Archeological findings suggest that glass was first created during the Bronze Age in the Middle East. To the southwest, in Egypt, glass beads have been found dating back to about 2500 B.C.E.
Glass is made from a mixture of silica sand, calcium oxide, soda, and magnesium, which is melted in a furnace at 2,730°F (1,500°C). Most early furnaces produced insufficient heat to melt the glass properly, so glass was a luxury item that few people could afford. This situation changed in the first century B.C.E. when the blowpipe was discovered.
Glass manufacturing spread throughout the Roman Empire in such quantities that glass was no longer a luxury. It flourished in Venice in the fifteenth century, where soda lime glass, known as cristallo, was developed. Venetian glass objects were said-to be the most delicate and graceful in the world.
Glass is normally a clear or translucent brittle material, but it may be colored, depending on the way it has been made. The three classes of ingredients used for making glass are: alkalies, earths, and metallic oxides. Crown-glass, used for windows, uses no lead but includes black manganese oxide. Cheap bottle glass uses iron oxide, alumina, and silica.
In the 1950s Sir Alastair Pilkington introduced "float glass production," a revolutionary method still used to make glass. In this process a film of glass, which is highly viscous, is floated onto molten tin, which is fluid, and, as the two do not mix, the contact surface between them is perfectly flat.
Other developments have included safety glass, heat-resistant glass, and fiberoptics, where light pulses are sent along thin fibers of glass. Fiberoptic devices are used in telecommunications and in medicine for viewing inaccessible parts of the human body.
