A method to assess the hygro-mechanical behaviour of original panel paintings, through in situ non-invasive continuous monitoring, to improve their conservation: a long-term study on the Mona Lisa

•Non-invasive methods and equipment to measure and monitor panel painting's behaviour.•Technological analysis and state of conservation of the Mona Lisa’s wooden panel.•Studying mechanical properties and conditions of an artwork painted on wood.•Monitoring mechanical response of panel paintings to environmental fluctuations.•Collecting data to feed and reliably calibrate numerical models.