Opacifying Crystalline Phases Present in Zirconium-Type Glazes

Various zirconium-type opacifiers were used in a group of glazes maturing in the range cone 04 to cone 11 and the crystalline phase producing opacity in these fired glazes was studied by elevated-temperature X-ray diffraction techniques. The results definitely show that zirconium silicate is the major crystalline phase that promotes opacity regardless of the zirconium opacifying agent added. The foregoing conclusion pertains only to the opacifying particle; this should not be construed to mean that other important characteristics of glazes do not vary with the form of zirconium addition. These other aspects will be discussed in detail in another paper.