Are you sure its dipped in gold? Orichalcum got its name from its similarity to gold - you may be looking at the result of a splash of an acidic liquid onto the coin. Id try to tone it - if you boil an egg and sit the coin next to it in a sealed container, it will quickly tone (obviously the gold should be unaffected). This will deposit some sulphur on it, so remember to rinse with distilled water afterwards (I'd dip first in a bicarb solution and then rinse with the distilled water).
























