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Refining and cupellation of precious metals

· 1 min read · Techniques

Illustration: Refining and cupellation of precious metals

To refine is to separate a precious metal from impurities and other metals. Cupellation is the oldest technique for doing it and is also used to assay purity.

Steps of the technique: Collect, Melt with lead, Cupel, Dissolve, Precipitate, Melt
Summary of the steps

Cupellation #

The alloy is melted with lead in a porous vessel (the cupel, made of bone ash). The base metals oxidize and are absorbed by the cupel, leaving gold and silver in a bead.

Parting #

To separate silver from gold, nitric acid is used, which dissolves the silver and leaves the gold. Current procedures use aqua regia or electrolysis.

What it is for #

To assay the fineness of an alloy, recycle workshop scrap and obtain high-purity metal.

Safety #

It involves acids, lead and high temperatures: it is laboratory or refinery work, with training and permits.

Step by step #

  1. Collect. Select the metal to refine.
  2. Melt with lead. With lead in a cupel crucible.
  3. Cupel. The lead oxidizes and carries off impurities.
  4. Dissolve. With acid (parting).
  5. Precipitate. Recover the precious metal.
  6. Melt. Melt into a high-purity ingot.

Tools and materials #

  • Furnace and cupels
  • Acids (only with training)
  • Full protective equipment
  • Ventilated laboratory

Common mistakes #

  • Working without training or ventilation.
  • Mixing incompatible substances.
  • Losses through splashes.
  • Disposing of residues illegally.

See also #

This entry was drafted with the help of AI and is pending review by the author.