Abstract: Disclosed herein are embodiments of a borosilicate glass composition as may be useful for windshield and other applications in particular due to unique fracture behavior.

Abstract: A hot-formed, chemically prestressable glass article having a low percentage of crystals or crystallites, in particular a plate-shaped, chemically prestressable glass article, as well as to a method and a device for its production are provided. The glass article has a composition including the components SiO2, Al2O3, and Li2O and a content of seed formers (ZrO2, SnO2, and TiO2) of at least 0.8 wt %, as well as at most ten crystals, including crystallites, per kilogram of glass, which have a maximum diameter greater than 1 ?m and up to at most 5 ?m.

Abstract: A glass exhibiting non-frangible behavior in a region where substantially higher central tension is possible without reaching frangibility is provided. This region allows greater extension of the depth of compression in which fracture-causing flaws are arrested, without rendering the glass frangible despite the presence of high central tension region in the sample.

Abstract: Glass stack configurations including a carrier plate, setter plates, and glass sheets for thermal treatment of the glass sheets to form glass ceramic articles are provided. The glass stacking configurations and components described herein are selected to improve thermal uniformity throughout a glass stack during ceramming processes while maintaining or even reducing the stresses in the resultant glass ceramic article. Accordingly, the glass ceramic articles made according to the various embodiments described herein exhibit improved optical qualities and less warp than glass ceramic articles made according to conventional processes. Various embodiments of carrier plates, setter plates, parting agent compositions, and methods of stacking glass sheets are described.

Abstract: A chemically strengthened glass having a thickness t of 2 mm or less, having a compressive stress value (CS90) at a portion of 90 ?m deep from a glass surface being 25 MPa or more, and satisfying a number of fragments generated within a size of 25 mm×25 mm being 20 or less in a fracture test according to an indenter indentation test under a condition of holding a load ranging from 5 kgf to 10 kgf for 15 seconds with a pyramidal diamond indenter having an indenter angle of a facing angle of 60°.

Abstract: A window assembly includes a first pane of glass. The first pane of glass is chemically strengthened and exhibits a surface compressive stress of 400 MPa or more. A second pane of glass has a first major surface and a second major surface. The second major surface of the second pane of glass and a first major surface of the first pane of glass face each other. The second pane of glass includes 68-74 weight % SiO2, 2-6 weight % MgO, 1-10 weight % CaO, 12-16 weight % Na2O, 0-1 weight % K2O, 0.8-2.0 weight % Fe2O3 (total iron), 0-1.25 weight % TiO2, and 0-1.25 weight % CeO2. A polymeric interlayer is provided between the first pane of glass and the second pane of glass. The window assembly exhibits a direct solar transmittance of 55% or less and a total solar transmittance of 65% or less.

Abstract: A stress measurement device for strengthened glass includes a polarization phase difference variable member configured to vary a polarization phase difference of a laser light by one wavelength of the laser light or more; an imaging element configured to image a plurality of times at a predetermined time interval a scattered light emitted according to the laser light with the varied polarization phase difference entering the strengthened glass, and obtain a plurality of images; and an arithmetic unit configured to measure a periodic change in luminance of the scattered light using the plurality of images, calculate a change in a phase of the change in luminance, and calculate a stress distribution in a depth direction from a surface of the strengthened glass based on the change in the phase.

Abstract: To provide a laminated glass excellent in edge foaming resistance and rigidity. Laminated glass 1 in which a pair of glass plates and an intermediate film 4 provided between the pair of glass plates, are laminated, wherein the shear storage modulus of said intermediate film 4 is from 2 to 100 MPa, and the outer peripheral edge of the intermediate film 4 is present inside than the outer peripheral edges of the two glass plates constituting said pair of glass panels, at least at a part of the entire outer periphery of the laminated glass 1.

Abstract: To provide a laminated glass excellent in edge foaming resistance and rigidity. Laminated glass 1 in which a pair of glass plates and an intermediate film 4 provided between the pair of glass plates, are laminated, wherein the shear storage modulus of said intermediate film 4 is from 2 to 100 MPa, and the outer peripheral edge of the intermediate film 4 is present inside than the outer peripheral edges of the two glass plates constituting said pair of glass panels, at least at a part of the entire outer periphery of the laminated glass 1.

