Bret Albright, age 13, of Providence, R.I., for his question:
WHAT IS USED TO MARE GLASS?
Glass is made primarily of silica that is malted at high temperatures with other chemicals. Soda lime glass makes up about 95 percent of all glass that is manufactured today. It is made of sand, which is silicon dioxide, lime, which is calcium carbonate, and sodium carbonate.
To make glass, the raw materials are melted and then formed.
Soda lime glass is used in windows, bottles, tableware, glass building blocks, lamps and hundreds of other useful objects.
All types of glass are made by several of six basic operations: mixing and melting, blowing, pressing, drawing, casting and rolling.
Raw materials are measured and then mechanically mixed. Cutlet, or broken glass of the same formula, often is added to a batch to speed melting. The batch is then fed automatically and continuously into a furnace.
Today's furnaces are large tanks that hold many tons of glass. They are made of ceramic blocks. In order to keep the glass puts, there is no mortar or other bond between the blocks. In the melting end of the furnace, the glass is exposed to jets of flame that shoot from either side to keep an even melting temperature.
Blowing molten glass by mouth used to be the chief way to form glass. Now most glass blowing is done on high speed automatic machinery.
Pressing is done when glass is partly melted. In pressing, a bit of glass is put into a mold sad pressed with a plunger so the hot glass spreads to fill the mold. This method often is used to make tableware, insulators and automobile headlights.
In drawing, molten glass forms long tubes, rods or threads. Glass is drawn to form thermometer tubing, fluorescent tubing, sheet glass and glass piping.
Casting is done by pouring liquid glass into heated molds.
Roiling is a method in which glass is squeezed into various shapes between rollers. The rolls can produce different thicknesses of glass.
Plate glass usually is rolled glass. The glass moves through a series of grinders. Coarse grained sand is used in the first grinding, while in a final grinding the grains are pinpoint size. Grinding smooths the surface of the glass and leaves it free of waves, bubbles and streaks.
Safety glass is used in automobile windshields and windows. If smashed, it will not splinter because a plastic binder is sandwiched or laminated between two or more layers of plate glass. The plastic binder holds onto the splinters. The rubberlike plastic binder and sheets of plate glass are cemented into one unit by heat sad pressure.
Glass was first formed millions of years ago. When hot lava containing silica was forced frog the core of the earth, it cooled to form glass. It didn't take man long to learn how to make his own.
Egyptians were making glass objects as far back as 3000 B.C. Glass containers were made by building up layers of hot glass around a form.