Troubleshooting · Pottery
Why your pot cracked: a pottery troubleshooting guide
Ceramic failures look alike and have quite different causes, and the difference matters because the fix happens at a different stage each time. This works through the common ones by where and when they appear.
Troubleshooting
- S-crack in the base of a thrown pot — A spiral crack in the floor. Two causes, usually together: the base was not compressed after opening the clay, and the base dried more slowly than the walls so it shrank later and pulled apart. Compress the floor firmly with a rib before pulling the walls, and dry the pot upside down on its rim.
- Cracks at a handle join — The handle and the body were at different moisture contents when joined, so they shrank by different amounts. Join at the same leather-hard state, score and slip both surfaces properly, and dry the whole assembly slowly under loose plastic.
- Rim cracks — The rim is the thinnest part and dries first. Cover the rim with plastic while the base catches up.
- Warping — Uneven drying, uneven wall thickness, or lifting a piece off the wheel while it is still soft. Dry slowly, evenly, out of draughts, and cut thrown work off with a wire rather than lifting it wet.
- Cracks appearing days later on the shelf — Almost always drying too fast. Bone-dry means dry all the way through, and a thick base can hold moisture for days after the surface looks dry.
- The piece exploded — Trapped moisture turning to steam, or a sealed air pocket expanding. Both destroy the piece and frequently others around it. The fixes are: wedge thoroughly to remove air, pierce any fully enclosed form so air can escape, ensure work is genuinely bone-dry, and ramp the first part of the firing slowly — many kiln schedules hold below 100°C specifically for this.
- Cracking along a join — A join made with insufficient scoring and slip, or between pieces at different moisture levels. It survives drying and fails under thermal stress.
- Black coring — A dark layer inside the wall of a fired piece. Organic material in the clay did not burn out because the firing was too fast or the kiln too tightly packed. Slow the firing and improve airflow.
- Crazing — a fine crackle network in the glaze — The glaze shrank more than the clay body on cooling and is under tension. Sometimes wanted as a decorative effect; on functional ware it lets liquid into the body and eventually stains and weakens it. Fix by matching glaze to body, or by adjusting the glaze’s expansion.
- Shivering — glaze flaking off edges and rims — The opposite: the body shrank more than the glaze, putting the glaze under compression until it lifts. More serious than crazing because the flakes are sharp and can end up in food. Do not use shivered ware.
- Pinholing — small holes in the glaze surface — Gas escaping through the glaze as it melts, or dust and grease on the bisque. Wipe bisque ware with a damp sponge before glazing, and consider a slower cooling that gives the glaze time to heal over.
- Crawling — glaze pulling away and leaving bare patches — The glaze did not adhere. Usually a dusty or oily bisque surface, or glaze applied too thickly so it cracked while drying and pulled apart in the melt.
- Running — Glaze applied too thickly, or fired above its range. Glaze that runs onto a kiln shelf fuses to it, and removing it is a job. Leave a clear margin at the foot.
- Dry, matt patches where a gloss was expected — Underfired, or applied too thinly. Check that the firing actually reached temperature — a pyrometric cone measures heat work, which is what matters, rather than a peak number on a controller.
Sources for this section
- Craft Potters Association (opens in a new tab) — Craft Potters Association of Great Britain · Specialist publisher · could not be reached
| Where | When it appeared | Most likely cause |
|---|---|---|
| Base, spiral | While drying | Base not compressed; uneven drying |
| Rim | While drying | Rim dried faster than the body |
| At a join | Drying or bisque | Different moisture at join; poor scoring |
| All over, fine network in glaze only | After glaze firing | Crazing — glaze/body expansion mismatch |
| Straight through the wall, sharp edges | On cooling | Dunting — cooled too fast |
| Whole piece in fragments | Bisque | Trapped moisture or air |
Questions this guide answers
Listed so you can tell at a glance whether this is the page you wanted. HobbyHQ keeps one guide per question family rather than a page per phrasing.
- why did my pot crack
- why did my pottery explode in the kiln
- what is crazing in pottery
- why did my clay warp
- what causes pinholes in glaze
- how do I stop handles cracking off
Sources for this section
- Craft Potters Association (opens in a new tab) — Craft Potters Association of Great Britain · Specialist publisher · could not be reached
Part of Pottery. Last reviewed 2026-08-13.