WO2012156707A1

WO2012156707A1 - Improvements in crystal glass

Info

Publication number: WO2012156707A1
Application number: PCT/GB2012/051052
Authority: WO
Inventors: Stephen David POLLOCK-HILL
Original assignee: Nazeing Glass Works Limited
Priority date: 2011-05-13
Filing date: 2012-05-11
Publication date: 2012-11-22
Also published as: GB201108052D0

Abstract

A crystal glass having a composition comprising the following components: approximately 30-70wt% silica sand; approximately 0.2-20wt% sodium carbonate (soda ash); approximately 6-14wt% calcium carbonate; approximately 5-20wt% potash; approximately 3-8wt% zinc carbonate; approximately 5-14wt% borax. The composition may further comprise one or more of: approximately 0.5-3wt% barium carbonate; approximately 0.5-2% potassium nitrate; approximately 0.1-2wt% antimony; approximately 0.1-0.5%wt hydrated alumina; approximately 3-8wt% strontium carbonate; approximately 0.1-5wt% cerium oxide; and approximately 0.01-2wt% erbium oxide.

Description

IMPROVEMENTS IN CRYSTAL GLASS

BACKGROUND Technical Field

The present invention relates generally to the field of crystal glass. More particularly, the present invention concerns what is believed to be the first lead-free crystal glass, which has been formulated to almost exclude, or to reduce to a minimum the use of toxic chemicals in its composition, a so-called "eco-friendly" glass, or "eco-glass". The invention also concerns the method for making the same for use in glassware articles, such as glassware, tableware, ornaments and lighting apparatus. The term "toxic" is used herein to refer to ingredients that have been defined as "Substances of Very High Concern" (SVHC's) and harmful to health by the European Chemicals Handling Agency (ECHA). At the time of writing, these include, by way of example, lead (Pb), barium (Ba), arsenic (As) antimony (Sb) and boron (B), all of which must be handled with great care. Their emissions from furnaces and chimneys must also be monitored in certain circumstances (i.e. lead) according to EU or national standards. Accordingly, "non-toxic" refers to ingredients other than those classed as SVHC's for the purpose of this invention.

Background and Description of the Related Art

Crystal continues to be a popular product due to its numerous desirable properties, when compared with non-crystal glass. Technically, the term 'crystal' cannot be applied within the EU unless it fulfils the requirements of crystal as defined by UK and European Standards (see below).

In order to meet the minimum requirements of crystal glass according to the British Standard 3828 1 973 and EU Standard 69/493 EEC of 19 March 2002, the glass must fulfil certain criteria.

Firstly, crystal glass by definition, has a higher refractive index (n = up to 1 .7) than non-crystal glass (n = 1 .5), which increases the amount of light refracted and reflected, and has increased dispersion, and which provides a measure of the degree to which a medium separates light into its component spectra, as in a prism, leading to a much greater "sparkle". It must exceed 1 .52 to be able to be called "crystal glass", Secondly, crystal glass has a density that sets it apart from non-crystal glass of at least 2.45 g/cm³.

Finally, crystal glass must contain zinc, barium, lead or potash either alone or in any combination of at least 1 0wt%.

Generally, crystal glass has a longer working temperature range than non- crystal glass (falling below the requirements for crystal), with a working range of between 800 ^-1250 *Ό. Generally, the viscosity of crystal glass is roughly 100 times less than that of non-crystal glass across working temperature ranges (up to approximately 1250°C). This means that practically, there are advantages as follows:

a) crystal glass can be worked at a lower temperature allowing it to be used for enamelling (fusing powdered glass to a substrate by firing between 750 °C and 850 °C) ; b) this wide working range allows the glass to be worked by hand over a longer period of time before it is necessary to reheat it;

c) it is easier to produce crystal glass articles without air bubbles; and d) the glass is softer, making it easier to cut with facets either by hand or machine.

Another characteristic feature of crystal glass is that it usually has a distinctive 'ring', which is used by consumers to distinguish it from non-crystal glass. The crystal glass oscillates when struck, producing the ring sound. This ring is hard to obtain and is often missing in non-crystal glass.

Most non-crystal glass has an approximate chemical composition of: 70% - 74% Si0₂ (silica); 12% - 16% Na₂0 (sodium oxide); 5% - 1 1 % CaO (calcium oxide); 1 % - 3% MgO (magnesium oxide); and 1 % - 3% Al₂0₃ (aluminium oxide). The attractive optical, sonar and working properties of crystal are in part, but not solely attributed to the addition of the lead oxide.

