These cone 6 porcelain mugs have glossy liner glazes and matte outers: VC71 (left) crazes, G2934 does not (it is highlighted using a felt marker and solvent). Crazing, while appropriate on non-functional ware, is unsanitary and severely weakens the ware (up to 300%). If your ware develops this your customers will bring it back for replacement. What will you do? The thermal expansion of VC71 is alot higher. It is a product of the chemistry (in this case, high sodium and low alumina). No change in firing will fix this, the body and glaze are not expansion compatible. Period. The fix: Change bodies and start all over. Use another glaze. Or, adjust this recipe to reduce its thermal expansion.
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