Diffractive pigment flakes include single layer or multiple layer flakes that have a diffractive structure formed on a surface thereof. The multiple layer flakes can have a symmetrical stacked coating structure on opposing sides of a reflective core layer, or can be formed with encapsulating coatings...http://www.google.ca/patents/US6692830?utm_source=gb-gplus-sharePatent US6692830 - Diffractive pigment flakes and compositions
