My Science School

            Safety glass is glass that has been strengthened. There are two kinds of this protective glass-laminated and toughened-and both were discovered by accident.

             In the early 1900s EdouardBenedictus, a French chemist knocked a glass flask on to the floor. Although the glass starred and cracked, it did not break. After examining the flask he realized that a coating of dried celluloid on the inside had held the fragments together.

             Some years later, when injuries from broken car windscreens increased, Benedictus recalled this incident. Using glass sheets and celluloid bonded together in an old letter press, he produced the world’s first sheet of laminated, or layered, glass. Since then the clarity of the glass has been improved to equal that of ordinary glass. But it will withstand the impact of a half-pound steel ball dropped from a height of 16 feet. Toughened glass was developed later, although in the 17th century, Prince Rupert, nephew of king Charles I of England, discovered that molten glass was turned into immensely strong pear-shaped drops when tipped into cold water. Prince Ruport’s drops, as they are called, can be hammered on an anvil without breaking, but if the tail of the drop is broken they crumble into dust.

             In 1874 a French scientist, de la Bastie, heated small sheets of glass and then quenched them in oil, increasing their strength dramatically. However these sheets of toughened glass were very small and it was not until the 1930s that sheets large enough for use in cars could be toughened.

            Laminated or toughened safety glass is now used all over the world in cars, buses, trains, aircraft, ships and shops and has proved its safety value.

Glass is made naturally from a fusion of silica (sand), soda and lime. This fusion can be achieved merely by lightning striking in a place where the right ingredients happen to be adjacent to each other. When glass is made by man, other ingredients are added, such as potash, lead oxide and boric oxide. Some of these ingredients are used to make glass clear, some to colour it, and others to give it a frosted effect.

      Glass was made by potters in Egypt for glazing stone beads as early as 12,000 B.C. As Egyptian culture progressed, craftsmen used glass for the manufacture of personal ornaments and bottles.

    A tremendous step forward in the use of glass was made by the Phoenicians in about 300 to 200 B.C. by the invention of the blow-pipe. The blowpipe is a hallow iron tube with a mouthpiece at one end and a knob shape at the other. The knob-shaped end is dipped into hot, viscous glass. A “gather” of molten glass can be blown by the worker into a hollow ball. The more he blows, the larger the ball.

    During the Roman civilization the art of glass-making reached near perfection. In the 3rd Century, the Romans cast glass on flat stones and produced the first window panes. The break-up of the Roman Empire and the ensuring Dark Ages brought an end to such cultural developments. The glazing of windows did not become wide spread over the whole of Europe until the 15th and 16th Centuries.

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Glass fiber is a mass of very fine strands of glass. When ordinary glass is spun into thin threads it is strong and bendable, unlike normal glass objects, which are brittle and break easily.

       These silky strands of glass can be woven into a material or massed together like cotton-wool. Glass fiber does not decay or corrode. It is a good insulator and a poor conductor of electricity. Curtains made of this material do not rot in damp conditions or in sunlight. Now that technical dyeing problems have been overcome, glass Fiber can be patterned.

    Many plastics tend to crack or bend under stress or impact, but  combining them with strands of glass fiber results in very light, strong and useful materials. Glass fibre increases their strength in much the same way as concrete is reinforced with steel rods. These mixtures are moulded to make such things as aircraft parts, car bodies mats of glass fiber are used for filters and washers, and blankets of the material provide good in solution for houses.

Picture credit: google