The nucleation and crystallization of thin layers of glasses (glazes) over ceramic substrates during the fast firing of tiles for pavements and wall files has been a topic of great interest for tile and ceramic paving industries in recent years. Here a wide range of glass-ceramic compositions having different types of crystallization microstructure has been investigated. Based on observations by scanning electron microscopy and energy-dispersive X-ray microanalysis, several aspects of nucleation and crystallization of these new types of glass-ceramic glazes are presented and discussed.