WO2019051148A1

WO2019051148A1 - Glass compositions and related methods

Info

Publication number: WO2019051148A1
Application number: PCT/US2018/049830
Authority: WO
Inventors: Mark C. PEISER
Original assignee: Peiser Mark C
Priority date: 2017-09-07
Filing date: 2018-09-07
Publication date: 2019-03-14

Abstract

The present disclosure provides glass compositions and methods of preparing such glass compositions. Advantageously, such glass compositions are suitable for use in small-scale, detailed techniques such as filigrana, and do not incorporate toxic metals such as lead, arsenic, or antimony. For example, the disclosed compositions may include, by weight, 35% to 50% SiO_2,8% to 16% TiO₂, 16% to 21% Al₂O₃, 3% to 8% B₂O₃, and 17% to 21% of R₂O, where R is Li, Na, K, or combinations thereof.

Description

GLASS COMPOSITIONS AND RELATED METHODS

TECHNICAL FIELD

[0001] This application relates to glass compositions and, more particularly, to glass compositions providing opaque glasses, and methods of making and using the same.

BACKGROUND

[0002] Glass is a material that has long been used in a wide variety of different applications, including, without limitation, art and decor, drinking vessels and tableware, lighting structures, building structures (e.g., windows, window panes, fiberglass), and high tech applications such as optics, optoelectronics, and fiber optic communications. Typical glass compositions are formulated or derived from silicates, such as silica (i.e., silicon dioxide (Si0₂) or quartz), the primary constituent of sand.

[0003] From an artistic standpoint, glass items have been handcrafted for centuries, using a range of techniques. One such technique is referred to as "filigrana," meaning "filigree glass," and is believed to have originated in Murano, Italy in the 16^th century. The term "filigrana" is a generic term used to refer to blown glass made with colorless, white, and sometimes colored canes embedded therein. To make the canes, a clear gather of glass is immersed in opaque white (or colored) molten glass and this is gathered over with clear glass. The tip is cooled, affixed to a surface, and the opposite end is drawn to a given length (typically about 20 to 40 feet). These canes can be used as-produced, or can be further processed to provide canes with varying levels of complexity, e.g., "complex" canes. For example, compound canes are prepared by cutting cane into sections and rolling over and picking some of them up with clear glass. The clear glass with canes associated therewith is reheated and the cane is pressed into the glass; this is processed by cooling the tip, affixing it to a surface, and drawing and twisting the material. Another complex came is provided by picking up canes (typically four) on a mass of clear glass, reheating and marvering to form a round mass, and then pulling and twisting the resulting round mass. The rods resulting from these techniques can be cut into canes of desired length and incorporated with other glass in various ways (e.g., by laying such canes alongside traditional glass rods, fusing them together, and molding the material into a shape from which it can be blown and shaped. Filigrana patterns are admired for their delicate balance of texture and transparency.

[0004] Glass compositions suitable for producing the canes are very limited. It is generally understood that formulating glass compositions that provide opaque glass structures, in which the opaque color permeates the entire body of the glass structures, is problematic. For example, some existing opaque glass compositions incorporate toxic metals, such as lead, arsenic, and/or antimony. This is a concern as such compositions can generate toxic fumes and/or dust that may be ingested or inhaled by persons or animals. Further, the fumes and dust may be distributed throughout the air, water, or land and potentially contaminate the surrounding environment. In particular, even today, in light of the numerous concerns associated with these toxic metals, the commercial standard composition comprises lead and arsenic.

[0005] Accordingly, and in view of the above problems, a need exists for improved glass compositions and methods of making and using the same, which are suitable for formation of opaque glass, as well as for other applications.

SUMMARY

[0006] Glass compositions and methods of making and using the same are described herein. In some embodiments, the instant compositions provide opaque glasses that are devoid of toxic materials, such as lead (Pb), arsenic (As), and/or antimony (Sb).

[0007] Further, the glass compositions described herein exhibit desirable viscosity attributes and coefficients of thermal expansion, rendering such glasses suitable for glass blowing, casting, molding, extruding, and/or hand-working techniques (e.g., pulling, twisting, hand-forming, etc.).

[0008] The disclosed glass compositions are also suitable for forming structures that are fully or partially encased in clear glass, for example, to provide canes or rods utilized in various glass-blowing techniques not limited to filigrana and reticello techniques. The glass compositions set forth herein are suitable for any glass formation technique not inconsistent with the instant disclosure.

