Abstract: A production method of synthetic silica glass according to the present invention comprises a first step of ejecting a silicon compound and a combustion gas containing oxygen and hydrogen from a burner to effect hydrolysis of the silicon compound in oxyhydrogen flame to produce fine particles of silica glass, and thereafter depositing and vitrifying the fine particles of silica glass on a target opposed to the burner to obtain a synthetic silica glass ingot; a second step of heating the synthetic silica glass ingot or the like obtained in the first step up to a first retention temperature of not less than 900° C., retaining the ingot or the like at the first retention temperature, and cooling the ingot or the like at a temperature decrease rate of not more than 10° C./h down to a temperature of not more than 500° C.; and a third step of heating the synthetic silica glass ingot or the like obtained in the second step up to a second retention temperature of not less than 500° C.

Abstract: The invention concerns a method and a device for heating glass sheets in an oven, which are transported therein by a conveyor with horizontal rollers and wherein their surfaces are heated by heating means arranged above and beneath the sheets, by radiation and by forced convection by injecting hot gas into the oven, the gas injected beneath being in the form of jets whereof the axis of symmetry is oblique relative to the forward moving direction of the sheets on the conveyor and directed towards their lower surface.

Abstract: An optical apparatus includes a container filled with a gas containing hydrogen, and an optical element of silica glass which is accommodated in the container. The optical element is subjected to a heat treatment in a hydrogen atmosphere before being accommodated in the container. Within the container, the hydrogen concentration of the gas containing hydrogen is set to be less than 4% by volume, and the hydrogen having a partial pressure of in the range of 0.01 to 500 kgf/cm2 (0.98 to 49,000 kPa). By maintaining the optical element in an ambient containing hydrogen, defects in the silica glass are minimized even when high energy light such as ultraviolet light is emitted over a long period. Therefore, an increase in transmission loss and optical distortions in the silica glass are prevented.

Abstract: The present invention provides a method for reducing the density of sites on the surface of fused silica optics that are prone to the initiation of laser-induced damage, resulting in optics which have far fewer catastrophic defects and are better capable of resisting optical deterioration upon exposure for a long period of time to a high-power laser beam having a wavelength of about 360 nm or less. The initiation of laser-induced damage is reduced by conditioning the optic at low fluences below levels that normally lead to catastrophic growth of damage. When the optic is then irradiated at its high fluence design limit, the concentration of catastrophic damage sites that form on the surface of the optic is greatly reduced.

Abstract: In a method for transporting fixed glazing to be equipped with a coating, particularly curved glazing, through a coating plant, the glazing is transported by means of a transport device through the plant in such a way that one of its main sides is covered with protection against the coating substance that is to be deposited.

Abstract: A method for manufacturing a synthesized silica glass optical member, the method comprising: providing a porous silica glass body; heating the porous silica glass body in an atmosphere containing hydrogen or oxygen, and sintering the porous silica glass body in an atmosphere containing fluorine compound. Furthermore, a synthesized silica glass optical member manufactured by the method.

Abstract: A furnace (10) and method for heating conveyed glass sheets within a housing (12) includes forced convection heaters (24) spaced along the direction of conveyance both below and above a roll conveyor (20). Each forced convection heater (24) includes a gas burner assembly (32) generally adjacent one of the housing side walls and has an outlet (34) through which products of combustion are supplied to the housing heating chamber (18) at a location intermediate its side walls. A hot gas distributor (38) of each forced convection heater (24) includes an inlet (40) that is spaced from the outlet (34) of the gas burner assembly (32), and the hot gas distributor (38) has a suction fan (42) for drawing in heated products of combustion together with spent recirculating gas in the heating chamber (18) for mixing to provide heated gas that is distributed to the conveyed glass sheets.

Abstract: Slurries to be supplied to the surface of a rotating glass substrate for texturing the surface to create streaks contain aggregates having diameters not larger than 0.51 &mgr;m of polycrystalline diamond particles that are dispersed in water or a water-based aqueous solution that is free of any substance having an etching effect on a glass material. A glass substrate is textured by supplying such a slurry material on its surface as the substrate is rotated and a polishing tape is pressed and run against the substrate surface.

Abstract: A conveyor belt including a series of predefined sections and elevated support structures at the edges of each section for supporting items on the belt above the belt at each section.

