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.
Famous quotes containing the word glass:
“I must sojourn once to the ballot-box before I die. I hear the ballot-box is a beautiful glass globe, so you can see all the votes as they go in. Now, the first time I vote Ill see if the womans vote looks any different from the restif it makes any stir or commotion. If it dont inside, it need not outside.”
—Sojourner Truth (c. 17971883)
“... 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)
“Vast chain of Being, which from God began,
Natures aethereal, human, angel, man,
Beast, bird, fish, insect! what no eye can see,
No glass can reach; from Infinite to thee,
From thee to Nothing!”
—Alexander Pope (16881744)