Behaviour of Cr3+ and Fe3+ ions in the gahnite crystallized from zinc opaque glazes

The amount of gahnite spinel crystallized in a glaze containing a large amount of ZnO and Al₂O₃ as well as the behaviour of Cr³⁺ ions in the glaze were studied. Crystallization of gahnite containing a small amount of Cr₂O₃ gave a pink opaque glaze. Almost all the Cr³⁺ ions migrated into the gahnite phase. The measurement of the lattice constant by X-ray diffraction analysis, as well as chemical analysis of the crystallized gahnite separated from the glaze, were used to determine the amount of Cr³⁺ ions in the gahnite phase. A similar phenomenon occurred when Fe₂O₃ was added to the base glaze composition.