Monitoring microclimate-induced deformations on hygroscopic materials using conoscopic holography sensors

Changes of temperature and relative humidity of the environment where the artefact is stored can cause deformations of the surface that can harm the object or affect the repeatability of the measurement. Currently, there are very few techniques and approaches that allow studying non-invasively the surface deformations of objects of different sizes maintaining accuracy of the order of micrometres. To address this problem, three different systems based on a conoscopic holography sensors have been tested on hygroscopic samples. Moreover, we implemented a low-cost apparatus for controlling relative humidity. Eventually, we investigated procedures that use reference standards, insensitive to thermal and hygrometric variations with the scope to assess short and long-term drifts of the instrumental set-up. We tested the approach on samples of paper and lambskin parchment and on a wooden icon.