This underglaze line includes many improved products for the replacement of the discontinued ARTEX underglazes. They may be used on greenware or bisque. Optimum color brilliance can be expected under oxidation firing conditions between cone 06 to cone 1. As with Artex underglazes, many of them will go higher, up to cone 10. Fired underglazes may also be used for a decorative matte surface without a protective covering glaze. Lead-Free Underglaze.