A method of manufacturing a mould part (8) for forming an article. The method comprises: providing a master (1) of an aluminium alloy or a zinc alloy with a surface (7) corresponding to the surface of the article to be formed by the mould part. A copper layer (3) is deposited on top of the master surface (7). Then a mould part layer (4) of nickel, a nickel alloy, cobalt or a cobalt alloy is plated on top of the copper layer. The master (1) is dissolved in a solution. The copper layer (3) is selectively etched from the mould part layer (4) in an alkaline etchant comprising free Cu(II) ions, a first complexing agent forming strong complexes with Cu(I) ions but not Ni ions or Co ions, a second complexing agent forming strong complexes with Cu(II) ions but not Ni ions or Co ions. Oxygen is supplied to the etchant for oxidizing Cu(I) ions to Cu (II) ions.