[0009] In one aspect, glass compositions are described herein. Such compositions comprise about 35-50 %, by weight, of Si0₂, 8-16 %, by weight, of Ti0_2, 16-21 %, by weight, of A1₂0₃, 3-8%, by weight, of B₂0₃, and 17-21 %, by weight, of R₂0, where R is Li, Na, K, or combinations thereof. The glass structures formed from the disclosed compositions are entirely opaque (or substantially entirely opaque), and extremely white, in certain embodiments, by virtue of incorporating titanium or titanium dioxide (Ti0₂). The opaque white color permeates the sectional portions of the glass structure to provide a substantially uniform and solidly white glass structure.

[0010] Moreover, opaque and colored (i.e., non-white) glass structures can also be formed using the compositions described herein as a respective base composition. Such a composition can further incorporate various additives, such as metal oxides, metal salts, or various other chemical compounds to provide colors, not limited to reds, yellows, blues, greens, or variations and/or combinations thereof. In some cases, oxides or salts of, for example, and without limitation, iron, cobalt, chromium, manganese, nickel, gold, silver, copper, cadmium, or combinations thereof may be incorporated into the disclosed compositions for providing opaquely colored glass structures.

[0011] In further aspects, opaque glass structures are disclosed. Such structures are formed from a glass composition comprising at least 35% Si0₂ and greater than 8% or greater than 10% by weight of Ti0₂. Such structures can comprise, in some instances, glass canes, rods, or other structures used in various glass-blowing techniques, including but not limited to filigrana techniques.

[0012] In yet further aspects, methods of making glass structures are disclosed. Such methods comprise providing a glass composition, heating the glass composition to form a molten glass, gathering an amount of molten glass on a surface, and forming the a amount of molten glass into a glass structure. The glass compositions for the methods and structures set forth herein can comprise at least 35% Si0₂, more than 8% of Ti0₂, and are devoid of Pb, As, and/or Sb.

[0013] Advantageously, the disclosed glass compositions can exhibit opacity. Although not intending to be limited by theory, it is believed that the disclosed compositions are phase separated opal glasses. In such glasses, at their melting temperature, they are homogeneous liquids; upon cooling, a white titanium dioxide phase separates from a glassy (usually substantially transparent) matrix. When this phase separation occurs, there is a marked increase in the viscosity of the glass. Such materials are in contrast to traditional opaque glass compositions used in, e.g., filigrana techniques and other applications, which are solid suspension opals. Solid suspension opals typically comprise lead glass which is supersaturated with arsenic. Such compositions rely on the limited solubility of arsenic, which is suspended throughout the material as white arsenic trioxide. These glasses generally have melting temperatures in excess of 2400°F to lower the viscosity sufficiently enough complete the melting and fining processes. Advantageously, the compositions disclosed herein can be melted and fined at lower temperatures (e.g., less than 2400°F, such as around 2300°F).

[0014] The invention includes, without limitation, the following embodiments.

[0015] Embodiment 1 : A method of preparing a filigrana glass product, comprising: providing a mixture comprising: 35% to 50%, by weight, of Si0₂; 8% to 16%, by weight, of Ti0₂; 16% to 21%, by weight, of A1₂0₃; 3% to 8%, by weight, of B₂0₃; and 17% to 21%, by weight, of R₂0, where R is Li, Na, K, or combinations thereof; melting the mixture; and forming canes by stretching the mixture.

[0016] Embodiment 2: The method of the preceding embodiment, further comprising combining the canes with molten glass and cooling so as to produce a filigrana glass product with canes embedded in transparent glass.

[0017] Embodiment 3: The method of any preceding embodiment, wherein the canes comprise white and substantially opaque cores at least partially surrounded by transparent material.

[0018] Embodiment 4: The method of any preceding embodiment, wherein the canes comprise non-white and substantially opaque cores at least partially surrounded by transparent material.

[0019] Embodiment 5: The method of any preceding embodiment, wherein the mixture and the canes are devoid of lead (Pb), arsenic (As), and antimony (Sb).

[0020] Embodiment 6: The method of any preceding embodiment, wherein the Si0₂, Ti0₂, B₂0₃ and A1₂0₃ are present in the form of particles having an average particle size of about 50-200 μπι.

[0021] Embodiment 7: The method of any preceding embodiment, wherein R₂0 comprises: < 1

%, by weight, of Li₂0; 12-15 %, by weight, of Na₂0; and/or 5-8 %, by weight, of K₂0.

