Active and eddy current pulsed thermography to detect surface crack and defect in historical and archaeological discoveries

Abstract

The present paper describes the results of an experimentation concerning the joint use of active thermography and eddy current pulsed thermography to assess the conservation state of historical and archaeological discoveries. The preservation of historical and archaeological heritage is today an open issue due to the amount of finds and to the costs of the current methodologies and technologies used. As a consequence, interventions are made only when a deterioration process is in progress. The use of non-invasive techniques is essential for such applications in order to not compromise the integrity of the find.Thermography has been used to measure the thermal response of a metallic historical artifact (an iron oil lamp) during the application of thermal solicitations. The authors propose the use of a hybrid technique combining the standard active thermography with the eddy current pulsed thermography. This hybrid technique is non-invasive and contactless and allows to detect surface cracks and defects which are not visible at naked eye. Results have shown clearly how the proposed thermographic technique allows to improve the effectiveness of the standard techniques to detect surface defects. The defects are more easily detectable because of the more accentuated contrast and better resolution of the thermographic images. The final aim of the paper is to describe how this improved technique can be used to diagnose, monitor and preserve the conservation state of historical or archaeological discoveries.