During the decarburisation and liquation process, the silver was largely transferred to the process lead and now needed to be separated from it. This process, known as cuppelation, involved selective oxidation of the process lead.
The lead oxide, known as litharge, flowed off the top. The remaining layer of litharge on the molten silver cracked and the almost pure precious metal became visible. If the silver was dark in colour, beer was used to lighten it.
The resulting lightened silver needed to be gently fired to remove any remaining impurities.