Glass: a fragile industry?

By Emma Hughes
Published: Monday, 25 March 2013

Glass manufacturing is a large consumer of many industrial minerals, including soda ash, quartz and limestone. It is also used in a wide variety of industries, such as construction, manufacturing and home ware. But with the economic recession still leaving a trail of devastation in many industries, how will the glass supply chain fare in 2013?

Glass is an amorphous, non-crystalline solid material recognised for its low-cost suitability for many everyday uses including transparent panes and receptacles. While the adaptability of glass to many different products and applications is recognisable, the use of industrial minerals in its formation is by no means limited - especially considering the variations between glass type and glass manufacturing process.

The most familiar and commonly produced type of glass is soda-lime glass. This glass is used widely in two main types - flat glass, designed for end uses such as window panes and in the automobile industry, and container glass, used to make receptacles such as tablewear and bottles.

Soda lime glass is produced using minerals such as soda ash, quartz (silica) and lime.

Glass can also be defined in a much wider sense to include every solid that possesses a non-crystalline, amorphous structure that exhibits a glass transition when heated towards the liquid state.

In this wider sense, glasses can be made of different classes of materials including metallic alloys, ionic melts, aqueous solutions, molecular liquids and polymers. For many applications, polymer glasses, such as acrylic glass, polycarbonate, polyethylene terephthalate, are a lighter alternative to traditional silica glasses.

Glass manufacturing is complex and encompasses an enormous range of compositions and product types. Materials for glassmaking can be classified in three groups: glass formers, fluxes and stabilisers.

Soda-lime glass

Soda lime glass is composed of approximately 75% silica (SiO2), sodium oxide (Na2O) from soda ash, lime (CaO) and several other minerals including stibnite (the main ore of antimony) and feldspar. The mix of minerals used to make soda-lime glass is termed ‘batch’.

The glass is produced by melting the batch in a glass furnace at temperatures of up to 1,675¡C (3,047¡F). The temperature of the furnace is limited by the quality of the furnace superstructure material, that is whether it can withstand higher temperatures, and by the glass composition.

“In the process of melting [solid to liquid] a viscous liquid is formed and the mass becomes clear and homogeneous at temperatures above 1,000 ¡C. When removed from the reactor, the glass acquires a shape allowing handling. By controlling the temperature of cooling, [this] avoids devitrification or crystallisation,” Felix Antonio Martinez Sendoya, Colombian Silica’s CEO of silica and business, told IM.

Relatively inexpensive minerals, such as soda ash, sand and feldspar, are added to the batch as fluxing agents to reduce the melting temperature of quartz and help to control the viscosity of glass.

For minerals such as feldspar (p74), the alkali content acts as flux, lowering the glass-melting temperature and thus reducing production costs. Coloured glass, such as that used to make green and brown bottles, is produced from raw materials containing iron oxide (see pp.42-45).

A typical batch for clear glass containers may consist of 155kg soda ash, 172kg limestone, 145kg feldspar and 5kg sodium sulphate. Flat glass batches require about 115kg of soda ash per 450kg of silica sand used [Industrial Minerals and Rocks, 7th Edition].

“Importantly, the manufacturing process [to make glass] is practically the same for all types; [what] changes from one specimen to another is the material. All of them have a greater or lesser proportion of silicon atoms,” Sendoya told IM.

While the materials used to make flat and container glass come from the same mineral batch, the physical process used to create the finished glass differs slightly.

For flat glass, the float process is administered, while for containers, glass blowing is performed. Float glass has a higher magnesium oxide and sodium oxide content compared with container glass, and lower silica, calcium oxide and aluminium oxide content. This means that the quality of container glass is higher, mainly due to the fact that it is required to be safe for use as homeware receptacles (for chemical durability against water).

Quartz (silica)

Industrial sand and gravel, often called silica, silica sand or quartz sand, includes sands and gravels with high silicon dioxide (SiO2) content. Silica is the major ingredient in virtually all types of glass including containers, flat glass, lighting glass, tableware, TV tubes and screens, decorative glass, fibreglass, optical glass and vacuum flasks. The commercial uses of glass (containers, windows, vehicle glazing) contain between 70 - 74% silica, the ultimate source of which is silica sand.

Glass manufacturers are principally concerned with the chemical composition of silica sands, particularly iron, chromite and other refractory mineral contents, according to the British Geological Survey (BGS).

