I have a Harbor Freight $40 tumbler. I played around with different things and here is the formula I came up with: Use almost any bath tub scum spray bottle type cleaner - 50 pennies at a time. Just enough cleaner to cover the coins. Then - use parakeet type gravel (small sandy stuff that is sharp edged). It only takes a table spoon or so of it with the cleaner. Seal it up as directed and let it run a few hours. Then, pour off the sludge into a cup (save it for the next run), take the tumbler canister outside to a hose or outside faucet and run a good stream into the can, and the sand will wash up and out. (DO NOT USE A SINK WITH A SEWER DRAIN AS THE GRAVEL WILL SETTLE IN A TRAP, OR MAY SETTLE IN THE SEWER LINES!) Be sure to mix it up while doing that. Dump the coins out on a towel and lay out to dry. They will mostly be shining. Sharp edges will still be on the cons! The thing that is oppressive are the clad pennies look dark but, if you look closely, it is the Zinc holes that make them look dark, but they are clean holes!