With the advent of computer controlled kilns, producing crystal glazes at medium and high temperatures is quite easy, just use a really fluid zinc glaze and fire a schedule that gives them opportunity to grow.
Adjust the final temperature on step 3 to match the temperature your kiln reads when it reaches cone 6.
Note that almost everyone who uses crystalline glazes either does not notice or has accepted the crazing that these naturally produce on typical porcelain clay bodies at middle at high temperatures. This is not necessary, a high expansion clay body can be employed to prevent this.
|1||176°C/hr to 372C||316°F/hr to 701F||2:08|
|2||398°C/hr to 1093C||716°F/hr to 1999F||3:57|
|3||65°C/hr to 1210C||117°F/hr to 2210F||5:45|
|4||398°C/hr to 1093C||716°F/hr to 1999F||6:03|
|5||398°C/hr to 1037C||716°F/hr to 1898F||6:11|
G2902B - Cone 6 Crystal Glaze
A type of ceramic glaze made by potters. Giant multicolored crystals grown on a super gloss low alumina glaze by controlling multiple holds and soaks during cooling