Duncan Crystal Glazes are nontoxic gloss glazes that contain glaze crystals that melt and flow during the firing, creating a distinctively interesting appearance. The easiest glaze to apply, each of the Crystal Glazes are different. Some glazes contain crystals of just one colour, while others contain several different coloured crystals. Due to the unique multicoloured bursts and specks while firing, you will have a different finish every time! The slope and temperature of the fire will also be a factor in your final product. While these glazes are nontoxic and suitable for the classroom, the glazes should never be considered dinnerware safe as crazing may develop due to the presence of the glaze crystal.