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Surface appearance

Surface appearance Imerys wollastonites improves the surface appearance of ceramic glazes and engobes

Due to their unique chemistry, Imerys wollastonites are excellent high brightness, low loss on ignition (LOI) additives which improve pinholes, cracking, crawling and matting in glazes and engobes.


Used as a fluxing agent and frit additive in glazes, Imerys wollastonite is an excellent low LOI source of calcium in glazes where it:

  • Improves surface smoothness and transparency
  • Reduces pinholes
  • Eliminates crawling
  • Reduces cracking and crazing
  • Maintains high brightness value during firing
  • Is an excellent matting agent for satin, matte and rustic glazes

In sanitaryware, replacing calcium carbonate with wollastonite in the glaze can eliminate glaze crazing completely.

Most pinholes are remnants of bubbles in the glaze. One of the many causes of pinholes is volatile components (CO2, H2O, etc.) contained in raw materials. Imerys wollastonite is an excellent calcium source because it is volatile free. Our wollastonites have a loss on ignition (LOI) rate typically below 0.5% meaning minimum CO2 is emitted during firing compared to other conventional calcium oxide sources, improving the surface appearance and strength of the glaze.

Chemical consistency and particle fineness are the most important factors when selecting wollastonite for use in glazes.

Fine grades such as our Nyad® M325 and Nyad® M400 are best suited to glaze applications.


Due to their high brightness, Imerys wollastonites are an excellent solution for improving whiteness in engobes. A 15 to 30% wollastonite loading in the formulation will improve whiteness, lowering opacifier demand. Imerys wollastonites are also used to eliminate crawling in engobes.

We recommend our Nyad® M100 and Nyad® M200 grades for engobes.