Abstract: Glass-based articles that include a hydrogen-containing layer extending from the surface of the article to a depth of layer. The hydrogen-containing layer includes a hydrogen concentration that decreases from a maximum hydrogen concentration to the depth of layer. The glass-based articles exhibit a high Vickers indentation cracking threshold. Glass compositions that are selected to promote the formation of the hydrogen-containing layer and methods of forming the glass-based article are also provided.

Abstract: An alkali-free glass of the present invention includes as a glass composition, in terms of mass %, 55% to 70% of SiO2, 15% to 25% of Al2O3, 0% to 1% of B2O3, 0% to 0.5% of Li2O+Na2O+K2O, 2% to 6% of MgO, 2% to 8% of CaO, 0% to 4% of SrO, and 6% to 12% of BaO, and has a strain point of more than 720° C.

Abstract: A glass-based substrate having a Young's modulus, a first surface, and a second surface. A coating, on at least one of the first and second surfaces, having a Young's modulus equal to or greater than the substrate Young's modulus. A compressive region having a compressive stress CS of from 750 MPa to 1200 MPa at a surface and extending to a depth of compression (DOC). The compressive region having a first portion and a second portion, the first portion extending from the first surface up to a first depth, the second portion extending from the first depth to the DOC, points in the first portion comprise a tangent having a slope that is less than ?15 MPa/micrometers and greater than ?60 MPa/micrometers, and points in the second portion comprise a tangent having a slope that is less than or equal to ?1 MPa/micrometers and greater than ?12 MPa/micrometers.

Abstract: A thermo-electric method for texturing a glass surface including, for example, simultaneously heating a glass substrate to a temperature less than its glass transition temperature and applying a bias across the glass substrate using a template electrode. The applied bias at the processing temperature induces localized ion migration within the glass, which results in the formation in the glass surface of a negative topographical image of the pattern formed in the electrode.

Abstract: An improved method and an improved apparatus are provided for producing a thin glass ribbon, which provide borders at the edges of the ribbon. The edges formed are of high mechanical quality and a formation of new secondary borders after the severing or at least the thickness of such secondary borders is reduced compared to the original borders. The method includes drawing the thin glass ribbon from a molten glass or from a preform, severing the borders, and cooling the resulting glass ribbon. The severing is effected at a location along the moving direction of the thin glass ribbon and at a time at which during the cooling of the thin glass ribbon the viscosity of the glass is in a range from 107 dPa·s to 1011 dPa·s, so that the edges of the thin glass ribbon newly produced by the severing of the borders are rounded off.

Abstract: Pre-sintered blanks based on lithium disilicate glass ceramic are described which are suitable in particular for the preparation of dental restorations.

Abstract: To provide a glass plate excellent in the internal transmittance of light rays in the visible region. A glass plate consisting of multicomponent oxide glass, which has an effective optical path length of from 25 to 200 cm, a thickness of from 0.5 to 10 mm, and an average internal transmittance in the visible region of at least 80% and a chromaticity Y of tristimulus values in the XYZ colorimetric system as defined in JIS Z8701 (Appendix) of at least 90%, under the effective optical path length.

Abstract: Methods for making a ceramic or glass-ceramic include spray-drying a mixture comprising batch materials to form agglomerated particles; bringing the agglomerated particles into contact with a plasma for a residence time sufficient to form fused particles; and annealing the fused particles at a temperature and for a time sufficient to form ceramic or glass-ceramic particles. The methods can be used to produce fused glass particles, ceramic or glass-ceramic particles, and ceramic or glass-ceramic articles, such as ceramic honeycombs.

Abstract: A method of making a substrate involves patterning the substrate into active areas and dicing lanes. After the substrate is patterned one or more stress layers are formed the substrate. A change in stress along a thickness of the substrate in the active areas is larger than a change in stress along the thickness of the substrate in the dicing lanes. The substrate is subsequently diced along the dicing lanes.

Abstract: The present invention relates to a method of fabricating an improved lithium silicate glass ceramic and to that material for the manufacture of blocks for dental appliances using a CAD/CAM process and hot pressing system. The lithium silicate material has a chemical composition that is different from those reported in the prior art with 1 to 10% of germanium dioxide in final composition. The softening points are close to the crystallization final temperature of 800° C. indicating that the samples will support the temperature process without shape deformation.

