A method of making a gas separation membrane, wherein said method comprises: (a) providing a plating vessel containing a volume of a first plating solution having a concentration of a gas-selective metal ion; (b) placing a porous support, having a first surface and a second surface with each said surface being opposed to the other to thereby define a support thickness, into said plating solution and thereby contacting said first surface with said plating solution for a first time period while maintaining plating conditions within said plating vessel so as to promote the electroless deposition of said gas-selective metal ion from said plating solution onto said first surface of said porous support; and (c) circulating said plating solution through said plating vessel at a first circulation rate such as to provide for a first residence time of said plating solution through said plating vessel that is in the range of from 0.1 minutes to 30 minutes; whereby a membrane layer of said gas-selective metal is deposited upon said first surface to thereby provide a supported membrane. (d) after said time period, removing said supported membrane from said plating solution and annealing said supported membrane to provide an annealed supported membrane having an annealed membrane layer; (e) placing said annealed supported membrane into a second plating solution, having a second gas-selective metal ion concentration, contained within said plating vessel or a second plating vessel and thereby contacting said annealed membrane layer with said second plating solution for a second time period while maintaining plating conditions within said plating vessel or said second plating vessel; (f) measuring the density of said annealed membrane layer to determine its density to liquid, and if said annealed membrane layer is determined to be liquid dense, then applying during the contacting of said annealed membrane layer with said second plating solution a pressure differential of a higher pressure and a lower pressure across said support thickness with said higher pressure being applied to the side of said first surface; and (g) circulating said second plating solution through said plating vessel or second plating vessel at a second circulation rate such as to provide for a second residence time of said second plating solution through said plating vessel or second plating vessel that is in the range of from 0.1 minutes to 30 minutes; whereby a second membrane layer of said second gas-selective metal is deposited upon said annealed membrane layer to thereby provide a second supported membrane. (a) providing a plating vessel containing a volume of a first plating solution having a concentration of a gas-selective metal ion; (b) placing a porous support, having a first surface and a second surface with each said surface being opposed to the other to thereby define a support thickness, into said plating solution and thereby contacting said first surface with said plating solution for a first time period while maintaining plating conditions within said plating vessel so as to promote the electroless deposition of said gas-selective metal ion from said plating solution onto said first surface of said porous support; and (c) circulating said plating solution through said plating vessel at a first circulation rate such as to provide for a first residence time of said plating solution through said plating vessel that is in the range of from 0.1 minutes to 30 minutes; (d) after said time period, removing said supported membrane from said plating solution and annealing said supported membrane to provide an annealed supported membrane having an annealed membrane layer; (e) placing said annealed supported membrane into a second plating solution, having a second gas-selective metal ion concentration, contained within said plating vessel or a second plating vessel and thereby contacting said annealed membrane layer with said second plating solution for a second time period while maintaining plating conditions within said plating vessel or said second plating vessel; (f) measuring the density of said annealed membrane layer to determine its density to liquid, and if said annealed membrane layer is determined to be liquid dense, then applying during the contacting of said annealed membrane layer with said second plating solution a pressure differential of a higher pressure and a lower pressure across said support thickness with said higher pressure being applied to the side of said first surface; and (g) circulating said second plating solution through said plating vessel or second plating vessel at a second circulation rate such as to provide for a second residence time of said second plating solution through said plating vessel or second plating vessel that is in the range of from 0.1 minutes to 30 minutes;