The thermal behaviour of a glass-ceramic glaze based on the system SiO2–CaO–ZnO–Al2O3 has been evaluated. Frit and kaolin were ball milling using dispersants and binders, and deposited on a green clay based ceramic support. The evolution of the glaze during the sintering step was observed that consisted of a glassy matrix, particles from kaolin and particles from frit. Particles from frit formed a nanostructure of interconnected nanoparticles. Pyroxenes devitrified from the glassy matrix and at higher temperatures they were dissolved in the glassy matrix. Both successes contributed to the final observed nanostructure produced by a spinodal decomposition process in which the crystalline phase had a pyroxene composition.