Characterization of material alterations in archaeological discoveries using thermography and emissivity changes

The present paper reports the results of a study focused on the characterization of the material alterations in archaeological discoveries. The proposed approach is based on the thermographic analysis of the thermal response of the different parts affected by degradation or alterations such as alveolisation process, erosion, damages, and deposition of iron oxide. Material alterations are characterized by changes of emissivity. Consequently, thermographic images show significant differences in the temperature values even if the object is in thermal equilibrium. This apparent temperature variation can be characterized and compensated by evaluating the emissivity of each part having material alteration. Material alterations are not always visible at naked eye and are even responsible for changes of the dynamic thermal response when external thermal solicitations happen. The erroneous interpretation of such features is inevitably cause of an incorrect analysis of data with consequent altered results. The paper focuses on this issue to advise operators to pay attention to such aspects. The proposed case study is a marble bust of a woman that dates back to ancient Rome. The results show the need to characterize the presence of material alterations by analysing the thermal response in static and dynamic conditions. Recommendations are provided to compensate the thermal changes in thermographic images by assessing emissivity variations.