Quality requirements depend on the type of glass being manufactured - whether it will be coloured or clear - and to some extent on the requirements of the individual glass manufacturer. Silica sand for colourless glass containers generally has an iron content of <0.035% Fe2O3 (ferric iron oxide), for flat glass in the range 0.040 to 0.1% Fe2O3 and for coloured glass containers 0.25% to 0.3% Fe2O3.

Global sand resources are large and widespread and somewhat unquantifiable. However, in terms of production, 140m tonnes silica sand was produced in 2012, according to the US Geological Survey (USGS). Some 49m tonnes of this sand were produced in the US, with around 17% of this being used to make glass.

While resources and production are on a large scale, several limitations surrounding silica sand exist worldwide including geographical distribution - which can often be a costly and uneconomic practice - environmental restrictions - related to potential health risks associated with the use of silica sand - and quality requirements for use, as outlined above.

Soda ash

The glass industry is the largest consumer of soda ash, particularly the glass-container sector. Soda ash has been used in glass manufacturing for more than 5,500 years [Industrial Minerals and Rocks, 7th Edition] and continues to be used in the industry today.

Soda ash is a source of sodium oxide that is used as a fluxing agent in container, fibre, and speciality glass manufacturing to reduce the temperature at which the raw materials, such as silica sand, melt. Soda ash also decomposes into sodium oxide and carbon dioxide, which rises through the glass melt and helps mix the ingredients.

In terms of supply, China continued to dominate last year, producing 23m tonnes in 2011, according to latest USGS data. The US followed, producing 14.5m tonnes in 2011, with a total value of approximately $1.3bn.

“China continues to be the largest and fastest-growing market for soda ash. Due to its size and the persistent over-capacity in the Chinese industry, it also has a strong impact on important markets for soda ash trade - Asia, and to a lesser extent, Latin America,” FMC Corp., the Wyoming, US-based producer, told IM.

However, while the usual players are continuing to produce within expectations, there are new entrants to the market, including some from developing countries.

“In developing countries, the soda ash [market] is growing by 5%; in the US and Europe demand is stable. Total growth is 2m tpa - 1m tpa in China [and] 1m in the rest of the world,” Novacarb, the France-based soda ash producer, told IM.

Turkey is a country that emerged as a key soda ash producer in 2012, with more than 2m tonnes of capacity logged in 2011.

“China continues to lead the way for new capacity coming on-stream, and Turkey has emerged as a new player with good access to European and Middle Eastern markets,” Dennis Kostick at the USGS told IM.


The recycling of glass has brought the cost of domestic container glass manufacturing down by significant amounts as cullet, the mixture of used glass broken down to be recycled, is used to replace part of the silica requirements in a glass batch. Cullet also has a much lower melting temperature - around 20-25% below a conventional batch - further reducing the cost by lowering the amount of flux required.

“Glass recycling is an increasingly important input into container glass production. [É] more than 68% [2010 data] of glass bottles and jars put on the market are collected for recycling and most of them [some 80%] are recycled in a bottle-to-bottle, closed-loop recycling system,” the European Container Glass Federation (Feve) told IM.

“[This means] that, once produced, glass can be used over and over again without down-cycling and by reducing use of new minerals and raw materials and preventing waste generation. Glass is mono-material and does not require any additional barriers to preserve food and drinks, making its recycling particularly easy. This is a good illustration of how a circular economy for packaging can work,” Feve added.

For every tonne of recycled glass, 1.2m tonnes of virgin raw materials are saved in the melting process, according to the federation. This is extremely important for the container glass industry because by using recycled glass also reduces the amount of energy used and CO2 emitted.

“It has a big contribution to the sustainability of the industry. That is why some of the mineral suppliers (for example Sibelco) are investing in recycling facilities (for example Pate),” Feve told IM.

While this is positive news for container glass manufactures, it is not so good for soda ash producers, which have seen decreased demand since the worldwide push to recycle got underway in earnest.


Feldspar acts as a fluxing agent in glass making and is used to bring the melting temperature of silica down. It is also a stabiliser. Stabilisers impart to the glass a high degree of resistance to physical and chemical attacks. Fluxes are oxides, including potassium oxide (K2O) and sodium oxide (Na2O) and stabilisers can be oxides such as alumina (Al2O3) [Industrial Minerals and Rocks, 7th Edition].