[0022] Embodiment 8: The method of any preceding embodiment, wherein the mixture further comprises an amount of P₂0₅, SrO, and/or MgO, wherein the amount is greater than 0% to about 4%.

[0023] Embodiment 9: The method of any preceding embodiment, wherein melting the mixture comprises heating to less than about 2500 °F. [0024] Embodiment 10: The method of any preceding embodiment, wherein melting the mixture comprises heating to less than about 2400 °F (e.g., about 2200 °F to about 2400 °F or about 2300 °F to about 2400 °F).

[0025] Embodiment 11: The method of any preceding embodiment, wherein forming the canes comprises blowing, casting, molding, pulling, twisting, or extruding the molten glass mixture into the glass structure.

[0026] Embodiment 12: The method of any preceding embodiment, further comprising annealing the glass structure.

[0027] Embodiment 13: The method of the preceding embodiment, wherein annealing the glass structure comprises cooling the glass structure from about 1200 °F to about 75°F.

[0028] Embodiment 14: A glass structure formed by the method of any preceding embodiment.

[0029] Embodiment 15: The glass structure of the preceding embodiment, comprising the canes at least partially encased in transparent glass.

[0030] Embodiment 16: A glass-containing product, comprising: canes comprising opaque cores, wherein the cores have average diameters of 0.05 to 30 mm, wherein the canes comprise: 35%to 50%, by weight, of Si0₂; 8% to 16%, by weight, of Ti0₂; 16% to 21%, by weight, of A1₂0₃; 3% to 8%, by weight, of B₂0₃; and 17% to 21%, by weight, of R₂0, where R is Li, Na, K, or combinations thereof; wherein the canes are present in a matrix of transparent glass, and wherein the canes exhibit little to no dispersion into the matrix of transparent glass surrounding them.

[0031] Embodiment 17: The glass-containing product of the preceding embodiment, wherein each opaque core has an average diameter that is less than about 0.5 mm (e.g., about 0.05 mm to about 0.5 mm or about 0.1 mm to about 0.5 mm).

[0032] Embodiment 18: The glass-containing product of any preceding embodiment, wherein each opaque core has an average diameter that is less than about 0.2 mm (e.g., about 0.05 mm to about 0.2 mm or about 0.1 mm to about 0.2 mm) or less than about 0.1 mm (e.g., about 0.05 mm to about 0.1 mm).

[0033] Embodiment 17: The glass-containing product of any preceding embodiment, wherein each opaque core has a diameter that varies < 1 mm along the cane (or that varies < 0.5 mm, < 0.2 mm, < 0.1 mm, less than 0.05 mm, or less than 0.01 mm along the cane).

[0034] Embodiment 18: An opaque glass structure formed from a composition comprising at least 35% Si0₂ and more than 8% of Ti0₂.

[0035] Embodiment 19: The opaque glass structure of the preceding embodiment, wherein the glass structure is a phase separated opal glass.

[0036] Embodiment 20: The opaque glass structure of any preceding embodiment, wherein the composition is devoid of lead (Pb), arsenic (As), and antimony (Sb).

[0037] Embodiment 21 : The opaque glass structure of any preceding embodiment, wherein the composition is suitable for filigrana. [0038] These and other features, aspects, and advantages of the disclosure will be apparent from a reading of the following detailed description together with the accompanying drawings, which are briefly described below. The invention includes any combination of two, three, four, or more of the above-noted embodiments as well as combinations of any two, three, four, or more features or elements set forth in this disclosure, regardless of whether such features or elements are expressly combined in a specific embodiment description herein. This disclosure is intended to be read holistically such that any separable features or elements of the disclosed invention, in any of its various aspects and

embodiments, should be viewed as intended to be combinable unless the context clearly dictates otherwise. Other aspects and advantages of the present invention will become apparent from the following.

BRIEF DESCRIPTION OF THE FIGURES

[0039] FIGs. 1A-1C are schematic illustrations of glass structures comprising the glass compositions according to the exemplary embodiments described herein.

DETAILED DESCRIPTION

[0040] Embodiments described herein can be understood more readily by reference to the following detailed description, examples, and figures (also referred to as "FIGs"). The glass compositions and methods described herein, however, are not limited to the specific embodiments presented in the detailed description, examples, and figures. It should be recognized that the exemplary embodiments herein are merely illustrative of the principles of the present invention. Numerous modifications and adaptations will be readily apparent to those of skill in the art without departing from the scope of the invention.

