I found these tips on a German website. Translated with google. Please do this on your own risk.
Washing-up liquid, toothbrush, toothpaste: These things everyone has in the house. For gentle cleaning, a small amount of washing-up liquid is dissolved in warm water. To soften the gold jewelery briefly, then carefully work with a very soft toothbrush. Stubborn stains dissolve with brush and toothpaste. Care should be taken to ensure that the toothpaste does not contain any abrasive material.
The cleaning can be done quickly and without much effort by means of dentist tablets. The tabs ensure a very gentle treatment. Aggressive agents, such as ammonia, should be dispensed with, the beauty of the jewelery might suffer.
If you would like to clean gold jewelery often, an ultrasound device can grow. In the small, handy device, jewelery is gently and safely cleansed and freed from all residues.
After cleaning, the gold jewelery must be carefully dried. With a soft cloth can be re-polished, the jewelry returns to its original luster. There are special polishing cloths for gold jewelery, which, with regular application, permanently prevent tarnishing.