A secret I learned from a co-worker that had a family member in the diamond industry (not for use on soft stones):
In a small bowl, add 1/3 cup of water, two drops of dish soap and a 1/4 cup of glass cleaner.
Microwave for 40 sec, or until hot.
Add jewelry to clean. Be careful not to use this on gems that are soft like opal and emeralds. ***use for gold, platinum and diamonds only***
soak for a 1 - 2 min. gently brush w and old toothbrush.
Rinse really well and dry.