The same 1.5 kg taken to 32 cm requires a 4.5 mm wall, which is where cylinders of this weight usually fail.

Know your ceiling before you start. For stoneware, mass in kilograms times 17 gives a realistic maximum height in centimetres with a 6 mm wall. That is 25 cm for 1.5 kg, 42 cm for 2.5 kg. Anything above that and you are thinning rather than throwing.

Four pulls, not two

The instinct is to pull as few times as possible, on the theory that each pull risks the wall. The reality is the opposite: a 12 mm wall taken to 6 mm in one pull is unstable and ribbed, while the same reduction over four pulls of 1.5 mm each stays even and lets you correct the profile as you go.

The rhythm that works: pull one from the base to the rim, then pull two and three starting 4 cm lower than the previous start so the material comes up from the lower wall, and pull four only on the top two-thirds. This keeps the base thick where it needs to be and stops the top third from going oval.

Keeping the top third true

Above 18 cm the wall becomes a lever and any variation in thickness translates into an oval rim. Two habits prevent it. First, slow the wheel from 140 to 100 rpm as you pass 15 cm — the faster wheel amplifies wobble at height. Second, support the outside of the wall with the flat of the left hand at the same height as the inside fingers, rather than letting the left hand drop away once the shape is established.

If the rim goes oval anyway, do not chase it with a rib. Stop, let the wall stiffen for 60 seconds, then take one final slow pass with both hands flat on the rim, pressing inward from opposite sides. A rim that is corrected after stiffening holds; a rim that is ribbed into shape while soft springs back.

Rim finish and what happens next

Finish the rim with a chamois and a slight outward flare of 1 to 2 mm. A rim that is thinner than the wall chips in use; a rim that flares outward is easier to drink from and less likely to crack under thermal shock.

Then cover the cylinder loosely with a plastic bag and let it stiffen to leather-hard for at least two hours before trimming. Stoneware at 6 mm takes about four hours in a 20 degree room to reach the cheese-hard state at which the foot ring can be cut cleanly.

Steps

1. Wedge 1.5 kg of stoneware, weigh it, and record the weight on the bat in pencil — you will want it if the pot fails and you repeat it.
2. Centre at 200 rpm, open to 1.5 cm, compress the floor with a rib.
3. Pull one at 140 rpm taking the wall from 12 mm to 10 mm, starting 1 cm up from the base.
4. Pull two at 130 rpm from 10 mm to 8.5 mm, starting 3 cm higher than pull one.
5. Pull three at 120 rpm from 8.5 mm to 7 mm, again starting higher so the material rises from the lower wall.
6. Pull four at 100 rpm on the top two-thirds only, finishing at 6 mm, with the left hand flat against the outside at the same height as the inside fingers.
7. Chamois the rim, flare it 1 to 2 mm outward, cover the pot with a bag and leave it to stiffen for at least two hours before cutting the foot.

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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