In addition, all ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a stated range of "1.0 to 10.0" should be considered to include any and all subranges beginning with a minimum value of 1.0 or more and ending with a maximum value of 10.0 or less, e.g., 1.0 to 5.3, or 4.7 to 10.0, or 3.6 to 7.9.A11 ranges disclosed herein are also to be considered to include the end points of the range, unless expressly stated otherwise. For example, a range of "between 5 and 10" or "5 to 10" or "5-10" should generally be considered to include the end points 5 and 10. Additionally, in any disclosed embodiment, the terms "substantially," "approximately," and "about" may be substituted with "within [a percentage] of what is specified, where the percentage includes 0.1, 1, 5, and 10 percent.

[0041] The terms "a" and "an" are defined as "one or more" unless this disclosure explicitly requires otherwise. The terms "comprise" (and any form of comprise, such as "comprises" and "comprising"), "have" (and any form of have, such as "has" and "having"), "include" (and any form of include, such as "includes" and "including") and "contain" (and any form of contain, such as "contains" and "containing") are open-ended linking verbs. As a result, a composition or other object that "comprises," "has," "includes" or "contains" one or more elements possesses those one or more elements, but is not limited to possessing only those elements. Likewise, a method that "comprises," "has," "includes" or "contains" one or more steps possesses those one or more steps, but is not limited to possessing only those one or more steps.

[0042] Moreover, any embodiment of any of the compositions, structures, and methods described herein can consist of, or consist essentially of— rather than comprise/include/contain/have— any of the described steps, elements, and/or features. Thus, in any of the claims, the term "consisting of or "consisting essentially of can be substituted for any of the open-ended linking verbs recited above, in order to change the scope of a given claim from what it would otherwise be using the open-ended linking verb.

[0043] The term "opaque" refers to a material, structure, or portions thereof, that is neither transparent nor translucent (or very minimally translucent), and cannot be seen through it at all, or only slightly and not clearly. Opaque materials can be comprised of a single, uniform color (white and non- white colors), multiple colors, or opaque areas of color (white and non-white colors). The opaque materials may be used alone or in combination with clear glass.

[0044] Numerous modifications and/or adaptations of the compositions and methods described herein will be readily apparent to those skilled in the art without departing from the present subject matter. I. Glass Compositions

[0045] It is important to appreciate that not all glass compositions are suitable for all purposes. The glass compositions disclosed herein exhibit a unique combination of properties, rendering them particularly suitable for use in techniques such as filigrana. As referenced above, filigrana involves the production of thin, opaque glass canes (leading to thin lines in the final glass product into which they are incorporated).

[0046] As such, one feature of a glass composition suitable for use in this technique is workability. The glass composition must exhibit suitable workability to allow it to be pulled to form canes. This process typically involves providing the composition in molten form and producing a rod therefrom, gathering over this over with clear glass, and stretching the resultant material significantly, to afford thin "canes." In some embodiments, as will be disclosed herein below, the presently described compositions have viscosities that are lower through the working temperature range and thus are easier to form and "pull" into cane form.

[0047] For certain filigrana techniques (e.g., granulari), it is desirable for the glass composition to have a higher temperature/viscosity curve than the glass into which the canes of this composition will be incorporated. Such viscosity characteristics ensure that the filigrana glass composition, being suffer, becomes telegraphed to the surface of the final product, producing, e.g., optical ripples on the surface. It is to be understood that the viscosity characteristics may be modified depending on the particular application by adjusting the ratios of the glass composition components as described herein.

[0048] A glass composition suitable for use in this technique further exhibits desirable optical characteristics. Classical filigrana glasses are pure white and desirably opaque. As such, in some embodiments, the compositions disclosed herein exhibit (in cooled form) opacity, e.g., opacity comparable to or exceeding industry standards. In some embodiments, the compositions are described as being "pure white." In some embodiments disclosed herein, glass compositions suitable for filigrana may exhibit some color other than pure white. Such color is advantageously opaque.

[0049] In addition, filigrana generally requires that the glass composition comprising the canes maintains a tight edge and does not bleed into the surrounding glass when incorporated within a glass product. Advantageously, glass compositions according to the present disclosure demonstrate line definition properties comparable to or exceeding industry standards.

