Abstract: Methods for identifying defective containers that include a) providing a container having an open rim end, a closed base end, an exterior surface and an interior surface; b) directing one or more sources of electromagnetic radiation toward the exterior surface or interior surface of the container; c) positioning one or more sensors for the electromagnetic radiation opposite the exterior or interior surface not directed to in b); d) accepting the container if the amount of electromagnetic radiation detected by the one or more sensors is within a predetermined range; and e) rejecting the container if the amount of electro-magnetic radiation is not within the predetermined range. The methods can be used in devices that contain a) conveying means for moving containers; b) means for directing sources of electromagnetic radiation; c) means for detecting electromagnetic radiation; and d) means for separating containers.