Defect · Cooling
Dunting
Also called: cooling crack, silica crack
Ringing crack or complete break running around or across a piece, occurring during cooling and often audible as a 'ping'.
- Appears at
- Cooling
- Severity
- Structural
- How common
- Common
Causes
Most likely
- ·Kiln cooled too rapidly through the quartz inversion (~1063°F / 573°C)
- ·Clay body under thermal stress from uneven wall thickness
Prevention
- ·Slow the cooling ramp through quartz inversion (hold or slow below 1100°F)
- ·Avoid opening the kiln until interior temperature is below 250°F
- ·Design forms with consistent wall thickness
Can it be fixed?
Not reliably — this one is prevented, not repaired. A cracked or bloated pot is a test tile now.
Questions
- Why does dunting happen?
- Most often: Kiln cooled too rapidly through the quartz inversion (~1063°F / 573°C). Other causes: Clay body under thermal stress from uneven wall thickness..
- Can dunting be fixed?
- Not reliably once it has happened; the fix is upstream, in prevention.
- How do I prevent dunting?
- Slow the cooling ramp through quartz inversion (hold or slow below 1100°F). Avoid opening the kiln until interior temperature is below 250°F. Design forms with consistent wall thickness.
Further reading. The industrial treatment of this defect in the Ceramicware Defects Handbook on Wikibooks (CC BY-SA 3.0).
Sources. Compiled from Claybench's defect reference — the descriptions, causes and remedies that appear consistently across standard ceramics references and studio practice; no single source. It is the same reference the photo diagnosis tool reasons over. Where the Wikibooks Ceramicware Defects Handbook covers a defect it is linked above.
Not sure which defect you're looking at?
Claybench can read a photo of the pot against this same reference and rank the likely causes for your clay, glaze and firing.