[0050] This combination of properties is provided by appropriate selection of components according to the present disclosure. Table 1 below contains exemplary components and amounts thereof in the glass compositions described herein.

Table 1. Exemplary Glass Compositional Ranges

* R is a metal or a metalloid (e.g. , Li, Na, K, or combinations thereof)

[0051] As shown in Table 1, the glass compositions described herein comprise and/or consist of at least about 35% Si0₂ by weight % of the composition. As such, Si0₂ is the primary component of the disclosed compositions (i.e., Si0₂ is present in a greater amount than any other single component). The Si0₂ can be present in the glass composition, for example, in an amount of about 35% to about 50% by weight, including about 35% to about 45% or about 37% to about 42% by weight.

[0052] The glass compositions disclosed herein further comprise and/or consist of at least about 8% Ti0₂ by weight or about 10% Ti0₂ by weight. The Ti0₂ may, for example, present in the glass composition in an amount of about 8% to about 16%, such as from about 10% to about 16%, 13% to about 16%, or about 14% to about 16% by weight, including about 11 wt.%, about 12 wt.%, about 13 wt.%, about 14 wt.%, about 15 wt.%, or about 16 wt.%. [0053] The glass compositions further comprise and/or consist of at least about 16% A1₂0₃. As such, in certain embodiments, A1₂0₃ makes up the second greatest amount of all single components present in the glass composition. In some embodiments, the content of A1₂0₃ in the glass compositions is about 16% to about 21% or about 17% to about 19% by weight of the glass composition.

[0054] In addition, the glass composition comprises or consists of at least about 17% by weight of R₂0, wherein R is an alkali metal (e.g., Li, Na, K), or a combination thereof. For example, in some embodiments, R₂0 is present in an amount of about 17% to about 21%, such as about 18% to about 21% or about 19% to about 21%. In some embodiments, this component includes a combination of Li₂0, Na₂0, and K₂0, which can be present in varying ratios. In some embodiments incorporating these three metal oxides, Na₂0 is present in the greatest quantity (e.g., about 10 to about 15%), K₂0 is present in the next greatest amount (e.g., about 5 to about 10%), and Li₂0 is present in the lowest amount (e.g., about 0.1 to about 1%). In certain embodiments, R₂0 comprises < 1 %, by weight, of Li₂0, 12-15 %, by weight, of Na₂0, and/or 5-8 %, by weight, of K₂O.The invention is understood to be not limited thereto, and in some embodiments, these components are present in different relative ratios with respect to one another, as long as the total R₂0 contribution to the weight of the glass composition is within the disclosed range.

[0055] B₂0₃ is present in the glass compositions in an amount of about 3 to 8 weight percent. For example, in some embodiments, the amount of B₂0₃ is about 5 to about 8 weight percent.

[0056] Also, in some embodiments, the glass compositions will contain relatively small amounts of other metal oxides, including SrO, P₂0₅, and/or MgO, which can make up (individually or in combination), for example, about 0% to about 4% (and, in some embodiments, about 2% to about 4%), by weight of the composition. For example, in some embodiments, the glass composition can include modifiers such as P₂0₅, MgO, derivatives thereof, or combinations thereof. In some embodiments, inclusion of these components can allow the viscosity curve to be adjusted to be similar to and suitable for other glass processing techniques (e.g., blowing processes such as casing and bit work). Where included, these modifiers can be provided in amounts of about 0% to about 4% by weight, e.g., about 2% to about 4% by weight (individually or in combination). In some embodiments, SrO can be incorporated within the disclosed glass compositions, e.g., in an amount of about 0% to about 4%, e.g., about 2% to about 4% by weight, e.g., about 3% by weight.

[0057] In one specific embodiment, the presently disclosed glass compositions comprises about 35- 50 % by weight of Si0₂, about 8-16 % by weight of Ti0₂, about 16-21 % by weight of A1₂0₃, about 3-8 % by weight of B₂0₃, and about 17-21 % by weight of R₂0 (e.g., where R is one or more of Li, Na, and K).

[0058] Notably, the glass compositions described herein are devoid of lead (Pb), antimony (Sb) and/or arsenic (As). By "devoid of is meant that no Pb, Sb, or As is intentionally added to the glass compositions disclosed herein (although very small amounts may be present as impurities in one or more of the other components of the glass composition). As such, the total amount of Pb, Sb, and As present in the disclosed glass compositions is generally less than 5% by weight, less than 3% by weight, less than 2% by weight, less than 1% by weight, less than 0.5% by weight, less than 0.1% by weight, less than 0.01% by weight, or less than 0.001% by weight. Such compositions are substantially nontoxic (including nontoxic) or at least substantially less toxic than existing compositions providing comparable opaque glass.