Lead crystal glass that is accepted as traditional "full lead crystal" contains at least 30% lead oxide, but any glass containing at least 24% lead oxide can be described as "lead crystal". The greater the lead content, the more attractive/ pleasing/ saleable the crystal glass tends to be due to the optical properties and the greater density. Glass containing less than 24% lead oxide, is known as crystal glass, providing it meets the required refractive and density limits as defined in the Standard.

In crystal glass, the lead oxide (usually litharge oxide or red lead powder) replaces calcium oxide, and potassium oxide replaces all or most of the sodium oxide. The lead oxide is locked into the chemical structure of the glass and since potassium ions are bound tightly in a lead-silica matrix, the glass absorbs less energy when struck to create the distinctive ring that is well-known to crystal ("a sonorous tone when struck') as defined by George Ravenscroft 1618 -1683 (original lead crystal inventor). The high atomic weight of lead (207.2 versus 40.08 for calcium) raises the density of the glass (to around 3.1 g/cm³ versus 2.4 g/cm³ or below for non-crystal glass). The lead also increases the solubility of tin, copper and antimony allowing it to be coloured and causes the low viscosity of the glass melt.

There has always been concern over the toxicity of the individual components of some crystal glass as opposed to the glass itself, particularly lead, barium, arsenic and antimony, and more recently, boron, or other derivatives of borates.

Reports have shown that under certain conditions (acidic - wine, fruit juice held for over 10 hours), unsafe quantities of lead oxide can leach out of glass and dissolve into the contents, and that long term storage of Port and Brandy in decanters can accumulate questionably dangerous quantities of lead. Recently, therefore, the word "lead" has been dropped from use by many suppliers when referring to crystal due to the bad publicity concerning this finding of toxicity in the leachate. There is now EU Guidance (published 2004, http://www.fda.gov/food/foodsafety/foodcontaminantsadulteration/metals/lead/ucm17 2050.htm), on the release of lead from lead crystal tableware, which has driven recent investigations into finding non-toxic crystal glass alternatives.

Barium increases the refractive index and density of glass. However, it is known to react violently with dilute acids, alcohol and water and soluble barium compounds are poisonous due to release of the soluble barium ion that can affect the nervous system, causing cardiac irregularities, tremors, weakness, anxiety, dyspnoea and paralysis. Arsenic, in elemental form and as arsenic compounds, is classified as "highly toxic" and "dangerous for the environment" in the European Union under directive 67/548/EEC. The International Agency for Research on Cancer (IARC) recognizes arsenic and arsenic compounds as group one carcinogens, and the EU lists arsenic trioxide, arsenic pentoxide and arsenate salts as category one carcinogens.

Antimony oxides, as additives in glass, serve as fining agents, aiding in the removal of microscopic bubbles. However, antimony and many of its compounds are toxic, and the effects of antimony poisoning are similar to arsenic poisoning. In small doses, antimony causes headaches, dizziness, and depression. In larger doses, such as prolonged skin contact, can cause dermatitis; otherwise it can damage the kidneys and the liver, causing violent and frequent vomiting and can lead to death in a few days. It is well documented that antimony leaches from polyethylene terephthalate (PET) bottles into liquids ("Antimony leaching from polyethylene terephthalate (PET) plastic used for bottled drinking water.", National Center for Biotechnology Information, U.S. National Library of Medicine. http://www.ncbi.nlm.nih.gov/pubmed/1 7707454), especially where fruit juice concentrates are concerned, where concentrates produced in the UK were found to contain up to 44.7 μg/L of antimony, well above the EU limits for tap water of 5 μg/L (Hansen, Claus et al (17 February 201 0) "Elevated antimony concentrations in commercial juices", Journal of Environmental Monitoring 12 (4): 822-4; and Borland, Sophie (1 March 2010) "Fruit juice cancer warning as scientists find harmful chemical in 16 drinks", Daily Mail). Boron in its various forms is a widely used chemical in glass, especially in heat resistant glass, known as borosilicate, and is manufactured under a number of brand trade names, such as Pyrex ^® (Corning Inc.), and Schott^® Duran^® , being of the best known. It gives a high range of co-efficient of expansion and improves the colour and optical property of glass. Although considered totally inert when heated at 1400*Ό in glass, nevertheless certain recent studies have proved a few toxic links with various forms of borates in the chemical powder form.

It is widely used in laboratories for chemical experiments allowing itself to be heated rapidly, and in oven to tableware and cookware.

