I say, and with God's help: The metal is purified by the impure metal that has mixed with impurity through disguise, and this is done by placing it in the fire until it becomes like embers, then it is extinguished with pure water three times while drying. As for if there is impurity on it, it is then purified by wiping, because it is one of the smooth things that are purified by wiping. Refer to: Nihayat al-Mirad by Abdul Ghani al-Nabulsi, pages 331-343, and God knows best.