A couple more such furnaces and ovens round out the process, before the glass is cooled. All this heat requires phenomenal energy consumption and resulting greenhouse gas emissions. Some calculate this could be as much as 2 tonnes of CO2, per 1 tonne of glass, when transport of such a heavy product is factored in. All this gives glass an Embodied Energy of about 12.7 MJ/kg. (By comparison aluminium is 170 (!!), cement 5.6 and kiln dried sawn softwood 3.4). Sand mining is not the most benign of raw material extraction methods either. So where's the good news?

Well, quite a bit, as it turn out. Glass is the prime ingredient in 'passive solar' designed buildings, that harness the heat of the sun to warm structures, without need of machine-based heating and air conditioning. Not to mention that wonderful hard-to-quantify joy of simply seeing the outside world, regardless of the weather. Given that modern persons spend 90% of their lives indoors, the sanity provided by glass is worth more than any phalanx of therapists.

Finished glass is inert and non-toxic. It is easy to clean and maintain, having a dense surface, which inhibits contamination. Glass is vastly recyclable and scrap glass, known as cullet, is a key production ingredient added to the raw materials noted above. Some standard glass production uses over 45% recycled post consumer content. Specialised production can ramp this up to 100%, such as creates this great glass tile by Aurora Glass (who use their profits to assist homeless and low-income people through emergency services, housing, jobs, training, other charitable endeavors.)

The glass mostly recycled is not that used in buildings or furniture but that which wraps around your favourite ale or wine – bottle glass. Construction glass normally ends up in the landfill and alas only occasionally reused in its original form. Yet while brittle and prone to breakage, undamaged glass can be reused almost indefinitely.

We could go on, but better that you drop by again, when we'll run profiles on how recycled glass is being worked into some creative products. The picture above is a design of Jasper Morrison's. He took old bottles, heated the tops and reformed them to create these beautiful carafe/vases. [by WM]