By Tim Lambert
Glass is sometimes made by lightning. If it strikes sand, it forms glass globules called fulgurites. There is also volcanic glass. If lava cools rapidly, it may form a dark, volcanic glass called obsidian. Early humans used it to make sharp cutting tools.
It’s not certain where people first started making glass from sand and ash, but it was probably either Iraq or Egypt around 2,500 BC. At first, glass was used to make beads, probably used for jewellery.
By about 1,500 BC, people in the Middle East had learned to make glass containers. People also learned to make glass in different colours. However, at first, glass was expensive, and only the wealthy could afford it.
About 50 BC, the Phoenicians, who lived in what is now Lebanon, invented glass blowing. That made glass vessels much cheaper. As a result, glass containers became far more common. In the 1st century AD, the Romans invented panes of glass for windows.
In the Middle Ages, from the 12th century to the 15th century, cathedrals in Europe were decorated with stained glass windows.
At the end of the 13th century, the first spectacles were made in Italy.
By the 15th century Venice was a centre of glassmaking. At that time Venetian craftsmen found a way to make plate glass mirrors. They coated the back of the glass with a mercuyr-tin amalgam. The new mirrors had a near perfect reflection.
Glass had other uses. About 1590 Hans and Zacharias Janssen used glass lenses to invent the microscope. In 1608 Hans Lipperhey invented the telescope.
In England in the 15th century, only a small minority could afford glass windows. However, they became more common in the 16th and 17th centuries. By the end of the 17th century, almost everyone could afford them. However, in 1695, a tax on windows was imposed in Britain. Some people bricked up some of their windows to avoid paying the tax. The tax was repealed in 1851.
Meanwhile, in 1674, George Ravenscroft patented a method of adding lead oxide to glass to make it clearer. It also made glass easier to use.
The Industrial Revolution brought many inventions.
For hundreds of years, glasses were used to correct short-sightedness and long-sightedness but in 1827 George Biddell Airy invented lenses to correct astigmatism.
In 1835, Justus von Liebig invented a method of adding a layer of metallic silver to glass. His invention made the mass production of mirrors possible.
In 1851, Joseph Paxton built an entire building, the Crystal Palace of glass. It housed the Great Exhibition of 1851.
In 1874, François Barthélémy Alfred Royer de la Bastie patented the first method of making tempered glass (glass that is much harder to break than normal glass). In 1903, Edouard Benedictus invented the first bulletproof glass.
In the 1950s, Alastair Pilkington revolutionised glass production by inventing float glass (molten glass is floated on top of a bath of molten tin and spreads out to form a level surface).
Fluoride glass was invented in 1984. It is used in optical fibres.
