3% and 2% Zircopax added to G2926B cone 6 clear. Why?

If you are interested in the most functional possible surface, consider a 2% zircon addition to your transparent glaze recipe (the outside glaze on these mugs is a copper blue, but that is not the one we are interested in). The clear glaze on the insides of these two identical cone 6 porcelain mugs has 3% and 2% zircon added. It is not being added to opacify, it is being added to toughen the surface and reduce the thermal expansion. The presence of the 2% zircon has not affected the gloss or transparency of the glaze on the right. However, the 3% on the left has opacified it just slightly and made the surface a little silky. So that is too much for this glaze (although it might be OK if the melt fluidity was higher).

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Materials	Zircon
Materials	Zircopax Zirconium silicate, its principle use in ceramics is as an opacifier in glazes. It is an expensive material, but less so than tin oxide.
Glossary	Glaze Durability Ceramic glazes vary widely in their resistance to wear and leaching by acids and bases. The principle factors that determine durability are the glaze chemistry and firing temperature.
Recipes	G2926B - Cone 6 Whiteware/Porcelain transparent glaze A base transparent glaze recipe created by Tony Hansen, it fires high gloss and ultra clear with low melt mobility.

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