»Untitled«, ca. 1970s by Nasreen Mohamedi.

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“Graphite Sequencer” by Caleb Coppock. Video. Graphite conducts electricity. Two wires brush against the surface of a paper disk as it spins. The wires are connected to a simple electronic tone generator. When a line of graphite is drawn across the disk, connecting the two wires, a tone is heard.