In metallurgy, a concentration based on the fact that liquid films in laminar flow possess a velocity that is not the same in all depths of the film. There is no flow at the bottom but maximum at or very near the top resulting from the internal friction of one layer upon another. By this principle, lighter particles are washed off while the heavier particles accumulate and are intermittently removed. This is basis of the stationary table, which has been known for thousands of years. Vanners and round tables have been developed from this basic principle, whereas bumping and shaking tables jointly utilize flowing film and other principles.