EP 0575758 A1 (Corning Inc) discloses a lead-free crystal glass containing at least two of the alkali metal oxides Li₂0, Na₂0, and K₂0 in nearly equal molar ratios and BaO, SrO, and ZnO. The lead-free crystal glass disclosed has the following composition: Si0₂ at 54-64wt%; BaO at 8-13wt%; Li₂0 at 0-3wt%; SrO at 8- 13wt%; Na₂0 at 0-6.5wt%; ZnO at 5.5-9wt%; K₂0 at 0-7wt%; BaO+SrO+ZnO at 22- 33wt%; Li₂0+Na₂0+K₂0 at 8-15wt%; wherein at least two of the three alkali metal oxides are included and are present in essentially equal molar ratios. In the disclosed preferred glass all three alkali metal oxides are present in essentially equal molar ratios. Whilst managing to avoid the use of lead, the glass described still includes the toxic component, Barium (at least 8wt%).

EP 0547263 A1 (Inn Crystal Glass GmbH) discloses a lead-free, zinc silicate crystal glass having a refractive index of at least 1 .52 and a composition, in % by weight based on 65.0-70.0 of Si0₂, 6.0-9.0 of CaO, 4.0-12.0 of K₂0, 4.0-12.0 of Na₂0, 0.5-5.0 of B₂0₃, 4.0-7.0 of ZnO, 0.1 -1 .0 of Sb₂0₃ and 1 .0-6.0 of Zr0₂ and/or Ti0₂, with the proviso that the total amount of oxide constituents is 100% by weight, and to the use thereof for the production of domestic and table glassware. The resultant crystal glass contains small quantities of antimony to reduce bubbles and is therefore, not 100% free of toxic components.

It is one object of the present invention to address one or more of the problems of the prior art as discussed herein or otherwise. It is another object of the present invention to address the problem of the use of toxic components whilst achieving the beneficial characteristics associated with crystal glass.

Therefore, it is now desired to provide an "eco-friendly" crystal glass that meets the minimum requirement for crystal glass.

It is further desired to provide a crystal glass that is virtually flawless, is simple to cut, polish and engrave, may be disposed of safely to land fill or bottle banks, due to lack of lead and other SVHC except in minimum quantities, and, as a possible further advantage, provides the distinctive crystal glass 'ring'.

The eco-friendly crystal glass referred to in this Patent has been tested to ensure it meets the British Standard and the EU Directive (above). SUMMARY OF THE INVENTION

In a first aspect of the present invention there is provided a crystal glass composition comprising the following components: approximately 30-70wt% silica sand; approximately 0.2-20wt% sodium carbonate (soda ash); approximately 6- 14wt% calcium carbonate; approximately 5-20wt% potash; approximately 3-8wt% zinc carbonate; approximately 5-14wt% borax.

The composition may further comprise one or more of: approximately 0.5- 3wt% barium carbonate; approximately 0.5-2% potassium nitrate; approximately 0.1 - 2wt% antimony; approximately 0.1 -0.5%wt hydrated alumina; approximately 3-8wt% strontium carbonate; approximately 0.1 -5wt% cerium oxide; and approximately 0.01 - 2wt% erbium oxide.

In a second aspect of the present invention there is provided a crystal glass composition comprising the following components: approximately 50-70wt% silica sand; approximately 15-20wt% sodium carbonate (soda ash); approximately 9- 12wt% calcium carbonate; approximately 5-10wt% potassium carbonate; approximately 3-8wt% zinc carbonate; approximately 5-10wt% boron oxide (borax); approximately 0.5-3wt% barium carbonate; approximately 0.5-2% potassium nitrate; approximately 0.1 -2wt% antimony; and approximately 0.1 -0.5%wt hydrated alumina.

The wt% of each component of the composition refers to the dry weight of the components.

With this composition, between approximately 8-16wt% of the chemicals are defined as SVHC, which is believed to be lower than another other "lead-free" crystal glass or other form of crystal glass on the market.

The refractive index has been measured at 1 .52974, (above the specified requirement of 1 .520) and the density has been measured at 2.521 gm/cm³ by the Archimedes calculation (above the minimum limit of 2.45 gm/cm³). Furthermore, since the composition contains zinc and potash in combination of at least 10wt%, it meets the criteria for a "crystal glass".

Preferably, the composition is made up with cobalt oxides and other oxidisers, as de-colourisers.

