Recycling of glass, starting from waste sorting, can be carried out by colour image analysis. Experimental tests, at laboratory scale, have been carried out to identify the spectral response of glass lighted with a white continuous spectrum. Different focousing conditions, optical field and surfaces status has been adopted. Starting from a statistical analysis of the data, it has been identified: i) the relevant parameters for glass sorting; ii) the correctness of the separation process. From the results it has been demonstrated the efficiency of the automatic procedures developed for separation of glass cullets up to 5 colour classes.