Cleaning Coins With A Sonic Jewelry Cleaner

May be some help in this recent discussion.
http://goccf.com/t/387862

It will shake loose dirt, but do nothing for toning.

In theory, sonication should be an excellent, harmless way to clean a coin, if there were some way of suspending a coin completely int he solution without the coin touching the sides, floor or lid of the container, other coins, or anything else.

Since levitation remains in science fiction, however, there is no such way of magically keeping a coin suspended in the solution like that. It will come into contact with some part of the sonic bath (usually the floor), and there, the sonication will cause the coin to rub back and forth rapidly in place. Keeping a coin in a sonic bath for a minute or two will do much the same kind of damage as sliding it back and forth across a table a few times.

It ought to be great for cleaning up metal detecting finds, but those generally would end up as "cleaned coins" anyway, no matter how you cleaned them.