Abstract: A gold alloy for black coloring comprising gold and at least one coloring metallic element selected from the group consisting of Cu, Fe, Co, and Ti, a gold alloy for black coloring having the composition described above and further comprising at least one alloying element selected from the group consisting of Pt, Pd, Rh, Ir, Ru, Os, Ag, and Ni; a method for the production of a processed article of gold alloy possessing a black surface layer by the steps of shaping the gold alloy mentioned above, heat-treating the shaped gold alloy, and cooling; and processed article of gold alloy obtained by the method.

Abstract: A dielectric waveguide consists of dielectric strips sandwiched between two parallel conductive plates whose inner surfaces are covered with thin dielectric layers. The other space of the waveguide is filled with an appropriate dielectric medium which can be air or any other low loss dielectric material whose dielectric constant is smaller than that of the dielectric strips. In this waveguide, radiated waves which might be generated at the curved sections and any other discontinuities of the dielectric strips can almost completely be suppressed due to the cutoff property of the conductive plates, if the electric field of electromagnetic waves to be transmitted is polarized primarily parallel to the conductive plates and relevant parameters of the waveguide are chosen to satisfy the following inequality: ##STR1## where .epsilon..sub.