Preferably, the silica sand is of a grade that is at least equivalent to any one of MAM1 , MAM1 S, MAM1 S T300 as can be obtained from Sibelco, Belgium. More preferably, the composition comprises approximately 50-60wt% of silica sand, even more preferably, approximately 50- 55wt% and most preferably, approximately 52.3wt%. Preferably, the composition comprises approximately 16-20wt% of sodium carbonate, most preferably approximately 18.8wt%.

Preferably, the composition comprises approximately 9-1 1 wt% of calcium carbonate, more preferably, approximately 9-10wt%, most preferably, approximately 9.3wt%.

Preferably, the composition comprises approximately 5-8wt% of potassium carbonate, more preferably, approximately 5-7wt% and most preferably, approximately 6.04wt%.

Preferably, the composition comprises approximately 0.5-2wt% of potassium nitrate, more preferably, approximately 0.7-1 .5wt% and most preferably, approximately 0.97wt%.

Preferably, the composition comprises approximately 4-7wt% of zinc carbonate, more preferably, approximately 4-5wt% and most preferably, approximately 4.89wt%. The composition may comprise approximately 4-7wt% of boron oxide (Boric

Acid), more preferably, approximately 5-7wt% and most preferably, approximately 6.03wt%.

Preferably, the Borax comprises borax pentahydrate or more preferably, anhydrous borax. Preferably, the composition comprises approximately 0.5-1 .5wt% of barium carbonate, more preferably 0.8-1 .2wt% and most preferably 0.97wt%. Preferably, the composition comprises approximately 0.2-1 .5wt% of antimony, more preferably, approximately 0.3-1 wt% and most preferably, approximately 0.53wt%.

Preferably, the composition comprises approximately 0.1 -0.4wt% of hydrated alumina, more preferably, approximately 0.2-0.3wt% and most preferably, approximately 0.24wt%.

Preferably, the composition comprises cobalt oxides. Preferably, the composition comprises approximately 0.1 -1 .0wt% of cobalt oxides, more preferably, approximately 0.2-0.5wt% and most preferably, approximately 0.4wt%. In a third aspect of the invention, there is provided an eco-friendly crystal glass having a composition comprising the following components: approximately 30- 70wt% silica sand; approximately 0.2-5wt% sodium carbonate (soda ash); approximately 6-14wt% calcium carbonate; approximately 10-20wt% potash; approximately 3-8wt% zinc carbonate; approximately 5-14wt% anhydrous borax; approximately 3-8wt% strontium carbonate; approximately 0.1 -5wt% cerium oxide; and approximately 0.01 -2wt% erbium oxide.

The resultant crystal glass meets the minimum requirements of crystal glass according to the British Standard 3828 1973 and EU Standard 69/493 EEC of 19 March 2002, having a refractive index of at least 1 .520, a density of at least 2.54 g/cm³ and contains zinc and potash in combination of at least 10wt%.

It will be appreciated that the preferred features described in relation to the each aspect of the invention may apply to the other aspects of the invention. Preferably, the composition is made up with cobalt oxides and other oxidisers.

Preferably, the composition comprises approximately 0.5-4wt% of sodium carbonate, more preferably, approximately 1 -3.7wt%, most preferably approximately 1 .4wt%.

Preferably, the composition comprises approximately 8-13wt% of calcium carbonate, more preferably, approximately 10-12wt%, most preferably, approximately 1 1 .1wt%.

Preferably, the composition comprises approximately 12-18wt% of potassium oxide (potash), more preferably, approximately 14-17wt%, most preferably, approximately 16.8wt%.

Most preferably, the composition comprises approximately 5.6wt% of zinc carbonate.

Preferably, the composition comprises approximately 6-12wt% of Borax, more preferably, approximately 7-1 1wt% and most preferably, approximately 7.5wt%. Preferably, the Borax comprises anhydrous borax.

Preferably, the composition comprises approximately 3-6wt% of strontium carbonate, more preferably, approximately 4-5.5wt% and most preferably, approximately 5.2wt%. Preferably, the composition comprises approximately 0.1 -4wt% of cerium oxide, more preferably, approximately 0.2-2.7wt% and most preferably, approximately 0.4wt%. Preferably, the composition comprises approximately 0.01 -1 .5wt% of erbium oxide, more preferably, approximately 0.01 -1 wt% and most preferably, approximately 0.04wt%.

Preferably, the composition comprises potassium nitrate. The composition may comprise less than 1wt% of potassium nitrate, preferably less than 0.1 wt%, more preferably, less than 0.01 wt% and most preferably approximately 0.006wt%.

