A process of depositing a coating (5) onto a substrate (3) by reactive sputtering in a closed chamber (1) in the presence of a plasma of a non-reactive gas, and a reactive gas containing the element or elements said coating has to be made of, according to which process use is made of a target (2) having a surface layer (4) directed towards the substrate and containing at least one of the elements to be sputter deposited onto this substrate, according to which process the thickness of said surface layer (4) during the cathode sputtering is controlled by adjusting the concentration of the gases in said closed chamber (1). The single figure.