Abstract: Light-transmitting plastic and/or glass bottles are tested at a station where selected portions of their internal surfaces scatter radiation issuing from a beam of monochromatic radiation. The scattered radiation is intercepted and monitored for the generation of signals which denote the presence or absence of impurities on the selected portions of the internal surfaces and/or certain substances in the walls adjacent the selected portions of the internal surfaces of tested bottles. Such signals are processed, and the processed signals are utilized to classify the bottles according to their defects and/or to segregate unsatisfactory bottles from acceptable bottles and/or to segregate glass bottles from plastic bottles and/or to classify satisfactory plastic bottles in accordance with the nature of their plastic materials. The scattered radiation can constitute Raman, Rayleigh and/or fluorescence radiation.