Abstract: A glass for a magnetic recording medium substrate permitting the realization of a magnetic recording medium substrate affording good chemical durability and having an extremely flat surface, a magnetic recording medium substrate comprised of this glass, a magnetic recording medium equipped with this substrate, and methods of manufacturing the same. The glass compositions disclosed comprise oxides of at least Si, Al, Li, Na, K, Sn and Ce, optionally Sb, but not comprising As or F. Additional oxides of Mg, Cs, Sr and Ba may be present. The oxides are presented as molar percentages, mass percentages and ratios thereof.

Abstract: Sodium containing aluminosilicate and boroaluminosilicate glasses are described herein. The glasses can be used as substrates or superstrates for photovoltaic devices, for example, thin film photovoltaic devices such as CIGS photovoltaic devices. These glasses can be characterized as having strain points ?535° C., for example, ?570° C., thermal expansion coefficients of from 8 to 9 ppm/° C., as well as liquidus viscosities in excess of 50,000 poise. As such they are ideally suited for being formed into sheet by the fusion process.

Abstract: A glass ceramic precursor glass and a glass ceramic having low levels of rhodium and a method of controlling the amount of rhodium in such glasses and glass ceramics. The precursor glass and glass ceramic contain from about 1 ppm to about 10 ppm and, in certain embodiments, from about 1 ppm to about 6 ppm rhodium. The method of controlling of reducing rhodium dissolution from a rhodium-containing material such as, for example, an alloy into a glass melt comprises controlling and/or lowering the partial pressure of oxygen at the rhodium-containing vessel/glass interface by imposing a high humidity condition around the external (non-glass-contact) surface of the rhodium-containing material. The lower concentration of rhodium minimizes its coloring effect on the white color of the glass ceramic.

Abstract: According to one aspect of the present invention, provided is glass for use in substrate for information recording medium, which comprises, denoted as molar percentages, a total of 70 to 85 percent of SiO2 and Al2O3, where SiO2 content is equal to or greater than 50 percent and Al2O3 content is equal to or greater than 3 percent; a total of equal to or greater than 10 percent of Li2O, Na2O and K2O; a total of 1 to 6 percent of CaO and MgO, where CaO content is greater than MgO content; a total of greater than 0 percent but equal to or lower than 4 percent of ZrO2, HfO2, Nb2O5, Ta2O5, La2O3 Y2O3 and TiO2; with the molar ratio of the total content of Li2O, Na2O and K2O to the total content of SiO2, Al2O3, ZrO2, HfO2, Nb2O5, Ta2O5, La2O3, Y2O3 and TiO2 ((Li2O+Na2O+K2O)/(SiO2+Al2O3+ZrO2+HfO2+Nb2O5+Ta2O5+La2O3+Y2O3+TiO2)) being equal to or less than 0.28.

Abstract: A crystallizable glass composition containing, in % by mole in glass component composition, 40 to 70% SiO2, 5 to 35% MgO, 5 to 35% BaO, 5 to 35% ZnO, 0 to 20% CaO, 0 to 20% SrO, 0 to 5% B2O3, 0 to 2% Al2O3, and 0 to 30% La2O3+Y2O3+Gd2O3+Nb2O5+Ta2O5. Provided is a crystallizable glass composition which has fluidity suitable for bonding, has a high coefficient of thermal expansion after undergoing thermal treatment, is less likely to degrade the power generation property of the fuel cell owing to evaporation of glass components even when exposed to high temperatures for a long period, and has excellent thermal resistance after bonding.

Abstract: Provided is the plate glass having high annealing temperature, high strength, excellent flatness and low viscosity, and manufacturing process thereof, which can be used for display and photovoltaic solar device. The plate glass contains (in mass %) boron oxide 0-3.9%, sodium oxide 0.01-14%, iron oxide 0.01-5%, fluorine oxide 0%, magnesia 7-22.2%, alumina 0.01-39%, wherein the content of silica is 1.9-4.1 times that of calcium oxide, the content of calcium oxide is 1.0-1.8 times that of magnesia.

Abstract: A process for producing a plate glass for a display device having a thickness of at most 1.5 mm by a float process, wherein the plate glass comprises, as represented by mole percentage based on the following oxides, from 67 to 75% of SiO2, from 0 to 4% of Al2O3, from 7 to 15% of Na2O, from 1 to 9% of K2O, from 6 to 14% of MgO and from 0 to 1.5% of ZrO2, has a total content of SiO2 and Al2O3 of from 71 to 75%, has a total content Na2O+K2O of Na2O and K2O of from 12 to 20%, and has a content of CaO of less than 1% if contained.

