GLASS

First made over 5,000 years ago, glass is a thick liquid that never completely sets (hardens). That is why old window panes are thicker at the bottom than at the top. Glass is still in widespread use because it is transparent (see-through), strong, and can be melted and recycled endlessly. Molten glass can be shaped in many ways, including flat panels for windows and threads for optic fibres. GLASS TECHNOLOGY is so advanced that glass can be made fire-resistant and shatterproof.

COLOURING GLASS

Coloured glass is created by dissolving metal compounds into melted sand. Different metal compounds create different colours. For example, selenium sulphide makes glass red. Iron and chromium compounds produce a deep green glass.

MAKING GLASS

MOLTEN GLASS

Sand, broken glass, soda, and limestone are heated in a furnace. At around 1,500°C (2,732°F), the mixture melts to form molten (liquid) glass, which is cut into individual globules of glass called gobs.

SHAPING

The gobs are dropped into bottle moulds. Compressed air blows the glass against the mould walls. The bottles are removed from the moulds and reheated slightly to remove imperfections.

COOLING

The bottles are cooled slowly on a moving conveyor belt under carefully controlled conditions. This ensures that no dust is trapped in them, and that the glass does not shatter.

GLASS TECHNOLOGY

Material scientists have developed and improved the properties of glass to suit a range of uses. Heat-proof oven doors are made by adding chemicals to molten glass so that the glass lets light but not heat through. Car windscreens are made shatterproof by cooling molten glass rapidly with jets of air. Test tubes and other glass apparatus used in science labs need to withstand the heat of a Bunsen flame. This kind of glass is made heat-proof by adding boron oxide to the raw materials to make borosilicate.

OPTICAL FIBRES

Molten glass can be pulled into extremely thin tubes called optical fibres. A beam of light is reflected down the tube, even as it bends around corners. Optical fibres are used in telephone cables. Pulses of light pass down the tube, and transmit information. Optical fibres are also used in endoscopes that allow doctors to see right inside our bodies.

Copyright © 2007 Dorling Kindersley

highlights

10 Nut-Free Lunch Ideas
Packing nut-free school lunches can be tricky! If your child has a nut allergy or his school has banned peanut butter, try these tasty and safe nut-free lunches.

Find Today's Newest & Best Children's Books!
Looking for newly released books for your child? Try our new Book Finder tool to search for new books by age, type, and theme, and create reading lists for kids!

Top 12 Fundraising Ideas
Need some new ideas for raising big money for your child’s school or team? Check out the best school fundraisers, suggested and reviewed by parents like you!

Ready for Kindergarten?
Try our award-winning Kindergarten Readiness app! This easy-to-use checklist comes with games and activities to help your child build essential skills for kindergarten. Download the Kindergarten Readiness app today!

stay connected

Sign up for our free email newsletters and receive the latest advice and information on all things parenting.

Enter your email address to sign up or manage your account.

Facebook icon Facebook icon Follow Us on Pinterest

editor’s picks