You don't want to etch away the underlying silver/copper, just de-oxidize it. People who do conservation for marine salvage and archaeology have lots of technical knowledge and skill on this topic, but I don't know how much is available for free.

At any rate, DO NOT apply any sort of solvent.

The baking soda/aluminum foil/hot water method is an electrolytic technique for silver only. But I would never try it on something old, would do my best to find a professional conservator first.