Zircopax is a generic brand name of zirconium silicate or zircon (see Zircon for more information). It is primarily used in ceramic to opacify glazes. In North America, the most popular zirconium opacifiers fall under the brand names of Zircopax Plus, Superpax, Zircosil and Excelopax. These vary according to particle size, the finer the size the greater the scattering of light (and thus the better the opacification). In addition, the finer sized materials contain a little extra silica for maximum whiteness. Of course, the amount of zircopax in a glaze determines the opacity. Small amounts (1-3%) may give no noticeable difference but are sometimes employed to improve glaze hardness. Since zircopax is refractory, the more that is added the more the degree of glaze melting (and melt viscosity) is going to be affected. Up to 15% or more might be needed to fully opacify a glaze. If higher amounts are needed the glaze formulation may need to be adjusted to reduce the amount of SiO2 or increase flux (to melt the glaze better).