I tried a recipe last night and ran the tumbler for 45 minutes and was amazed at the results. I need to give a shout-out to T.C. for posting his recipe. You only need enough lemon juice to cover the coins (3-4 oz) and about 3 tablespoons of salt. After 45 minutes the coins came out like new. Well at least 99% did. I then reused the concoction to clean the pennies. This method is the way to go. I paid a little over $2 for the lemon juice and you get 2 containers of salt for a dollar at the local Dollar General store. You can clean about 16 batches of coins with a 32oz bottle if you do your silver 1st and then reuse the same mixture for the pennies.
Please try this, you will be amazed at the results.