Abstract: A spectacle glass which is colorless in the visible spectrum range, not transmissive in the ultraviolet spectrum range below 350 nm, has a refractive index n.sub.d higher than 1.56 and an Abbe number of more than 45, and which has an extremely low density, has the following composition (in % by weight):______________________________________ 12-40 P.sub.2 O.sub.5 13-34 Al.sub.2 O.sub.3 8-30 SiO.sub.2 0-16 B.sub.2 O.sub.3 4-12 TiO.sub.2 0-4 ZrO.sub.2 2-18 CaO 0-4 MgO 0-15 Na.sub.2 O 0-11 K.sub.2 O 0-6 Li.sub.2 O 0-12 Nb.sub.2 O.sub.5 0-8 ZnO.

Abstract: An ophthalmic glass particularly useful as a segment glass consists essentially of, in weight percent:______________________________________ SiO.sub.2 23-32 B.sub.2 O.sub.3 4-7 Al.sub.2 O.sub.3 0.5-3 BaO 23-30 PbO 15-30 TiO.sub.2 0.5-10 La.sub.2 O.sub.3 5-20 Nb.sub.2 O.sub.5 0-1.

Abstract: A thallium-containing optical glass composition which comprises the following oxides in the indicated proportions in mole %: SiO.sub.2 35-80, Tl.sub.2 O 1-30, Tl.sub.2 O+R.sub.2 O (R being an alkali metal) 1-35, ZnO 0-35, GeO.sub.2 0-30, BaO 0-25, TiO.sub.2 0-20, MgO 0-20, B.sub.2 O.sub.3 0-less than 10, ZrO.sub.2 0-2, Al.sub.2 O.sub.3 0-8, SnO 0-5, CaO 0-10, SrO 0-10, PbO 0-10, La.sub.2 O.sub.3 0-5, Bi.sub.2 O.sub.3 0-8, and Ta.sub.2 O.sub.5 0-2, and satisfies the following relations:5.ltoreq.ZnO+GeO.sub.2 +BaO+TiO.sub.2 +MgO+B.sub.2 O.sub.3 .ltoreq.40,0.1.ltoreq.ZrO.sub.2 +Al.sub.2 O.sub.3 +SnO.ltoreq.8,and0.ltoreq.CaO+SrO+PbO+La.sub.2 O.sub.3 +Bi.sub.2 O.sub.3 +Ta.sub.2 O.sub.5 .ltoreq.10.

Abstract: A thallium-containing optical glass composition which contains the following oxides in the indicated proportions in mole %:______________________________________ SiO.sub.2 35-80 Tl.sub.2 O 4-26 Tl.sub.2 O + R.sub.2 O 8-42 (in which R is an alkali metal) ZnO 6-26 ZrO.sub.2 0-2 Al.sub.2 O.sub.3 0-8 SnO and/or SnO.sub.2 0-5 B.sub.2 O.sub.3 0-less than 10 ______________________________________and satisfies the following relations:O.ltoreq.K.sub.2 O.ltoreq.104.ltoreq.Na.sub.2 O+Li.sub.2 O.ltoreq.260.1.ltoreq.ZrO.sub.2 +Al.sub.2 O.sub.3 +SnO and/or SnO.sub.2 .ltoreq.

Abstract: A new phototropic glass in which the phototropic properties arise from precipitations of silver halide and which in the unirradiated condition is slightly tinted or completely colorless while showing a brown color in the light-exposed condition, comprises, in known phototropic glass compositions, an additional content of at least 0.001 wt % of TeO.sub.2 and/or Yb.sub.2 O.sub.3.

