Abstract: Glass containers coated with a transparent polymer film, co-mingled with similar but non-coated containers, are identified without contact as they are moving on a conveyor. An optical position sensor triggers a stroboscope to emit a pulse of light that is directed to pass through the container. A light receptor essentially receives only that strobe light which has passed through the center of the container; light passing tangentially through the side of the container is blocked from the receptor. The light is filtered so that the receptor receives substantially only light in a wavelength range which will be attenuated by the polymer coating. Circuitry discriminates between the greater intensity of received light which has passed through an uncoated container and the lesser intensity of light through a coated container. Containers of the one type may be segregated from those of the other type by reject or sorting apparatus.