What is glass made up of?

Glass is one of the world's oldest and most versatile man-made materials. We cannot imagine life without it. It’s everywhere – windows, mirrors, tumblers, computer screens, construction – and it comes in so many varieties. But the source of all glass it same. Believe it or not, glass is made up of liquid sand!  

How does sand turn to glass?  
Theoretically, a bucket of sand form the local beach can also turn to glass when heated. But we don’t see that happening by the roadside. Sand melts at the incredibly high temperature of 1700°C (3090°F). This is approximately the same temperature a space shuttle reaches as it re-enters earth’s atmosphere from outer space. So, to get glass from sand, we need to heat it to a level enough to power a rocket!  

The sand commonly used to make glass is made up of small grains of quartz crystals, which are actually molecules of silicon dioxide, also known as silica. When those molecules are heated in glass making furnaces, the sand melts and loses its crystalline structure, which it doesn’t regain on cooling. The new structure, on a molecular level, is somewhere in between a liquid and a solid. This in-between state is what material scientists call an amorphous solid. It has some of the crystalline structure of a solid coupled with the molecular randomness of a liquid. And that is what we call glass.  

Varieties of glass 
Depending on what is mixed with sand, glass can have a variety of properties. The level of clarity, its colour, toughness, opacity – are all results of experiments with sand mixture.  For example, manufacturers use thermal tempering to heat and then cool the mixture ultra-rapidly to get tougher glass. One of the most popular types is soda-lime glass. This is a combination of soda ash (sodium carbonate), limestone, and sand. Soda reduces the melting point of sand. So, both cost and energy can be saved. On the other hand, soda reduces the chemical durability of sand, and the molecules can actually dissolve in liquids! No one wants that. So, limestone (calcium carbonate) is added as a stabiliser.