These special effects glazes are among the easiest to use and create some of the most dazzling effects. Crackle glazes create random hairline cracks with interesting patterns. They allow some clay color to show through the glaze. They are non-toxic but not recommended for dinnerware. The remaining glazes feature opaque gloss colors with embedded color crystals that melt and run during the firing process. Each firing results in unique and magical flow patterns that give these glazes their magical appeal. Non-toxic and dinnerware safe.