Abstract: Light-transmissive ceramics are disclosed composed of a plurality of oxides each having a negative standard Gibbs energy of formation (.DELTA.Gf.sup.0) with an absolute value greater than 1581.9 KJ/mol. The light-transmissive ceramics are produced by subjecting the oxides to hot isostatic pressing at a high temperature under a high pressure after they have been subjected to primary sintering. The light-transmissive ceramics of Al.sub.2 O.sub.3 /La.sub.2 O.sub.3 are of a composite structure with particles of La.sub.2 O.sub.3 being present between particles of Al.sub.2 O.sub.3, rather than Al.sub.2 O.sub.3 and La.sub.2 O.sub.3 forming a solid solution. In the composite structure, the particles of La.sub.2 O.sub.3 have sizes that are 1/3 to 1/30 of the particles of Al.sub.2 O.sub.3. Maximum size particles of Al.sub.2 O.sub.3 have a longer axis of 30 .mu.m or less and a shorter axis of 20 .mu.m or less, and maximum size particles of La.sub.2 O.sub.3 or the like have a longer axis of 10 .mu.

Abstract: A ceramic filter having good permeability and a superior durability, and a process for manufacturing the same. This filter comprises a porous support made of a ceramic, a fine intermediate layer formed on one surface of said support and comprised of at least one kind of particles selected from particles of SnO.sub.2, TiO.sub.2, ZrO.sub.2 or CeO.sub.2 and having a particle diameter of not more than 500 .ANG., and a thin film formed on the surface of said fine intermediate layer and comprised of at least one particles selected from particles of SnO.sub.2, TiO.sub.2, ZrO.sub.2 or CeO.sub.2 and having a particle diameter of not more than 300 .ANG. and smaller than the particle diameter of the particles that constitute said fine intermediate layer.