If you look at a piece of glass from an angle, why does it have a bluish or green tint?

by | Feb 1, 2010 10:00 PM ET

You Asked:

If you look at a piece of glass from an angle, why does it have a bluish or green tint? --- Mariel, Santo Domingo, Dominican Republic

Marshall Brain Answers:

"Normal glass" has a little bit of iron oxide in it, and that iron is causing the greenish tint. You see it on the edge because, when you look at the glass edge-on, you are looking through inches of glass. If you had a window that was 6 inches thick, the green color would be very obvious.

You can take the greenish tint in two directions. If you remove the iron oxide you get much clearer glass, as you can see on this page: Low-iron glass – Clarity you can see

Or you can add iron to make the glass greener. Green beer bottles have more iron oxide. You can also add iron to make tinted glass for a car. As pointed out in this patent, "A typical green tinted automotive glass

has about 0.5 percent by weight total iron, with the ratio of FeO to total iron being about 0.25."

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