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.
- Shutting the kiln off and cooling naturally.