Historically, optical glasses were developed to provide desired optical characteristics; specifically, refractive index and dispersion. The batch composition required to achieve the optical performance demanded by industry sometimes resulted in glasses with weak chemical resistance. Due to the many different chemical constituents found in optical glass, it is impossible to define a single test method which can suffice as a means of describing the chemical behavior of all glasses. Since even a slight attack of the surface layer can render the optical element totally useless, the processor must gather and evaluate all the information available concerning the chemical behavior of the glass in order to minimize the risk of disastrous surface changes during processing.
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