• “Fire it higher or longer.” If the glaze was genuinely underfired, that may help. But most studio glazes that leach are already well melted or over-fluxed. Extra firing often doesn’t solve the underlying chemistry issues.
• “Just add more flux.” Durable functional glazes are not made by maximizing melting. Excessive flux usually reduces chemical durability. Good functional glazes need an appropriate balance of fluxes, SiO2 and Al2O3.
• “Gerstley Borate (or Gillespie Borate) makes glazes soft because it has little alumina.” These materials are simply sources of B2O3 (and other oxides). A glaze gets its alumina from the entire recipe, not from one ingredient.
• “A glossy glaze is a durable glaze.” Surface appearance tells you very little about chemical durability.
• “It survived vinegar, so it’s dishwasher safe.” Dishwashers expose glazes to repeated hot alkaline detergents, which can be much more aggressive than weak food acids.
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