Invented by Ray Lubow, the oil-can method uses a rotating disc of anodized aluminium coated with a suspension of carbon particles. An AC signal to a conductive neoprene wiper transfers the charge to the high impedance disc. As the particles pass by the wiper, they act as thousands of tiny capacitors, holding a small part of the charge. A second wiper reads this representation of the signal, and sends it to a voltage amplifier that mixes it with the original source. To protect the charge held in each capacitor and to lubricate the entire assembly, the disc runs inside a sealed can with enough of a special oil to assure that an even coating is applied as it spins.