How to determine the axis of a polaroid? I have found a polaroid from an old LCD device. It is rectangular in shape and does not have any markings on it. I wanted to somehow determine its axis, maybe not exact. I have tried to use it in front of a TV and phone screen, but I can't understand anything from that. I also know about polarised blue sky, but I don't know how it can help. So can anyone please suggest a way to know it (approximate) axis.
 A: Polarized light results from reflection on transparent objects.   Find a
plate of glass, and look at a reflection in it, at about 45 degrees.   The orientation 
of the polarizer that dims the reflection the most, is with the polarization
axis of the polarizer antiparallel to the plate ( most nearly aligned with the
perpendicular to the surface).
This is most effective at Brewster's angle, and is the basis of devices
like sugar refractometers for beer-making.
Alternately, if you can find a polarizer filter for a camera, there's usually a mark
indicating the axis orientation for that filter; when your polarizer is
in front of that filter and at right angles to its polarization, the
view from behind (camera-side) of the sandwich will be dark.
A: Well, I know answer by @Whit3rd is best, but for reference, which I think I found by some study:
On a clear day, put your polaroid in front of blue sky, a little bit away from the Sun. Rotate the polaroid in such a position such that brightness of sky is least. And now, the line from Sun to the polaroid becomes the axis.
For example, if Sun is on the head and you are looking in front, with sky at its minimum brightness, the vertical will be the axis.
