There are two methods of obtaining copper - by smelting and by electrolysis. It is desirable to mix different ores so that they will be in proper condition for smelting, as one often acts as a flux to the other. The whole mass is roasted (heated to a high temperature) for twelve hours in the furnace, from which it is raked out in a black and pulverized condition. The next process is smelting,, during which the slag or earthy part of the ore rises to the surface, and is cleared off, after which the metal is run into pits filled with water. This causes it to become granulated. These two processes are repeated twice, and then the metal is again roasted so as to oxidize completely the iron and other metals still combined with the copper. Finally the copper is toughened by being covered in a furnace with charcoal. While in the furnace it is stirred with a pole of birch wood to cause ebullition. The grain gradually becomes finer, the color lighter, and the metal more malleable. Copper obtained in this way, however, is not 100% pure.