The invention relates to a process of selectively treating parts of the surface of a porous dental ceramic comprising the steps of a) providing a composition and a porous dental ceramic having an outer surface, b) applying the composition to only a part of the outer surface of the porous dental ceramic, c) optionally drying the porous dental ceramic, and d) optionally firing the porous dental ceramic, wherein the composition comprises—a liquid being miscible with water, but not being water, —a whitening agent comprising nano-sized metal oxide particles, metal ion containing components or mixtures thereof which precipitate if the composition is adjusted to a pH above 5, —acid, complexing agent or mixture thereof. The invention also relates to a dental ceramic article obtainable by a process.