Abstract: Provided are a glass substrate for information recording media wherein air bubbles can be sufficiently removed, and an information recording medium using the glass substrate. The glass substrate contains 65 to 90 mass % of SiO2+Al2O3+B2O3 (where SiO2 is 45 to 75 mass %, Al2O3 is 1 to 20 mass %, and B2O3 is 0 to 8 mass %), 7 to 20 mass % of R2O (where R represents Li, Na, or K), 0.1 to 12 mass % of R?O (where R? represents Mg, Ca, Sr, Ba, or Zn), and 0.5 to 10 mass % of TiO2+ZrO2. Moreover, the glass substrate contains at least one multivalent element selected from among a group consisting of V, Mn, Ni, Mo, Sn, Ce, and Bi; the molar ratio of the total amount of the oxide of the multivalent element to the total amount of TiO2+ZrO2 is within the range of 0.05 to 0.50.

Abstract: A dopant host containing, in terms of mole %, 20 to 50% SiO2, 30 to 60% (exclusive of 30%) Al2O3, 10 to 40% B2O3, and 2 to 10% RO, wherein R represents alkaline earth metal, or being a laminate including a boron component volatilization layer containing, in terms of mole %, 30 to 60% SiO2, 10 to 30% Al2O3, 15 to 50% B2O3, and 2 to 10% RO, wherein R represents alkaline earth metal, and a heat resistant layer containing, in terms of mole %, 8 to 30% SiO2, 50 to 85% Al2O3, 5 to 20% B2O3, and 0.5 to 7% RO, wherein R represents alkaline earth metal. A process for producing a boron dopant for a semiconductor including the steps of slurrying a starting material powder containing a boron-containing crystalline glass powder, forming the slurry to prepare a green sheet, and sintering the green sheet.

Abstract: Embodiments of glass composition including at least about 65 mol % SiO2, Al2O3 in the range from about 7 mol % to about 11 mol %, Na2O in the range from about 13 mol % to about 16 mol %; and a non-zero amount of one or more alkali earth metal oxides selected from MgO, CaO and ZnO, wherein the sum of the alkali earth metal oxides is up to about 6 mol %, are disclosed. The glass compositions can be processed using fusion forming processes and float forming processes and are ion exchangeable. Glass articles including such glass compositions and methods of forming such glass articles are also disclosed. The glass articles of one or more embodiments exhibit a Vickers indentation crack initiation load of at least 8 kgf.

Abstract: A tempered glass substrate has a compression stress layer on a surface thereof, and has a glass composition comprising, in terms of mass %, 40 to 70% of SiO2, 12 to 21% of Al2O3, 0 to 3.5% of Li2O, 10 to 20% of Na2O, 0 to 15% of K2O, and 0 to 4.5% of TiO2, wherein the tempered glass substrate has a plate thickness of 1.5 mm or less, and an internal tensile stress in the tempered glass substrate is 15 to 150 MPa.

Abstract: Ion exchangeable glasses that comprise at least one of a transition metal oxide or a rare earth oxide and have compositions that simultaneously promote a surface layer having a high compressive stress and deep depth of layer or, alternatively, reduced ion exchange time.

Abstract: The present invention relates to a chemically strengthened glass for a display device, having a visible light transmittance Tva of 50% or more and less than 91% at a thickness of 1 mm using A light source, and an excitation purity Pe of less than 0.5% at a thickness of 1 mm.

Abstract: A glass composition including SiO2 in an amount from 74.5 to 80.0% by weight, Al2O3 in an amount from 5.0 to 9.5%>> by weight, MgO in an amount from 8.75 to 14.75% by weight, CaO in an amount from 0.0 to 3.0% by weight, Li2O in an amount from 2.0 to 3.25% by weight, Na2O in an amount from 0.0 to 2.0% by weight is provided. Glass fibers formed from the inventive composition may be used in applications that require high strength, high stiffness, and low weight. Such applications include woven fabrics for use in forming wind blades, armor plating, and aerospace structures.

Abstract: To provide glass to be used for chemically tempered glass, of which the strength is less likely to be reduced even when indentations are formed thereon. Glass for chemical tempering, which comprises, as represented by mole percentage based on oxides, from 62 to 68% of SiO2, from 6 to 12% of Al2O3, from 7 to 13% of MgO, from 9 to 17% of Na2O, and from 0 to 7% of K2O, wherein the difference obtained by subtracting the content of Al2O3 from the total content of Na2O and K2O is less than 10%, and when ZrO2 is contained, its content is at most 0.8%. Chemically tempered glass obtained by chemically tempering such glass for chemical tempering. Such chemically tempered glass has a compressive stress layer formed on the glass surface, which has a thickness of at least 30 ?m and a surface compressive stress of at least 550 MPa.

