Cone 6: Midnight Rain is a blue-green breaking gloss glaze that contains a black crystal. As the crystal melts and moves, a black oil-like streak is created in the glaze. Cone 10: Crystals melt and integrate into base glaze, darkening the color. Increased movement. TIP: SW-100 Blue Surf is the base glaze. For a lighter crystal effect, you may try applying two coats of SW-100 Blue Surf with a third coat of SW-115 Midnight Rain.