A comprehensive investigation is made of the particulars of structure and phase formation in zirconium-containing frits and semi-fritted glaze coatings obtained with such frits. It is found that the high physical-chemical and decorative-aesthetic characteristics, most importantly the durability of the coatings (3 – 4), are the result of directed phase formation, a rational combination of crystalline opacifying phases and their uniform distribution in the glassy matrix, and the formation of a uniform glass crystal structure.