Try lemon juice or anything else with ascorbic acid. Not all acids are the same. For example, acetic acid (vinegar) doesn't form complexes with metals like citric acid does. It has virtually no reducing power. If the gold plating is involved (i.e., oxidized/"tarnished" by sulfur), reducing it will reverse the process. Same goes for the more complicated aluminum foil and sodium bicarbonate method. The aluminum foil is oxidized (loses one or more electrons) and the silver/gold is reduced back to metal.
If you have an ultrasonic cleaner, I would use that with the various liquids, not just dipping in them. Of course, abrasives will remove both the tarnish and gold plating, which is probably very thin.