Glaze compositions for ceramic substrates

Glaze compositions for ceramic substrates such as an alumina substrate are described. In a first embodiment, the glaze composition consists of 55 to 75 mol % SiO2, 1 to 15 mol % Al2O3, 3 to 20 mol % CaO, 1 to 13 mol % BaO and 0.1 to 5 mol % Y2O3. In a second embodiment, the glaze composition consists essentially of 55 to 75 mol % SiO2, 1 to 15 mol % Al2O3, 3 to 20 mol % CaO, 1 to 13 mol % BaO, 1 to 5 mol % Y2O3, 25 mol % or less SrO, 7 mol % or less B2O3, 2 mol % or less ZnO and 2 mol % or less MgO. In a third embodiment, the glaze composition consists essentially of 58 to 75 mol % SiO2, 2 to 15 mol % Al2O3, 0.5 to 5 mol % La2O3, 2 to 20 mol % CaO and 1 to 13 mol % BaO. In a fourth embodiment, the glaze composition consists essentially of 58 to 75 mol % SiO2, 2 to 15 mol % Al2O3, 0.5 to 5 mol % La2O3, 2 to 20 mol % CaO, 1 to 13 mol % BaO, 25 mol % or less SrO, 2 mol % or less MgO, 7 mol % or less B2O3, and 5 mol % or less Y2O3. These glaze compositions are suitable for use in surface glazing of ceramic substrates for thermal heads, printer heads, etc.