<p>A new method has been developed which can visually display the effect of ultrasonic field in cleaning process. Using colloidal nanoparticles, sol-gel coatings were prepared and subjected to ultrasonic cleaning in water. It was found that periodic patterns appeared in the optical images of the sol-gel coatings. The results from the transmission spectra and atomic force microscopy images demonstrated that the periodic patterns were attributed to the partial removal of the sol-gel coatings. The removal amount of sol-gel coating reflected the spatial distribution of acoustic field in the ultrasonic cleaning tank. A mechanism for the removal of coating composed of nanoparticles was proposed based on experimental observations. In the initial stage, cavitation played a main role in detaching coating, while in the later stage, the movement of cavitation bubbles accelerated coating removal.</p> Graphical abstract <p></p>