Glaze is composed of glassy phase, pores and a small amount of crystal phase. The glazed product is
endowed high technological properties such as low water absorption, good cleanability, high bending
strength and abrasion resistance, excellent chemical and soil resistance. Nevertheless, surface degradation
mightlead to opening of closed bubbles in glaze thus diminishing the cleanability. As a result, a study
of bubble formation in glaze layer would favor the improvement of mechanical property and cleanability
of final products. In this paper, glaze slurry was prepared by milling for 30 min, then applied to green
bodies and dried for later use. The same glaze was fired in hot stage microscope to measure melting
behavior. Two characteristic points were obtained: start of melting temperature of 1184 ◦C; half sphere
temperature of 1220 ◦C. The firing curves applied to glaze can be designed according to the characteristic
points, and then the dried samples were fired. The bubbles in fired glaze were observed by 3D depth
of field microscope. Microhardness was performed using Vickers hardness tester. A solution was proposed
to decrease bubbles and increase microhardness via changing firing process. The results showed
the formation of bubbles in glaze was determined by firing process.