I'm looking for theory rather than a package or download. It's one of those "teach a man a fish...." things.

How do I create sparkle paint? Think "low-rider" paint, drum kits from the 1960s, that sort of thing. The base coat and the clear coat are fairly easy, but the sparkles are the challenge. The only way I can think of is a noise applied to specularity which is "activated" when light shines perpendicular to each sparkle "chip". Any ideas?