Mayco ASKIT-1 Astro Gems Textural Glaze Kit for Ceramics - Set of 3 Best Selling Colors in 4 Ounce Jars with Free How to Paint Ceramics Booklet Astro Gems are an underglaze-based textural glaze that contains tiny crystals. When fired, these crystals provide jewel-like spots on the matte surface of the glaze. Astro Gems can be applied to both greenware and bisque. Astro Gems Textural Glazes are designed to mature at cone 06/05. Certified Non-Toxic. Not recommended for use on dinnerware. Made in USA. Kiln required.