Crystalline Glazes

Crystalline Glazes are seductive and instantly capture the eye. How exhilarating to create a glaze that suggests floating galaxies, frosty windows, rare gemstones, or flowers. Enthusiasm for this glaze technique has greatly increased over the last few years, perhaps because of new advances in kiln technology and computer temperature controllers. Many more potters are now exploring the potential of this glaze technique, making new and exciting discoveries, including reduction firing.

For the purpose of growing crystals, the kiln is taken up in temperature to around 300°F beyond the melting temperature of the glaze, (typically cone 6 to 12), which allows some of the zinc-silicate nuclei, or seed crystals, to dissolve. The crystals will grow from the few remaining nuclei.

After reaching top temperature, the kiln is cooled either by shutting it off or using a predetermined cooling rate, until it reaches the temperature where the crystals will grow. This is usually somewhere around 2100°F–1900°F. When the glaze is molten, all these ingredients float around in a liquid matrix. By holding the temperature at the point where the glaze is still slightly molten but just beginning to stiffen, the crystals form, with their size being determined by the amount of time they remain in this state. (Typically 3–5 hours). The kiln is then shut off and cooled naturally.