This is a quick 'n dirty way of building a cheap polariscope.
I got the idea when I pondered what to do with a bunch of cheap 3D cinema glasses I have.
Some background information:
One might think that these glasses are not suitable for this kind of use as they are circular polarized, but there's a trick for this. The quarter wave plate has to be on the correct side, otherwise you will only get linear polarization.
You should definitely play around with some of these before you mount them, there's a bunch of strange effects to discover.