The chemical compositions of optical glasses are optimized with highest priority for achieving best dispersion properties. From color-correction aspects, highly desirable glass types are located at the edges of the Abbe diagram glass island and can be produced only with sophisticated melting techniques from unique compositions. In such cases, dispersion properties prevail against all other properties such as thermal expansion, hardness, or chemical resistance.
Glass types for precise pressing must behave in a neutral manner against pressing tool materials and hence are tested and adapted accordingly. If possible, the compositions of optical glasses will be adjusted for better workability. The degrees of freedom for such adaptation, however, are restricted.
Chemical resistance is not a single, well-defined, unambiguous quantity. There is a large manifold of possible environments acting on glass during its processing. Grinding and polishing agents, environmental humidity, and even different quality grades of processing water may lead to different reactions of the glass items.
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