I finally got myself a polarizing film. By this I can now polarize the light falling on the sample by placing the film between the light source and the sample and further by placing another film between the lens and the eye/camera I can block the same polarized light so that only light whose polarization is affected by the sample goes through. You can read more about it here, but we have some great physicists on our forum who might explain this even better than what one reads on wikipedia. See the below video for my setup.
I used Beach sand (courtesy my colleague Gurmeet), NaCl salt, and recrystallized Baking soda to study their birefringence. Sodium chloride (salt) doesnt have any birefringence, but both the beach sand and Sodium bicarbonate have some interesting patterns– Why is this so? Obviously, this must have a lot of applications in studying minerals. There is a nice foldscope post on this (http://microcosmos.foldscope.com/?p=1937). Here are a few other posts on cross-polars using a foldscope (http://microcosmos.foldscope.com/?s=polarized+light)
Now to try it on everything that passes through my foldscope.