The initial product of copper smelting was impure black copper, which was then repeatedly melted to purify it, alternately oxidizing and reducing it. In one of the melting stages, lead was added.  Gold and silver preferentially dissolved in this, thus providing a means of recovering these precious metals.  To produce purer copper suitable for making copper plates or hollow-ware, further melting processes were undertaken, using charcoal as fuel.  The repeated application of such fire-refining processes was capable of producing copper that was 99.25% pure.