Refining refers to the act of purifying an impure metal, such as silver. There are a few ways to refine silver, but there is one ancient way of extracting silver from lead called cupellation. Cupellation is not only the most ancient method for refining silver and other precious metals, but also the most commonly used. Although cupellation does not require the use of expensive machines, it consistently renders more accurate results than do modern methods like spectrophotometry.
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Cupellation works by dissolving a precious alloy, such as silver, with fused lead in a magnesite crucible that absorbs all non-precious metals, such as lead. The result is a small ball of pure silver. For the process to work correctly, make sure the furnace is at the correct temperature and the cupels are smooth and free of debris. Clean debris off cupels with a low-pressure air can.
Melting the Lead
Put the empty cupels into the furnace for 10 minutes to get rid of moisture and any remaining debris. Place the pounded lead buttons into the cupel in the furnace. Doing so oxidises the lead, which is then absorbed into the cupels.
Lead Buttons Open
The lead will melts immediately as long as the cupels are thoroughly heated. A dark scum then covers the melted lead. If the temperature is high enough, the dark scum disappears in just a few minutes and the lead appears bright, which means the lead button has opened and the lead has begun oxidising.
Loss of silver during cupellation is not usually significant if you've followed all the necessary steps and kept the furnace at the precise temperature. Silver oxidises with more ease than gold does and the results of extracting lead from silver are very good since the resulting bead tends to be a high percentage of pure silver.
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