Glass

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What is Glass

Glass occurs naturally as obsidian, a black glass produced by volcanic activity. However, the term glass is generally used to describe manufactured glass.

According to tradition, the technique for manufacturing glass was accidentally discovered by Phoenician merchants (from an ancient civilisation in the Mediterranean coast) in about 5000 BC. The account tells how a merchant ship carrying a load of soda (sodium bicarbonate) stopped at a beach in what was then Palestine. The crew used lumps of soda to surround their cooking fire, and as it became hot, the soda combined with the sand, and liquid glass ran out.

Glass was certainly known to the Egyptians from very early times - the oldest known glass object is a small charm from Egypt, estimated to be about 9000 years old.

Modern glass is transparent, hard, unreactive, and easily shaped. This makes it very suitable for making windows, bottles and eyeglasses. =

Glass melts gradually over a range of temperatures. Molten glass can be rolled into flat sheets, or shaped into bottles, jars, etc. by machines. It can also be blown or moulded into works of art. Slow cooling is necessary to stop the glass becoming brittle.

Glass is a very, very slow-moving liquid made from:

silicon dioxide (from sand)
sodium oxide (from sodium carbonate), and
calcium oxide (from limestone)

Glass can be coloured by adding other chemicals:

A major advantage of glass is that it is easily recycled. A small amount of recycled glass is added during the glass-manufacturing process.

Types of Glass

Cut or lead crystal glass has lead oxide added, which gives a denser, more attractive glass.

Fibre optic cable is a relatively new use for glass. It is revolutionising the sending of digital data from place to place.

When molten glass is stretched into fine fibres, the resulting mat of interlocking threads, called fibreglass, can be used for all sorts of products, from home insulation to making surfboards.

Adding boric acid to glass produces borosilicate glass (Pyrex), which is much tougher than ordinary glass and can be heated to a high temperature without melting. This makes it useful for laboratory glassware and oven cookware.

Safety glass (a particularly tough glass) is made by sandwiching a layer of clear plastic between glass layers.

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