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:
“Sunshine of late afternoon—
On the glass tray
a glass pitcher, the tumbler
turned down, by which
a key is lying—And the
immaculate white bed”
—William Carlos Williams (1883–1963)
“O, what a noble mind is here o’erthrown!
The courtier’s, soldier’s, scholar’s,eye, tongue, sword,
Th’ expectancy and rose of the fair state,
The glass of fashion and the mold of form,
Th’ observed of all observers, quite, quite down!”
—William Shakespeare (1564–1616)
“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 (1688–1744)