Thermography is a non-invasive investigative technique that enables an in-depth evaluation of the state of preservation of architectural elements, facilitating the preventive evaluation with regard to time, cost and manner of intervention. Thermographic survey techniques utilise the emission, by all bodies, of electromagnetic energy in the infrared range, which is detected by means of digital cameras that are sensitive to this wavelength.
Thermic images are obtained by the conversion of infrared thermal energy into electrical signals, which return video images in false-colour scales (each colour corresponds to a detected thermal level). The radiant energy of an object is a function of its surface temperature and, by carrying out appropriate calibrations, the thermographic image provides an indirect measurement of the surface temperature of a building.
The thermic behaviour of a material is conditioned by its thermal conductivity and specific heat capacity: differences between the values of these two parameters lead the component materials of masonry to assume different temperatures when subjected to an identical thermic stress. The technique offers the possibility of making measurements from a distance without the expense of erecting scaffolding and the real-time availability of the data obtained, which can be reproduced instantly in digital format.
The areas of application in the cultural heritage sector range from the analysis of building structures (highlighting the use of different construction techniques, the presence of walled-up or modified doors or windows, and the presence of moisture within the masonry), to a variety of artefacts in which one would like to distinguish between original and restored elements or in discerning the internal structure. Moreover, it is possible, by targeted heating of areas previously identified, to analyse the modes of propagation of the induced thermal wave and obtain qualitative information concerning the presence of not only voids, cracks or general discontinuities in the material, but also of "intrusive" elements such as, for example, nails or clamps inside composite structures.
The thermographic technique is employed essentially in monitoring the condition of antique plasterwork and wall paintings, e.g., evaluating adhesion to the wall (discontinuity, risk of detachment and loss of material).
- infilled antique openings;
- service channelling (hydric, sanitary, thermic);
- cavities;
- architectonic details incorporated into or masked by subsequent interventions;
- stone elements;
- wooden structures incorporated into the masonry;
- structural elements (arches, columns, lintels, etc.);
- wall fabric;
- walled-up metallic objects (girders, struts, chains, keys, etc.);
- keying between different masonries.
In the case of painted wall surfaces and mosaics, thermography allows for the detection of:
- structural and subsurface heterogeneity;
- lesions and fissures;
- detachment of plaster and cladding;
- moisture distribution within masonries;
- anomalies in the inserted mortars and cements;
- delamination of the paintings;
- detachments of mosaic tesserae.