Abstract: A method of producing a glazed ceramic substrate, which is useful for a hybrid integrated circuit or a thermal head of a thermal printer for instance, by applying a glass onto a major surface of a ceramic substrate, firing the substrate to form a molten glass layer on the substrate surface and cooling the fired substrate. To obtain the glazed ceramic substrate with high flatness despite the tendency of the substrate to warp due to difference in thermal expansion coefficient between the ceramic and the glass, a refractory base which supports the substrate during the firing and cooling steps is so shaped as to allow the substrate to deform during the firing step reversely to the expected warp at the cooling step, so that the warp at the cooling step is offset by the preceding deformation. For example, the upper surface of the base is shaped into a continuous and concave surface.

Abstract: A glazed ceramic substrate for use in electric or electronic devices, obtained by forming a glass coating layer directly on a major surface of a ceramic substrate such as an alumina substrate. The glass as the material of the coating layer contains 50-60 Wt % of SiO.sub.2, 10-30 Wt % of Al.sub.2 O.sub.3, 15-30 Wt % of CaO and MgO, and 2-6 Wt % of ZrO.sub.2 as essential components, optionally with the addition of small amount(s) of at least one of TiO.sub.2, BaO, ZnO, PbO, P.sub.2 O.sub.5, B.sub.2 O.sub.3, Na.sub.2 O and K.sub.2 O. The coating layer formed of this glass is excellent in its high-temperature stability, so that the glazed ceramic substrate is particularly suitable for use in thermal heads of thermal printing devices.

Abstract: A glass composition particularly useful for producing alkali-resistant glass fibers, containing, by weight, from 53 to 63% SiO.sub.2, from 21 to 23% ZrO.sub.2 and from 10 to 21% Na.sub.2 O.