Glass is made via heating sand (which mostly contains silicon dioxide) at a temperature of 1700°C (3092°F). Thus, glass industries require large supply of heat. LPG and natural gas being the cleanest fuels augment quality and reduce technical difficulties which arise during manufacturing.
In glass factories, sand is mixed with waste glass (for re-cycling), sodium carbonate, and calcium carbonate (soda ash and limestone) and is heated in a furnace. The result of this heating is soda-lime-silica glass. This is the ordinary glass we see all around us.

There are four major segments in the glass industry.

  1. Container Glass: Glass packaging products, such as bottles and jars.
  2. Float Glass: Windows for residential and commercial construction, automobile windshields, mirrors, instrumentation gauges and furniture such as tabletops and cabinet doors.
  3. Fibre Glass: Building insulation (glass wool), textile fibres used to reinforce plastics and other materials for the transportation, marine and construction industries.
  4. Specialty Glass: Handmade glasses, tableware and oven-wares, flat panel display glasses, light bulbs, television tubes, fiber optics and scientific and medical equipment.

Since re – cycling is crucial these days, re – heating becomes an essential component in the glass industry. Special furnaces are used while re – heating glassware. During the production of complicated shapes, the glassware may have to be reheated numerous times to keep it moldable. This is done via a process called “annealing”. Annealing is a process where the glass is heated and then slowly cooled to relieve internal stresses after manufacture. Annealing is mostly via in long ovens often called “lehrs” via making the glass travel on a steel conveyor belt. Gas is directly fired for finer temperature control.