HISTORY AND SCIENCE OF GLASS
The session set off with the nature of glass. Children were enlightened with the fact that Glass is an amorphous solid material, typically brittle and optically transparent. Quartz sand (silica) is the main raw material in commercial glass production. Silica, the most prevalent ingredient in the Earth's crust, is found as quartz and sand. This material can be obtained from the ashes of certain plants and from processing salt. Children were amazed to hear that in nature, quartz occurs when lightning strikes sand. The process of making glass was explained through video which facilitated the children to understand. The process includes melting the Ingredients, Blowing, Pressing, Drawing, Annealing and Tempering.
Children were inquisitive to know that Silica, soda ash and lime are the main ingredients in glass which is added to the mixture to create certain properties. Barium is sometimes used to increase glass' brilliance, and boron can be added to increase heat resistance. Chemicals that reduce the melting point of the silica are also frequently used. Sometimes recycled glass, called cullet, is also added. Once glass has been melted and placing a ball of melted glass at the end of a hollow iron tube, Air is then blown into the tube to shape the glass on the other end. Air can be blown in manually or by machine. The glass is reheated often during this process so that it stays pliable. When the glass blower is finished, it is allowed to cool. In the pressing method of glass making, the liquid glass is poured into a mold and then pressed into shape by either a machine or a special tool. This is how bowls and ashtrays are made. Glass drawing is used to make flat and tubular pieces, such as glass for windows and test tubes. The annealing process involves making the glass hot again and then allowing it to cool slowly. When glass is tempered it is also reheated, but tempered glass is cooled very quickly with air. Depending on the desired properties, the finished glass can be coated with different materials to further increase strength, reduce glare or add other desired traits.