Process to mold precision glass articles

A process for molding a glass lens having dimensional tolerances finer than 0.1% and surface figure tolerances finer than 0.2 .lambda./cm in the visible range of the radiation spectrum, which comprises the steps of:

• (a) preparing a mold having the precise internal configuration to produce said desired dimensional and surface figure tolerances in said glass lens;
• (b) preparing a glass preform closely matching the configuration of said mold;
• (c) exposing said preform to a temperature at which said glass exhibits a viscosity within the range of 10.sup.8 -10.sup.12 poises until said preform or a part thereof is heated to said temperature;
• (d) exposing said mold to a temperature substantially the same as that of said glass preform until said mold is heated to said temperature;
• (e) then placing said preform inside said mold;
• (f) applying a load to said mold with said preform therewithin, while said mold and at least that part of said preform in the vicinity of said mold are at substantially the same temperature, that temperature being within the range at which said glass exhibits a viscosity of 10.sup.8 -10.sup.12 poises, to force said preform into conformity with the surface of said mold to produce said glass lens of said dimensional and surface figure tolerances;
• (g) removing said glass lens from said mold at a temperature where said glass exhibits a viscosity of at least 10.sup.11, but not more than 10.sup.13, poises;
• and thereafter
• (h) fine annealing said glass lens to develop a controlled, uniform, and isotropic refractive index therein while retaining said dimensional and surface figure tolerances.