Understanding Glass

Understanding glass

Glass, in its simplest form, is silica - the same basic substance as beach sand - that is heated until it
melts, then shaped into the desired product.

Glass is transparent because silica has unusual qualities. When it is melted, its molecules - like those
of other liquids and gases - become randomly organized, allowing light to pass through. When it cools
to a solid state, however, the molecules remain random yet become rigid like other solids. Light
continues to pass through this now-solid material.

There are different processes used in making window glass:

Sheet glass is produced by drawing a sheet of glass from the molten liquid. It is the lowest in cost but
has noticeable waviness due to variations in thickness.

Float glass is produced by floating glass on a tank of molten tin. It is much flatter than sheet glass and
nearly as flat as plate glass. Float glass has largely replaced both sheet and plate glass.

Plate glass is produced by grinding and polishing to a high degree of flatness. It is used primarily for
large display windows.

Tempered glass is produced by rapid cooling of the glass to achieve unrelieved tension in its surfaces.
The process results in five times the impact strength of untempered glass and relatively harmless small
fragments when it is shattered. Building codes generally require tempered glass for glazed doors (patio
and French doors) and overhead windows (skylights and sloped sun-space glazings).

Tempered glass also is used in the side windows of vehicles. Windshields are typically made of
laminated glass - glass in which a thin layer of plastic has been embedded. When laminated glass is
broken, the shards stick to the plastic and shattering is prevented.