Chladni

Philosophy — the figure is the silence. Ernst Chladni covered a metal plate with sand and bowed it. The sand did not paint the vibration. It painted the places that refused to vibrate. A note is a motion; its portrait is the motionless set. Textbook applets pick one eigenmode and stop there, as if a plate had only one thing to say. Two notes at once, and the figure is not the sum of two drawings but the silence they share: grains pile brightest where both modes are still, dimmer along the private nodes of each. Opposite parity puts the diagonal at a node of one note and an antinode of the other, so a chord refuses the textbook X. Pull one note and the diagonal comes back. That is the plate agreeing to be a specimen.

Technique — two modes, not a wave grid. This is not a discretized wave equation. The plate is Wheatstone’s closed-form square figures, cosine sum and difference, with Kirchhoff frequencies ω ∝ m² + n². Default pair (4,1)⁻ and (4,3)⁺: opposite parity, so the diagonal is a node of one note and an antinode of the other. Ratio 25/17 ≈ 1.471, a fifth 34 cents flat of just 3/2. Octave, fourth and tritone are other pairs from the same family, always with the lower Kirchhoff number as A so one note drops the higher pitch (fourth is (3,2)⁻+(4,1)⁺ at 17/13; tritone is (5,2)⁻+(5,4)⁺ at 41/29, half a cent from √2). Sixteen thousand grains hop when instantaneous |z| exceeds a threshold and then walk downhill of the time-averaged energy ½(A²ψA² + B²ψB²). Shared nodes never hop. Changing interval or one note stirs the salt for three seconds so a new silence can be found; between interventions the figure holds. A single note is one constraint, a corridor rather than an intersection, so the quiet threshold scales with the slider (TH·(1 − 0.75·lock)) and the specimen tightens toward a hairline while the chord stays untouched. One note fades B’s amplitude to zero, which is how you watch a chord collapse into a specimen. Sound, if you ask for it, is two sines at 196 Hz times that ratio — G3 and (for the fifth) almost D4. Browsers block autoplay; the button is the gesture.

Aesthetics — presence is the drawing. Hue is not carrying a parameter this time. The figure is where the grains are, and the antinodes are empty on purpose. Salt on iron, nearest-neighbour upscale, the grain is the pixel. Switch to ink and the same silence becomes a lithograph. Hold X for the signed plate — the thing the dust is fleeing, the sound as a picture. That overlay is momentary on purpose: the default frame stays the quiet.