Abstract: An optical glass comprising, in % by weight21.0 to 35.0% SiO.sub.2 ;0 to 10.0% B.sub.2 O.sub.3 ;0 to 4.0% Al.sub.2 O.sub.3 ;0.5 to 4.0% Li.sub.2 O;33.0 to 55.0% BaO+SrO+CaO+MgO+ZnO, with the proviso of19.0 to 45.0% BaO,0 to 15.0% SrO,0 to 20.0% CaO,0 to 5.0% MgO, and1.5 to 20.0% ZnO;8.0 to 23.0% La.sub.2 O.sub.3 ;2.0 to 8.0% ZrO.sub.2 ;0 to 10.0% TiO.sub.2 ;0 to 4.5% Nb.sub.2 O.sub.5 +Ta.sub.2 O.sub.5 ;0 to 5.0% WO.sub.3 ; and0 to 5.0% PbO.

Abstract: A phosphate optical glass comprises P.sub.2 O.sub.5 of 40-55 weight percents, R.sub.2 O of 20-40 weight percents (wherein R is an alkali metal or a mixture of alkali metals selected from the group consisting of Li, Na and K), TiO.sub.2 of 8-20 weight percents, WO.sub.3 of 1-12 weight percents (providing that the WO.sub.3 content be less than TiO.sub.2), As.sub.2 O.sub.3 of 0.1-4 weight percents, MgO of 0-7, CaO of 0-11, BaO of 0-12, ZnO of 0-12 PbO of 0-18, Nb.sub.2 O.sub.5 of 0-20, Ta.sub.2 O.sub.5 of 0-10, SiO.sub.2 of 0-3, ZrO.sub.2 of 0-3, La.sub.2 O.sub.3 of 0-3, Y.sub.2 O.sub.3 of 0-3 and F of 0-5.

Abstract: A cesium-containing optical glass comprising, by weight, 32-56% of SiO.sub.2, 6-25% of K.sub.2 O, 6-32% of Cs.sub.2 O, 0-30% of BaO, 0-2.5% of MgO, 5-34% of ZnO, 0-3% of ZrO.sub.2 and 0-5% of SnO.sub.2, provided that the total proportion of BaO, MgO and ZnO is 8-40% and the total proportion of ZrO.sub.2 and SnO.sub.2 is 0.2-6%. When this cesium-containing optical glass is treated in a molten bath containing potassium nitrate, the cesium ion in the glass is easily exchanged with a potassium ion and therefore, the cesium ion concentration gradually decreases radially outwardly from the central axis and the potassium ion concentration gradually increases in that direction. Thus, there is obtained a light converge-type lens in which the refractive index gradually decreases in the same direction.

Abstract: This invention is concerned with the preparation of moldable optical glasses having refractive indices of about 1.65-1.735, dispersions of about 38-58, transition temperatures lower than about 500.degree. C., softening points lower than about 600.degree. C., and satisfactory chemical durability consisting essentially, expressed in terms of parts by weight as calculated from the batch, of______________________________________ B.sub.2 O.sub.3 22-38 BaO 3-33 La.sub.2 O.sub.3 5-33 PbO 0-36 ZnO 0-14 CdO 0-12 SrO 0-10 BaO + La.sub.2 O.sub.3 + PbO + ZnO + CdO + SrO 55-68 Li.sub.2 O 0-4 Na.sub.2 O 0-4 Li.sub.2 O + Na.sub.2 O 1.5-4 F 1-8.

Abstract: An acid-soluble glass used in manufacture of a flexible fiber optic bundle and a process for manufacturing a flexible fiber optic bundle using the glass. The glass has a composition expressed by mol percent comprising more than 15.0% and less than 41.0% of SiO.sub.2, more than 29.0% and less than 54.0% of B.sub.2 O.sub.3, more than 6.0% and less than 23.0% of BaO, and more than 5.0% and less than 19.0% of at least one alkali metal oxide selected from the group consisting of Na.sub.2 O, K.sub.2 O and Li.sub.2 O, the total amount of SiO.sub.2, B.sub.2 O.sub.3 and BaO being more than 71.0% and less than 80.0%.

