Abstract: A method and/or system is provided for detecting and/or identifying inclusions (e.g., nickel sulfide based inclusions/defects) in glass such as soda-lime-silica based float glass. In certain example instances, during and/or after the glass-making process, following the stage in the float process where the glass sheet is formed and floated on a molten material (e.g., tin bath) and cooled or allowed to cool such as via an annealing lehr, energy such as infrared (IR) energy is directed at the resulting glass and reflectance at various wavelengths is analyzed to detect inclusions.

Abstract: A glass-ceramic article comprises a petalite crystalline phase and a lithium silicate crystalline phase. The weight percentage of each of the petalite crystalline phase and the lithium silicate crystalline phase in the glass-ceramic article are greater than each of the weight percentages of other crystalline phases present in the glass-ceramic article. The glass-ceramic article has a transmittance color coordinate in the CIELAB color space of: L*=from 20 to 90; a*=from ?20 to 40; and b*=from ?60 to 60 for a CIE illuminant F02 under SCI UVC conditions. In some embodiments, the colorant is selected from the group consisting of TiO2, Fe2O3, NiO, Co3O4, MnO2, Cr2O3, CuO, Au, Ag, and V2O5.

Abstract: A glass-ceramic article comprises: a center-volume composition comprising (on an oxide basis): 55-75 mol % SiO2; 0.2-10 mol % Al2O3; 0-5 mol % B2O3; 15-30 mol % Li2O; 0-2 mol % Na2O; 0-2 mol % K2O; 0-5 mol % MgO; 0-2 mol % ZnO; 0.2-3.0 mol % P2O5; 0.1-10 mol % ZrO2; 0-4 mol % TiO2; and 0-1.0 mol % SnO2. Lithium disilicate and either ?-spodumene or ?-quartz are the two predominant crystalline phases (by weight) of the glass-ceramic article. The glass-ceramic article further comprises tetragonal ZrO2 as a crystalline phase. The composition of the glass-ceramic article from a primary surface into a thickness of the glass-ceramic article can comprise over 10 mol % Na2O (on an oxide basis), with the mole percentage of Na2O decreasing from the primary surface towards the center-volume. The glass-ceramic article exhibits a ring-on-ring load-to-failure of at least 120 kgf, when the thickness of the glass-ceramic article is 0.3 mm to 2.0 mm.

Abstract: Dental composite composition including a glass ceramic and a curable organic material is described in which the glass ceramic includes a crystal phase having an average grain size of 50 to 400 nm, and the dental composite composition is provided as a dental prosthetic material exhibiting superior transparency and mechanical properties comparing to conventional composite products containing micro-sized crystal grains and also has excellent aesthetics and processability required for prosthetic materials for same-day dental prosthetic service.

Abstract: The present invention relates to a glass ceramic including crystals, and including, in mol % in terms of oxides: 65-75% of SiO2; 3-6% of Al2O3; 15-25% of Li2O; 0.2-4% of P2O5; 0.5-5% of ZrO2; and 0.01-0.5% of HfO2, in which the crystals include one or more kinds of crystals selected from the group consisting of ?-spodumene crystals, petalite crystals, and eucryptite crystals.

Abstract: Provided is a glass for a magnetic recording medium substrate, which is an amorphous oxide glass, in which an SiO2 content ranges from 56 mol % to 80 mol %, an Li2O content ranges from 1 mol % to 10 mol %, a B2O3 content ranges from 0 mol % to 4 mol %, a total content of MgO and CaO (MgO+CaO) ranges from 9 mol % to 40 mol %, and the oxide glass has a specific gravity of 2.75 g/cm3 or less, a glass transition temperature of 650° C. or higher, and a Young's modulus of 90 GPa or more.

Abstract: A glass-ceramic article that includes an article having a glass-ceramic composition, the composition including: SiO2 from about 45% to about 65%, Al2O3 from about 14% to about 28%, TiO2 from about 2% to about 4%, ZrO2 from about 3% to about 4.5%, MgO from about 4.5% to about 12%, and ZnO from about 0.1 to about 4% (by weight of oxide). The article can include a coefficient of thermal expansion (CTE) of about 20×10?7 K?1 to about 160×10?7 K?1, as measured over a temperature range from 25° C. to 300° C.

