Glass is made from sand, a chemical called sodium, and limestone. They are all heated together in a very hot fire until they turn into liquid. The liquid is then cooled a little, and air is blown through it to shape it into things like bottles, jars, and glasses. Machines in factories shape the glass but sometimes people do it by hand.
Some people are especially trained to make wonderful glass shapes. They are called glass blowers.
Different chemicals are added to the hot liquid to colour the glass
The first glass things known, were beads made from rough lumps of glass. That was 4,000 years ago in Asia.