Abstract: An acid-soluble glass for use in making a flexible optical fiber bundle, which comprises the following composition:20.0 mol %<SiO.sub.2 <48.0 mol %25.0 mol %<B.sub.2 O.sub.3 <50.0 mol %5.0 mol %.ltoreq.BaO.ltoreq.6.0 mol %7.0 mol %<Na.sub.2 O, K.sub.2 O, or Li.sub.2 O, or total of the two or more thereof<18.0 mol %71.0 mol %<SiO.sub.2 +B.sub.2 O.sub.3 +BaO<80.0 mol %7.4 mol %<ZnO<12.0 mol %1.8 mol %<Al.sub.2 O.sub.3 <7 mol %The acid-soluble glass exhibits a high solubility in an acid, a high resistance to water, and a high viscosity at the fiber-forming temperature.

Abstract: The instant invention is directed to optical glass compositions capable of being shaped under the combined action of temperature and pressure in a mold so as to obtain articles having surfaces exhibiting highly precise reproduction of the mold walls. The inventive glasses demonstrate softening points not exceeding 500.degree. C., refractive indices between about 1.65-1.82, Abbe number between about 27-39, and consist essentially, in weight percent, of______________________________________ SiO.sub.2 8-20 B.sub.2 O.sub.3 5-20 PbO 50-70 Al.sub.2 O.sub.

Abstract: An optical quality glass suitable for use in ophthalmic lenses having a refractive index of at least 1.59, an Abbe number of at least 40.5, a density of no greater than 2.67 g/cm.sup.-3, and a coefficient of thermal expansion .alpha. of less than 90.times.10.sup.-7 per .degree.C. contains at least 90 mole % of SiO.sub.2, Li.sub.2 O, Na.sub.2 O, K.sub.2 O, CaO, and TiO.sub.2, and essentially does not contain Al.sub.2 O.sub.3, B.sub.2 O.sub.3, or oxides of elements having atomic weights above 90, such as Nb.sub.2 O.sub.5, La.sub.2 O.sub.3, or ZrO.sub.2.

Abstract: An optical glass comprising, in % by weight,18 to 38% P.sub.2 O.sub.5 ;3 to 30% Na.sub.2 O+K.sub.2 O,with the proviso of0 to 30% Na.sub.2 O and0 to 30% K.sub.2 O;8 to 65% PbO;1 to 45% Ta.sub.2 O.sub.5 ;0 to 20% Nb.sub.2 O.sub.5 ;0 to 15% TiO.sub.2 +WO.sub.3 ;0 to 25% BaO+CaO+ZnO+SrO+MgO,with the proviso of0 to 25% BaO,0 to 5% CaO,0 to 25% ZnO,0 to 20% SrO, and0 to 10% MgO;0 to 15% B.sub.2 O.sub.3 ;0 to 3% Li.sub.2 O;0 to 3% Al.sub.2 O.sub.3 ;0 to 3% ZrO.sub.2 ;0 to 3% Y.sub.2 O.sub.3 ;0 to 3% Gd.sub.2 O.sub.3 ; and0 to 3% La.sub.2 O.sub.3.

Abstract: Glasses consisting of 45-55 mol. % P.sub.2 O.sub.5, 15-40 mol. % BaO, 5-15 mol. % Li.sub.2 O, 5-35 mol. % PbO, 0-2 mol. % Al.sub.2 O.sub.3 and 0-6 mol. % F are suitable for the precision pressing of lenses.

Abstract: A borosilicate glass composition suitable for use as an eyeglass lens, characterized by having a refractive index nd.gtoreq.1.58, an Abbe number vd.gtoreq.45, a density .rho..ltoreq.2.75 g/cm.sup.3, and an excellent aptitude for chemical hardening, consisting essentially of the following composition, in weight percent:______________________________________ SiO.sub.2 51-65 B.sub.2 O.sub.3 2-14 Al.sub.2 O.sub.3 0-5 SiO.sub.2 + B.sub.2 O.sub.3 + Al.sub.2 O.sub.3 62-73 Li.sub.2 O 4-13 Na.sub.2 O 0-4 K.sub.2 O 0-4 Li.sub.2 O + Na.sub.2 O + K.sub.2 O 7-15 CaO 1-19 MgO 0-11 CaO + MgO 6-22 TiO.sub.2 0-8 ZrO.sub.2 0-9.

