For the reproducible manufacturing of particularly uniform and brilliant i.e., highly bright copper coatings that are leveled and ductile as well, a copper plating bath is utilized that contains as an additive a mixture of oligomeric phenazinium compounds. The mixture contains at least one phenazinium compound selected from the group comprising compounds containing two monomeric units and compounds containing three monomeric units having the general chemical formulae and set forth in the patent claims and in the specification as well as further oligomeric phenazinium compounds.