Nondestructive testing of murals in situ by infrared thermal imaging

Chinese ancient murals are an important part of Chinese cultural heritages, with rich historical, artistic and scientific values. After decay of hundreds of years, there are generally a variety of serious diseases, such as hollow, crack, efflorescence in substrate layer and the peeling, fading of pigment layer. Although the diagnosis and identification of surface diseases in pigment layer are relatively easy, it is quite challenging to determine the crack, cavity, detachment, hollow, porosity and deep structural information in substrate layer. In this paper, the square heating thermography is used to conduct in-situ nondestructive testing and health evaluating of different murals. Due to the immovable of the mural and the limited space in its location, a portable device consisting of a long-wave infrared camera and two rotatable halogen lamps is used to facilitate detailed inspection of the murals. During the test, the heating time and imaging rate were determined, and a set of transient thermal images were taken in different regions one by one. A thermal tomography method was applied for quantitative 3D evaluation of murals, which can not only realize the detection and evaluation of cracks, hollow, cavities, porosity and supporting structure information in the deep structural murals, but also quantitative evaluate the disease distribution in the murals. Through the application of the infrared thermal imaging on the murals, it can deeply insight into the internal structure of the murals and provide an important basis for the assessment of the structural stability of the murals, which will benefit for the conservation and restoration of murals in the future.