This technique reveals the internal stresses in plastic objects as a rainbow of colours.
Pretty well any transparent plastic object will work. You need to back-illuminate the object with polarised light. A common source is a laptop screen displaying a grey image, ideally full-screen.
You also need to attach a polarising filter to your lens and rotate it until the screen turns black – the colours should also then be at their strongest. As exposure times tend to be quite long, a sturdy tripod is essential.
As with most techniques of this kind, experimentation is the key.
Photographer: Nick McDonald