Abstract: Methods of modifying fibers, such as glass fibers, are disclosed. The modified fibers can be used, for example, in a lead acid battery.

Abstract: A method for shifting the absorption peak wavelength in the wavelength range 900-1600 nm of an infrared radiation absorbing glass from less than 1100 nm to 1100 nm or longer without substantially changing the tint of the glass, comprising the step of irradiating with ultraviolet light of 400 nm or shorter at an energy density of 1.0×106 J/m2/hr or more to increase the content of FeO in the irradiated glass by reducing Fe (III) to Fe (II), the ultraviolet light irradiated glass thereby comprising 0.02 wt. % or more FeO in terms of Fe2O3. The glass to be irradiated comprises, in % by weight: 65 to 80% SiO2, 0 to 5% Al2O3, 0 to 10% MgO, 5 to 15% CaO, 10 to 18% Na2O, 0 to 5% K2O, 5 to 15% MgO+CaO, 10 to 20% Na2O+K2O, and 0 to 5% B2O3; 0.02% or more total iron oxide (T-Fe2O3) in terms of Fe2O3, 0 to 2.0% CeO2, 0 to 1.0% TiO2, 0 to 0.005% CoO, and 0 to 0.005% Se.

Abstract: A process of poling a silica material such as an optical fiber whereby electro-optic non-linearities are induced so that the material can function as a phase modulator and switch in optical communications applications. The poling is effected at an elevated temperature on the order of 450° C. or higher, using an electric field on the order of 800 V/&mgr;m or higher for a period of time in the range of one minute to several tens of minutes.

Abstract: An object of the present invention is to overcome the problems of the prior art technique, and to provide a heat treatment method as well as a heat treatment apparatus capable of heat treating, with higher efficiency, a synthetic quartz glass for optical use having higher homogeneity and higher purity. Another object of the present invention is to provide and a synthetic quartz glass for optical use.

Abstract: A process is provided for producing a transparent pane structure for motor vehicles, especially a transparent cover for motor vehicle roofs, in which under an outside pane there is a multilayer electrochrome element for influencing the transparency of the pane structure. In the process, the inside of the outer pane is coated with a complete, functional electrochrome package. Furthermore, a transparent pane structure produced using this process is provided.

Abstract: Disclosed is a method for controlling a heat treatment in the process of fabricating a high purity silica glass via a sol-gel process using a low temperature heater having an inhalation line and an exhaust line. Accordingly, the method includes the steps of (a) identifying whether or not the diameter of the exhaust line is varied; (b) controlling the mass flow of the process gas according to the changed diameter of the exhaust line in step (a); (c) measuring an exhaust gas velocity discharged through the exhaust line; (d) comparing the exhaust gas velocity measured in the step (c) with the exhaust gas velocity after the scale of the exhaust line is varied; and, (e) repeating steps (b)-(d) if the comparison result in step (d) is different.

Abstract: The present invention relates to a quartz glass blank for an optical component for transmission of ultraviolet radiation of a wavelength of 250 nm or shorter, and to a use of the quartz glass blank in microlithography in combination with ultraviolet radiation of a wavelength of 250 nm or shorter. Moreover, the invention relates to a procedure for manufacture of the quartz glass blank. A quartz glass blank of the described type should show little induced absorption and be optimized with respect to compaction and decompaction.

Abstract: A method for heat treating a synthetic quartz glass for optical use in a heating furnace, that comprises covering the surroundings of a synthetic quartz glass body with a SiO2 powder having a mean dissolved hydrogen molecule concentration of 1×1019 molecules/cm3 or higher, and then heat treating the body.

Abstract: A synthetic quartz glass to be used for light with a wavelength of from 150 to 200 nm, wherein the OH group concentration is at most 100 ppm, the hydrogen molecule concentration is at most 1×1017 molecules/cm3, reduction type defects are at most 1×1015 defects/cm3, and the relation between &Dgr;k163 and &Dgr;k190, as between before and after irradiation of ultraviolet rays, satisfies 0<&Dgr;k163<&Dgr;k190, and a process for its production.

Abstract: A heat diffusion plate and a heating plate are placed in a heat treatment chamber in this order. The heating plate is used for preliminarily heating a glass substrate to a temperature in a range from 200° C. to 400° C. The glass substrate thus preliminarily heated is subjected to a heat treatment by flash light irradiation by a xenon flash lamp. The flash light irradiation makes it possible to uniformly heat an amorphous silicon film on the glass substrate, and consequently to be poly-crystallized. Thus, it becomes possible to provide a heat treatment technique capable of carrying out a uniform heat treatment on the silicon film on the glass substrate sufficiently.