Abstract: The present invention is directed to fluorophosphate glasses containing about 3-21.5% Nb.sub.2 O.sub.5 and exhibiting softening points below 500.degree. C. The inventive glasses contemplate two general composition areas in weight percent:______________________________________ P.sub.2 O.sub.5 35-46 P.sub.2 O.sub.5 20-35 Al.sub.2 O.sub.3 3.5-6.5 Li.sub.2 O 0.5-5 Li.sub.2 O 0.8-3.0 Na.sub.2 O 0-10 Na.sub.2 O 3-10 Li.sub.2 O + Na.sub.2 O 0.5-10 Li.sub.2 O + Na.sub.2 O 5-10.5 PbO 0-40 BaO 18-44 Sb.sub.2 O.sub.3 0-25 CaO 0-12 PbO + Sb.sub.2 O.sub.3 20-50 SrO 0-15 BaO 0-20 MgO 0-7 Al.sub.2 O.sub.3 0-5 BaO + CaO + SrO + MgO 28-47 Nb.sub.2 O.sub.5 13-21.5 CaO + SrO + MgO <15 F 1-12 Nb.sub.2 O.sub.5 3-8.5 F 4.

Abstract: This specification discloses fluophosphate optical glass of low dispersion containing no beryllium and arsenic and having an optical constant nd=1.43-1.48 and .nu.d=85-97 and which can be produced stably and easily.

Abstract: This invention is directed to the production of glasses within the Li.sub.2 O-K.sub.2 O-ZrO.sub.2 -F-P.sub.2 O.sub.5 system having batch compositions as generally depicted in terms of mole percent in FIG. 2.

Abstract: There is provided a multi-component system glass fiber for optical communication which comprises a multi-component system glass for core having a composition comprising SiO.sub.2, BaO, Al.sub.2 O.sub.3, B.sub.2 O.sub.3, at least one alkali metal oxide selected from Na.sub.2 O, K.sub.2 O and Li.sub.2 O, MgO and CaO in amounts as specified in the specification and claims, and a multi-component system glass for clad layer having a composition comprising SiO.sub.2, Al.sub.2 O.sub.3, B.sub.2 O.sub.3, Na.sub.2 O, K.sub.2 O, Li.sub.2 O, at least one alkaline earth metal selected from MgO and CaO in amounts as specified in the specification and claims. The core in the glass fiber for optical communication according to the present invention shows lower optical loss and the clad layer shows high weathering resistance, and the glass fiber according to the present invention suffers from no devitrification during fiber drawing and is excellent in dimensional stability.

Abstract: Mercury thallium fluorophosphate glasses are disclosed that have very low transition temperatures, very high refractive indices and dielectric constants, and are resistant to moisture attack. The glasses are free of alkali metals and substitute thallium chloride in the glass batch as a modifier. The melted glass is largely oxide in nature, but the halogens appear to facilitate melting of these soft glasses.

Abstract: This invention relates to the production of glasses especially suitable for ophthalmic lenses, the glasses exhibiting refractive indices between about 1.695-1.705, dispersive indices between about 40.5-43.2, densities below about 3.2 g/cm.sup.3, weight losses as measured in the AO test of less than 0.15 mg/cm.sup.2, transmittances at 400 nm in 10 mm thickness of at least 75%, and consisting essentially, in weight percent of______________________________________ CaO 16-21.5 La.sub.2 O.sub.3 6-15 TiO.sub.2 3.5-<9 Al.sub.2 O.sub.3 5.5-12 Nb.sub.2 O.sub.5 3-11 ZrO.sub.2 2-10 B.sub.2 O.sub.3 20.5-25 SiO.sub.

