Pigment flakes are provided which can be used to produce colorant compositions having color shifting properties. The pigment flakes can have a symmetrical coating structure on opposing sides of a reflector layer, can have an asymmetrical coating structure with all of the layers on one side of the reflector...http://www.google.se/patents/US6686042?utm_source=gb-gplus-sharePatent US6686042 - Optically variable pigments and foils with enhanced color shifting properties
