, in improving their surface appearance. In principle, the workpieces are placed into a barrel (often with a many-sided cross section to prevent bunching up of the workpieces). When a barrel is rotated, mutual impact removes surface protuberances. Much-improved surface texture occurs when a tumbling medium is added, either in a liquid carrier (wet) or by itself (dry). The medium is chosen to suit the purpose and may range from metallic or nonmetallic balls to chips, stones, or conventional abrasives.