Infrared radiation for the detection of structural irregularities in historical material

The knowledge about invisible internal defects like blister, cracks and debondings are a crucial and important factor for experts working on historical materials. One contact-less and therefore non-destructive technique is heat flow measurement using infrared radiation. For tests on paintings on wood and plaster a special thermographic online system can be used. The system contains a conveyor belt on which the material can be moved very homogenously along infrared sources to warm up the surfaces. Observation of the heat flow will provide information about the historical production procedures and about the degree of degradation. To get more information about the extreme top layer of the material the very fast pulse-thermography technique can be used. The penetration of the heat will deliver additional details about the surface conditions. Finally a transmission setup can be used to show how historical watermarks can be visualized even if the paper is covered with much ink on the surface that visible marks can not be recognized. The feasibility of this technique will be demonstrated on historical terracotta, original Russian icons and on Rembrandts hand drawings.