Abstract: A glass substrate for an information recording medium has an acid resistance represented by an etching rate of at most 45 nm/min. upon contact with a hydrofluoric acid having a temperature of 50° C. and a concentration of 0.1 weight %. The glass substrate has a recording surface having an average surface roughness Ra smaller than 0.3 nm.

Abstract: A method and apparatus for heating glass sheets in preparation of tempering. A furnace (1) is provided with upper and lower convection blasting conduits (11, 14) extending lengthwise of the furnace. The furnace is also provided with upper and lower radiation heating elements (12, 16). The convection heating air is pressurized with a compressor (3), cleaned with a filter (4). The upper convection heating air is heated with air discharged from the furnace in a plurality of separate heat exchangers (7), through which the convection heating air is passed into the upper convection blasting conduits (11). The amount of air discharged from the furnace (1) through the heat exchangers (7) is substantially equal to that blasted into the furnace for convection heating.

Abstract: Thin glass sheets may be processed in an effective fashion by electrostatically charging the sheets and applying them to an oppositely electrostatically charged carrier sheet. After processing is completed the carrier sheet may be removed and the processed sheet may be applied to its intended application such as to act as the front panel of an electronic display.

Abstract: High purity silicon oxyfluoride glass suitable for use as a photomask substrates for photolithography applications in the VUV wavelength region below 190 nm is disclosed. The inventive silicon oxyfluoride glass is transmissive at wavelengths around 157 nm, making it particularly useful as a photomask substrate at the 157 nm wavelength region. The inventive photomask substrate is a “dry,” silicon oxyfluoride glass which contains doped O2 molecules and which exhibits very high transmittance and laser transmission durability in the vacuum ultraviolet (VUV) wavelength region. In addition to containing fluorine and having little or no OH content, the inventive silicon oxyfluoride glass suitable for use as a photomask substrate at 157 nm contains intersticial O2 molecules which provide improved endurance to laser exposure. Preferably the O2 doped silicon oxyfluoride glass is characterized by having less than 1×1017 molecules/cm3 of molecular hydrogen and low chlorine levels.

Abstract: A method and plant for treating laminated glass having at least two glass sheets between which is arranged at least on intermediate sheet of non-glass material. The glass is attacked in a basic solution of fragmented laminated glass, so as to obtain an attack medium, wherein the fragments are disintegrated into non-laminated glass fragments and non-glass material, separating in a) the basic solution, b) the disintegrated non-laminated fragments and c) the disintegrated fragments of the non-glass material, and neutralizing the disintegrated fragments “b) and c)” before their subsequent recycling or upgrading.

Abstract: A conveyor belt including a series of predefined sections and elevated support structures at the edges of each section for supporting items on the belt above the belt at each section.

Abstract: A plurality of fixing holes are made in the upper and side faces of a hollow rectangular prism block body at least the top and four side faces of which are quartz glass or monocrystalline quartz rectangular plates. A plurality of reference members, each having a reference measuring face with which the fore end of a probe of a measuring apparatus is brought into contact, are inserted into the fixing holes, respectively, and secured in place. An inspection master block ensuring a high inspection accuracy by minimizing the effect of ambient temperature variation and a method for producing the same are thereby provided.

Abstract: A furnace particularly for heat treatments of glass sheets, comprising a longitudinally-elongated chamber which contains roller conveyor elements for the glass sheets. The furnace comprises irradiation-heating elements combined with first and second elements for heating by forced air convection in which the air temperature is controlled by adjusting its circulation rate, the elements being located respectively above and below the conveyor elements and therefore above and below the sheets being treated.

Abstract: High purity silicon oxyfluoride glass suitable for use as a photomask substrates for photolithography applications in the VUV wavelength region below 190 nm is disclosed. The inventive silicon oxyfluoride glass is transmissive at wavelengths around 157 nm, making it particularly useful as a photomask substrate at the 157 nm wavelength region. The inventive photomask substrate is a “dry,” silicon oxyfluoride glass which contains doped O2 molecules and which exhibits very high transmittance and laser transmission durability in the vacuum ultraviolet (VUV) wavelength region. In addition to containing fluorine and having little or no OH content, the inventive silicon oxyfluoride glass suitable for use as a photomask substrate at 157 nm contains intersticial O2 molecules which provide improved endurance to laser exposure. Preferably the O2 doped silicon oxyfluoride glass is characterized by having less than 1×1017 molecules/cm3 of molecular hydrogen and low chlorine levels.

