The effect of iron content on crystallization of a mica glaze as coating for fast firing stoneware substrates has been investigated. Measurements by differential thermal analysis (DTA) combined with X-ray diffraction (XRD) and scanning electron microscopy (SEM) have shown the development of preferential crystal orientation in the mica glass-ceramic glaze. By comparison with amorphous and partly crystalline glazes, an enhancement of the mechanical properties of coatings with aligned and interlocked crystals of mica has been observed.