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:
“It is difficult to read. The page is dark.
Yet he knows what it is that he expects.
The page is blank or a frame without a glass
Or a glass that is empty when he looks.”
—Wallace Stevens (1879–1955)
“They are, as it were, train-bearers in the pageant of life, and hold a glass up to humanity, frailer than itself. We see ourselves at second-hand in them: they show us all that we are, all that we wish to be, and all that we dread to be.... What brings the resemblance nearer is, that, as they imitate us, we, in our turn, imitate them.... There is no class of society whom so many persons regard with affection as actors.”
—William Hazlitt (1778–1830)
“Before the beginning of years
There came to the making of man
Time, with a gift of tears;
Grief, with a glass that ran;”
—A.C. (Algernon Charles)