Such glasses are superior in performance to concrete and to other barium borate glasses.
2.
The most common compositions are based on lead borates ( leaded borate glass or borosilicate glass ).
3.
However borate glass with more than 20 mol . % of lanthanum oxide is very durable under ambient conditions.
4.
Borate glasses have lower wavelength-refraction dependence in the blue region of spectrum than silicate glasses with the same Abbe number.
5.
After 1930, George W . Morey introduced the lanthanum oxide and oxides of other rare earth elements in borate glasses, greatly expanding the available range of high-index low-dispersion glasses.
6.
Glasses most closely approach the ideal of homogeneity and isotropy, and for accurate work, minerals are usually prepared by dissolving them in a borate glass, and casting them into a flat disc or " bead ".
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