A silica-free MgO–CaO–BaO–Al2O3–ZrO2 glass was converted into glass-ceramic by adding zirconia as a nucleating agent. The crystallization and properties of the glass-ceramics were investigated. It was found that ZrO2 is an efficient nucleating agent for the present calcium aluminate glass. Addition of an appropriate amount of ZrO2 changed the crystallization behavior from surface nucleation to internal nucleation. The primary crystalline phase was Ca3Al2O6, which exhibited bulk nucleation. When the crystallizing time was increased, BaAl2O4 formed as a surface layer that grew from the surface into the interior of the sample. The hardness was increased when the parent glass was converted into glass-ceramics. The glass-ceramics without BaAl2O4 surface layer have visible-to-infrared transparency comparable with the parent glass. The transparency was substantially reduced after the development of the surface layer.
