Abstract: Porous, ceramic layers, which also have a diffusion-limiting action, are as a rule manufactured by selectively adding pore formers to the ceramic sinter material. The porosity of the layer created in this way lies in the micrometer range. The known processes for manufacturing layers of this type are intended for application to planar substrates. Suitability for spherical surfaces and a porosity of the layer in the nanometer range is provided herein by an oxide ceramic powder having a BET specific surface area in the range of about 5 to 50 m.sup.2 /g and having a mean primary particle size of about 20 to 450 nm. The powder is first pretreated at a temperature of about 800.degree. C. to 1150.degree. C. and then mixed with untreated, oxide ceramic powder. The mixture is then applied to a high temperature-stable base, and burned-in (fired) at a temperatures of about 1000.degree. C. to 1350.degree. C. Optionally, instead of the thermally pretreated oxide ceramic powder, a recrystallized glass powder can be used.