Tin Oxide – SnO₂ (m.p. 2066^o F/1130^oC) the most effective opacifier at all temperature ranges from terra cotta to porcelain. Amounts of 4-5% are typical, however, as little as 2%, and as much as 8%, are used in a glaze. Any of the Zircon opacifiers such as Zircopax, will substitute, although a greater percentage will be necessary (up to 10%) for similar results.