Infrared imaging techniques for the stratigraphic analysis of cultural heritage

This thesis provides an overview on the infrared imaging techniques focusing on the ones working in the middle-wave infrared range, namely pulsed thermography and reflectography, for the study of layered Cultural Heritage items. In the framework of non-destructive methods, middle-wave techniques, especially the thermography, are commonly used singularly for the stratigraphic analysis of artefacts. In this thesis, the two techniques were used together in a combined approach for the characterisation of subsurface features not visible at naked eye in several multi-layered structures, as painted artefacts on different supports and bookbinding of library heritage, simulated in laboratory samples. Among other advantages, the non-destructive nature and the use of the same device as detector that ensures the pixel-by-pixel correspondence of thermographic and reflectographic images make this approach suitable as diagnostic survey in many application, without compromising the artefact and aimed to assess its preservation state. A theoretical modelling was also proposed for the characterisation of the blurring in thermographic images and the quantitative evaluation the edges distortion in the detection of hidden text buried inside the bookbinding. The confirm of the capabilities of the proposed techniques and approach was achieved by their application on the study of original artefacts coming from several museums and institutions with different structures and conservative issues, comparing, in many cases, the thermographic and reflectographic results with the ones obtained with other imaging techniques for a more complete characterisation of the layered structure of a particular kinds of artefacts.