Glass is Amazing!

by | Jul 13, 2018


Glass is extremely important to modern life. Steven Johnson in his fantastic book How We Got to Now – Six Innovations that Made the Modern World lists glass as one of the six innovations most important to how we live. What does glass do for us?

  • The most obvious benefit of glass is that it used in windows. Our houses have light during the day and views of the outside. Glass windows also allow us to drive in cars and fly in airplanes without exposure to the elements.
  • Glass is a necessary ingredient of a mirror.
  • Fiberglass has many different uses, from insulation to surfboards.
  • Curving glass into lenses gave us magnifying glasses and then spectacles, without which hundreds of millions of people could not read due to far-farsightedness or could not see at a distance due to nearsightedness.
  • Then glass was used to create microscopes which allowed us to learn about small organisms, bacteria, viruses and cells. Without the microscope we’d likely be in the dark ages of biology. Imagine the state of medicine without an understanding of cells, viruses and bacteria.
  • Glass lens in telescopes were necessary to determine most of what we know about the universe and our place in it. Observations using telescopes waer important for Newtonian physics as wells as relativity.
  • Glass lenses are necessary for cameras to exist and capture images. As well as video. Imagine life without pictures, TV or movies. And SELFIES!
  • Fiber optic cables are key ingredients of our modern communication system and the internet.
  • Glass is a great substance out of which  to drink water, wine or whiskey.
  • This list could go on and on.

So, glass is pretty amazing. But what exactly is glass? There is a popular myth that glass is a liquid, but in a very slow state of flow. Proof of this is claimed by the fact that very old windows and stained glass are often thicker on the bottom than the top, suggesting that glass at room temperature is a liquid and flows towards the bottom of the window over long periods of time.

However, glass is not a liquid. Or a solid. Instead it’s an amorphous solid. Those old windows? They are thicker at the bottom than the top due to how glass was manufactured back in the day.

To understand glass a quick physics refresher is helpful. There are three primary states of matter we experience on Earth: Gas, liquid and solid.* The differences between these states of matter have to do with their molecular structure.  A solid has regularly structured molecules in a crystalline structure. When a solid is heated to it’s melting point (for water 32 degrees), it loses is crystallized structure and the molecules move independently from each other but don’t separate completely from other atoms. At boiling point (212 degrees for water) there is so much kinetic energy that the molecules fly around and bounce off each other resulting in a gaseous state.  From a molecular viewpoint, here’s how water looks as a solid, liquid and gas:


For most molecules, when they are cooled below their melting point they return to their crystalline structure and become solids again. For example, liquid water returns to ice when cooled below 32 degrees.

Glass is different, as it cools below melting point it does not regain its crystalline structure. Thus, glass has the mechanical rigidity of a solid, but the random disordered arrangement of liquids. Glass can be made from many types of molecules with this characteristic, but the most common are silica based such as silicon dioxide.  Here’s what Silicon Dioxides looks like as a solid (quartz) and as an amorphous solid (glass):


Why is glass transparent? As you may know, atoms are mostly empty space (see We (and Everything Else) are Mostly Empty Space), so a great question is why light doesn’t pass through everything. The answer has to do with how the electrons in various substances absorb light photons in order to change energy levels. Atoms in glass molecules have the right characteristic that visible light photons do not have enough energy for electrons to jump to the next energy level so that visible light just passes through and is not absorbed. Here’s a video with an explanation:

*the fourth state of matter is plasma – not common on Earth but actually the most common form of matter in the universe.

1 Comment

  1. Great IFOD. Informative and Glass is indeed one of the many amazing materials that has led to Humans becoming the earths dominate species. Hope we do not destroy all other species in our continued expansion of the world’s human population. This ball we live on can only support so many of us.


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