Glass is a non-crystalline often transparent amorphous solid, that has widespread practical technological and decorative use in for example windows panes, tableware and optics.
Glass is most often formed by rapid cooling of the molten form, some glasses such as volcanic glass are naturally occurring. The most familiar and historically the oldest, types of manufactured glass are "Silicate glasses " based on the chemical compound silica ( Silicon dioxide or quartz ) the primary constituent of sand. Soda-lime glass containing around 70% silica, accounts for around 90% of manufactured glass. The term glass, in popular usage, is often used to refer only to this type of material, although silica-free glasses often have desirable properties for applications in modern communications technology. Some objects, such as drinking glasses and eyeglasses, are so commonly made of silicate-based glass that they are simply called by the name of the material.
Although brittle, silicate glass is extremely durable and many examples of glass fragment exist from early glass-making cultures. Archaeological evidence suggests glass-making dates back to at least 3600 BC in Mesopotamia, Egypt or Syria. The earliest known glass objects were beads perhaps created accidentally during metalworking or the production of faience. Due to its ease of formability into any sharp, glass has been traditionally used for vessels, such as bowls, vases, bottles, jars and drinking glasses. In its most solid forms, it has also been used for paperweight and marbles. Glass can be coloured by adding metal salts or pained and printed with vitreous enamels, leading to its use in stained glass windows and other glass art objects.
Glass is an optically transparent material produced by fusing together silicon oxide with sodium oxide, boron oxide and a trace amount of transition metal oxide is added to impart colour to the glass.
By changing the compositions almost eight hundred different types of glasses are manufactured. Quartz glass is obtained from only silicon dioxide.
Pyrex glass is obtained by fusing together 60 to 80 % SiO2, 10 to 25% B2O3 and remaining amount of Al2O3.
Soda lime glass is produced by fusing 75% SiO2, 15% Na2O and 10% CaO. Red glass contain trace amount of gold and copper. Yellow glass contains UO2. Blue glass contains CoO or CuO. Green glass contains Fe2O3 or CuO.