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The invention relates to a method to remove metaloxides from at least the surface of a substrate comprising a stone-like material that contains at least one earth-alkaline metal, wherein an aqueous alkaline solution comprising thioglycolate salts is brought into contact with said metaloxide-containing substrate for a relatively short but sufficient time to allow said solution to react with and bind to said oxides. The surface is subsequently brought into contact with water during at least one rinsing operation and wiped to remove the reaction products comprising the so bonded metaloxides.