Kiln Cooling Rate Calculator
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Kiln Cooling Rate Calculator
Calculate safe kiln cooling rates for each temperature zone, with critical guidance for the quartz inversion at 573°C to prevent dunting and thermal shock.
Reviewed by ClayCalc Editorial · Updated
Cone 06=999°C, Cone 6=1222°C, Cone 10=1305°C.
Thicker pieces need slower cooling.
Results
Enter your measurements above and click Calculate.
Kiln Cooling: Why It Matters
Cooling is as important as heating. Most kiln cracking ("dunting") happens during cooling, not heating. The primary danger point is the quartz inversion at 573°C.
The Quartz Inversion at 573°C
At 573°C, crystalline silica (α-quartz) undergoes a sudden reversible phase transformation. On cooling, beta-quartz converts back to alpha-quartz with a sudden 2% volume decrease. If the kiln cools too fast through this zone, the rapid volume change creates enough stress to crack — or shatter — the ware. This is called dunting.
Safe Cooling Rate Zones
| Temperature Zone | Max Rate (°C/hr) | Reason |
|---|---|---|
| Peak → 1000°C | 150–200 | Glaze liquid, safe to cool fast |
| 1000 → 700°C | 100–150 | Glaze stiffening / freezing |
| 700 → 600°C | 80–100 | Approach quartz inversion |
| ⚠ 600 → 530°C | 50–100 | CRITICAL — quartz inversion at 573°C |
| 530 → 200°C | 100–150 | Safe zone again |
| Below 200°C | Free cool | Can open kiln carefully |
Thickness Effect
Thicker pieces retain heat unevenly — the outside cools faster than the interior. This thermal gradient creates internal stress. For pieces over 20mm thick, reduce all rates by approximately 25–40%.
Crystalline Glazes
Zinc silicate crystals are extremely fragile. Crystalline glaze programs control the entire cooling schedule, often including holds at specific temperatures to grow crystals. Never free-cool a crystalline kiln.
Method & review note
About this calculation
Produces a planning estimate from the values entered. Nameplate power, utility billing, kiln condition, load and witness cones remain the authoritative studio checks.
Reference: Orton Ceramic — Pyrometric Cone Resources. See the editorial methodology for testing, precision and corrections.
Input handling: Values are sent to the ClayCalc server for this request and are not written to the application database.