Dark oud leather

(32.7% SiO2 and 64.3% ZrO2) Zircopax is the brand name of zirconium silicate. It is often used for semi-blackout, and fine materials such as Superpax used for full blackout. Zirconium silicate is used primarily as an opacity material in glass at all temperatures. Although tin oxide is more effective, zirconium materials are much cheaper, more stable in reducing and less reactive with some colorants (such as chromium). Although zirconium oxide is effective as an opacifying material, zirconium silicate disperses better and is cheaper as glazes can withstand or be reformulated to withstand added silica.