an improved two - step replication process for fabrication of porous metallic membranes is provided . a negative of a porous non - metallic template is made by infiltration of a liquid precursor into the template , curing the precursor to form a solid negative , and removing the template to expose the negative . metal is deposited to surround the exposed negative . removal of the negative provides a porous metallic membrane having pores which replicate the pores of the original template membrane . the negative is kept immersed in a liquid at all times between removing the template and depositing the metal . this immersion eliminates damage to the negative that would be incurred in drying the negative out between these processing steps . another aspect of the invention is metallic membranes prepared according to the preceding method . for example , metallic membranes having pores smaller on one side than on the other side of the membrane are provided .