While looking for posts on snow, of all things, I came a cross DotPainter's interesting post on iridescence and decided to experiment.

The picture here uses a shader in the highlight channel that mixes 8 colors (the rainbow plus white) based on slope. I didn't spend much time fine tuning the slope bands; the color grading could be improved and more of the red portion made visible with some tweaking.

This technique is basically what DotPainter suggested and looks good for a quick effect. By the nature of slope, though, you get a bar color banding on spherical surfaces when the color bands ought really to be round. But on some surfaces, like the glass, it is hard to tell.

Anyway, a nice technique for the toolkit but I wanted to try a formula shader shown in the next post.

Marc