Spectrum 536 Bright Blue Opaque Underglaze Size:4 oz and becomes a deep lilac

and becomes a deep lilac color and begins to burn out at cone 10

That means that it's presence enables reducing feldspar content which in turn provides even more opportunity to source Al2O3 from kaolin or clay

Does not react well with oxides and should not be fired in heavy reduction

Fire Opal is great on its own

Spectrum 536 Bright Blue Opaque Underglaze Size:4 oz and becomes a deep lilacFor use on clay or greenware: apply one, two or three coats and let dry and bisque fire to shelf cone 04. If desired, apply a clear or colored translucent glaze and fire to cone 06. For use on bisque: apply one, two or three coats and let dry. Apply a clear or other colored translucent glaze and fire to cone 06. The samples shown are fired to cone 05 but can be fired to low temperature (cone 06 04) to high temperature (cone 9 10). Some color variation