[0059] Although the glass composition provided herein is described specifically with respect to its use in filigrana, it is noted that it may have much broader applicability. For example, the compositions can be used in glass blowing and hand-working formation techniques other than filigrana techniques.

[0060] The glass compositions described herein have desirable viscosity curves and suitable expansion coefficients. The compositions described herein are particularly suitable, for example, in terms of viscosity and expansion coefficients, for filigrana glass-formation techniques, glass blowing techniques, and other hand-working techniques.

[0061] The glass compositions described herein, in some embodiments, advantageously produce a titanium opal glass, which is a phase separated glass. The temperature and extent of the phase separation provide the desired opacity, which can be controlled by the composition. In some embodiments, the phase separation occurs spontaneously upon cooling from the melt. In other embodiments, the phase separation occurs during a further heat treatment, such as during an annealing cycle. The phase separation, and its control, has implications on the opacity, viscosity, and/or color, while allowing fluid melt at relatively low temperatures.

[0062] Additionally, it is to be understood that glass compositions described herein can comprise any combination of features described hereinabove not inconsistent with the objectives of the present disclosure. Numerous modifications and adaptations will be readily apparent to those of skill in the art without departing from the scope of the invention. II. Methods of Making Glass Structures from Glass Compositions

[0063] In another aspect, methods of making glass compositions are described herein. Such methods initially comprise providing a glass composition. Any glass composition described hereinabove in Section I may be provided and used.

[0064] In one embodiment, the glass composition is provided by combining the components referenced above to form a glass composition precursor. The components can be combined in any order and are generally intimately mixed so as to form a substantially homogenous glass composition precursor mixture.

[0065] Prior to mixing, it may be desirable to ensure the sizes of the particles within the constituent powders are of a particular size. In some embodiments, the Si0₂ may be provided in the form of silica flour. Incorporating silica in the form of silica flour can be desirable, e.g., to obtain low melting temperature of the glass composition (e.g., below about 2300 °F). However, the invention is not limited thereto; other forms of Si0₂ with other particle sizes can be used. In certain embodiments, Si0₂ and Ti0₂ powders or particles can optionally be sifted and/or sorted using a 100 sized mesh such that extreme particles sizes (i.e., particles that are too large or too small) are not incorporated in the resultant glass compositions. The Si0₂ and Ti0₂ powders or particles can have an average particle size of about 50-500 μιη, preferably around 50-200 μιη, which form dense glass compositions and dense, opaque glass structures. In some embodiments, each of the other ingredients may be kept at 100 mesh particle sizes or finer. In some embodiments, each of the additional materials (e.g., A1₂0₃, P₂0₅, MgO B₂0₃, SrO R₂0, oxides, etc.) can also (optionally) be sifted and sorted so that such materials have an average particle size of between about 50-500 μιη, preferably around 50-200 μιη, or any subrange therebetween.

[0066] As such, in certain embodiments, the disclosed method may further comprise processing a glass composition precursor component to obtain the desired particle size (or size range). Such processing may include, e.g., sifting and/or sorting to ensure the component has an average particle size within the ranges referenced herein above.

[0067] The method can further comprise heating the resultant mixture (containing the glass composition precursor components described herein above) to form a molten glass. The glass composition can be heated in a furnace to temperatures of between about 2000-2500 °F to melt the glass and form a container (e.g., crucible, vessel, etc.) of molten glass. The molten glass, or an amount or portion thereof, may then be cast or gathered on or over a surface of a forming structure or tool, such as, for example and without limitation, a punty, puntil rod, pipe, tube, rod, mandrel, pontil, block, mold, bench, pad, paddle, or casting frame, and formed into a glass structure. During formation, the molten glass can partially solidify, and the structure can be reheated and continually reformed or reworked, until a desired structure is obtained. The glass structures can comprise and/or be formed into bars or canes (e.g., via casting or blowing) and then be reheated and formed into a subsequent glass structure at a later time.

[0068] The glass structures can be formed using various methods and techniques, including, without limitation, blowing, casting, molding, pulling, twisting, or extruding the molten glass mixture into the glass structure.

