The soak temperature is set slightly above the annealing point of the glass family, typically 516 °C for soda-lime and around 560 °C for borosilicate. Soak time scales roughly with the square of the thickness, because heat has to diffuse out from the centre. The cooling rate through the strain point is limited by the same square law, which is why doubling the thickness can quadruple the schedule.
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Enter a thickness and oven load, then calculate.
About this calculator
Annealing schedules are driven by thickness, not by size. A thin-walled vessel the size of a bucket may anneal faster than a solid paperweight the size of your fist, because the centre of the solid piece has to lose its heat through a long path.
Select the glass type, enter the thickest wall or section in millimetres, the kiln power rating and how full the oven is. The calculator returns the soak temperature, the soak duration, the maximum cooling rate and the total schedule length.
Things to keep in mind
- Never cool faster than the calculated rate, even if the piece looks fine. Stress-driven cracks arrive days later.
- A full oven cools more slowly than an empty one, so the schedule can be slightly gentler with a heavy load.
- Hold through the strain point, not just the annealing point. Most cracked pieces fail because cooling started too early.
- Log the actual curve and compare it with the plan. The gap between them is where problems hide.
Reference only. Results are based on published ranges for common glass families and are intended for learning. Always verify against your own materials and equipment, and follow the manufacturer's instructions.