Crystalline glaze recipes contain zinc oxide, silica, and fluxes.
crystals of zinc silicate (Zn2SiO4) are formed.
A window of approx. 72 C (130 F) exists in which to grow crystals.
Crystalline glaze is fired higher than the melting temp. of the glaze, at least 222 C (400 F) hotter. Once this point is reached, the temp. should be quickly reduced to the temp. range for crystal formation, then kept within this range for a predetermined time.
Sequence to promoting crystal formation:
Getting to max. temp. as quickly as possible.
Rapidly cooling to the crystal growing range.
Extendeds oaking, or slowly dropping and raising the temp. within the crystal growing range during the crystal growth period.