Glasses exhibit interesting properties and have been extensively utilized, not just in the present-day world, but in prehistoric times as well. It is what makes them one of the hottest areas of Materials research.
During the Stone Age (1.5 million years ago), glasses were used as natural materials. Many of them were very strong and people made weapons from them. Fast forward to 3500 BC, there were several technology-based developments and people started processing glasses to make decorative items such as jewelry. Then came the Medieval Period (fifth to 15th century AD), during which glasses were considered as status symbols. They found their use in the exquisite architecture (like window panes) of buildings and began to be shaped into spectacles that we know of today. Talking about the present times, the world has explored many more properties and processing conditions to engineer glasses with far superior qualities than was ever possible.
How are glasses formed? By the rapid cooling of a liquid. The liquid needs to be cooled (supercooling) below a reference state (its melting point). What happens next? This process essentially traps all the atoms in a metastable structure. Metastability indicates that glasses are not in their true stable form – given enough time they eventually tend to convert into a more stable structure. Some people call them solid because glasses behave like solids, for all practical purposes. But, on the other hand, they also resemble liquids, based on their structure. Under the right conditions, any material can theoretically form a glass! Isn’t it fascinating?
A detailed story explaining some of the most interesting properties of these original super-cool materials was published on Medium which can be found here. It is based on one of the sessions (delivered by Raghavan Ranganathan, faculty in the Material Science and Engineering discipline) of the Virtual Seminar Series by IIT Gandhinagar.