Glass

Glass

Glass is a made by melting a mixture of sand and other minerals in a furnace at temperatures of 1700 degrees Celsius.

Silica in the form of sand is the main ingredient of glass, and this is combined with soda ash and limestone in special pots which are placed into the furnace. Broken, recycled glass known as 'cullet' is added to the ingredients to speed up the melting process. Other materials can be added to produce different colours or properties. For example, adding the minerals cobalt or sulphur will produce coloured glass.

A recipe for glass
sand or silica (SiO2)
sodium carbonate (Na2CO3)
limestone (CaCO3)
magnesium carbonate (MgCO3)
additives to improve the quality of the glass, and to colour the glass.

While it is still molten (a hot liquid), glass can be manipulated by glass blowers to form bottles and other decorative articles. They blow air into the liquid glass through a long pipe.
You can see a video of glass blowing at this site: http://www.historyforkids.org/learn/science/glass.htm

Glass has been made since the times of the Ancient Egyptians, about 3000 years ago. The Egyptians made glass beads and used them as jewellery.

This ancient glass was found in the ruins of the ancient Roman city of Pompeii

In factories today, bottle blowing machines produce bottles and jars by pressing and blowing the molten glass inside a mould. Flat glass is made by floating the molten glass onto flat beds of tin. Glass can also be coated, heat-treated, engraved or decorated. It is used to make optical fibres for use in medicine and for parts for modern communications.

flat sheets of glass are used as a wall on a modern skyscraper

Some other things made with glass
Aquariums, Christmas tree ornaments, engraved glassware, doors, furniture tops, scientific apparatus such as test tubes, mirrors, ornaments, stained glass for windows, other windows and car windshields.

Naturally formed glass
Obsidian is a naturally formed glassy stone. It forms when sand shoots out of an erupting volcano. It melts in the volcanic lava and when it comes into contact with water it cools quickly. The glass is dark green to black. Obsidian has been used by ancient peoples since the Stone Age, as a cutting tool, for tips for spears, and for ceremonial purposes.

a stained glass window

For more information about how glass is made go to:
http://www.glasstopsdirect.com/how-glass-made.php

Go here to read about recycled glass
http://www.britglass.org.uk/Education/RecyclingCycle.html

Acknowledge this source in your bibliography like this:
Thomas, R & Sydenham, S. Glass. [Online] www.kidcyber.com.au (2009)