I. Introduction and Background
THZ imaging is a rapidly developing technique with many applications in a variety of fields from biomedicine to material science, from security to environmental studies. Recently the application of THz imaging to art conservation has been proposed [1]. When compared with other techniques currently applied to the characterization of materials used in art, like mid infrared spectroscopy and X-ray analysis, which are used to identify organic and inorganic materials respectively, Terahertz spectroscopy is expected to identify composites themselves and to give clear and direct information for art conservation.