Abstract: An apparatus and process permit the material of construction and the color of transparent and partly transparent containers to be determined rapidly and accurately. To determine the material of construction, polarized light is passed through the container, portions of the transmitted beam are analyzed by parallel and cross polarizers, the intensities of the analyzed beams are measured, and the sum and difference of the analyzed beams are determined. Preferably, the determination is made with at least two wavelengths of polarized light, and the sums and differences of the intensities of the different wavelengths are determined. Glass containers do not alter the polarization of the transmitted light, while many types of plastic containers do alter the polarization, and this difference serves as the basis for the differentiation.