CALCULATOR
COE Compatibility Calculator
Check whether two glasses can be worked together before you ruin both.
Inputs
Coefficient of expansion × 10⁻⁷/°C. Soda-lime is around 90, borosilicate around 33.
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blended expansion
- Difference
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- Mismatch
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- Mix
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- Verdict
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Things this does not account for
- The blended figure is a linear approximation, valid for a mechanical mixture rather than a true melt.
- Even a matched COE is not a guarantee — viscosity and annealing point also have to be compatible.
- Never mix a 90 COE glass with a 33 COE glass. There is no ratio that makes that work.
How this works
Two glasses with different coefficients of expansion will crack when they are fused, and it is not a matter of skill. The mismatch builds stress as the piece cools, and the stress concentrates at the joint. The rule of thumb is that a mismatch of more than about 5 % is risky and more than 10 % is a guaranteed failure.