In a fourth aspect of the present invention there is provided a method for making an eco-friendly very low toxic contents crystal glass comprising the steps of:

(a) combining ingredients according to the first aspect of the invention; (b) forming a homogenous mixture of the combined components by heating said combined components to a temperature of between approximately 1380^ and approximately 1440°C for a period of between approximately 16 hours and 30 hours; and

(c) cooling the mixture to form the non-toxic crystal glass. Preferably, the components are combined as dry ingredients.

Preferably, the mixture is heated to a temperature of between approximately 1400*Ό and approximately 1470°C, most preferably, to a temperature of approximately 1450*Ό in step (b). Preferably, the mixture is heated for a period of between approximately 16 hours and approximately 18 hours, most preferably, for a period of approximately 20 hours. Preferably, prior to the cooling step (c), the mixture is formed into a crystal glass. Most preferably, the mixture is first cooled partially first to a lower working temperature in the range of approximately 1220-1270 °C before forming an article.

It will be appreciated that the preferred features described in relation to all of the above aspects of the invention apply to the other aspects of the invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

A crystal glass according to an embodiment of the invention is substantially clear (easily seen though, transparent, substantially free from flaw, blemish, or impurity). A crystal glass according to an exemplary embodiment of the invention is substantially colourless (substantially without hue).

The eco-friendly crystal glass of all embodiments of the invention meet the minimum British Standard 3828 1973 and EU Standard 69/493 EEC of 19 March 2002 for crystal glass for density, refractive index and composition, in addition to providing the desirable, recognisable tonal ring and not comprising any toxic components susceptible to leaching.

METHOD

The following exemplary method has been used in the production of embodiments of the invention.

The method uses a typical batch process apparatus comprising a weighing apparatus, a hopper, a mixing drum, batch bins and a furnace.

The weighing apparatus is used to weigh the individual dry ingredients before placing in the hopper. The hopper provides a feeding chute into the mixing drum via a lip and the mixing drum is rotatable to mix the components together. The mixing drum has a release chute for dispensing of the mixed components, the chute being accessed through release door. The open release door allows the mixed dry components to be collected in batch bins. The batch bins are used to transport the mixed components from the mixing drum to the furnace.

Before beginning the method of making the glass, a series of quality checks are performed as follows:

• Ensure mixing drum, release chute and entrance lip to mixer is clean.

• Ensure release door is fully shut and chute is closed.

• Ensure hopper is clean.

The batch process comprises the following steps:

1 . Dry components are weighed out according to either Example 1 or 2 below;

2. The dry components are placed into the hopper;

3. Rotation of the mixing drum is started;

4. The hopper is raised to empty all contents into the rotating mixing drum;

5. The hopper is lowered;

6. The dry components are mixed in the rotating mixing drum for approximately three minutes or until thoroughly mixed to form a pre-mix;

7. A batch bin is placed under the release chute; 8. The release door is opened to dispense the pre-mix into the batch bin; and

9. Batch bin is transported to the furnace for heating.

In the furnace, the pre-mix is heated to a temperature of approximately 1420*Ό, at which temperature all of the components melt and fuse together.

The heated mixture is partially cooled to a working temperature in the approximate range of 1220-1270*Ό before being poured into moulds or subjected to other shape forming techniques and rested to cool and anneal.

EXAMPLE 1 An exemplary first embodiment of an eco-friendly crystal glass according to the invention comprises the following composition:

The components are subjected to the above described method. The resultant crystal glass has a refractive index measuring at 1 .52974, (above the specified requirement of 1 .520) and a density of 2.521 gm/cm³ by the Archimedes calculation (above the minimum limit of 2.45 gm/cm³). It also has a pleasing colour (a slight blue tint) and minimal bubbles. The crystal glass also has a distinctive 'ring' when struck. The resultant crystal glass also comprises zinc and potash, thereby complying with the British Standard 3828 1973 and EU Standard 69/493 EEC of 19 March 2002 requirements for crystal glass.

Furthermore, the only components included in the formulation categorised as toxic at the time of writing, are barium, borax and antimony, which comprises only 7.53wt% of the total composition, less than any other known patented glasses, and these components are firmly locked in the crystal glass during manufacture and cannot be leached or dissolved from the glass. Further still, the crystal glass does not comprise any lead or arsenic, which are regarded as toxic and so, is not susceptible to leaching of those toxic components. Accordingly, the crystal glass is classes as "eco-friendly", or eco-crystal glass.

