PURPOSE: To suppress alteration of the surface of a metallic product and to prevent the deterioration of the optical characteristic of the product surface over a long period by forming a transparent protective film consisting of a compd. excellent in gas barriering property on the surface of the product.
CONSTITUTION: A protective film 2 or 5 consisting essentially of the nitride or carbide of one kind among Si, Al, B, etc., is formed by sputtering on a metallic substrate 3 such as silver tableware and copper works of art or on the surface of a silver film 6, etc., formed on a glass substrate 7. Namely, the protective films 2 and 5 consisting of an Si3N4 film with the atomic ratio of N to Si controlled to 1.25-1.40 and contg. ≤1.0% O2 as an impurity are formed in ≥20 thickness. This Si3N4 protective film is excellent in gas barriering property and light transmittancy, the color tone and the brightness inherent in Ag or Cu are not deteriorated over a long period, and the resistance to wear and chemicals is improved.
NOSHIRO MAKOTO
OSAKI HISASHI
KADOWAKI KAZUO
