Digitalfire Ceramic Materials Database

Logged in as Level 2 access: Logout

You should always be testing. But it is wasted without an audit trail. Document your lifetime of recipes, firing schedules, test results, pictures and much more in a private account at It is the future, the next step after desktop Digitalfire Insight.

Watch the video, learn more or sign-up at


Zirconium Silicate

Oxide Weight183.34
Formula Weight183.34
Enter the formula and formula weight directly into the Insight MDT dialog (since it records materials as formulas).
Enter the analysis into an Insight recipe and enter the LOI using Override Calculated LOI (in the Calc menu). It will calculate the formula.
MLPT - Melting Point (MP) 2550C

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).

Zircopax affects glaze melt viscosity, surface smoothness, thermal expansion and color development and can be implicated in a range of glazes faults associated with these. Please read the page on zircon for more information.

Zirconium prices are have increased rapidly in recent years, reflecting the world supply situation. Even though the material is very expensive, Zircopax is added to the body recipe of “porcellanato” tiles. It is a very effective body whitener, especially for casting porcelain. Excessive additions give the porcelain an artificial "white plastic" appearance.

Typical Properties:

Formula: ZrSio4 Weight: 183.1
Linear Coefficient of Expansion (25-700C cm/cm/degreeC): 42 x 10 -7
Specific gravity: 4.5

Particle Size: Zircopax Superpax Excelopax
Microns, Ave. 1.3 .74 .55
Bulk density lbs/cu ft 100 75 75
Surface area, m2/g 4.5 9.8 12.8


Out Bound Links

In Bound Links


An example of G2571A cone 10R matte with 10% added zircopax (right). The zircopax version is very bright white compared to the original.

Opacifying a cone 10 reduction magnesia matte glaze. On the left: G2571A dolomite matte, a popular recipe (from Tony Hansen). Right: 10% Zircopax has been added. Both are on a buff stoneware (H550 from Plainsman Clays).

By Tony Hansen

XML for Import into INSIGHT

<?xml version="1.0" encoding="UTF-8"?> <material name="Zircopax" descrip="Zirconium Silicate" searchkey="" loi="0.00" casnumber="366497-20-3"> <oxides> <oxide symbol="SiO2" name="Silicon Dioxide, Silica" status="" percent="32.790" tolerance=""/> <oxide symbol="ZrO2" name="Zirconium Dioxide" status="U" percent="67.210" tolerance=""/> </oxides> </material>

Feedback, Suggestions

Your email address


Your Name


Copyright 2003, 2008, All Rights Reserved
Get a free INSIGHT software trial

INSIGHT is ceramic chemistry
calculation software that runs on
Windows, Mac and Linux and talks
to this web site. ()