Moisture monitoring of historical frescoes by timed infrared thermography

The subflorescence and efflorescence phenomena are widely acknowledged as the major causes of permanent damage to fresco wall paintings. They are related to the occurrence of cycles of dry/wet conditions inside the walls. Therefore it is essential to identify the presence of water on the decorated surfaces and inside the walls. Additionally it is important to evaluate the source and the effects of dynamic environmental conditions on the water over time. In the artistic heritage conservation field, non-invasive imaging techniques such as infrared thermography are now largely used, mainly to pair with other quantitative local analysis. NDT testing in industrial applications have confirmed that active infrared thermography with continuous timed images acquisition can improve the outcomes of thermal analysis. In spite of that, in cultural heritage investigations these techniques have not been yet used extensively on regular basis. This paper illustrates an application of these principles in order to evaluate the decay of fresco mural paintings in a medieval chapel, located in North-West of Italy. One important feature of this study is the use of a robotic system called aIRview, that can be utilized to automatically acquire and process thermal images at the pace of 30 m2 per minute. It encloses optical sensors revealing heat flows and special targets designed to work in the infrared range. Multiple accurate thermal views of the inside walls of the building have been produced in a survey that lasted several days. Signal processing algorithms based on Fast Fourier Transform analysis have been applied to the acquired data in order to formulate trustworthy hypotheses about the deterioration mechanisms.