Best way that I have found, and I found it here on T-Net. Quarters and dimes, (Clad), with a rock tumbler, I will put say 50 quarters, or 100 dimes in the barrel, and add lemon juice just enough to cover the coins, add two teaspoons of salt, the gravel, and tumble for about an hour, dump it in a strainer, (I do it outside) rinse really well, (the salt), and your good to go. Sure, you can mix quarters with dimes together and then tumble. When I said 50 quarters or 100 dimes, I was going by what was recommended with a tumbler saying 100 pennies max. I figured 100 dimes, and quarters being bigger.... Nickles, same thing, EXCEPT, do NOT mix with clad quarter or dimes, the copper content will most likely turn the nickels, "Pink". And you may want to keep enough gravel stuff to use just for the nickels, again, the copper part of the clad may leave traces of copper in the gravel. To keep that part simple for guys like me, I ordered two different colors of gravel from "Finch Products", one in blue (for nickels) and the other in red (for the clad), and keep them separate in their own containers. OK then, a bit long winded of a reply, but there you have it SocJolley.