Chladni's disc: Bowed disk forms patterns in sprinkled salt.

Chladni's Figures : Vibrational modes of a metal plate. Salt or sand sprinkled on metal plate. Various patterns can be produced: with 4, 6,8,10,12 or 14 rays... For best results, pinch one part of the rim of the plate, then 'saw' the bow with an even vertical motion on another part of the rim.