Glass has been used for many centuries for windows, optical lenses and decorative purposes. But there are also many technological advances that have been made possible thanks to the unusual properties of glass. Here are just a few examples.
Fibre optics
Thin strands of optically pure glass, as thin as human hair, are used to carry digital information over long distances. Signals are sent along the core of each glass fibre as pulses of laser light and thousands of these fibres are bundled together to form a cable. Fibre optics is light, flexible and relatively inexpensive. They are ideal for investigative medical instruments used to see inside a patient, and for telephone, television and computer cables. Unlike metal cables that conduct heat or electricity, fibre optic signals are not affected by other fibres in the same cable. This means that you can get a clear telephone and television signal at the same time.
Mirrors
Shiny, smooth surfaces, such as metals, are the best reflectors of light. A mirror, made from a sheet of glass with a thin layer of silver on the back, reflects light almost perfectly. Glass for mirrors must be completely flat so that the image is not distorted. Float glass is ideal. The glass is first washed and then coated with a tin compound. This ensures that the silver deposit is embedded in the surface of the glass. The silver is deposited by the action of several chemicals. It is then covered with copper, red paint and varnish to protect the layers of metal.
Glass ceramics
Glass can be made stronger if its molecules are forced into a regular pattern. Chemical substances are added to glass and, through intense heat treatment, these particles act as ‘seeds’ around which crystals form. The crystallised glass is called glass ceramic. Glass ceramics can be heated or cooled without cracking, so they are ideal for ovens, freezers, stoves and fireplaces. Glass ceramics are also used for missile and rocket nose cones and as thermal insulation to protect space shuttles as they re-enter the Earth’s atmosphere.
Soluble glass
Glass made from silica and soda, which dissolves in water, has some unusual medical uses. Soluble glass pills can be made containing drugs or vitamins in the centre and are particularly useful in veterinary medicine. If the pill is fed to a sheep, for example, the glass slowly dissolves, releasing drugs or vitamins into the stomach. In this way, large doses of medication can enter an animal’s bloodstream.
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