I think you mean gold-tone. Gold is 99.8% chemically inert. True gold does not tarnish or rust under normal circumstances (it pretty much takes a laboratory). A gold coin in burnt and salted earth under a pile of corpses in a mass grave of an ancient raided village would look like newly minted pulled out of the ground 2000 years later. Gold also tends to be rather slick. SO any grime collected in deep crevices is not likely to be bound to it's surface through something like galvanic corrosion which effect lesser noble metals. It's merely cradling it and it should wipe clean with dry soft bristled brushing.
As for true silver. Wood ash and warm water. 1:1 ratio mixed into a slurry and a soft bristle brush. Flushing away the slurry afterward can be a bit annoying and a careful process depending on the nature of a piece. If that is a concern let it first dry fully (and naturally with no applied heat) and then dry brush it away. Nothing will reveal it's prime luster better.
But really I wouldn't personally want to do much more to silver then to dry buff it. As it is at it's most beautiful with a nice patina. A characteristic that tends to raise value in all respects.
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