[0069] Once a desired glass structure is obtained, it can optionally be annealed. Where used, annealing temperatures can range from between 600-1200 °F, or any subrange therebetween (e.g., 700- 1200 °F, 900-1200 °F, etc.).

[0070] Various methods of forming glass structures can comprise any combination of aspects described hereinabove not inconsistent with the objectives of the present disclosure. Numerous modifications will be readily apparent without departing from the disclosed subject matter.

III. Glass Structures

[0071] In further aspects, glass structures are disclosed. Such structures can be formed using any of the glass composition described hereinabove in Section I and using any of the methods described in Section II. [0072] In certain embodiments, the glass structures described herein are canes or rods useful for other glass forming techniques. For example, the canes or rods can be used in filigrana techniques.

[0073] In some embodiments, the glass rods comprise an opaque center partially or fully encased in a layer of clear glass. "Opaque" as used herein means impenetrable to light, and is typically evaluated visually (with the naked eye). Advantageously, the opacity exhibited by glasses prepared according to the present disclosure can be equal to or exceed commercial standards for opacity. As referenced above, this opacity is associated, at least in part, with the phase separated opal nature of the processed glass disclosed herein. Although not intending to be limited by theory, the opacity is believed to arise due, at least in part, to the high refractive index of Ti0₂ and the referenced particle sizes in the precursor components.

[0074] The center can be white, non-white, or combinations of white and non-white colors. The rods can be stretched or pulled into long rods having lengths between 4-45 feet, or any subrange thereof, and diameters ranging from 3-30 mm, or any subrange thereof. Notably, there is a clearly defined line between the opaque center and the layer of clear glass. The surfaces of the opaque center are substantially smooth along the length of the rod, and the thickness of the opaque center can vary minimally (e.g., < 1 mm, < 0.5 mm, etc.). These canes can be incorporated within other glass compositions (e.g., within clear/transparent glass) to form decorative aspects within the final product. The clear/transparent glass may, in some embodiments, be in the form of vessels, art panes, and the like.

[0075] Such features as noted above render the presently described glass compositions particularly suitable for artistic techniques valuing canes of consistent diameters and carefully defined edges, e.g., filigrana techniques. In the classical filigrana techniques, the opaque glass is encased (partially or fully) in a transparent glass casing. FIGs. 1A-1C illustrate exemplary glass structures, generally designated 100, which may be used for filigrana techniques.

[0076] Referring to FIGs. 1A-1C, rod-like glass structures also known as "canes" can be formed using the compositions and methods described above. The canes can comprise an opaque portion, such as an opaque center 102 and a clear portion, such as a clear glass enclosure 104. The opaque center 102 can be fully or partially encased in the clear enclosure 104. The canes or bars may be formed as an initial glass structure via any suitable technique (e.g., casting, extruding, pulling, blowing, etc.) and then subsequently re-heated and formed into a subsequent structure (e.g., a final work product).

[0077] In certain embodiments, the opaque center 102 has a circular cross section comprising a diameter of 0.5 to 30 mm, or any subrange thereof (e.g., 0.5-5 mm, 0.5-10 mm, 0.5-10 mm, etc.). The length of the structure 100 can be vary between about 4-45 ft., or any subrange thereof (e.g., 4-6 ft., 4-8 ft., 4-12 ft., 10-20 ft., etc.). The length and width of the structure 100 can be obtained via pulling or stretching the molten glass between two surfaces as it solidifies. The structures 100 can optionally be cut into smaller rods or canes, having lengths of about 1-12 inches, or any subrange thereof, (e.g., 2-6 in., 2-4 in., 6-12 in., etc.) for use in filigrana techniques. [0078] There are various options for materials comprising the glass casing or enclosure 104. The enclosures 104 for hand working can vary in terms of "stiffness" and values of thermal expansions, mostly greater than 90 x 10^"7, or between about 90 x 10^"7 and 104 x 10^"7 or any subrange thereof (e.g., between about 96 x 10^"7 and 104 x 10^"7, between about 96 x 10^"7 and 100 x 10^"7, etc.).

[0079] As noted above, although the glass compositions disclosed herein find particular use as canes within filigrana glass products, these glass compositions are relevant and useful in other contexts as well. As such, other glass structures can be formed according to this disclosure using the described glass composition precursor. Such structures may include, without limitation, glass ware (e.g., goblets, cups, wine glasses, etc.), table ware, vases, art, panes, etc.

