In a method for etching material to be etched, which consists at least partly of metal, an acid is used, which attacks the metal solely after the addition of an oxidizing agent directly before the actual etching operation. The addition of the oxidizing agent takes place in a quantity which slightly exceeds the quantity stoichiometrically necessary for removing the entire metal, so that a small residue of oxidizing agent remains in the etching medium dropping from the material to be etched. This residual oxidizing agent is then removed from the etching medium by a special device, which contains an excess of metal able to be etched by the etching medium.