Crystalline glaze firing has very special requirements. You need to heat rapidly and cool rapidly plus you need to be able to hold high temperatures for long periods of time to grow the crystals.
Crystalline Glazes are often fired to around 2300-2400°F or cone 10-11. Computer controllers, modified to ones specifications, are typically used to carry out a programmed firing.
After heating the glaze to a full melt, the kiln is dropped quickly to temperatures within the range of 1825-2185°F. At these intervals, a “heat-soak” (hold) is maintained, to initiate and form the crystals. The temperature and duration create different sizes, patterns, & colors within the crystal and the corresponding background.