Abstract: A glass-ceramic article includes 50 mol. % to 80 mol. % SiO2; 10 mol. % to 25 mol. % Al2O3; 5 mol. % to 20 mol. % MgO; 0 mol. % to 10 mol. % Li2O; and 1 mol. % to 3 mol. % of a nucleating agent. The nucleating agent is selected from the group consisting of ZrO2, TiO2, SnO2, HfO2, Ta2O5, Nb2O5, Y2O3, and combinations thereof. The nucleating agent may comprise greater than or equal to 50% ZrO2 and less than 50% of at least one compound selected from the group consisting of TiO2, SnO2, HfO2, Ta2O5, Nb2O5, Y2O3, and combinations thereof. The glass-ceramic article may have a molar ratio of MgO to Li2O of greater than or equal to 1:1. The glass-ceramic article may satisfy the relationship 0.85?(MgO (mol %)+Li2O (mol %))/Al2O3 (mol %)?1.2. The glass-ceramic article may comprise a crystalline phase comprising hexagonal stuffed ?-quartz and glass.

Abstract: A coating for protecting a substrate from corrosion includes a first layer having a first composition applied on the substrate. The coating has a thickness of at least 0.5 ?m. The first composition includes an intercalated mixture of a polymer and a clay according to a formula of (Px/C1-x)v, where v comprises a volume of the intercalated mixture applied to the substrate.

Abstract: The present invention discloses a microcrystalline glass, a microcrystalline glass product, and a manufacturing method therefor. The main crystal phase of the microcrystalline glass comprises lithium silicate and a quartz crystal phase. The haze of the microcrystalline glass of the thickness of 0.55 mm is below 0.6%. The microcrystalline glass comprises the following components in percentage by weight: SiO2: 65-85%; Al2O3: 1-15%; Li2O: 5-15%; ZrO2: 0.1-10%; P2O5: 0.1-10%; K2O: 0-10%; MgO: 0-10%; ZnO: 0-10%. A four-point bending strength of the microcrystalline glass product is more than 600 Mpa.

Abstract: Transparent, dyed cook top or hob with improved color display capability, consisting of a glass ceramic with high quartz mixed crystals as predominant crystal phase, whereby the glass-ceramic contains none of the chemical refining agents arsenic oxide and/or antimony, with transmission values of greater than 0.1% in the range of the visible light within the entire wavelength range greater than 450 nm, a light transmission in the visible of 0.8-2.5% and a transmission in the infrared at 1600 nm of 45-85%.

Abstract: A crystallized glass that: has a visible light transmittance of at least 85% when the thickness thereof is converted to 0.8 mm; has a haze value of no more than 1.0% when the thickness thereof is converted to 0.8 mm; contains, in terms of mass % on an oxide basis, 58%-70% SiO2, 15%-30% Al2O3, 2%-10% Li2O, 0%-5% Na2O, 0%-2% K2O, 0%-1.8% SrO, 0%-2% BaO, 0.5%-6% SnO2, 0.5%-6% ZrO2, and 0%-6% P2O5; has a total SrO and BaO content of 0.1%-3%; and has a total Na2O and K2O content of 1%-5%.

Abstract: A transparent coloured lithium aluminium silicate glass ceramic and method of producing are provided. The glass ceramic has a brightness Y of 0.1% to 80% at thickness 4 mm. The glass ceramic has a D65 standard illuminant light, after passing through the glass ceramic with thickness 4 mm, with a colour locus in a white region W1 determined by coordinates in a chromaticity diagram CIExyY-2°: White region W1 x y 0.27 0.21 0.22 0.25 0.32 0.37 0.45 0.45 0.47 0.34 0.36 0.29.

Abstract: A glass-based article having an amorphous phase and a crystalline phase, and a first surface and a second surface opposing the first surface thereby defining a thickness (t) of the glass-based article. The glass-based article having a stress profile with a surface compressive stress (CS) and a maximum central tension (CT). The maximum CT is greater than or equal to 50 MPa and less than or equal to 200 MPa and is positioned within the glass-based article at a range from greater than or equal to 0.4·t and less than or equal to 0.6·t. The surface CS is greater than or equal to 200 MPa and less than or equal to 500 MPa, and a depth of compression (DOC) is from greater than or equal to 0.14·t and less than or equal to 0.25·t.