Abstract: An improved optical glass having an index of refraction of .gtoreq.1.69, an Abbe number of .gtoreq.38, and a density of .ltoreq.3.25 g/cm.sup.3, represents a further development of another optical glass recently provided by the same inventors. The new glass has improved suitability for continuous-tank manufacture and increased acidproofness and differs from the other glass in its content of 0.5-4.0% by weight of P.sub.2 O.sub.5 ; its sum total of SiO.sub.2 +B.sub.2 O.sub.3 +Al.sub.2 O.sub.3 +P.sub.2 O.sub.5 being 38.5-41.5% by weight; and its sum total of MgO+CaO being 13-17.5% by weight. The full glass composition, e.g. is in % by weight:______________________________________ SiO.sub.2 26.0-32.5 B.sub.2 O.sub.3 6.0-12.0 Al.sub.2 O.sub.3 0-3.0 P.sub.2 O.sub.5 0.5-4.0 SiO.sub.2 + B.sub.2 O.sub.3 + Al.sub.2 O.sub.3 + P.sub.2 O.sub.5 = 38.5-41.5 Li.sub.2 O 0-5 Na.sub.2 O 0-6 K.sub.2 O 0-8 Li.sub.2 O + Na.sub.2 O + K.sub.2 O = 4.5-12.0 MgO 0-8 CaO 9-16 MgO + CaO = 13-17.

Abstract: An optical and ophthalmic glass having an index of refraction of .gtoreq.1.69, an Abbe number of .gtoreq.37, and a density of .ltoreq.3.30 g/cm.sup.3, consists essentially of (in % by weight):______________________________________ SiO.sub.2 18-36 B.sub.2 O.sub.3 3-18 GeO.sub.2 0-8 Al.sub.2 O.sub.3 0-6, wherein SiO.sub.2 + B.sub.2 O.sub.3 + Al.sub.2 O.sub.3 + GeO.sub.2 25-39 P.sub.2 O.sub.5 0-14, wherein SiO.sub.2 + B.sub.2 O.sub.3 + Al.sub.2 O.sub.3 + GeO.sub.2 + P.sub.2 O.sub.5 = 30-44 Li.sub.2 O 0-12 Na.sub.2 O 0-14 K.sub.2 O 0-18 Li.sub.2 O + Na.sub.2 O + K.sub.2 O = 2-18 MgO 0-15 CaO 7-25 MgO + CaO 15-32 SrO 0-13 BaO 0-17 ZnO 0-15 PbO 0-10 SrO + BaO + ZnO + PbO 0-20 TiO.sub.2 3-14 Nb.sub.2 O.sub.5 0-13 WO.sub.3 0-10 TiO.sub.2 + Nb.sub.2 O.sub.5 + WO.sub.3 = 10-21 ZrO.sub.2 0-15, La.sub.2 O.sub.3 0-20 Y.sub.2 O.sub.3 0-16 Gd.sub.2 O.sub.3 0-16 Yb.sub.2 O.sub.3 0-10 La.sub.2 O.sub.3 + Y.sub.2 O.sub.3 + Gd.sub.2 O.sub.3 + Yb.sub.2 O.sub.3 = 0-20 Ta.sub.2 O.sub.5 0-13 HfO.sub.2 0-5 SnO.sub.2 0-6.

