The infrared examination of paintings

Abstract

This chapter discusses the properties of Infrared Radiation, including its generation, detection, interaction with materials, and utilization for graphic objects, paintings, and for dyed textiles. The invisible infrared radiation that was discovered by the astronomer William Herschel, extends in increasing wavelength beyond the red end of the visible spectrum. It comprises the wavelength range from 0.78 Âμm to 1 mm. The upper end of this region merges continuously into the microwave band. According to Plank's law IR photons have less energy than visible light. Therefore, they excite in molecules vibrational or rotational states only, and no electronic transitions occur. Therefore, special detection methods have to be applied. The IR spectrum is divided arbitrarily in four bands. Infrared examinations reveal, the ultraviolet investigations, object states, which the naked eye cannot see. Whereas UV radiation is readily absorbed or scattered already in the surface layers of objects, infrared radiation penetrates quite often into opaque strata. This property makes IR a helpful instrument in many fields of research concerned with history of art, archaeology, and conservation of works of art.