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Zircopax Plus

Description: Zirconium Silicate Opacifier

Oxide Analysis Formula
HfO2 1.30% 1.09
TiO2 0.10% 0.22
ZrO2 64.80% 92.48
Al2O3 0.58% 1.00
SiO2 32.50% 95.10
Fe2O3 0.02% 0.02
Oxide Weight 17,463.10
Formula Weight 17,463.10


The designation 'Plus' refers to the particle size, it is a finer grained version zirconium silicate (also known as Superpax). This material is a more potent opacifier than Zircopax, testing will be required to determine how much less to use when substituting.

Related Information

My first zircopax kiln shelf

A zircon kiln shelf

It is 5 mm thick (compared to the 17mm of the cordierite one). It weighs 650 grams (vs. 1700 grams). It will perform at any temperature that my test kiln can do, and far in excess of that. It is made from a body I slurry up (80% Zircopax Plus, 16.5% 60-80 Molochite grog, 3.5% Veegum T). The body is plastic and easy to roll and had 4.2% drying shrinkage at 15.3% water. The shelf warped slightly during drying (I should have dried it between sheets of plasterboard). Firing at cone 4 yielded a shrinkage of 1%. Notice that cone on the shelf: It has not stuck even though no kiln wash was used! Zircopax is super refractory! This is sinter bonded, so the higher the temperature you can fire the stronger it will be. Although it would be very hard to make full 18 or 22-inch shelves for larger kilns, smaller ones designed to "network" would enable a tighter load of ware with a much lower shelf-to-ware weight ratio (especially using my own lightweight posts). Like alumina, this does not have the thermal shock resistance of cordierite, uneven heating can crack these.

Ultrox Original Container Bag

These bags actually contain Zircopax Plus since Trebol is the new owner of the company.


Materials Superpax
Materials Magnesium Zirconium Silicate
Materials Zircopax
Materials Tin Oxide
Materials Zircon
Materials Zircosil
Materials Opax
Materials Ultrox
Typecodes Opacifier
Opacifiers are powders that turn transparent glazes opaque by various chemical and physical mechanisms (and combinations of mechanisms).


Density (Specific Gravity) 2550


Glaze OpacifierSuperpax is a very fine grade zirconium silicate opacifier and will produce a whiter result than less expensive grades. See Zircopax.
By Tony Hansen
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