I once replaced the gold inlay on a Turkish barrel by amalgam plating; dangerous, but the results were excellent. It would not be suitable for narrow rings, I think.
I dissolved the smallest gold coin I could get: a Mexican peso, in mercury; the part to be plated was cleaned and etched with nitric acid, the amalgam applied with a small stiff brush, and the barrel was then gently heated until the mercury had evaporated.
I was fortunate enough to have access to a laboratory with a fume cupboard and filter; I would not have dared to do it in my workshop, or even outside....