Abstract: A glass-based article may include from about 45 mol. % to about 80 mol. % SiO2; from about 0 mol. % to about 10 mol. % Na2O; less than about 5 mol. % K2O; a non-zero amount of Al2O; and an amorphous phase and a crystalline phase. The article may further in include a stress profile comprising a surface compressive stress (CS) and a maximum central tension (CT). A ratio of Li2O (mol. %) to R2O (mol. %) in the article is from about 0.5 to about 1, where R2O is the sum of Li2O, Na2O, and K2O in the article. CT may be greater than or equal to about 50 MPa and less than about 100 MPa. CS may be greater than 2.0·CT. A depth of compression (DOC) of the stress profile may be greater than or equal to 0.14·t and less than or equal to 0.25·t, where t is the thickness of the article.

Abstract: Multicolored glass-based articles and methods of manufacture are disclosed. The method includes forming a glass-based part and exposing a first region to radiation and a second region to radiation such that the first and second regions have different sized metallic nanoparticles, resulting in a multicolored glass article.

Abstract: A black lithium silicate glass ceramic is provided. The glass ceramic includes lithium silicate as a primary crystal phase and at least one of petalite, ?-quartz, ?-spodumene, cristobalite, and lithium phosphate as a secondary crystal phase. The glass ceramic is characterized by the color coordinates: L*: 20.0 to 40.0, a*: ?1.0 to 1.0, and b*: ?5.0 to 2.0. The glass ceramic may be ion exchanged. Methods for producing the glass ceramic are also provided.

Abstract: Glass ceramics having SiO2 as main crystal phase and precursors thereof are described which are characterized by very good mechanical and optical properties and in particular can be used as restoration material in dentistry.

Abstract: Quartz solid solution glass ceramics and precursors thereof are described, which are characterized by very good mechanical and optical properties and in particular can be used as restoration material in dentistry.

Abstract: The object of the present application is ?-quartz glass-ceramics (having very interesting optical, thermal expansion and feasibility properties), the articles including said glass-ceramics; the precursor glasses of said glass-ceramics, as well as the methods for elaborating said glass-ceramics and said articles. Said glass-ceramics having a composition, free, except for inevitable trace amounts, of arsenic oxide, antimony oxide and rare earth oxide, which contains, expressed in percentages by weight of oxides: 64 to 70% of SiO2, 18 to 24% of Al2O3, 4 to 5% of Li2O, 0 to 0.6% of SnO2, >1.9 to 4% of TiO2, 1 to 2.5% of ZrO2, 0 to 1.5% of MgO, 0 to 3% of ZnO, >0.3 to 1 of CaO, 0 to 3% of BaO, 0 to 3% of SrO, with BaO+SrO?3%, 0 to 1.5% of Na2O, 0 to 2% of K2O, with 0.

Abstract: The present invention provides a ceramic powder, in which ?-eucryptite or a ?-quartz solid solution is precipitated as a main crystal phase, and which includes TiO2 and/or ZrO2.

Abstract: Doped, low-temperature co-fired ceramic (LTCC) insulating substrates and related wiring boards and methods of manufacture are disclosed. The doped, LTCC insulating substrate is formed from a baked (e.g., sintered) glass-ceramic aggregate material formed from a glass material, a ceramic filler material, and a composite oxide. The crystallized glass-ceramic aggregate is then doped with Iron and/or Manganese before baking. Iron or Manganese can further reduce dielectric loss and the loss tangent of the LTCC insulating substrate formed from that glass material. The glass material becomes crystallized due to an oxide crystal phase being deposited on the glass material during baking, which reduces the dielectric losses. This may be important for the application use as wiring boards for high radio-frequency (RF) electrical circuits where low dielectric loss and loss tangent is desired to achieve a desired signal transmission delay performance.

Abstract: The present invention relates to a precision component and also to a glass-ceramic which can be used for producing the precision component.

Abstract: Photosensitive lithium zinc aluminosilicate glasses that can be selectively irradiated and cerammed to provide patterned regions of glass and lithium-based glass ceramic, and composite glass articles made from such glasses and glass ceramics are provided. Compressive and tensile stress at the interface of the lithium-based glass-ceramic and lithium zinc aluminosilicate glass may be used to frustrate crack propagation in such a composite glass/glass ceramic article. Methods of making composite glass articles comprising such lithium-based glass ceramics and lithium zinc aluminosilicate glasses are also provided.

