Effect of ZnO/MgO ratio on the crystallization and optical properties of spinel opaque glazes

The effect of the ZnO/MgO ratio on the crystallization and optical properties of glass-ceramic glazes from the SiO2-Al2O3-ZnO-MgO-CaO-K2O-Na2O-B2O3 system was studied. The glazes with different ZnO/MgO ratios were characterized by differential scanning calorimetry, X-ray powder diffraction, Raman spectroscopy, scanning electron microscopy, energy dispersive spectroscopy analysis and a spectrophotometer. The results reveal that the A glaze without ZnO content contains forsterite and sapphirine. The B and C glazes with intermediate ZnO/MgO ratio contain enstatite and spinel solid solution. The D to F glazes with higher ZnO/MgO ratio crystallize spinel solid solution as the only crystalline phase. The amount of spinel solid solution, lightness values (L*), gloss values and the reflectance of the studied glazes increase with the ZnO/MgO ratio.