I would clean it by putting it in a jar large enough to cover it with white vinegar (5%) for a minute or two. Afterwards, bring it out, dripping wet, and cover it with baking soda. Rub it with your fingers until the baking soda takes the tarnish off, rinse under tapwater, and dry. If it is gold it should clean up nicely. Plating (if any) will come off as you rub it. You might look at the edges with a magnifier to make sure it isn't plated first.