Abstract: A group of glass-ceramic compositions nucleated with ZrO2 and P2O5 can develop a microstructure composed of spherulite grains, which produce a high fracture toughness (about 1.5 MPa·m0.5 or higher). Also, the glass-ceramic articles can be cerammed to have a CTE value of 30×10?7/° C. or lower.

Abstract: Crystallizable glasses, glass-ceramics, IXable glass-ceramics, and IX glass-ceramics are disclosed. The glass-ceramics exhibit ?-spodumene ss as the predominant crystalline phase. These glasses and glass-ceramics, in mole %, include: 62-75 SiO2; 10.5-18 Al2O3; 5-14 Li2O; 2-12 B2O3; and 0.4-2 Fe2O3. Additionally, these glasses and glass-ceramics can exhibit the following criteria: a ratio: [ Li 2 ? O + Na 2 ? O + K 2 ? O + MgO + ZnO ] [ Al 2 ? O 3 ] between 0.8 to 1.5. The glass-ceramics also exhibit colors at an observer angle of 10° and a CIE illuminant F02 determined with specular reflectance of a* between ?0.5 and 0.5, b* between ?2.5 and +2, and L* between 90 and 93.

Abstract: One subject of the invention is a cooking device comprising internal elements including at least one heating means, control and/or monitoring means and at least one light-emitting device, said internal elements being covered with at least one glass or glass-ceramic plate colored using vanadium oxide, at least one light-emitting device not being of red color seen through said plate, said plate intrinsically having a light transmission ranging from 2.3% to 40% and an optical transmission of at least 0.6% for at least one wavelength within the region ranging from 420 to 480 nm, said cooking device being such that at least one masking means intended to mask at least one part of said internal elements is placed on top of, underneath or within said plate.

Abstract: A highly crystalline transparent, translucent or opaque lithium aluminium silicate (LAS) glass-ceramic which has a proportion of residual glass phase of less than 20% by weight and also the use thereof is described.

Abstract: Disclosed are a chloroethylene-based nanocomposite composition comprising a chloroethylene-based resin; a nanoclay comprising a coupling agent bonded thereto; and at least one polymer selected from unsaturated organic acid-based resins or polycarboxylic acid-based resins, and a method of preparing the same.

Abstract: Glass ceramics having SiO2 as main crystal phase and precursors thereof are described which are characterized by very good mechanical and optical properties and in particular can be used as restoration material in dentistry.

Abstract: The present disclosure relates to a component for low-temperature applications, a process for producing such a component, and the use thereof.

Abstract: A glass ceramic substrate made of a transparent, colored LAS glass ceramic is provided. The glass ceramic has a gradient layer with keatite solid solution and an underlying core with high-quartz solid solution as predominant crystal phase. The keatite solid solution in a depth of 10 ?m or greater exceeds 50% of the sum of the high-quartz solid solution proportion and keatite solid solution proportion. The ceramization includes a crystal transformation step, in which the high-quartz solid solution is transformed at a maximum temperature in the range of 910° to 980° and a time period of between 1 and 25 minutes in part into the keatite solid solution.

Abstract: Provided is a filler powder that has a lower coefficient of thermal expansion than silica powder and is less likely to cause quality and color alteration of a resin when blended into the resin. The filler powder is made of a crystallized glass in which ?-quartz solid solution and/or ?-eucryptite is precipitated. The filler powder preferably has an average particle size D50 of 5 ?m or less. The filler powder preferably has a coefficient of thermal expansion of 5×10?7/° C. or less in a range of 30 to 150° C.

Abstract: Crystallizable glasses, glass-ceramics, IXable glass-ceramics, and IX glass-ceramics are disclosed. The glass-ceramics exhibit ?-spodumene ss as the predominant crystalline phase. These glasses and glass-ceramics, in mole %, include: 62-75 SiO2; 10.5-18 Al2O3; 5-14 Li2O; 2-12 B2O3; and 0.4-2 Fe2O3. Additionally, these glasses and glass-ceramics can exhibit the following criteria: a ratio: [ Li 2 ? O + Na 2 ? O + K 2 ? O + MgO + Zn ? O ] [ Al 2 ? O 3 ] between 0.8 to 1.5. The glass-ceramics also exhibit colors at an observer angle of 10° and a CIE illuminant F02 determined with specular reflectance of a* between ?0.5 and 0.5, b* between ?2.5 and +2, and L* between 90 and 93.

