Polarizing Filter and cross polarization

If you have a computer with an LCD monitor and a camera with a polarizing filter on the lens you can create some really colourful photos like this:

All you do is place a piece of plastic (the above is a cd case with ice on the surface) in front of an LCD screen and photography it using a camera that has a polariser attached to the lens (or held in front of the lens)
By rotating the filter you can increase the strength (saturation) of colours.

Try with cd or cassette cases, plastic glass, plastic cutlery, geometry items, filter cases and other similar hard plastic items.
The patterns revealed show stress in the plastic.