Abstract: A glass for a magnetic recording medium substrate permitting the realization of a magnetic recording medium substrate affording good chemical durability and having an extremely flat surface, a magnetic recording medium substrate comprised of this glass, a magnetic recording medium equipped with this substrate, and methods of manufacturing the same. The glass is an oxide glass not including As or F.

Abstract: An object is to devise a tempered glass substrate that has high mechanical strength and hardly undergoes breakage even though having a large size. A tempered glass substrate has a compressive stress layer in a surface thereof, and includes 1 piece/cm3 or less of devitrified stones containing Zr.

Abstract: Described herein are alkali-free, boroalumino silicate glasses exhibiting desirable physical and chemical properties for use as substrates in flat panel display devices, such as, active matrix liquid crystal displays (AMLCDs) and active matrix organic light emitting diode displays (AMOLEDs). In accordance with certain of its aspects, the glasses possess good dimensional stability as a function of temperature. The glasses comprise in mol percent on an oxide basis: 70-74.5 SiO2, 10.5-13.5 AL2O3, 0-2.5 B2O3, 3-7 MgO, 3-7 CaO, 0-4 SrO, 1.5-6 BaO, 0-0.3 SnO2, 0-03 CeO2, 0-0.5 As2O3, 0-0.5 Sb2O3, 0.01-0.08 Fe2O3 and F+Cl+BrRO/Al2O31.7 and 0.2MgO/RO0.45, RO being the sum of MgO, BaO, SrO and CaO.

Abstract: Disclosed are alkali aluminosilicate glasses having unexpected resistance to indentation cracking. The glasses obtain this high resistance as a result of a high level of surface compression accompanied by a shallow depth of layer. The advantaged glasses show greater resistance to radial crack formation from Vickers indentation than glasses with the same compressive stress, but higher depths of layer.

Abstract: A silicate glass that is tough and scratch resistant. The toughness is increased by minimizing the number of non-bridging oxygen atoms in the glass. In one embodiment, the silicate glass is an aluminoborosilicate glass in which ?15 mol %?(R2O+R?O—Al2O3—ZrO2)—B2O3?4 mol %, where R is one of Li, Na, K, Rb, and Cs, and R? is one of Mg, Ca, Sr, and Ba.

Abstract: Intermediate to high CTE glass compositions and laminates formed from the same are described. The glasses described herein have properties, such as liquidus viscosity or liquidus temperature, which make them particularly well suited for use in fusion forming processes, such as the fusion down draw process and/or the fusion lamination process. Further, the glass composition may be used in a laminated glass article, such as a laminated glass article formed by a fusion laminate process, to provide strengthened laminates via clad compression as a result of CTE mismatch between the core glass and clad glass.

Abstract: To provide a method for producing chemically tempered glass, whereby frequency of replacement of the molten salt can be reduced. A method for producing chemically tempered glass, which comprises repeating ion exchange treatment of immersing glass in a molten salt, wherein the glass comprises, as represented by mole percentage, from 61 to 77% of SiO2, from 1 to 18% of Al2O3, from 3 to 15% of MgO, from 0 to 5% of CaO, from 0 to 4% of ZrO2, from 8 to 18% of Na2O and from 0 to 6% of K2O; SiO2+Al2O3 is from 65 to 85%; MgO+CaO is from 3 to 15%; and R calculated by the following formula by using contents of the respective components, is at least 0.66: R=0.029×SiO2+0.021×Al2O3+0.016×MgO?0.004×CaO+0.016×ZrO2+0.029×Na2O+0×K2O?2.

Abstract: The object of the invention is a substrate for photovoltaic cell comprising at least one sheet of float glass provided on a face of at least one electrode, characterized in that said glass has a chemical composition comprising the following constituents, in a weight content that varies within the limits defined below: SiO2 69-75% Al2O3 ?0-3% CaO + MgO 11-16.2%? MgO ?0-6.5% Na2O 9-12.4%? K2O ?0-1.5%.

