For those wanting to explore an alternate to crystalline glaze without the hassle and headaches: how about Mica Crystals.   A simple variation to the standard crystalline formula fired to cone 6: with a slow cool from 2100 to 1900F @ 200F an hour. Option: or do a ramp hold at 2025F for two hours. The formula was set to a median of the top three formula limits, and loosely based on a crystalline glaze recipe: Frit 3195  50% Zinc           5% Mica         20% Silica        25% Rutile