Firing

Kiln Ramp Rate Calculator

Calculate total firing time and check ramp rates against critical temperature danger zones.

Updated May 2026

Start Temperature

°C

Target Temperature

°C

Ramp Rate

°C/hr

Hold Time at Peak

min

error

Results

calculate

Enter your measurements above and click Calculate.

Critical Temperature Zones in Firing

This calculator checks your ramp rate against five critical temperature zones where exceeding safe rates risks damaging your ware:

Zone	Range	Max Safe Rate	Why
Steam zone	0–120°C	60°C/hr	Expels residual mechanical water
Chemical water	120–300°C	100°C/hr	Chemically bound water release
Quartz inversion	500–600°C	60°C/hr	α→β quartz transition (573°C)
Danger zone	600–700°C	80°C/hr	Multiple crystal inversions
Vitrification	1050–1150°C	100°C/hr	Liquid phase formation

The same inversion dangers apply on cooling. Always cool slowly through the quartz inversion zone (600–500°C) to prevent dunting — thermal shock cracking from rapid crystal contraction.

lightbulb Quick Tips

check_circle Never skip slow ramping below 120°C — steam from residual moisture will crack even thoroughly dried pieces.
check_circle The quartz inversion at 573°C is critical on both heating AND cooling. Slow through this range both ways.
check_circle A soak (hold) at peak temperature improves heat work and glaze maturity without raising peak temperature.
check_circle Do not open the kiln below 100°C — thermal shock from cool air causes dunting (cracking from inversion).

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Frequently Asked Questions

What is the quartz inversion and why does it matter? expand_more

At 573°C, quartz crystals abruptly change crystal structure (alpha to beta quartz), expanding about 2% in volume. This happens in both heating and cooling. Rapid temperature change at this point causes thermal shock and cracking.

How fast should I ramp during the initial steam phase? expand_more

Heat slowly (30–60°C/hr) from room temperature to 120°C to drive off mechanical water without steam damage. For thick or previously dried work, you can heat to 120°C faster; the key is to hold at 120°C until steam stops.

What is candling and when should I use it? expand_more

Candling means holding at a low temperature (80–120°C) for 1–4 hours with the kiln lid cracked to vent steam before beginning to ramp up. Essential for thick pieces, freshly made work, or reclaimed clay.