| http://www.w3.org/ns/prov#value | - Therefore, it was found in accordance with our researches that a glass composition comprising the following oxides in a weight percentage composition of 58 - 63% SiO2, 19 - 23.5% ZrO2, 1 - 2% Li2 O, 13 - 17% Na2 O, 0.5 - 3% K2 O, 0 - 0.5% RO, 0 - 0.5% Al2 O3 and 0 - 0.5% Mx Oy wherein R is an alkaline earth metal, M is a metal other than an alkaline earth metal, x and y are positive integers where
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