The upper half of this small vase has a high-zinc crystal glaze. The lower half is just a functional cone 6 transparent (with the same amount of cobalt to produce the blue color). The piece was not slow-cooled to grow the crystals. The high degree of melt fluidity is clearly visible.
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