Glitter bands
When glitter is poured onto violin plates that are freely suspended above a loudspeaker, the glitter bounces up and down, and moves towards the nodal
lines of important low-frequency resonances. In an attempt to compensate for the natural variation in the properties of the wood used to make a violin, many scientifically minded violin makers adjust the arching and thickness of the top and bottom plates to achieve particular resonant frequencies and nodal patterns in an instrument.