PURPOSE: To provided an attractive blackish color tone to a thin film, by forming a thin film in an atmosphere of a mixture of N 2 and inert gas containing small amounts of O 2 and CO 2 at the time of forming a thin film of Ti on the surfaces of outer ornament parts such as watch case, etc., by an ion plating method.
CONSTITUTION: An outer ornament 3 having conductive surface, such as watchcase, is fixed, as a material to be treated, to a holder 4 in a reaction vessel 1, and a metallic Ti 5 is disposed in a position opposite to the above. After the inside of the reaction vessel 1 is evacuated through an outlet 6, a gaseous mixture having a composition consisting of, by volume, 0.1W5.0% O 2 , 0.1W3.0% CO 2 , >50% N 2 , and the balance inert gas of Ar, He, etc., is supplied via an air inlet 7 at a pressure of 5×10 -4 W1×10 -2 Torr. Subsequently, by using the material 3 to be treated as cathode and also using Ti 5 as anode, a D.C. voltage of 1W450V is impressed from an electric power source 9 so as to evaporated Ti 5 by means of an electron beam from an electron gun 8. In this way, the thin film having jewellike brightness and blackish color tone and also having Ti as matrix can be formed on the surface of the material 3 to be treated.