# Refining and cupellation of precious metals

> Refining purifies gold and silver; cupellation separates precious metals from base metals with lead and bone ash, an ancient assay technique.

- Source: https://www.711grados.com/en/refining-and-cupellation/
- Language: en
- Note: This entry was drafted with the help of AI and is pending review by the author.
- Published: 2026-07-19
- Updated: 2026-07-19
- Translation (es): https://www.711grados.com/es/afinado-y-cupelacion/
- Author: Sandra Sánchez
- Site: 711 Grados (https://www.711grados.com/)

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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](https://www.711grados.com/media/diagrams/afino-steps.en.svg "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

- [Jewelry alloys: how they are made](https://www.711grados.com/en/jewelry-alloys-how-they-are-made/)
- [Gold](https://www.711grados.com/en/gold/)
- [Silver](https://www.711grados.com/en/silver/)
- [Metal ingots and casting grain](https://www.711grados.com/en/metal-ingots-and-casting-grain/)