How to Make Your Own Ice Colours
Interference colours in ice are easily visible, if a piece of ice is placed on a flat surface and viewed through a polarizing filter at a shallow angle. Almost any piece of ice will do. The melting ice quickly produces small fissures that fill with air. Interference colours will soon show up, fading after a certain time.
The process can probably be understood as follows: the light travelling through the ice is partly refracted and partly reflected at the boundary of the ice and the fissure. The refracted light crosses the air-filled fissure and will again be partly reflected, the remaining rays travelling back through the fissure and the first ice layer, interfering with the light directly reflected at the first ice-air boundary.
Nikon D80, Tamron SP DI macro lens f=90 mm/1:2.8. Processed with Adobe Photoshop Elements 6.0.