Abstract: A method for producing a ceramic is disclosed. The method involves comminuting a batch composed of from 6 to 95 percent of particulate ZrO.sub.2 and from 5 to 94 percent of particulate Al.sub.2 O.sub.3. A part of the particulate ZrO.sub.2 is in a metastable tetragonal crystal structure, for example, as a consequence of 3.sup.m/o of Y.sub.2 O.sub.3 dissolved therein and a part has a monoclinic crystal structure. The comminuted batch is compacted into a shape, and the shape is fired. The degree of comminution of the batch, the firing conditions and the proportions of stabilized and monoclinic ZrO.sub.2 in the batch are controlled to produce a dense, gas impervious ceramic which contains both metastable tatragonal and monoclinic ZrO.sub.2, and in such proportions that the ceramic has improved strength by comparison with an otherwise identical ceramic wherein all of the ZrO.sub.2 is in either a metastable tetragonal or a monoclinic crystal structure.