Duncan CRKIT-3 Crackles Glaze Kit for Ceramics - Set of 4 Best Selling Colors in 4 Ounce Jars with Free How to Paint Ceramics Booklet Duncan Crackles Glazes are specially formulated to create cracks when fired. Using Crackles Glazes on your pieces results in a distinctive aged, antique look. Use them alone on bisque for subtle color through the cracks or apply over underglaze designs for a unique expression. For extra depth, highlight the cracks created in the firing by antiquing the piece with ink or acrylic paint. Crackles glazes are designed to mature at cone 06/05. Apply to shelf cone 04 bisque. Certified Non-Toxic but not for use on food containers. Made in USA. Kiln required.