[0080] Some embodiments described herein are further illustrated in the following non -limiting example.

EXAMPLE

Exemplary Glass Composition

Various non-toxic glass compositions have been prepared for obtaining extreme opaqueness, extreme whiteness or non-whiteness, desirable viscosity curves, and suitable expansion coefficients. The compositions described herein are particularly suitable, for example, in terms of viscosity and expansion coefficients, for filigrana glass-formation techniques, glass blowing techniques, and other hand-working techniques. In addition to glass blowing and hand-working techniques, the glass compositions described herein may also be cast, molded, pulled, or extruded into glass structures. Table 2 below contains a specific, yet exemplary embodiment of a sample glass composition prepared.

Table 2. Exemplary Glass Composition

[0081] The composition in Table 2 provides a composition having a coefficient of thermal expansion of about 96 x 10^"7. This material was worked by various skilled filigrana artists and was found to be excellent in terms of opacity, tightness of edge, and whiteness. [0082] Various embodiments of the present invention have been described in fulfillment of the various objectives the invention. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations thereof will be readily apparent to those skilled in the art without departing from the spirit and scope of the invention.

Claims

1. A method of preparing a filigrana glass product, comprising:

providing a mixture comprising:

35 % to 50%, by weight, of Si0₂;

8% to 16%, by weight, of Ti0₂;

16% to 21%, by weight, of A1₂0₃;

3% to 8%, by weight, of B₂0₃; and

17% to 21%, by weight, of R₂0, where R is Li, Na, K, or combinations thereof;

melting the mixture; and

forming canes by stretching the mixture .

2. The method of claim 1, further comprising combining the canes with molten glass and cooling so as to produce a filigrana glass product with canes embedded in transparent glass.

3. The method of claim 1, wherein the canes comprise white and substantially opaque cores at least partially surrounded by transparent material.

4. The method of claim 1, wherein the canes comprise non-white and substantially opaque cores at least partially surrounded by transparent material .

5. The method of claim 1, wherein the mixture and the canes are devoid of lead (Pb), arsenic (As), and antimony (Sb).

6. The method of claim 1, wherein the Si0₂, Ti0₂, B₂0₃ and A1₂0₃ are present in the form of particles having an average particle size of about 50-200 μπι.

7. The method of claim 1, wherein R₂0 comprises:

< 1 %, by weight, of Li₂0;

12-15 %, by weight, of Na₂0; and/or

5-8 %, by weight, of K₂0.

8. The method of claim 1, wherein the mixture further comprises an amount of P₂0₅, SrO, and/or MgO, wherein the amount is greater than 0% to about 4%.

9. The method of claim 1, wherein melting the mixture comprises heating to less than about 2500 °F.

10. The method of claim 1, wherein melting the mixture comprises heating the glass composition to less than about 2400 °F.

11. The method of claim 1, wherein forming the canes comprises blowing, casting, molding, pulling, twisting, or extruding the molten glass mixture into the glass structure.

12. The method of claim 1, further comprising annealing the glass structure.

13. The method of claim 12, wherein annealing the glass structure comprises cooling the glass structure from about 1200 °F to about 75°F.

14. A glass structure formed by the method of any of claims 1-13.

15. The glass structure of claim 14, comprising the canes at least partially encased in transparent glass.

16. A glass-containing product, comprising:

canes comprising opaque cores, wherein the cores have average diameters of 0.05 to 30 mm, wherein the canes comprise:

35%to 50%, by weight, of Si0₂;

8% to 16%, by weight, of Ti0₂;

16% to 21%, by weight, of A1₂0₃;

3% to 8%, by weight, of B₂0₃; and

17% to 21%, by weight, of R₂0, where R is Li, Na, K, or combinations thereof;

wherein the canes are present in a matrix of transparent glass, and

wherein the canes exhibit little to no dispersion into the matrix of transparent glass surrounding them. 17. The glass-containing product of claim 16, wherein each opaque core has an average diameter that is less than about 0.5 mm.

18. The glass-containing product of claim 16, wherein each opaque core has an average diameter that is less than about 0.5 mm.

19. The glass-containing product of claim 16, wherein each opaque core has a diameter that varies < 1 mm along the cane.

20. An opaque glass structure formed from a composition comprising at least 35% Si0₂ and more than 8% of Ti0₂.

21. The opaque glass structure of claim 20, wherein the glass structure is a phase separated opal glass.