Most glass is made of silica sand (silica, or silicon dioxide), with a little soda ash (sodium carbonate) and limestone (calcium carbonate) added to lower the sand’s melting temperature.
Early humans got the idea for making glass after finding chunks formed by lightning strikes on the beach. These early humans originally cast it like metal and then ground and polished it, which was a laborious process.
At about 50 B.C., Romans figured out how to blow glass using hollow metal tubes, which suddenly made glass inexpensive and practical for a variety of cups, bottles, and other vessels.
