GB948301A - Improvements in or relating to the manufacture of optical glass - Google Patents

Abstract

Optical glass is manufactured and purified by founding the glass from calcium oxide, aluminium oxide, and one or more of the modifiers silicon dioxide, magnesium oxide, and barium oxide, and heating under vacuum at a pressure such that impurities are evaporated and loss of glass-forming constituents and modifiers is eliminated or reduced. Purification may take place at 1100-1750 DEG C. at a pressure of 0.01 to 200 microns of mercury. Impurities referred to are water vapour, carbon dioxide, oxygen, nitrogen, sulphur dioxide, and sodium and potassium oxides. Preferably, the glass-forming constituents and modifiers are combined in proportions which form a eutectic. In examples, the constituents are calcined, mixed, made into a paste with water, and founded in a platinum crucible at 1500 DEG C.; the glass is poured on to a cooled slab and the broken pieces heated in a graphite crucible under vacuum at a temperature rising to 1650-1750 DEG C. The Provisional Specification mentions as modifiers the compounds germanium oxide, calcium fluoride, and barium fluoride, and gives an additional example in which the modifier contains calcium fluoride.