PURPOSE: To manufacture an exterior part of a watch having physical properties similar to those of stainless steel, by cuplicating an electroformed mold for an exterior parts of a watch, the mold which has precise engraved surface, with synthetic resin etc., by making duplicated body made of Ni by electroforming, then by making boron diffuse and permeate into the surface thereof to form boride.

CONSTITUTION: An electroformed mold 1 having an engraved surface 2 corresponding to the shape of the watch case body is made of synthetic resin or rubber. The engraved surface 2 is finished previously to a flat mirror surface or a pattern finish. On the engraved surface 2 of the electroformed mold 1 is formed an electroconductive silver film 3 with an electroless silver plating soln. contg. a silver salt and a reducing agent. Then the electroformed mold is put into a Ni-plating soln., and a duplicated body 4 of a prescribed thickness is formed through Ni plating by energizing for a predetermined time. After completion of the electroforming, the duplicated body is separated from the electroformed mold 1, immersed into boron powder and is heated to form a hardened layer 5 by diffusion and permeation of the boron into the surface of Ni. Hereby, a watch case similar in color tone and hardness to stainless steel is manufactured.