Abstract: A method is provided for manufacturing a synthetic silica glass. The method includes the steps of maintaining a silica glass member, which is formed using a flame hydrolysis method and having an OH group concentration of about 500 ppm to about 1300 ppm, at a predetermined holding temperature for a predetermined period of time so as to substantially relax the structure of the silica glass member. The method further includes the step of subsequently cooling the silica glass member to a first predetermined temperature at a cooling rate of about 10 K/hour or less, and thereafter, cooling the silica glass member to a second predetermined temperature at a cooling rate of about 1 K/hour or less. The method further includes the step of further cooling the silica glass member to a third predetermined temperature at a cooling rate of about 10 K/hour or less.

Abstract: A thermoplastic resin composition comprises a compatible resin blend of a polyester sulfonate salt ionomer and a polyamide and at least one difunctional epoxy compound having at least one cyclohexane ring moiety and two terminal epoxy functional groups, wherein at least one of the two terminal epoxy functional groups is a substituent on the at least one cyclohexane ring moiety; and, optionally, a catalyst compound or rubber impact modifier.

Abstract: A manufacturing method for a glass product not having a rotatively symmetric body like an optical fiber fixing member but having a fine structure as of optical fiber engagement portions, to transfer the fine structure with a high precision without creating molding burrs, includes the steps of placing a glass material in a cavity defined by a lower mold, an upper mold, and a side mold, molding the glass material in the cavity with pressure into the glass product in so controlling that the glass material has a viscosity range of 106.5 to 109.

Abstract: The invention relates to a method for heating glass sheets to be tempered or heat-strengthened, in which method glass sheets are heated in a preheating furnace (1) by applying a hot-air blast and convection heating produced thereby to the opposite sides of a glass sheet and the preheated glass sheet is transferred from the preheating furnace (1) into a radiation heating furnace (2) for heating the glass sheet to a tempering temperature. During the convection heating of a glass sheet, the rotating speed of a hot-air fan (5) is increased while adjusting the heating effect of heating resistances (6) so as to maintain the temperature of blasted air substantially constant. Thus, the diminishing temperature difference between glass and air is compensated for by controlling the coefficient of heat transfer.

Abstract: A method for heated mold changing at a forming station (24) is performed by apparatus (32) in a heated chamber (22) where heated glass sheets are cyclically formed. A switching station (318) is located adjacent the forming station (24). An unloading station (320) and a mold preheating station (322) are each located adjacent the switching station. An unloading cart (324) is initially movable from the loading station (320) to the switching station (318) and then to the forming station (24) to receive one or more heated molds from the forming station and is subsequently moved from the forming station back through the switching station to the unloading station to permit unloading of each heated mold. A loading cart supports a second mold or a pair of molds for heating within the mold preheating station (322) and is movable from the mold preheating station to the switching station (318) and then to the forming station for mold loading.

Abstract: Silica grain of desired properties and size is created in a vacuum chamber. Fine silica powder is injected in the chamber or silica powder is formed in situ by combusting precursors. A plasma is formed centrally in the chamber to soften the silica powders so that they stick together and form larger grains of desired size. The grains are collected, doped, fused and flowed into tubes or rods. A puller pulls the tube or rod through a chamber seal into a lower connected vacuum chamber. The tube or rod is converted to rods and fibers or plates and bars in the connected chamber. Fused silica in a crucible tray is subjected to ultrasound or other oscillations for outgassing. Gases are removed by closely positioned vacuum ports.

Abstract: Provided is a method for manufacturing a glass optical element having at least one concave surface, comprising the following steps: softening a glass molding material by heating, molding the softened material with a first mold having a first molding surface and a second mold having a second molding surface by applying a pressure, the first molding surface comprising a first concave surface, the second molding surface comprising a convex surface, planar surface or second concave surface, the second concave surface having a curvature radius greater than that of said first concave surface, whereby shapes of the first molding surface and the second molding surface are transferred to the material, cooling the material so that a temperature of the material reaches a temperature equal to or lower than glass transition temperature (Tg), and removing the cooled material from either of said first mold or said second mold.

