Effects of glass frit oxides on crystallization and zircon pigment dissolution in whiteware coatings

In experimental whiteware coatings comprised of zircon pigment and multi-oxide silicate glass frits that incorporated ZrO2, the quantity, size, and morphology of zircon that precipitated during "fast-firing" were mainly dependent upon the ZnO, SrO, and Al2O3:alkali levels. In these frits, little or no zircon pigment dissolution occurred, and zircon crystallization was nearly complete by 1000 degrees C. Microstructures of the coatings were consistent over a range of peak firing temperatures from 1000 degrees to 1100 degrees C. Fritted ZnO in these coatings stimulated zircon crystallization and produced high opacity. Replacing ZnO with SrO in the same frits prevented zircon from precipitating and resulted in transparent coatings. In frits without ZrO2 significant zircon pigment dissolution and crystallization of calcium-based silicates occurred during firing, In these unstable coatings, crystallization and dissolution increased from 1000 degrees to 1100 degrees C and produced a range of microstructures. Raising the Al2O3:alkali ratio caused frits with ZrO2 to precipitate more zircon, and frits without ZrO2 to farm less of the calcium-based silicates and dissolve less pigment.