Abstract: A glass that is down-drawable and ion exchangeable. The glass has a temperature T35kp which the viscosity is 35 kilopoise. T35kp is less than the breakdown temperature Tbreakdown of zircon.

Abstract: A tempered glass according to one embodiment of the present invention is a tempered glass having a compression stress layer in a surface thereof, the tempered glass including as a glass composition, in terms of mass %, 45 to 75% of SiO2, 10 to 25% of Al2O3, 0 to 10% of B2O2, 0 to 8% of MgO, 0 to 20% of SrO+BaO, and 0 to 14% of Na2O. Herein, the term “SrO+BaO” refers to the total amount of SrO and BaO.

Abstract: Provided are: a glass substrate for p-Si TFT flat panel displays that is composed of a glass having high characteristic temperatures in the low-temperature viscosity range, typified by the strain point and glass transition point, having a small heat shrinkage rate, and being capable of avoiding the occurrence of the problem regarding the erosion/wear of a melting tank at the time of melting through direct electrical heating; and a method for manufacturing same. The present glass substrate is composed of a glass comprising 52-78 mass % of SiO2, 3-25 mass % of Al2O3, 3-15 mass % of B2O3, 3-25 mass % of RO, wherein RO is total amount of MgO, CaO, SrO, and BaO, 0.01-1 mass % of Fe2O3, and 0-0.3 mass % of Sb2O3, and substantially not comprising As2O3, the glass having a mass ratio (SiO2+Al2O3)/B2O3 in a range of 7-30 and a mass ratio (SiO2+Al2O3)/RO equal to or greater than 6.

Abstract: The present invention provides a glass substrate having high glass transition temperature and small compaction (C) in a heat treatment at a low temperature (150 to 300° C.), the glass substrate including SiO2, Al2O3, B2O3, MgO, CaO, SrO, BaO, ZrO2, Na2O, K2O, and Li2O, wherein each amount of these compounds is specifically limited, Al2O3+K2O is 7 to 27 mass %, Na2O+K2O is 11.5 to 22 mass %, MgO+CaO+SrO+BaO is 0.2 to 14 mass %, MgO+0.357Al2O3?0.239K2O?5.58 is ?3.0 to 1.5, Na2O+0.272Al2O3+0.876K2O?16.77 is ?2.5 to 2.5, a glass transition temperature is 500° C. or higher, and an average thermal expansion coefficient at 50 to 350° C. is 100×10?7/° C. or less.

Abstract: A Glass for chemical tempering, which includes, as represented by mole percentage based on the following oxides, from 60 to 75% of SiO2, from 5 to 15% of Al2O3, more than 7 and at most 12% of MgO, from 0 to 3% of CaO, from 0 to 3% of ZrO2, from 10 to 20% of Li2O, from 0 to 8% of Na2O and from 0 to 5% of K2O, and has a total content R2O of Li2O, Na2O and K2O of at most 25%, and a ratio Li2O/R2O of the Li2O content to R2O of from 0.5 to 1.0.

Abstract: Described herein are various glass compositions, glass articles, and information storage devices that comprise the glass articles as substrates therefor, along with methods for their manufacture and use.

Abstract: A method for producing bubble-free glasses is provided, in which a glass mixture that is arsenic-free and antimony-free with the exception of any unavoidable raw material impurities and a sulfate compound and SnO2 as refining agents are used. The glass mixture is melted and primarily refined in a first region of a melting tank, an average melting temperature (T1) is set at T1>1560° C. and an average melt residence time (t1) is set at t1>2 hours. The proportion of SO3 resulting from the decomposition of the sulfate compound is reduced to less than 0.002 wt. % as the primary refinement is carried out. A secondary refinement is carried out in a second region of the melting tank, an average melting temperature (T2) is set at T2>1640° C. and an average melt residence time (t2) is set at t2>1 hour.

Abstract: A method for producing bubble-free glasses is provided, in which a glass mixture that is arsenic-free, antimony-free and tin-free with the exception of any unavoidable raw material impurities and at least one sulfate compound as a refining agent are used. The glass mixture and refining agent are melted and primarily refined in a first region of a melting tank, an average melting temperature (T1) is set at T1>1580° C. and an average melt residence time (t1) is set at t1>2 hours. A secondary refinement is carried out in a second region, an average melting temperature (T2) is set at T2>1660° C. and an average melt residence time (t2) is set at t2>1 hour, and the proportion of the SO3 resulting from decomposition of the sulfate is reduced to less than 0.002 wt. %.