Glass: How is it made?
Dr. Universe: How is glass made? And, what is it made out of? What about thick glass like they are putting up on the Space Needle? – Tali, almost 8 years old, Seattle, Wash.
Dear Tali,
We can make glass in factories and we can find it in nature. Some volcanoes make glass. When they spew out lava, it often cools into obsidian, a black glass. Glass can also form on sandy beaches. Small tubes with smooth glass on the inside may appear after super-hot lightning strikes the sand.
In fact, sand is one of the most important ingredients we use to make glass. We may also use things like seashells, salt, and other chemicals. That’s what I found out when I visited my friend John McCloy, an engineer at Washington State University. McCloy and graduate student Jose Marcial were testing out different materials to make glass in the lab.
Marcial explained that glass is made of molecules—think of them as building blocks—arranged in a pretty random order. Most of the time we think of glass as a solid. But the way its molecules are arranged actually allows it to act as both a solid and a liquid. When we heat up the mix of sand, seashells, salt, and other chemicals, it can become molten, kind of like lava.
In the lab, Marcial poured a mixture of solid materials into a tiny metal cup. He heated it way up until the mix turned to something in-between a solid and liquid, similar to a thick honey. It was so hot that as Marcial poured it out onto a table, the molten material started glowing orange. As the mix cooled down, the molten liquid turned to a solid piece of glass right before our very eyes.
Marcial said that in factories, glass is made in a similar way. We take sand, add in different chemicals, heat it up, and pour it out onto a bed of molten metal. Just as oil sits on top of water, the lighter, liquid-like glass material floats atop the metal.
As everything cools down, the metal stays molten, but the glass on top solidifies. The glass might end up in a pair of eyeglasses, a computer screen, fish tank, or window. The big pieces of glass you see in buildings or observation decks are often made up of thinner layers of glass that have been combined.
As you’ve observed, the Space Needle is getting a big renovation. According to friends at the Space Needle, more than 10 types of glass will be used to renovate the landmark. They will also bring in 176 tons of glass during construction—that’s more than twice the weight of a NASA space shuttle.
As you can see, glass is made in lots of different ways. Believe it or not, you can also make something very similar to glass in your kitchen. Instead of grains of sand, salt, and seashells, you can use tiny grains of sugar.
With the help of a grown-up you can make your own edible sugar glass by mixing together ingredients like sugar, corn syrup, water, and cream of tartar. Try it out sometime and let me know what you learn at Dr.Universe@wsu.edu.
Sincerely,
Dr. Universe
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