Abstract: A method of applying a dielectric layer to a substrate, comprises applying a metallic suspension, for example, a layer of so-called "conducting silver" which is a suspension of silver particles in an organic binder or solvent to the substrate surface in an area which is not to receive the dielectric layer so as to form a mask. The organic binder or solvent is advantageously decomposed by heating so as to leave the metallic deposit mask. Thereafter, a layer of dielectric material is applied over the substrate in the areas which are not covered by the mask and, subsequently, the mask is removed, such as by dissolving it. A mask-forming coating for the application of the dielectric layers on the substrate comprises a metallic suspension which may be in the form of a lacquer-type liquid or paste which contain noble metals, for example, in the form of tinsels as the conducting constituent and also include organic binders or solvents of various kinds.