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Speaker 1: Hi Am Marshall Brain with today's question, what makes glass transparent?
Speaker 1: Glass is so common that most of us take it
Speaker 1: completely for granted. But just what is it about glass
Speaker 1: that makes it transparent? Why can't we see through a
Speaker 1: window but not through the wooden frame that surrounds it.
Speaker 1: Scientists are still researching this question, but here's one way
Speaker 1: to think about it. You've probably noticed that most liquids
Speaker 1: and gases are transparent water, cooking oil, rubbing alcohol, air,
Speaker 1: natural gas, and so on. Our are all clear. That's
Speaker 1: because of a fundamental difference between solids, liquids, and gases.
Speaker 1: When a substance is in its solid state, normally, its
Speaker 1: molecules are highly organized in relation to one another, strengthening
Speaker 1: the bond between them and giving the substance rigidity. The
Speaker 1: atoms are not moving around freely. As the substance changes
Speaker 1: from a solid to a liquid, however, the strength of
Speaker 1: the bond lessons and the molecules begin to align themselves
Speaker 1: randomly and they can also move around. If we follow
Speaker 1: the substances progression to a gas, we see that the
Speaker 1: molecular bond is greatly weakened and the relationship of the
Speaker 1: molecules to one another is almost completely random. This progression
Speaker 1: from ordered to random organization is the primary reason that
Speaker 1: light can pass through liquids and gases. Just like bricks
Speaker 1: are stechnically on top of one another, the ordered molecules
Speaker 1: of most solids are virtually impenetrable to light waves. Depending
Speaker 1: on the substance, the light waves will be reflected, scattered, absorbed,
Speaker 1: or more likely some combination of the three. But as
Speaker 1: the substance changes to a liquid or gas, and the
Speaker 1: molecules are not stacked neatly anymore, gaps and holes occur
Speaker 1: that allow portions of the light waves to pass through.
Speaker 1: The greater the amount of randomness of the molecular organization
Speaker 1: of the substance, the easier it is for light to
Speaker 1: pass through. Although forms of glass such as obsidian a
Speaker 1: volcanic glass can occur naturally, glass is generally a man
Speaker 1: made substance. Here's the basic way to make glass. You
Speaker 1: take the most common glass material, silicon, which is just
Speaker 1: plain old sand like you would find on the beach.
Speaker 1: You heat it to an extreme temperature until it becomes liquid,
Speaker 1: and then you cool it. The resulting substance has a
Speaker 1: molecular structure that's very random, like a liquid, yet that
Speaker 1: retains the strong bond and rigidity of a solid. A
Speaker 1: similar method called quenching is used with plastics to make
Speaker 1: them transparent or translucent. Quenching causes the polymers, the long
Speaker 1: chain molecules in the plastic to settle into a random
Speaker 1: pattern that allows light to pass through. You can even
Speaker 1: use this process with organic substances. Clearer or translucent candy
Speaker 1: is created by heating the ingredients of the recipe and
Speaker 1: then rapidly cooling them. Notice that clear glass, clear plastic,
Speaker 1: and clear candy are all solids that are melted and
Speaker 1: then cooled. It's the same kind of process. Do you
Speaker 1: have any ideas or suggestions for this podcast. If so,
Speaker 1: please send me an email at podcast at how stuff
Speaker 1: works dot com. For more on this and thousands of
Speaker 1: other topics, go to how stuff works dot com and
Speaker 1: be sure to check out the brain Stuff blog on
Speaker 1: the how stuff works dot com home page. Brain Stuff
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Speaker 1: experience for a fraction of the price. The quality of
Speaker 1: the shave is so important that Harry's purchased the factory
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