Infrared thermographic nondestructive testing of frescos: Thermal modeling and image processing of three dimensional heat diffusion phenomena

A method for thermographic testing of ancient wall frescos is described. Experimental results were obtained by testing the Fogolino fresco in Bergamo, Italy, using a transient thermal nondestructive testing technique. It was found that the main difficulties in testing the fresco were caused by nonuniform surface patterns in both the optical and infrared (thermal) wavelength ranges. This multiwavelength surface clutter leads to numerous artifacts when applying sophisticated data processing algorithms such as dynamic thermal tomography. A three dimensional data filtering technique is proposed that will take into account both uneven heating and lateral heat diffusion, thus diminishing the effect of surface clutter.