A quantitative analysis of IRT data for the evaluation of plaster degradation at the Dome of Magdeburg (Germany)

Infrared Thermography (IRT) is a helpful method for the nondestructive evaluation of artworks and buildings of historical interest since it is able to provide indications about most of degradation sources, such as alteration of material consistency, formation of microcracks, debondings, etc. The most used procedures for physical and geometrical characterization of the thermal anomaly sources are based on numerical models that solve the forward thermal problem, i.e. they find the solution of the Fourier differential equation, which describes the heat transfer in a medium. In this framework, we present a Finite Difference method to evaluate the conservation state of the Dome of Magdeburg (Germany). Numerical simulations have shown a very good match between the experimental and theoretical curves for all the considered anomalous areas, for both 1D and 2D formulations, providing an average percentage error of the order of 0.1%. In particular, the study allowed to define thickness, depth and nature (density, thermal conductivity and specific heat) of the thermal anomaly sources, attributable to the degradation of the lime mortar layer at different depths. The application of the codes provided helpful indications for restoration work planning.