Glass

November 24, 2012 9:43 am

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Glass
Glass is a wonderful substance. It’s hard and firm, yet we can see through it. Glass can protect us from the wind and the rain. But it lets sunlight through, which is useful for keeping our homes light and bright. Glass is also brittle, which means it breaks easily. But there are ways to make it strong.
HOW IS GLASS MADE?
Glass is made by melting silica, a chemical that comes from sand. At extremely high temperatures, silica melts and becomes liquid. Other substances are usually added to the melted silica to make the glass strong. In its liquid state, glass can be molded into different shapes.
Glass was first made at least 4,000 years ago. About 2,000 years ago, people in the Middle East discovered that molten (melted) glass could be blown into different shapes. They put a gob of glass on the end of a metal tube. Then they blew air through the tube. The glass at the end of the tube expanded, just like a balloon. Glass blowing remained the usual method for making glass vessels until the early 1900s. In 1903, an automatic glass blowing machine was invented.
Glass can also be made into sheets that are flat and smooth. It can be shaped in molds. Substances can be added to glass to give it color. And once glass is cold, it can be decorated by cutting and painting.
Glass can be recycled. It is sorted by color and then melted in big furnaces. The molten glass is formed into new shapes.
HOW IS GLASS USED?
Glass is quite cheap to produce because it is made from sand. Glass is used for making everyday items such as windows, bottles, and drinking glasses.
Many beautiful objects are made of glass. Artists have produced elaborate shapes and elegant designs in glass. Stained-glass windows in churches are made of pieces of colored glass. The pieces are fitted together to form a picture.
Glass can be made strong enough to stop a speeding bullet. Bulletproof glass is made by layering sheets of glass with sheets of plastic. Car windshields are made of shatterproof glass. They crack rather than shatter if they are hit. This makes them much safer.
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