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.
Other articles related to "glasses, glass":
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Famous quotes containing the words glasses and/or glass:
“Midnight has come and the great Christ Church bell
And many a lesser bell sound through the room;
And it is All Souls Night.
And two long glasses brimmed with muscatel
Bubble upon the table. A ghost may come;
For it is a ghosts right....”
—William Butler Yeats (18651939)
“the loose fragrant cavendish
and the shag,
And the bright Virginia
loose under the bright glass cases,”
—Ezra Pound (18851972)