Glass is an amorphous (non-crystalline) solid material. Glasses are typically brittle and optically transparent.
The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica (SiO2) plus sodium oxide Na2O from soda ash, lime CaO, and several minor additives. Often, the term glass is used in a restricted sense to refer to this specific use.
In science, however, the term glass is usually defined in a much wider sense, including every solid that possesses a non-crystalline (i.e., amorphous) structure and that exhibits a glass transition when heated towards the liquid state. In this wider sense, glasses can be made of quite different classes of materials: metallic alloys, ionic melts, aqueous solutions, molecular liquids, and polymers. For many applications (bottles, eyewear) polymer glasses (acrylic glass, polycarbonate, polyethylene terephthalate) are a lighter alternative to traditional silica glasses.
Read more about Glass: Silicate Glass, Structure, Glass Versus Supercooled Liquid, Glass Art
Famous quotes containing the word glass:
“When God at first made man,
Having a glass of blessings standing by,
Let us, said He, pour on him all we can:
Let the worlds riches, which dispersed lie,
Contract into a span.”
—George Herbert (15931633)
“We are little airy creatures,
All of different voice and features:
One of us in glass is set,
One of us youll find in jet,
Tother you may see in tin,
And the fourth a box within;
If the fifth you should pursue,
It can never fly from you.”
—Jonathan Swift (16671745)
“... this I conceive to be no time to prate of moral influences. Our mens nerves require their accustomed narcotics and a glass of whiskey is a powerful friend in a sunstroke, and these poor fellows fall senseless on their heavy drills.”
—Clara Barton (18211912)