Effects of VCI Chemical Coating of Metal Surface A coated layer such as painting or greasing prevents oxygen in the air and water vapor from oxidizing with ions on the metal surface. However, painting and greasing when poorly maintained catalyzes rusting, not to mention added overhead costs to wash-off. VCI releases a chemical vapor which forms a chemical layer on the metal surface. This invisible layer of chemicals prevents oxidization, and naturally dissipates when air-flow is reintroduced.