Abstract: A process for bending tempered glass. The process involves adhering two sheets of tempered glass in overlying relation and positioning a containment barrier such as vinyl sheets over the adhered unit. The glass is fractured and the unit manipulated into a desired shape. Once the adhesion has set, the vinyl is removed.

Abstract: A method for fabricating a mold tool for molding optical elements is taught which comprises heating a mold tool blank made from a vitreous material to a temperature above the glass transition temperature of the vitreous material; generating an axial viscosity gradient in the mold tool blank; pressing a punch into an optical quality mold surface of the mold tool blank, the punch including a pressing surface with a predetermined geometry for forming an optical feature; cooling the mold tool blank to a temperature below the glass transition temperature of the material; and removing the punch from the mold tool blank thereby creating the optical feature in the optical quality mold surface. The axial viscosity gradient is achieved by creating an axial thermal gradient.

Abstract: A number of unique processes are disclosed for manufacture of sintered high-purity quartz glass products in which a shaped silica body or preform is made from an aqueous slurry of micronized silica particles by gel casting, slip casting or electrophoretic deposition. The silica particles may comprise a major portion by weight of crystalline silica. In one embodiment of the invention the sintered quartz glass is transparent, substantially bubble-free and suitable for scientific or optical uses. In another embodiment the porous silica preform is fired in steam to increase the hydroxyl content and then nitrided in a nitrogen-hydrogen reducing atmosphere. A minute amount of chemically-combined nitrogen in the high-purity quartz glass is sufficient to provide a tremendous improvement in physical properties and an incredible increase in the resistance to devitrification.

Abstract: A simple and economical method is described for compacting or shrinking flat glass panes. The method ensures high temperature homogeneity in the glass. First, the glass panes are cleaned and then a stack of glass panes to be treated is assembled without applying a release agent to any of the glass panes. Then the stack of glass panes is placed between ceramic panels made of silicon-infiltrated silicon carbide and this stack together with the ceramic panels is subjected to a heat treatment in a radiation furnace at temperatures ranging from 300° C. to 900° C. The ceramic panels have a thermal conductivity, which, in the region of the heat treatment temperature, is at least 5 times as large as that of the glass panes. The ratio of the total thickness of the ceramic panels to the height of the glass stack should be at least 1/&lgr;/40W/(mK), wherein &lgr; is the thermal conductivity of the ceramic panel at the temperatures of the heat treatment.

Abstract: The application discloses a number of unique sintered quartz glass products together with new silica compositions and processes for making and using such products. Nitrided clear and opaque nitrided quartz products are disclosed having incredible physical properties resulting from the incorporation of very small, but effective, amounts (e.g., 25 ppm or more) of chemically bound nitrogen. Opaque quartz glass heat shields with remarkable resistance to transmission of infrared radiation are disclosed which can have a high bubble population density, such as 80 to 120 per mm2. These heat shields make possible remarkable improvement in the performance of tube furnaces and other reactors used in processing silicon wafers and other electronic components.

Abstract: A laser beam is radiated from a laser source. The laser beam radiated from the laser source is converged at a converging point inside of a work member to form cracks at the converging point and in its nearby area, by making a cross section of the laser beam at the converging point have a shape long in a first direction perpendicular to an optical axis of the laser beam. Markers easy to increase contrast can be formed in the work member.

Abstract: A sintered dense glass, alumina-doped optical fiber preform is stretched and is then heated to a temperature of 1490-1495° C. to remove bubbles without causing crystallization. Thereafter, the stretched glass body is either drawn directly into an optical fiber or overclad and then drawn into a fiber.

Abstract: A method for making a furnace for heating a glass sheet by lower electric resistance elements (50) supported by a furnace housing (12) below a roll conveyor (40) and by supplying a gas burner heated hot gas flow from a forced convection heater (56) that provides a dominant mode of external heat for heating the conveyed glass sheet from above. The furnace is manufactured by retrofitting an electric resistance heater type glass sheet furnace that initially has both lower and upper electric resistance elements (50) located below and above the roller conveyor (40). The lower electric resistance elements (50) are maintained while the upper electric resistance elements (50) are replaced with a gas burner forced convection heater (56).