Abstract: The present disclosure relates to an insulation material for a conductor bar of an electric machine. An object of the invention is to provide for an alternative insulation material in the field of electric machines. The object is solved by an insulation material for a conductor bar for an electric machine comprising glass-ceramic flakes made from a heat treated silica glass precursor in the shape of flakes. Further disclosed are a corresponding method and the use of glass-ceramic flakes as an insulation material for a conductor bar of an electric machine.

Abstract: A colored glass, a surface of which is roughened in whole or in part. In the colored glass, an average value of gloss values measured at 9 points in the surface thereof at an incident angle of 60° in accordance with JIS 28741 (1991) is 30 or less, a ratio of a difference between a maximum gloss value and a minimum gloss value to the maximum gloss value is 20% or less, and a minimum value of visible-light transmittance at a thickness of 0.8 mm is 70% or less.

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: A surface that includes a three-dimensional surface, wherein a notch is present in said three-dimensional surface. The surface further includes a metal edge inserted into the notch and attached to the three-dimensional surface.

Abstract: Disclosed herein are glass-ceramics having crystalline phases including ?-spodumene ss and either (i) pseudobrookite or (ii) vanadium or vanadium containing compounds so as to be colored and opaque glass-ceramics having coordinates, determined from total reflectance—specular included—measurements, in the CIELAB color space of the following ranges: L*=from about 20 to about 45; a*=from about ?2 to about +2; and b*=from about ?12 to about +1. Such CIELAB color space coordinates can be substantially uniform throughout the glass-ceramics. In each of the proceeding, ?-quartz ss can be substantially absent from the crystalline phases. If present, ?-quartz ss can be less than about 20 wt % or, alternatively, less than about 15 wt % of the crystalline phases. Also Further crystalline phases might include spinel ss (e.g., hercynite and/or gahnite-hercynite ss), rutile, magnesium zinc phosphate, or spinel ss (e.g., hercynite and/or gahnite-hercynite ss) and rutile.

Abstract: Crystallizable glasses, glass-ceramics, IXable glass-ceramics, and IX glass-ceramics are disclosed. The glass-ceramics exhibit ?-spodumene ss as the predominant crystalline phase. These glasses and glass-ceramics, in mole %, include: 60-75 SiO2; 10-18 Al2O3; 5-14 Li2O; and 4.5 B2O3. The glass-ceramics also have a Vickers initiation crack threshold of at least about 25 kgf.

Abstract: Disclosed is a sintering process for ceramic sheets. After biscuit firing and glazing, a green body is placed in a kiln, wherein the temperature of the kiln is controlled such that: when the kiln temperature is 100-400° C., the temperature rise duration is 1-2 hours when the kiln temperature is 400-900° C., the temperature rise duration is 2-3 hours; when the kiln temperature is 900-1100° C., the temperature rise duration must reach 3 hours or more; when the kiln temperature is 1100-1350° C. the temperature rise duration is controlled to be 3-4 hours; and after the temperature reaches 1350° C., heat-preservation cooling is conducted; when the temperature drops to 1230-1270° C., the temperature is raised again to 1290-1310° C.; when the temperature drops again to 880-920° C., the kiln cover is opened for cooling, and the finished product is taken out.

Abstract: Beta-quartz glass-ceramics containing in their composition neither arsenic oxide nor antimony oxide and having a controlled transmission curve, articles made using the glass-ceramics, including cooktops, and precursor glasses of such glass-ceramics.

Abstract: A composition for ceramic substrates that includes a mixture of borosilicate glass powder and ceramic powder. The borosilicate glass powder contains 4% to 8% by weight B2O3, 38% to 44% by weight SiO2, 3% to 10% by weight Al2O3, and 40% to 48% by weight MO, where MO is at least one selected from CaO, MgO, and BaO. The mixing proportions of the borosilicate glass powder and the ceramic powder are 50% to 56% by weight the borosilicate glass powder and 50% to 44% by weight the ceramic powder. The ceramic powder has an average particle diameter D50 of 0.4 to 1.5 ?m.