Abstract: Fluorophosphate optical glass has the following composition in percent by weight:(a) By metaphosphate raw material conversion:______________________________________ Al(PO.sub.3).sub.3 13.0-39.0 Mg(PO.sub.3).sub.2 0-24.0 Ca(PO.sub.3).sub.2 1.0-20.0 Ba(PO.sub.3).sub.2 5.0-19.0 ______________________________________(The total amount of metaphosphate raw materials is 31-49 percent by weight.)(b) By fluoride raw material conversion: ______________________________________ MgF.sub.2 2.0-13.0 SrF.sub.2 0-20.0 BaF.sub.2 1.0-33.0 AlF.sub.3 0-8.0 YF.sub.3 0-8.0 ______________________________________(The total amount of fluoride raw materials is 19-47 percent by weight.)(c) By oxide raw material conversion: ______________________________________ BaO 10.0-36.0 Y.sub.2 O.sub.3 and/or Yb.sub.2 O.sub.3 1.5-12.0 ZnO 0-6.0 PbO 0-29.0 Nb.sub.2 O.sub.5 0-22.0 ______________________________________(The total amount of oxide raw materials is 20-42 percent by weight.

Abstract: Glass microspheres and other glass elements based on B.sub.2 O.sub.3, BaO, SiO.sub.2 and TiO.sub.2 have an improved combination of crushing strength, index of refraction, and, especially in some formulations, chemical resistance. The microspheres are especially adapted for use as retroreflective elements in pavement markings.

Abstract: This invention provides a light-transmitting glass having superior weatherability which has the following composition in % by weight:______________________________________ SiO.sub.2 38-70 B.sub.2 O.sub.3 4-22 Na.sub.2 O 8-24 K.sub.2 O 0-15 Li.sub.2 O 0-15 Cs.sub.2 O 0-15 Al.sub.2 O.sub.3 1-22 ZnO 1-16 TiO.sub.2 0-7 ZrO.sub.2 0-7 CaO 0-7 BaO 0-7 MgO 0-7 ______________________________________provided that Na.sub.2 O+K.sub.2 O+Li.sub.2 O+Cs.sub.2 O is 13 to 24, and Al.sub.2 O.sub.3 +ZnO+TiO.sub.2 +ZrO.sub.2 +CaO+BaO+MgO is 2 to 32.The aforesaid multicomponent glass exhibits superior water resistance even when used as a covering ingredient of a light-transmitting glass fiber.

Abstract: The present invention is directed to the production of essentially dry alkali metal (R.sup.1) aluminofluorophosphate glasses optionally containing at least one divalent metal (R.sup.2) which exhibits a transition temperature below about 350.degree. C., good chemical durability, resistance to weathering, and glass stability, and which demonstrate the capability of being molded at temperatures below 400.degree. C. into complex shapes. The alkali metal aluminofluorophosphate glasses consist essentially, as analyzed on an atomic basis, between about R.sup.1 AlP.sub.2 F.sub.2 O.sub.6 and R.sup.1 .sub.3.75 AlP.sub.3 F.sub.4 O.sub.9 with the requirement that the components comply with the following atomic ratios:F:Al >2 but <4 (preferred 3.+-.0.5)P:Al >2 but <3R.sup.1 :P >0.5 but <1.24 (preferred >0.75 but <1.1)Those values, expressed in terms of weight percent as analyzed on the oxide basis, convert to the following approximate ranges:R.sup.1.sub.2 O 13-38Al.sub.2 O.sub.3 16-23P.sub.2 O.sub.

Abstract: The present invention is drawn to glasses suitable for the fabrication of segments or buttons for multifocal ophthalmic lenses. The inventive glasses have refractive indices ranging between about 1.745-1.771, an Abbe number greater than 29 for a refractive index of 1.771 and greater than 31 for a refractive index of 1.745, a softening point between about 640.degree.-700.degree. C., a coefficient of thermal expansion (25.degree.-300.degree. C.) between about 90-98.times.10.sup.-7 /.degree.C., and satisfactory chemical durability. The glasses consist essentially, expressed in terms of weight percent on the oxide basis, of______________________________________ SiO.sub.2 28-32.5 Na.sub.2 O 2-9 K.sub.2 O 0-4 Li.sub.2 O 0-1 K.sub.2 O + Na.sub.2 O + Li.sub.2 O 4-10.5 BaO 0-22 La.sub.2 O.sub.3 0-20 BaO + La.sub.2 O.sub.3 14-22 PbO 28.5-34 ZnO 0-4 TiO.sub.2 0-9 ZrO.sub.2 2-6.5 Nb.sub.2 O.sub.5 0-10 TiO.sub.2 + Nb.sub.2 O.sub.5 4.5-12 ZrO.sub.2 + TiO.sub.2 + Nb.sub.2 O.sub.

