Zircosil 5 Micron Opacifier BA960

A very fine version of zirconium silicate, a 6-9% addition produces semi-opaque glazes.
It gives approximately 67% of the opacity of Zirconium Oxide i.e. if your recipe calls for 10 parts of Zirconium Oxide you will need approximately 15 parts of Zircosil to achieve similar opacity.