glazing info
Every glaze recipe contains silica (the basic ingredient of glass) and "fluxes" - elements that lower the temperature at which the silica melts. Common fluxes include calcium (whiting) and magnesium carbonate (which is found in talc). Glaze ingredients are in powdered form. To be used, they are measured, mixed with water, and applied to the surface of bisque-fired (once-fired) pottery. The pots are then "fired" in the kiln once again. As the kiln temperature rises, the ingredients in the glaze melt together. When the temperature is lowered, the glaze re-solidifies.
By adding the zinc oxide (as a flux) to the glaze recipe, and stalling the cooling process at specific temperatures, a potter can stimulate crystal growth. Why? Because when the glaze liquefies, the zinc oxide binds to the silica and the resulting "seeds" give the glaze a foundation, or lattice, on which it can solidify in a regular pattern as it cools - instead of its usual random form.
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