STATION 3. Acid Descale The purpose of the Acid Descale is to remove light oxidation from the work and to neutralize the alkaline film left by the cleaner tank. Surface oxidation present on the parts during electropolishing can affect the quality of the resulting finish, particularly for critical applications such as medical and pharmaceutical products. Alkaline drag-in from the cleaner tank will gradually destroy the total acid content of the electropolishing bath, causing quality problems. Scale conditions and removal methods vary widely; however, some care must be exercised to ensure that the method chosen is compatible with the electropolishing bath and the overall design of the electropolishing line. For example, nitric acid drag-in to the electropolishing bath must be prevented if spent electropolishing solution is to be returned to the manufacturing site for waste treatment. Therefore, methods incorporating nitric acid should be used as a last resort. Similarly, methods using pollutants such as chromic acid should be avoided unless provisions are made to accommodate the heavy metal in the waste treatment system. Oxide scales, such as welding scale, may also be removed by mechanical means. Bead blasting, grinding, and buffing of scaled or discolored areas may eliminate the need for acid descaling. The choice of mechanical finishing method may affect the quality of the surface finish after electropolishing.