Tumblers treat the surfaces of small metal, wood, ceramic, or stone parts and pieces by rotating or vibrating them in a container with abrasive media. They are used to debur, finish, or polish multiple small parts at once, offering greater efficiency than hand-finishing. Centrifugal magnetic finishing machines are used to burnish small, nonferrous metals. Vibratory tumblers are used to finish rocks, gems, or parts. Manual separating screens are used to separate tumbling media from workpieces.