Look around you: windows, bottles, glasses, phone screens. Glass is everywhere, but few people know that it starts as something very ordinary — sand.
Much of the sand in the world is made mostly of a material called silica. To make glass, workers heat silica sand in a huge oven, together with a few other materials, such as soda ash and limestone. The temperature must be extremely high — well over a thousand degrees. At this heat, the sand melts and becomes a thick, hot liquid, a little like honey.
While the glass is still soft, it can be shaped. Glassblowers blow air through a long pipe into a ball of hot glass, just like blowing up a balloon. In factories, machines press the hot glass into moulds, or float it on a bath of melted tin to make flat window glass. Then the glass is cooled slowly, so that it does not crack.
People have been making glass for thousands of years, and today much of it can be recycled. Old bottles are broken into small pieces, melted and made into new bottles. Recycling glass saves sand and energy, because broken glass melts at a lower temperature than sand. So next time you finish a bottle, remember: put it in the recycling bin, not in the rubbish.