The raw glass for the manufacture of ophthalmic lenses is available in various geometries.
The most usable one is the blank as basic material for spectacle lens makers. Blanks are made by an automatic process where the pressing of molten glass, flowing directly out of the melting tank, is done in one continuous operation.
The conventional crown glass types are classified as follows:
- clear and tinted prescription glass types, i.e. glass with a luminous transmittance of 80 % or larger
- which, in general, are only manufactured in thicknesses sufficient for the production of 2.0 mm thick lenses without correction
|D0891||UV-W 0891||clear||Refractive index (n) = 1.5|
|D0886||BS 558||clear||Refractive index (n) = 1.58|