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Graphic element Research > Growth > Research projects > Materials & technologies projects > Checking out alternative metals for glass making
Graphic element Checking out alternative metals for glass making

Lead crystal glass is a quality European export but the very fact that it contains lead means workers may be at risk from metal-laden fumes and makes waste disposal difficult. Multidisciplinary teams worked successfully together in a CRAFT project to show that proposed alternatives have low potential toxicity and can be disposed of safely in ordinary landfill sites. The alternative metals were used to make glass crystal that even experienced experts find difficult to tell apart from lead crystal. There is now pressure from some sectors of the industry to redefine crystal glass, thus allowing safe and environmentally friendly crystal to be made using these alternative metals.

The European definition of lead crystal as glass that contains a minimum of 24% lead oxide is a feature that once contributed to its reputation for quality. Today, however, it is causing consumer disquiet. Denmark wants to ban all imports containing lead, while some states in the USA require lead crystal glass to carry a health warning.

From the consumer's point of view, there is minimal risk as virtually no lead leaches from glass during normal use. However, lead is an extremely toxic metal that is retained for a long time in the body. For glass workers, exposure to high levels of lead is a potential occupational hazard and the toxicity of glass waste also poses long-term problems for waste disposal.

A safe alternative to lead?

"This is a thorny issue," says Professor Nick Priest of Middlesex University in London. "Other metals can be used in glass-making to impart the same physical properties, but we had no safety information for any of them."

Large companies that control the international markets and that have their own research and development departments dominate the glass industry. European SMEs find it difficult to compete in the best of circumstances but, a couple of years ago, with building pressure from Denmark and the USA, they decided to take the initiative. In late 1997, SMEs from Ireland, Norway, Portugal, Sweden and the UK formed a research partnership under a BRITE-EURAM CRAFT project to assess the safety of lead substitutes within crystal glass. To help, they recruited research organisations in Ireland, Sweden and the UK.

The project set out to answer questions in three main areas.

1. Consumer safety: could alternative metals be used to make glass that was safe for ordinary people to use? Would the metals in crystal glass containers leach out into liquids such as orange juice and wine making the containers unsafe to use?
2. Worker safety: how are workers exposed to toxic metals during crystal glass manufacture? Does the manufacture of crystal glass containing metals such as bismuth, barium and strontium present a hazard to workers in the crystal industry?
3. Environmental impact: did the alternatives present any environmental problems in disposal or recycling?

Complex multi-tasking

The collaboration between the numerous partners occurred at many levels and was very complex. Analytical tasks were shared between the different RTD suppliers. Companies assisted by setting up manufacturing runs specifically for the project, to produce test beakers of standard size. Firms also allowed their current manufacturing processes to be fully monitored and they contributed specially produced waste for disposal studies.

"Many of the tasks were carried out by several partners jointly, so that fully multidisciplinary teams could work together. The planning and logistics of the various sub-projects was not easy but everything went very smoothly," confirms Professor Priest. "Without this sort of co-operation, it would have been difficult for any single SME to have obtained the information that came out of the project in just 24 months. This is helping SMEs involved to compete on a more equal footing with the few giant glass manufacturers within the industry."

  Alternatives pose no safety risks

The results showed that none of the metals tested - bismuth, barium, strontium, zinc and titanium - pose any risk to safety during the manufacturing, waste disposal or product usage stages. Products made from glass containing these metals are virtually indistinguishable from the highest quality lead crystal and the manufacturing process is unhampered - although it is yet to be confirmed that crystal glass can be cut and polished in the same way as traditional lead crystal.

"A key finding from the factory studies is that most metal exposure occurs at the hot blowing stage in the process," observes Professor Priest. The fumes produced by heated glass are absorbed easily through the lungs, whereas the fine mist of glass fragments produced during cutting is relatively harmless. In the tests, most of the other metals proved not to be volatile when heated, so they present a low inhalation risk. Bismuth is volatile and is toxic, but human volunteer studies, using the radioactive isotope 207Bi, showed that, unlike lead, bismuth is not retained in the body.

  A new era in glass making?

By the end of the project, the CRAFT study had failed to find any evidence to suggest that the alternative metals could not be used in safe and effective glass manufacture. Moreover, the crystal glasses did not leach under landfill conditions, had a high potential for recycling within the art glass and ceramic glaze industries and could even be legally recycled within container glass streams. The study generated sufficient data for the creation of safety cases for a wide variety of different possible and likely crystal glass compositions.

"Now that we have the data to go forward, we have made this available to the whole of the glass industry. It is difficult to predict what will happen in the near future, but there seems a good chance that this project will enable SMEs that manufacture uncut glass to take the initiative to switch over to alternative methods of producing crystal glass. Further research may allow manufacturers of cut products to make a similar switch," explains Nick Priest. This could give them a significant advantage in new and developing international markets.

It would seem that the SMEs can look forward to breaking into new markets as producers of safe, environmentally friendly glass.

A safe alternative to lead?
Complex multi-tasking
Alternatives pose no safety risks
A new era in glass making?

Key data

Improved materials for manufacture are being developed as part of the New materials and production technologies generic action. European SMEs in the lead crystal glass industry collaborated with RTD centres in a CRAFT project to evaluate the safety of alternative metal additives such as bismuth and barium to replace lead.

Project: Evaluation of the biosafety of lead substitutes used in the manufacture of unleaded crystal glass (BRST-CT97-5122)

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