During glass manufacture, feldspar has two functions, acting as a flux by providing alkaline oxides (K2O and Na2O) and as a stabiliser by providing alumina and calcium oxide. A typical batch for container glass contains around 8% feldspar, according to Roskill Information Services.

Feldspar is the most abundant group of minerals in the Earth’s crust, forming about 60% of terrestrial rocks. Feldspar reserves are found in various countries, including India, Czech Republic, Portugal and Poland among others. Turkey and Italy are the top two producing countries, accounting for about 50% of the world production with almost 10m tpa in 2012, according to USGS estimates.

Identified and hypothetical resources of feldspar are more than adequate to meet anticipated world demand, the USGS added, which states that quantitative data on resources of feldspar existing in feldspathic sands, granites, and pegmatites generally have not been compiled.

“Ample geologic evidence indicates that resources are large, although not always conveniently accessible to the principal centres of consumption,” it said in its most recent feldspar report.

Other materials that can be used for glassmaking include fluorspar, lime, chromite, olivine, staurolite and zircon sands, according to the USGS.

Glass markets: handle with care

Soda-lime glass, while the most abundantly manufactured form of glass, has experienced testing times during the past few years as the global economic crisis significantly slowed the amount of new building as well as the amount of manufacturing worldwide.

Glass was hit hard by a crash in the global housing market during the period 2008-2012. This collapse, in turn, caused the prices for some minerals used to produce glass - such as soda ash - to dip to the point where prices for the mineral were as low as they can feasibly go.

Other glass-using industries, such as automobile manufacturing, also took a knock, which again filtered down to the raw materials demand level.

Despite this, international chemicals company Solvay, the world’s number one synthetic soda ash producer, said that a drop in demand for flat glass in the construction and automotive industries was buoyed by strong performance in the container glass sector.

Feve agreed with this statement, telling IM: “The container glass industry produces some 20m tpa glass. In terms of tonnage, the biggest markets for the container glass industry is the beverage sector. Beer, spirits and wines account for the largest share. Overall, glass packaging represents one-third of the European beverage market in units.”

“While the beverage market is important, the food sector is increasingly offering an important growth opportunity for glass packaging. This is certainly linked to new market trends orientated by consumers demand for high-quality, natural, organic food. More than any other material, glass can best communicate to consumers these product characteristics. Glass is a packaging reference for brands and for consumers,” the federation added.

While some glass markets dipped in 2012, this year has already begun to show some promise. In the housing sector, for example, 23 markets have demonstrated better year-on-year statistics in Q3 2012 compared with Q3 2011, according to a report by Global Property Guide. Recovery of the US housing market has been particularly evident, with growth in Q3 2012 being the highest since Q2 2006, according to the Federal Housing Finance Agency (FHFA), the Guide reported.

“Certainly our sector saw a dip during the crisis years, but we see that we are now almost back to the pre-crisis levels in terms of tonnage. According to latest available figures [H1 2012], glass packaging production volumes in Europe grew by 1.9%. The growth is in response to the increasing demand on the domestic and outside EU markets. This builds on the positive trend recorded in 2011,” Feve told IM.

“Despite the unstable economic and financial crisis that negatively affects the whole European manufacturing sector, these records shed a positive light on the stability and future prosperity of the European container glass sector. This is certainly due to the fact that consumers continue to have a strong preference for glass - 74% of consumers would recommend glass as a packaging material [Insites 2010],” the federation added.

Despite these encouraging results, the impact of the global economic crisis is still evident across the glass industry.

Increased production costs, unilateral CO2 costs, fluctuating and unfavourable exchange rates, and high labour costs hamper the cost competitiveness at global level of the container glass sector, Feve said,

“Combined, these challenges delay long-term investment decisions and, rather, become incentives for delocalisation of production sites and R&D investments outside EU to more industry friendly environments with lower costs,” it added.


The fact that glass is faced with economic challenges is viewed as a minor hurdle for many working in the industry, even at the industrial minerals level, as glass remains the number-one option industrial minerals producers of borates, silica sand and soda ash. This is because it is used for many industries including automobile, tableware, cosmetics and construction.

This continued market demand will, in turn, increase the call for industrial minerals such as soda ash, silica, limestone and fluxes including feldspar.

