1. An automatic process for inspecting and sorting non-metallic objects that belong to at least two different categories and pass in an essentially single-layer stream on a conveying plane of a conveyor belt, comprising: temporarily subjecting a surface layer ( 4 ) of said passing objects ( 1 ) to the caloric radiation of at least one remote heating means ( 5 ), so as to deliver to each of these passing objects ( 1 ) a non-altering heat pulse that is identical for all of the passing objects in terms of heat energy applied per unit of surface area in the conveying plane ( 2 ); after a determined length of time has elapsed following the application of the heat pulse, acquiring at least one thermal image of each of said passing objects by means of at least one linear or matrix thermal sensor ( 6 ); processing data contained in the acquired thermal image to determine a thickness of the surface layer ( 4 ) affected by the caloric radiation of the passing objects, and classifying each passing object ( 1 ) based on the data, and delivering a control or actuation signal for each passing object; and separating the passing objects ( 1 ) based on at least one of i) a class or category and ii) the delivered control or actuation signal for each passing object, wherein the constituent material of said surface layer ( 4 ) of the passing objects ( 1 ) is identical for all of the passing objects, and wherein for each passing object ( 1 ), the determined length of time that elapses between an application of the caloric radiation and the acquisition of the thermal image is sufficient i) for said surface layer ( 4 ) to absorb an essentially homogeneous distribution of caloric energy such that a temperature difference after heating said passing objects on the surface is essentially inversely proportional to the thickness of this surface layer ( 4 ), and also ii) so that the phenomena of lateral thermal diffusion, cooling by radiation and convection are negligible.