Abstract: The method of the present invention overcomes the hot-sticking problems between an inorganic non-metallic material (=insulator) to be molded and a forming die by maintaining an assembly comprising a forming die and the insulator in a polarized state during molding. Processes using said method lead to an improved surface quality of the molded insulator. A device for reducing said hot-sticking comprises a die (2) which acts as conductor, an electrode (3) which may act as support for the insulator (1) to be molded, means (5) for polarizing the assembly of said conductor, insulator and electrode which means (5) are connected by live electric wires (4) with said die and electrode.

Abstract: A method and furnace for heating a glass sheet by lower electric resistance elements (50) supported by a furnace housing (12) below a roll conveyor (40) and by supplying a gas burner heated hot gas flow from a forced convection heater (56) that provides a dominant mode of external heat for heating the conveyed glass sheet from above. The furnace can also be manufactured by retrofitting an electric resistance heater type glass sheet furnace.

Abstract: In a method for molding glass products having a fine structure as of an optical fiber holder with a high size precision, a mold used for the molding has the fine structure in a size such that a size difference occurring when the glass product is cooled down to a room temperature where at the end of molding with a pressure a size of the fine structure of the mold for glass product and a size of a fine structure of the glass product formed by transfer of the fine structure of the mold are the same as one another is so adjusted that a size of the fine structure of the completed glass product falls within a permissive size precision range. The mold may has a size satisfying, as a size of a fine structure at a room temperature, a formula [1+(.alpha.g-.alpha.m).times..DELTA.T+.alpha.g'.times..DELTA.T'].times.Sg, wherein Sg denotes a size of a fine structure of thc glass product at the room temperature; .alpha.

Abstract: A furnace for heating glass sheets moving along the axis of the furnace has at least one differentiated heating cell, the heating elements of which disposed at the vault side are constituted of sets of electrical resistors controlled in temperature or in power independently for each set. A portion of the electrical resistors are mounted parallel to the axis of the furnace, the other heating cells each constituting a longitudinal heating zone independent of the other longitudinal zones and having, at the vault side, heating elements composed of sets of electrical resistors subdivided into several independent transverse sub-zones, in which the electrical resistors are mounted perpendicularly to the axis of the furnace. The invention is applicable to the manufacture of curved and toughened panes.

Abstract: Applicants have discovered that exposing optical fiber to an electrical arc produces a perturbation in its refractive index and that gratings can be made by exposing fiber to arcs at a series of locations along its length. In a first variation of the process, the fiber is exposed under tension to a high current arc (>15 mA) for a prolonged period of time (>2 s). Using this method, long period gratings can be successfully fabricated from fiber without the use of special dopants. In a second variation, the fiber is doped and the tension is reduced. The resulting grating is optically weaker but mechanically stronger. A third variation uses hydrogen-sensitized fibers and reduced currents and times. The resulting grating is optically and mechanically strong.

Abstract: A forced convection heating apparatus and process for heating glass sheets therewithin includes a housing (200) having an interior region, a conveyor for conveying the glass sheets through the interior region of the housing (200), a gas burner (204) operably associated with the housing (200) for producing hot combustion gases, thereby providing a heat input to the apparatus. An adjustor (210) is operably connected to, and controls, the inputs to the gas burner (204) to vary the heat input, and, thereby, maintain the temperature of the working fluid at a preselected set point. At least one velocity control for controlling the impingement velocity of the working fluid onto the top and/or bottom surfaces of the glass sheet is also provided. The impingement velocity, and thereby the rate of convective heat exchange between the working fluid and the glass sheet, is controlled independently of the heat input to the apparatus.

Abstract: A flat glass panel 1 for a picture display device of the flat type, is formed by two glass cover plates (3, 5) with at least one glass plate (4, 4', 4", . . . ) between them, and a vitreous frit (8) between the cover plates along the outer edges of the cover plates so as to obtain a box-type glass panel in which a channel structure is present. After heating to the melting temperature of the frit (8), the panel is cooled down to a transitional temperature of the frit, while the space between the cover plates is partly exhausted during the cooling-down phase at a temperature which lies between the melting temperature and the transitional temperature of the frit. Then the temperature is kept constant at approximately the transitional temperature until the frit has become undeformable, said space (13) between the cover plates (3, 5) being fully evacuated then. Finally, cooling-down continues to room temperature, and the space (13) inside the panel is hermetically sealed off.