Validation of contactless vibro-acoustic imaging for the detection of glaze delamination in glazed ceramic tiles

For glazed ceramic tiles, glaze delamination is a decay problem greatly demanding for effective risk-based preventive conservation. The present study faces the problem of the early detection of adhesion failure between the glaze and the clay substrate, exploring the potential of a vibro-acoustic imaging (VAI) technique in helping to prevent the glaze falls off and lacunas. The imaging technique is based on the Laser Doppler Vibrometry (LDV) joint to a contactless acoustic excitation of the tiles in the frequency interval (1 - 20) kHz. The results on historical Portuguese azulejos and laboratory models demonstrate that hidden cavities, a few hundreds of microns deep, are correctly identified and characterized.