I know. I am looking for a robust low cost solution. I have found that if you look at the number #5 though a opposed circular polarizers you get an array of colors with light and dark spots. ref the video. If you look at the same plastic with the second circular polarizer reversed (+ for -) the light and dark spots are reversed and the colors are transposed. If you through 3d movie glasses one eye sees the opposite of what the other eye sees. Its crazy. Axil were you doing that?
If you serialize the flow of plastic particles, each particle is analyzed based on it own optical characterization. To get high speed throughput, Process a 1000 particles a second one at a time. Multiple parallel particle paths can provide any level of desired throughput. http://www.angelfire.com/scifi2/zpt/temp/PlasticCir.mp4
