Abstract: A method is provided for molding high-precision glass products where a piece of glass is heated at least in its surface portion and pressed between a pair of molds. Relative movement of the molds toward each other during the pressing is caused to follow change in dimension of a heated interval control member provided between the pair of molds, the interval control member having a coefficient of thermal expansion which is equal to or larger than that of the glass piece and therefore being capable of thermal contraction in the pressing direction by an amount which is substantially equivalent to or larger than that of the glass piece in the pressing direction due to cooling of the glass piece, and the change in dimension of the interval control member being caused by thermal contraction due to cooling thereof.

Abstract: According to one aspect of the invention, there is provided glass for a photomask consisting, in weight percent, of 45 to 62% SiO.sub.2, 3 to 15% B.sub.2 O.sub.3, 12 to 25% Al.sub.2 O.sub.3, 5 to 15% MgO, 0 to 5% CaO, 0 to 5% SrO, 0 to 5% BaO, 0 to 5% ZnO, 0.5 to 5% PbO, 0 to 20% La.sub.2 O.sub.3 +Gd.sub.2 O.sub.3 +Y.sub.2 O.sub.3, 0 to 1.5% Na.sub.2 O, 0 to 1.5% K.sub.2 O, 0 to 0.5% As.sub.2 O.sub.3 and 0 to 6% Sb.sub.2 O.sub.3. This glass is easy to melt and homogenize and has good resistivity to phase separation and excellent heat resisting and refractory properties, chemical durability, ultraviolet transmittance and metal vapor deposition property. According to another aspect of the invention, there is provided glass for a photomask consisting, in weight %, 45 to 60% SiO.sub.2, 0.5 to 12% B.sub.2 O.sub.3, 10 to 22% Al.sub.2 O.sub.3, 5 to 17% MgO, 0 to 5% CaO, 0 to 8% SrO, 1.5 to 15% BaO, 1.5 to 17% ZnO, 0.5 to 10% PbO, the total content of ZnO and PbO being at least 6%, 0 to 7% Ta.sub.2 O.sub.5 +Nb.sub.

Abstract: According to the first method according to the present invention, there is provided a method for manufacturing glass products by casting low viscosity glass into a mould while controlling free flow of the glass by storing and holding the glass continuously fed out of a feeder outlet in a region under the lower surface of a control member provided below the feeder outlet after a cutting step, whereby the operation for setting a next mould to receive the glass in position is facilitated, the shape of the flowing glass after cutting is made stable and homogeneous gob can be produced.

Abstract: An optical glass of a B.sub.2 O.sub.3 --SiO.sub.2 --La.sub.2 O.sub.3 --Yb.sub.2 O.sub.3 system and additionally containing SnO.sub.2 is stable in spectral transmissivity, is scarcely liable to tinting and has high refractive and low dispersive characteristics.

Abstract: An optical glass consisting basically of a B.sub.2 O.sub.3 -La.sub.2 O.sub.3 - ZrO.sub.2 -Nb.sub.2 O.sub.5 -PbO-BaO (and/or ZnO) system is free from a poisonous CdO or ThO.sub.2 component and has an excellent light transmission property in a transition region from an ultraviolet portion to a visible portion as compared with conventional optical glasses having the same optical properties.

Abstract: An optical glass consisting essentially of a B.sub.2 O.sub.3 --La.sub.2 O.sub.3 --Gd.sub.2 O.sub.3 --WO.sub.3 --ZrO.sub.2 and/or Ta.sub.2 O.sub.5 system has high refractive and low dispersive characteristics with optical constants of 1.85-1.96 for Nd and 43-28 for .nu.d, is free of poisonous ThO.sub.2, CdO and BeO ingredients, and suitable for mass production.

Abstract: An optical glass consisting essentially of a B.sub.2 O.sub.3 -SiO.sub.2 -La.sub.2 O.sub.3 -Gd.sub.2 O.sub.3 -Y.sub.2 O.sub.3 system and additionally containing ZrO.sub.2 has high refractive and low dispersive characteristics and is free of a poisonous thorium oxide ingredient.