Glass has many uses because of its transparency high resistance to chemical attack, effectiveness as an electrical insulator, and ability to contain a vacuum glass is a brittle material and characteristically exhibits compressive strength much greater than its tensile strength. Window glass as mentioned earlier. It was known until the fifteenth century, however that the use of window glass become general.
The term float glass pertains to all glasses produced in a flat form, regardless of the method of manufacture unlike hollowware, it was not until the middle ages that glass glassblowerrs were finally successful in taken flat sheets of
glass for windows and further processing. Mechanical production process were developed which later, effectively after 1920. Today manual production of flat glasses is the exception rather than the rule.
Toughened glass is a type of soda-lime-silica glass with a sheet thickness 4-12 mm. The sheet has a central tensile stress of 500-1200 kg/cm2 and a ratio of surface compressive stress to central tensile stress of 2:1 to 4:1. The article is toughened by heat exchange with an oil (or chilled air) in which these is maintained from 0.01 - 0.07 % liquid. The boiling point liquid may be an organic liquid such as carbon tetrachloride, methanol, benzene, toluene, trimethyl alcohol, ethyl alcohol or Xylene etc.