Electroless metal coatings incorporating particulate matter of varied nominal sizes

In a process of the electroless metallization of a substrate comprising contacting said substrate with an electroless plating bath to deposit a metallic layer on the surface of said substrate, said plating bath comprising a metal salt, an electroless reducing agent thereof, and a quantity of finely divided insoluble particulate matter, said particulate matter being suspended in said plating bath, and thereafter smoothing the surface of said metallic layer thereby decreasing the surface roughness of said metallic layer, the improvement comprising utilizing as the particulate matter an admixture of one chemical substance having at least two distinct sizes of particulate matter, at least one of said sizes being relatively larger than at least one of said other sizes, such that the amount of energy required to smooth the surface of said metallic layer is reduced in comparison with the amount of energy normally required to smooth surfaces formed by the same general process, but using primarily only the larger size of particulate matter and furthermore wherein the relative ratio for the large size to the small size is less than 10:1.