Polishing water is the name given to the remaining detergent sludge after filtering the water coming out of the polishing system. Since it will contain detergent, its recovery will be the same as the ultrasonic rate. Recyclesmiths and jewelry workshop workers added nitric acid to the main tank, disrupting the detergent and allowing it to be filtered as sludge. In the system they use, a double polishing bag is placed and the mud removed after the filtering process is dried and becomes ready for aqua regia.