Pre-Treated Polishing Corn Cob is blended with various additives and can be used in a vibratory tumbler to achieve a high-luster finish on ferrous & non-ferrous metals. Every 10lb bag of Pre-Treated cob has 1lb of "Re-Charging" powder in it. Corn cob will need to be "Re-Charged" every 40-60 hours of use to maintain polishing effectiveness. Re-charging powder is available in the "Tumbling & Polishing Media" category. 20lbs per cubic foot.