Abstract: Methods, compositions, and articles provide for LAS-type glass-ceramics having specific thermo-mechanical, optical and coloration characteristics to yield generally brown-grey products. The glass-ceramic materials may include as colorants iron oxide, vanadium oxide, chromium oxide, cobalt oxide, nickel oxide and/or cerium oxide.

Abstract: Crystallizable glasses, glass-ceramics, IXable glass-ceramics, and IX glass-ceramics are disclosed. The glass-ceramics exhibit ?-spodumene ss as the predominant crystalline phase. These glasses and glass-ceramics, in mole %, include: 62-75 SiO2; 10.5-18 Al2O3; 5-14 Li2O; 2-12 B2O3; and 0.4-2 Fe2O3. Additionally, these glasses and glass-ceramics can exhibit the following criteria: a ? ? ratio ? : ? [ Li 2 ? O + Na 2 ? O + K 2 ? O + MgO + ZnO _ ] ? [ Al 2 ? O 3 ] between 0.8 to 1.5. The glass-ceramics also exhibit colors at an observer angle of 10° and a CIE illuminant F02 determined with specular reflectance of a* between ?0.5 and 0.5, b* between ?2.5 and +2, and L* between 90 and 93.

Abstract: Transparent or transparent dyed lithium aluminum silicate (LAS) glass ceramic material is provided that has an adapted thermal expansion. The material includes high-quartz mixed crystals as the predominant crystalline phase, and a thermal expansion between room temperature and 700° C. from 1.0 to 2.5·10?6/K.

Abstract: To provide a crystallized glass capable of attaining the same clarification effect as in the composition containing an arsenic component and an antimony component even in the case of having the composition containing no arsenic component, while maintaining various physical properties peculiar to a Li2O—Al2O3—SiO2-based crystallized glass. Disclosed is a crystallized glass which is characterized by containing a predetermined amount of Li2O, Al2O3, and SiO2 components (on an oxide basis), and containing a predetermined amount of BaO component (on an oxide basis) and the like. This crystallized glass preferably contains ?-quartz and/or ?-quartz solid solution as main crystal phase(s), an average crystal particle size of the main crystal phase(s) being preferably within a range between 5 and 200 nm.

Abstract: Disclosed herein are one or more of formable and/or color-tunable, crystallizable glasses; formed and/or color-tuned glass-ceramics; IXable, formed and/or color-tuned glass-ceramics; IX, formed and/or color-tuned glass-ceramics; a machine or equipment including a formed and/or color-tuned glass-ceramic; a machine or equipment including an IXable, formed and/or color-tuned glass-ceramics; a machine or equipment including an IX, formed and/or color-tuned glass-ceramics; one or more processes for making formable, crystallizable glasses crystallizable; one or more processes for making formable and/or color-tunable, crystallizable glasses; one or more processes for making formed and/or color-tuned glass-ceramics; one or more processes for making IXable, formed and/or color-tuned glass-ceramics; one or more processes for making IX, formed and/or color-tuned glass-ceramics; and one or more processes for using any one of formable and/or color-tunable, crystallizable glasses; formed and/or color-tuned glass-ceramics;

Abstract: To provide a crystallized glass housing excellent in properties suitable for a housing for an electronic device, such as shielding properties, high strength and production cost. A crystallized glass housing made of crystallized glass, said crystallized glass having a diffused transmittance of 15% or less in the entire light wavelength region of from 380 nm to 780 nm, as measured by using an integrated sphere.

Abstract: Process for preparing glass-ceramic body including the steps of providing a basic glass body and subjecting the basic glass body to a thermal treatment whereby a crystalline phase embedded in a glass matrix is formed. The basic glass body is made of a composition comprising 65 to 72 wt-% SiO2, at least 10.1 wt-% Li2O and at least 10.1 wt-% Al2O3 based on the total weight of the composition, the proportion of Li2O to Al2O3 being from 1:1 to 1.5:1. The thermal treatment involves a nucleation step followed by several crystallization steps at different temperatures, whereby at least two different crystalline phases are formed.