The big idea
Look at a window. It is hard and solid, but you can see right through it. That is glass! And here is a surprise: glass is made mostly from sand, the same kind of stuff you find on a beach.
How it works
Sand is made of tiny grains. Each grain is a bit cloudy, and a pile of sand is not see-through at all.
When sand is melted and cooled in the right way, the tiny pieces inside it get stuck in a jumble. They do not line up in neat rows, and there are no grains or gaps left. Light can zoom straight through without bumping into edges. So you can see through it.
Glass feels like a solid because it is a solid. It is hard and keeps its shape.
How it's made
- Workers mix sand with two other powders. One is called soda ash. It helps the sand melt more easily. The other is limestone. It makes the glass strong so water cannot spoil it.
- They add broken bits of old glass, too. Old glass melts easily, so this saves energy.
- The mix goes into a giant oven called a furnace. It is much, much hotter than a kitchen oven: hot enough to make the mix glow orange! It melts into a glowing, runny liquid, a bit like thick honey.
- For windows, the runny glass is poured onto a pool of hot melted metal. It floats and spreads out flat and smooth, like pancake batter in a pan.
- The glass cools very slowly so it does not crack. Then machines cut it into big sheets.
For bottles and jars, blobs of hot glass are puffed into moulds with air, a bit like blowing up a balloon inside a box.
Try this!
Look at the glass things in your home: a window, a jar, a glass of water. Which ones are flat? Which ones are curved? Hold a clear jar up and look through it. Do things look bent or wobbly? Put your jars in the recycling bin when they are empty.
Never touch broken glass. If something breaks, tell an adult and stay back.
Wow!
People have been making glass for more than 4,000 years. A glass jar can be recycled over and over, and it still makes a jar just as good as the first one!