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 . the color of the container , whether it be glass or plastic , is determined by calculating a color index as the difference in the transmitted intensity for light of different wavelengths , and this difference , particularly when normalized by the sum of the transmitted intensities , serves as a color index for characterizing the color of the container . an automated apparatus for performing this determination is provided .