Viewing Crystals with Polarized Light

by Maria Carver | Jun 4, 2022 | 0 comments

Epsom salt crystals under polarized light
Epsom salt crystals. Photo © Maria Carver.

Viewing crystals with a microscope is lots of fun! Home grown crystals from sugar, salt, and other household items, are beautiful on their own, but some details are best seen when viewed with a light polarization filter. You can make your own light polarizing filter at home!
You will need:

  • A microscope. I use 40 power (40x).
  • A pair of polarized sunglasses. They don’t have to be expensive, just make sure they’re labeled “Polarized.” Gray lenses work best.
  • Water soluble crystals such as sugar, salt, Epsom salt, citric acid, etc.

What to do:
Let’s start with the crystals. If you have never grown crystals to look at under the microscope, I would recommend that you start with Epsom salt (Magnesium sulfate). The crystals it makes are spectacular, grow fast, and reflect the polarized light beautifully! Start with a tablespoon of hot water. Stir in some Epsom salt, one teaspoonful at a time, until no more will dissolve (This is what you call a saturated solution). Spread a drop of this solution on a microscope slide and set aside to dry. You may want to try several while you’re at it, because each one will be unique! If you’re having trouble spreading the solution on the slide, try adding a drop of dish soap to the solution. Follow this method for any other solutions you would like to try!

Now for the filter! Pop the lenses out of the sunglasses. You will notice that if you hold one lens over the other at a right angle, it will look very dark. That means that they are polarized, and that is the angle you will want them at when they are on your microscope. Put one lens above the specimen, and one lens below. Depending on your microscope, you may need to tape them in place if there’s nothing to rest them on. Keep the top lens up off the crystals. Light the specimen from below the bottom lens. If you have them angled right, you should see beautiful colors when you look into your microscope. You can adjust one of the lenses by turning it back and forth until you see the most color.

How it works:
Well…let’s just say it’s complicated! The filter actually aligns the light waves, so that they are all going in the same direction. The way these “polarized” light waves interact with the internal stress in the crystals causing the beautiful colors is called “Birefringence.” This phenomenon actually has some really useful applications! For example, using polarized light allows us to observe stress on glass and plastic structures, showing which parts are likely to break. Pretty amazing isn’t it?

God’s handiwork is so beautiful! I hope you enjoy getting this glimpse of His creation as much as I have!

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