Surface study of films formed on copper and brass at open circuit potential

► Oxide films formed on copper and brass were studied in borax 0.1 mol L−1 solution. ► Voltammetries, XPS and Raman show that the film on Cu contains Cu2O and CuO. ► In the case of brass the same corrosion products are found, together with ZnO. ► The surface products containing zinc are much more soluble than those with copper. ► Adding in Cl−, copper-chloride compounds incorporate to the films on both materials.