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Glaze Thermal Expansion (COE) Calculator
Glaze
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Glaze
Glaze Thermal Expansion (COE) Calculator
Calculate the coefficient of thermal expansion (COE) of a glaze from its oxide composition.
Updated
Enter oxide mole fractions from your glaze UMF analysis. Leave unused oxides blank.
+3.8
−3.0
−5.0
+13.0
+6.0
+28.6
+39.4
+27.0
+20.0
+5.0
+3.9
+11.0
+10.5
+11.3
+16.7
error
Results
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Enter your measurements above and click Calculate.
Appen Coefficients & Glaze Fit
This calculator uses Appen oxide coefficients (×10⁻⁷/°C) to estimate Coefficient of Thermal Expansion (COE). The COE is the weighted sum of each oxide's contribution normalized to total mole fractions.
COE = Σ (mole_fraction_i × coeff_i)
Glaze fit depends on the difference between glaze and clay body COE. The glaze should contract slightly less than the body on cooling — putting it in mild compression — which produces a harder, more durable surface and prevents crazing.
| Result | Cause | Fix |
|---|---|---|
| Crazing | Glaze COE > Clay COE | Lower glaze COE (add Al₂O₃, reduce Na₂O) |
| Shivering | Glaze COE << Clay COE | Raise glaze COE (add Na₂O or K₂O feldspar) |
Frequently Asked Questions
What is the ideal COE difference between glaze and clay body? expand_more
The glaze COE should be slightly lower than the clay body COE (by about 0.5–1.0 × 10⁻⁷). This puts the glaze in slight compression when cooling, which prevents crazing and produces a harder, more durable surface.
What causes crazing in glazes? expand_more
Crazing occurs when the glaze COE is higher than the clay body COE, causing the glaze to contract more than the clay on cooling and pulling apart into a network of cracks.
What causes shivering in glazes? expand_more
Shivering is the opposite of crazing — when the glaze COE is much lower than the clay body, the glaze is under too much compression and spalls or chips off. This is less common but more dangerous on functional ware.
Which oxides raise COE the most? expand_more
Alkali fluxes raise COE dramatically: Na₂O (+39.4), K₂O (+28.6), Li₂O (+27.0). Alumina (Al₂O₃) and boron (B₂O₃) lower COE significantly. Silica has a modest positive effect.