Photoelasticity

DG again today.  C came the other two couldn't.  So we went back over what we had done these last two weeks on:
Photoelasticity when you have polarised(1) light going through hard plastic objects (2) the light is split into many colours and you pick this up when you have a polarising filter on you camera.  (3)
1.  the light from a computer or tablet screen
2 . see-through plastic cutlery, set square, protractor, some see-through rulers or crumpled up cellophane sheet - various packaging materials and see -through plastic champagne glasses.
3.  if you don't have a polarising lens you could try with polarising sun glasses?

Back in Photoshop you can do whatever you want but try inverting or solarising the shot.

To twist the glasses I used 'Step and Repeat'.  Plearn in Photoshop