Abstract: Glass objects, lenses in particular, can be pressed with precision from a glass which contains 45-55 mol. % P.sub.2 O.sub.5, 15-40 mol. % BaO, 5-15 mol. % Li.sub.2 O, 5-35 mol. % PbO, 0-2 mol. % Al.sub.2 O.sub.3 and 0-6 mol. % F.

Abstract: An optical glass having n.sub.D =1.63.+-.(1.5.times.10.sup.-2), v.sub.D =59.5.+-.1.0, a high chemical stability and a low tendency to crystallization is provided, consisting essentially of (in percent. by weight):______________________________________ SiO.sub.2 23-27 B.sub.2 O.sub.3 24-30 SrO 18-31 La.sub.2 O.sub.3 10-16 Al.sub.2 O.sub.3 2-4 BaO 0-10 CaO 0-5 ZnO 0-6 Y.sub.2 O.sub.3 0-5 ZrO.sub.2 0-2 Li.sub.2 O, Na.sub.2 O and/or K.sub.2 O 0-1.5 As.sub.2 O.sub.3 and/or Sb.sub.2 O.sub.3 0-1 F and/or Cl 0-1, ______________________________________wherein the sum of SiO.sub.2 +B.sub.2 O.sub.3 is 50-53, the weight ratio SiO.sub.2 :B.sub.2 O.sub.3 is 0.8-1.0, the sum SrO+BaO is 26-31, and the sum ZnO+La.sub.2 O.sub.3 is 12-17.

Abstract: Glasses containing fluorine. These glasses are characterized by the fact that they contain at least 25% in moles, approximately, of a fluoride or a mixture of fluorides MX(X.sub.1).sub.2, in which:X and X.sub.1 each represent a fluorine atom,and M then represents a metal chosen from among the group consisting ofgallium, iron, chromium, vanadium, indium, and the rare earths,or X represents an oxygen atom,X.sub.1 represents a fluorine atom,and M then represents a titanium atom, it being understood that the said glasses contain no hydrofluoric acid as a network former and that, in the case in which M represents a gallium or indium atom, the glasses do not contain more than 15% in moles of BaPO.sub.3 F.Application notably in obtaining glasses containing various cations conferring particular optical or magneto-optical properties.

Abstract: A potassium fluoro-borate glass, including silica and optionally alumina, containing at least 20 mole % potassium computed as K.sub.2 (O,F.sub.2), and wherein there are more fluorine atoms in the glass than oxygen atoms. The range of compositions includes low refractive index glasses, some with refractive indices less than that of silica, and high coefficient of thermal expansion glasses, some with coefficients matching those of aluminum, copper and brass.

Abstract: Glass compositions in the tin-phosphorus-oxyfluoride composition system exhibiting very low glass transition temperatures and capable of being modified by the addition of selected constituents to exhibit excellent stability in a humid environment, are described.

Abstract: A pentagonal prism for use in a viewfinder of a single lens reflex camera is made of a glass whose refractive index and Abbe number are not less than 1.6 and 45, respectively. Effective optical path regions on a pair of roof surfaces of the prism are left transparent so that viewfinder light can be totally reflected at both of the roof surfaces. A light absorbing paint is coated in an upper front surface, a pair of said surfaces of the prism as well as at regions other than effective optical path region of the roof surfaces, a bottom light incident surface and a rear light exit surface of the prism. The light absorbing paint prevents the occurrence of ghost images in the view field of the viewfinder. New type glasses suited for the prism are proposed.