Optical articles prepared from hydrated glasses

Abstract

A glass article having an optical quality surface smoothness can be formed by molding a 'silanol' glass material against a die having a molding surface which is a mirror of that required for the glass article, thereby obviating glass grinding and polishing steps. The article is prepared by first forming an anhydrous base glass comprising, in mole percent on the oxide basis, about 72 to 82% SiO.sub.2, 10 to 17% Na.sub.2 O and/or K.sub.2 O, and 5 to 15% of an oxide or oxides selected from ZnO and PbO. The base glass may include up to 5% Al.sub.2 O.sub.3 and up to 3% of B.sub.2 O.sub.3, BaO and/or MgO. The anhydrous base glass is then hydrated to include a water content ranging from 0.5 to 10% by weight to form a 'silanol' glass. That glass is then molded against the die surface at a temperature ranging from about 250.degree. C. to 500.degree. C. and a pressure ranging from about 4,000 to 20,000 psi for a period of time sufficient to replicate the surface smoothness of the die on the glass and, depending on the molding process, yield a glass article containing about 0.5 to 10% by weight of 'tightly' bound total water.