Ammonia.
AB mentioned ammonia in his morning post and I would just like to pass on this tip to you if you don't already know it. I use ammonia all the time to clean jewellery after polishing, the polishing leaves a lot of dirt and excess polish on the article so to clean it off here's what you do. Find an old small cooking pot that you don't use anymore, put in a pint of water and one tablespoon of ammonia plus a teaspoon of washing powder. If it's a ring tie a piece of fine wire or string around it and dangle the string over the side of the pot, (This is to avoid scalding your fingers when taking it out of the pot). bring the contents of the pot slowly to the boil and let it simmer for five minutes, then take the article out via the string and using a used toothbrush gently dab the ring all over until the dirt is gone. use a tissue to dry it off and thats it,
I find that if you use the ultrasonic cleaner it loosens any small stones that may be set in a ring especially if the article is old, the ammonia way is the safest for a small job.