| 摘要 |
PROBLEM TO BE SOLVED: To prevent the direct sticking of free water to the surface of lead glass and to prevent yellowing by forming a transparent film of silica on the surface of the lead glass. SOLUTION: A transparent film 4 formed on the surface of lead glass 1 may comprise any material if the material blocks interrupt the direct contact of the surface of the lead glass 1 with the external environment and has transparency but a film of silica is adopted from the viewpoint of the denseness, hardness and adhesion of the film and the antireflection of the glass surface. The transparent film 4 preferably has a refractive index close to that of the lead glass 1 because strong interference color is developed in the transparent film and impairs the appearance of the glass in the case of remarkably different refractive indexes. The thickness of the transparent film 4 is preferably <=0.5μm. In the case of >0.5μm, interference fringes are formed on the surface of the glass and impair light transmittance. Though a higher baking temperature gives a denser film in the formation of the transparent film 4, the lead glass 1 is deformed at a baking temperature above the strain point (450 deg.C) of the glass, accordingly the baking temperature is preferably set at the strain point or below.
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