Fun with Polarising Film...

Polarising film is an interesting material to play around with since it can produce amazing patterns and colours when combined with the right materials.

At work we have a light box that is fitted out with a square of polarising film the same size and the top of the box, this produces a polarised light source. Normally this light box is used in conjunction with a sheet of clear plastic covered with strips Selotape (cellulose tape) at different angles, which produces many varying colours due to the interaction of the natural bio-refringent properties of the tape and the polarised light, to see the effect of this you need to be looking through an additional sheet of polarising film.

Here is an image taken with this set-up:



The polarising properties inherent in the tape also occur naturally in minerals such as mica. Removing the Selotaped layer and replacing it with chips of mica produced similar results, with the main difference that it was possible to see different colours in one chip meaning that the polarising properties could change across one chip where as with the tape the only variation was the angle of the tape. In the mica the changes are to do with angle and also the thickness of the layer and how the minerals were layed down.

This image shows the change in colour between different chips and across the same chip:



Here is a close up of an individual chip showing its variations:



Additionally this polarising film set-up can be used to show the stress patterns occurring in plastic objects. Using this set-up I have looked at clear plastic ruler and a clear plastic drawing pin. When looked at with polarised light and a polarised filter the stress patterns evident in the material show up as changes in the colour of light. In these images the stress patterns are ones inherent to the plastic and were set into the objects as they cooled, but it is possible to show instantaneous stresses caused by the bending of plastics this way too.

Here are the stress patterns in a plastic ruler:



And the stress patterns in Plastic Drawing Pins:



For additional pictures taken during this session please see: here

Many thanks to www.Greenweld.co.uk for the Polarising Film and Mica chips, Check them out!!