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