Zirconium(IV) silicate, also known as zirconium orthosilicate, or zircon flour, goes by the brand names Zircosil, Excelopax, and Zircopax.
It is an effective glaze opacifier.
Small amounts (1-3%) will not add much opacity, but will harden the glaze.
The glaze may require up to 15% to fully opacify.
Zircopax affects surface smoothness, thermal expansion, and color development.
It is a very effective body whitener, especially for casting porcelain.Excessive amounts of Zircopax give the porcelain an artificial appearance more resembling plastic than porcelain.
Compared to other chemicals, it is less expensive than tin oxide, but less effective as well.
It is less expensive than zirconium oxide as a whitener, but the glaze must be formulated to tolerate the added silica.