An acoustic non invasive technique for the diagnosis of plaster detachment in frescos

The detachment of painted plaster portions from the substratum is a serious problem concerning artistic frescos. At present, the standard procedure consists in the manual inspection, but it only produces approximate information. This work describes a non-invasive experimental procedure based on the structural acoustic interaction in an acoustic duct, excited by a loudspeaker and closed by the frescoed wall. The analysis of the acoustic pressure field allows the diagnosis of detachments through the alterations to the system modal parameters produced by the changes of the boundary conditions. Experiments conducted on fresco specimens and comparisons with other methods show the potentiality of this acoustic technique.