Porcelain has no grog and almost no plastic memory, so a wall that is uneven by 1 mm at the base is 3 mm out by the rim. Pulling a 22 cm cylinder to a consistent 6 mm in three passes is a matter of water discipline, hand position at the 4 o'clock station, and knowing when to stop pulling and let the wall stand.
H 22 · Ø8.5 / Ø9.5 / Ø4.5 cm
Why porcelain punishes uneven pulling
Stoneware with 15 percent grog tolerates being pushed around; the grog particles lock and the wall stays where you leave it. Porcelain is 50 percent feldspar and silica with fine kaolin, and it stays plastic over a narrower moisture window — about 2 percent of water content separates workable from slumping.
The practical consequence is that you cannot correct a porcelain wall after the fact. Every pass has to end with the wall where you want it. Three passes at 6 mm is both faster and more reliable than five passes at 8 mm followed by a corrective pull.
Water discipline
Wet both hands once before the first pull, and then not again until the second. Dip only the fingertips, shake off the drip, and keep the sponge in the left hand to clear the rim between passes rather than wetting the body. Slip on a porcelain wall is lubrication for collapse: the outer 2 mm soften and the wall bends under its own weight at about 15 cm of height.
If the wall starts to lean, stop and let the wheel spin for 30 seconds with your hands off. Porcelain stiffens fast in moving air. A wall that leans at 20 cm will usually stand if you let it dry for a minute rather than fighting it.
Hand position at the 4 o'clock station
The classic pull happens at 4 o'clock on the wheel head. The outside hand has its knuckle braced against the wheel head or the bat with the index finger pressing inward; the inside hand has two fingers — index and middle — pinching the wall from within at exactly the same height, thumb outside for support.
The critical detail is the vertical relationship of the hands. The inside fingers must be 3 to 5 mm below the outside knuckle. If they are level, you thin the wall; if the inside fingers are above, you thicken it and leave a bulge. For porcelain specifically, keep them just below level and accept a wall that is 0.5 mm thicker at the top — that extra half millimetre is what keeps the rim from warping in the firing.
Judging thickness without a caliper
Pinch the rim between finger and thumb. At 6 mm you can just feel the wall flex under moderate pressure, and the pinch leaves a mark that fades in about ten seconds. If it leaves a permanent dent, the wall is under 4 mm and the pot will slump during the second pull.
For anything you intend to repeat, buy a set of pot calipers and use them at the end of each pass: measure the wall at the base, mid-height and 2 cm below the rim. Porcelain dries fast enough that you can see a 1 mm variation across three measurements and correct it in the next pass, not after the fact.
Steps
- Centre 1.5 kg of porcelain at 180 rpm, open to 1.5 cm, and compress the floor thoroughly — porcelain is more prone to S-cracks than stoneware.
- Wet both hands once and start the first pull at 140 rpm, pinching from the base and rising 4 cm at a time, three rises to the full height.
- Clear the rim with a sponge and check the wall with calipers before starting the second pull.
- Second pull at 120 rpm with fingertips only, taking the wall from 9 mm to 7 mm over three rises.
- Third pull at 100 rpm with no added water, thinning to 6 mm and shaping the profile — porcelain responds to shaping pressure better than to thinning pressure.
- Stop the wheel, sponge the rim, and let the cylinder stand for a minute before any further shaping.
- Compress the rim between finger and thumb and leave a 1 mm thickening at the top to resist warping.
Where it goes wrong
- Wetting the hands again mid-pull. On porcelain this is the fastest way to a collapsed wall.
- Pulling five passes to fix one thin spot. Thin spots on porcelain cannot be corrected by pulling; the wall just gets thinner everywhere.
- Leaving slip ridges on the inside. They dry hard and show up as a spiral shadow after firing.
- Starting the second pull too early. If the first wall has not stiffened for 60 seconds it will slump under the inside hand.
| Symptom | Cause |
|---|---|
| Cylinder spirals and collapses at about 15 cm | over-wetting softened the outer wall below the load it has to carry. |
| Rim is wavy when viewed from above | the inside fingers were above the outside knuckle and the wall was thickened unevenly. |
| Vertical split along one side | a thin spot from the first pass that was pulled out further in the second. |
| Base cracked after firing | insufficient compression of the porcelain floor before the first pull. |
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.
Same cone — Cone 9
Nothing is fired to this cone yet.