Glass is also classed as a material of the future as it is recyclable, re-usable and refillable.

“This makes it certainly a reference for the circular economy - where there is a big change from the linear economy model to the circular model. This is based on recycling, which closes the loop,” Feve said.

Glass fibre

Glass fibre is made up of bulk, chopped fibres or strands of glass and durable plastic resin. It is used in reinforcing plastics and composites as well as other specialised electrical and thermal applications.

Minerals used in the creation of glass fibre are similar to those employed in the creation of other forms of glass. These include silica sand, limestone, soda ash, borates, kaolin, lithium minerals, potash, feldspar, fluorspar and sodium sulphate.

The most common glass fibre is a calcium-alumina borosilicate with an alkali content of less than 1%. It is commonly known as e-type glass, since it was originally developed for use in electrical insulation systems.

E-type glass was created in the 1950s to insulate electronics. Today, uses for glass fibre include mats, thermal insulation, electrical insulation, sound insulation, reinforcement of various materials, tent poles, sound absorption, heat- and corrosion-resistant fabrics and automobile bodies.

Glass fibre is used in consumer goods such as hot tubs, bath tubs and boats. It is also used in water storage tanks, for pipes in the oil and gas industry, as well as in households and offices, in roofing and cladding.

Glass fibre production

Glass fibres are produced by running molten glass from a direct-melt furnace into a platinum alloy bushing containing a large number of small holes, from each of which a glass filament is drawn.

Filaments for commercial use are normally between nine and 15 microns in diameter. The filaments are layered with an emulsion before being gathered into fibres.

The fibres are strong and they have excellent electrical properties. They are also resistant to most chemicals and moisture wear. They are non-combustible, with a melting point around 1,500ºC.

Glass fibre industry

The fastest-growing industry sector for glass fibre is in insulation, as populations become more concerned with energy conservation. The European Union’s push to improve energy consumption by 20% by 2020 has seen many governments offer free or subsidised insulation and this is welcome news for glass fibre minerals such as kaolin and borates.

Outside of the EU, Russia is aiming to reduce energy consumption by 40% in 2020 and China has invested heavily in rebuilding ‘energy poor’ housing and has pledged $23bn for energy efficient projects.

The Obama administration in the US has launched ambitious energy-saving initiatives, including a $2,000 tax credit for residential homeowners who insulate properly and make their existing properties more energy efficient.

In Australia, the government pledged in 2009 to install free ceiling insulation in around 2.7m homes under the Energy Efficient Homes Package. However, the Home Insulation Programme was later shelved in favour of a new scheme and then abandoned in April 2010. The scheme was controversial, due to worker fatalities while installing the insulation, and costly, due to compensation payment.

Source: this section is taken from the article On a roll: glass fibre featured in IM’s October issue.

Borosilicate glass

Glass accounts for three major borate applications: insulation fibreglass, textile fibreglass, and borosilicate glass. These applications are in addition to a multitude of minor end uses.

Insulation fibreglass

Insulation fibreglass is the principal insulating material used in the construction industry. Composed of very thin fibres spun from molten glass, its purpose is to trap and hold air. Borates are incorporated into the formulation to aid melting, inhibit devitrification and improve the aqueous durability of the finished product. Borates also ensure that the insulation fibreglass has adequate recovery after prolonged compression in order to save transportation.

Textile fibreglass

When compared to insulation fibreglass, textile glass fibres are coarser with higher B2O3 content. This type of glass was originally used for electrical purposes, and low sodium levels were important. Now, however, major applications include reinforcements for plastics, yet the low sodium tolerance still applies.

Borosilicate glass

Borosilicate glass is a general classification referring to glasses having the common characteristics of containing a relatively high level of B2O3. Borates impart many distinct properties to borosilicate glass: thermal shock resistance, chemical resistance, aqueous durability, and physical strength.

Uses include oven-to-table cookware, laboratory ware, pharmaceutical containers, lighting lenses, tubing, and vacuum flasks. Nuclear waste encapsulation relies on the high tolerance and low leaching of borosilicate glasses.

Small quantities of borates are used in other vitreous products including container glasses and art glasses. Optical glasses, microspheres, glass-ceramics, “Vycor” glass, sealing frits and high-tech glass for space exploration applications all rely on boron to help melt or to fine-tune the final product properties.

Source: Rio Tinto Minerals