This is a quick 'n dirty way of building a cheap polariscope. I call it a 'Make it Glow box', because when you put a translucent object on it, it looks like it emits light itself, since the direct background light is blocked by the polarization filters. You can also photograph the objects by holding the second polarizer in front of your camera, or by using a standard polarizing filter on the camera.
How does it work?
Light from below is polarized in one direction using a polarization filter. A translucent object on top of this first polarization filter scatters light in all directions and depending on the material depolarizes the light. A second polarization filter perpendicular on the first one blocks all direct polarized light, but the light scattered through the object is still visible.
What can we do with it?
A polariscope can be used to see through stuff, in the past it was used for seed testing, it is used for showing 'stress' patterns in for instance glasses or other transparent materials, and for testing gems for authenticity.
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Step 1: Stuff You Need
The polarization filters used are from sunglasses. I got some unprocessed samples from the local optician store. A led flashlight is used as light source. A piece of baking paper act as extra diffuser between the light source and the first polarizer. A carton box, duct tape and a tie-wrap is used to put everything together.
A razor knife and a pencil is all you need.
Step 2: Cut the Hole for the First Polarizer
put one of the polarizers on the box, mark its size and cut it out.
(cut a little bit less than the size of the polarizer)
Step 3: Mount the Flashlight.
Open the box, position the flashlight opposite the polarizer.
You need to make two small holes to fix the flashlight with a tie-wrap and a larger hole to get access to the flashlights on/off switch.
Cut the holes and mount the flashlight.
Step 4: Mount the First Polarizer
Put a piece of baking paper and the polarizer over the hole.
Fix everything together with duct-tape and close the box.