Cathodic electrocoating:

The parts are then dipped into the electrodeposition paint, which consists of pigments, bonding agents and solvents. The tank uses the cataphoresis principle: it contains anodic molecules (positive charge) while the workpiece is the cathode (negative charge). DC voltage creates an electrical field, attracting the paint pigments to the surface of the component, where they stay. This layer grows and grows, until it forms a sealed, insulating coat.