SHEILA TERRY / SCIENCE PHOTO LIBRARY SHEILA TERRY / SCIENCE PHOTO LIBRARY
When silica, the main constituent of sand, is heated together with sodium carbonate, the melting point of the silica is lowered from around 2000 degrees Celsius to 1000 degrees. This effect underlies the account of the discovery of glass in Naturalis Historia by Pliny the Elder, the Roman first century historian. He describes how a group of mariners built a campfire on a sandy beach with the help of lumps of the ship's cargo of nitre ( the Roman name for sodium carbonate). They noticed that the fire was producing a stream of molten sand. However further additives such as lime (calcium oxide) would be required to make a usable silicate glass. Also, there is doubt that a campfire temperature would have reached 1000 C. Many legends have attempted to explain the discovery of glassmaking. Where and when is uncertain, but not thought to predate 3000 BCE.
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