What is glass made out of?

 What is more relaxing than enjoying a hot beverage from the comfort of your house and watching the colored autumn leaves falling from trees? Nothing beats that, right? But, have you ever wondered what is that transparent material in windows that protects you from the weather, yet lets you see the wonders of nature from a safe place? Yes! I am talking about glass. 

The main ingredients of glass are silicon and oxygen. A small mix of additional, different ingredients are used to change the rigidness, color, and clarity of the glass. Old civilizations learned that by melting sand, a very common material made of silicon dioxide, they could mold it in many different shapes during the cooling process, resulting in a clear and strong material. However, melting sand is no easy task for you need a modest temperature of 1,723 °C (3,133 °F) to do this! To make this process easier, ancient glassblowers, people dedicated to making glass, discovered that adding small amounts of soda ash (sodium carbonate), limestone (calcium oxide), magnesia (magnesium oxide), or alumina (aluminum oxide) resulted in a material that was easier to melt, but it also affected the rigidity of the glass formed. 

Now that we learned what glass is made of, what gives it its color? As mentioned earlier, adding small amounts of other materials changes the rigidity, the same process is done to change the color of glass, but this time glassblowers use small amounts of metal. Common colors result from adding small amounts of different metals. Brown glass contains iron-sulfur or nickel; blue glass contains copper or cobalt; red glass contains gold, copper-tin, or selenium-cadmium; and green glass contains iron or chromium ions. Because different colored glass contains different metals, recycling facilities separate the different colored bottles to avoid changing the color and rigidity of the recycled glass.

While today, the metal in colored glass is very common and safe, several decades ago, from the 1940s to the 1970s, people used metal ions that are not so safe.  Some of those dangerous metals were uranium (for a green-glow in the dark-color), thorium (for camera lenses), or lead (for more refractive glass). But not to worry! We now use safer alternatives. So enjoy watching the change of seasons through your cozy living room window.

 By Dr. Jose Veleta