Method and apparatus for sorting desired pieces of material from undesired material present in mixtures thereof. A piece of material from a mixture of pieces of desired and undesired materials is irradiated with a plurality of wavelengths of near-infrared radiation. The absorptions by the irradiated...http://www.google.co.uk/patents/US4915827?utm_source=gb-gplus-sharePatent US4915827 - Method and apparatus for optical sorting of materials using near infrared absorbtion criteria
