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Lens material Abbe Number Crown Glass 58 CR39 58 Trivex 43 1.
It is softer than crown glass (see above), with a higher index of refraction and higher dispersion.
For most designs, prisms made of barium light crown glass (Bak4) are preferred over the industry-standard borosilicate crown glass (Bk7).
Archaeological evidence which would support an occupation in the early 19th century includes coins and medals dating to the War of 1812 or earlier, creamware or "Old Blue" transferware ceramics, fragments of crown glass windows, blown and hand-moulded glass bottles, metal buttons stamped or cast from a mould, and gun parts related to this period.
Flint glass (containing lead) produced a rather wider spectrum than crown glass (ordinary window glass) did.