The crystal glass according to embodiments of the invention as also expected to have a greater chemical resistance than lead crystal.

EXAMPLE 2

An alternative second embodiment of a crystal glass according to the invention comprises:

The components are subjected to the above described method.

It was found that bubbles in the glass could be controlled with a lower wt% of cerium oxide and the wt% of both Erbium oxide and the cobalt oxides (as decolourising agents) could be reduced significantly to achieve an acceptable colour to the glass, which was found to have a pleasing slight gold tint. The resultant crystal glass also has a distinctive 'ring' when struck, comparable with lead crystal, has a refractive index and a density that meets the minimum British Standard 3828 1973 and EU Standard 69/493 EEC of 19 March 2002 for crystal glass. The resultant crystal glass also comprises zinc and potash, thereby complying with the British Standard 3828 1973 and EU Standard 69/493 EEC of 19 March 2002 requirements for crystal glass. Furthermore, the crystal glass does not comprise any one of lead, barium, arsenic or antimony, regarded as toxic and so, is not susceptible to leaching of those toxic components. In this composition, the only component which is included in the formulation categorised as toxic at the time of writing is borax which comprises only 7.51 wt% of the total composition, less than any other known patented glasses, and this component is firmly locked in the crystal glass during manufacture and cannot be leached or dissolved from the glass. Again, the crystal glass according to this embodiment of the invention is also expected to have a greater chemical resistance than lead crystal.

Accordingly, the crystal glass is classes as "eco-friendly", or eco-crystal glass. Although a few examples have been shown and described, it will be appreciated by those skilled in glass making that various changes and modifications might be made without departing from the scope of the invention.

Claims

1 . A crystal glass composition comprising the following components: approximately 30-70wt% silica sand; approximately 0.2-20wt% sodium carbonate (soda ash); approximately 6-14wt% calcium carbonate; approximately 5-20wt% potash; approximately 3-8wt% zinc carbonate; approximately 5-14wt% borax.

2. The composition further comprising one or more of: approximately 0.5-3wt% barium carbonate; approximately 0.5-2% potassium nitrate; approximately 0.1 - 2wt% antimony; approximately 0.1 -0.5%wt hydrated alumina; approximately 3- 8wt% strontium carbonate; approximately 0.1 -5wt% cerium oxide; and approximately 0.01 -2wt% erbium oxide.

3. A crystal glass composition comprising the following components: approximately 50-70wt% silica sand; approximately 15-20wt% sodium carbonate (soda ash); approximately 9-12wt% calcium carbonate; approximately 5-10wt% potassium carbonate; approximately 3-8wt% zinc carbonate; approximately 5-10wt% boron oxide (borax); approximately 0.5-3wt% barium carbonate; approximately 0.5-2% potassium nitrate; approximately 0.1 -2wt% antimony; and approximately 0.1 - 0.5%wt hydrated alumina.

4. A crystal glass composition comprising the following components: approximately 30-70wt% silica sand; approximately 0.2-5wt% sodium carbonate (soda ash); approximately 6-14wt% calcium carbonate; approximately 10-20wt% potash; approximately 3-8wt% zinc carbonate; approximately 5-14wt% anhydrous borax; approximately 3-8wt% strontium carbonate; approximately 0.1 -5wt% cerium oxide; and approximately 0.01 -2wt% erbium oxide.

5. The crystal glass according to claim 1 -4, wherein the silica sand is of a grade that is at least equivalent to any one of MAM1 , MAM1 S, MAM1 S T300.

6. The crystal glass according to any preceding claim, wherein the composition comprises 50-60wt% of silica sand.

7. The crystal glass according to any preceding claim, wherein the composition comprises cobalt oxides and other oxidisers.

8. A method for making an eco-friendly very low toxic contents crystal glass comprising the steps of:

(c) cooling the mixture to form the non-toxic crystal glass.

9. The method according to claim 8, wherein the components are combined as dry ingredients.

10. The method according to any one of claims 8 or 9, wherein the mixture is heated to a temperature of between approximately 1400*Ό and approximately 1470*Ό in step (b).

1 1 . The method according to any one of claims 8 - 10, wherein the mixture is heated for a period of between approximately 16 hours and approximately 18 hours.

12. The method according to any one of claims 8 - 1 1 , wherein prior to the cooling step (c), the mixture is formed into a crystal glass article.

13. The method according to claim 12, wherein the mixture is first cooled partially to a lower working temperature in the range of approximately 1220-1270°C to form an article.