PROBLEM TO BE SOLVED: To obtain an evaluating method for easily specifying the type and concentration of corrosive gas by adopting a constitution to cover the part of a test piece with a transparent protective film which is invariable in transparency and non-releasable even if it is left to stand. ;SOLUTION: The test piece 4 is covered at one or both ends or the surface with a transparent protective film 41 of circular shape or the like, and the external appearance showing the state of the piece 4 at the time of manufacturing is preserved on the covering part by the film 41. The piece 4 is formed out of a metal piece such as copper, silver, an iron-nickel alloy, aluminum or iron corresponding to a comparison metal test piece. The transparent film 41 is formed out of an inorganic oxide film of SiO2. In or So-covered in thickness of 300Å or more by a sputtering method or depositing method or an organic polymer film formed by partial painting such as masking or dipping or screen printing. The transparent film 41 of the piece 4 has excellent weather resistance to corrosive gas. Even if the film 41 is left to stand for a long period in an environment of the corrosive gas, its transparency is not lost, and the film 41 is not released from the surface of the piece.;COPYRIGHT: (C)1997,JPO
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