| http://www.w3.org/ns/prov#value | - A glass consisting essentially of up to a total of from 45 to 65% by weight of MO and Zn() in the ratio of between about 1.25/1 to 2/ 1, where MO is a substance selected from the group consisting of 13210, SrO and mixtures thereof; 25 to 45% by weight of B 0 and 10 to 20.1% by weight of K 0 and Na O in the ratio of approximately 2/ 1. 6.
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