What is Cupellation?

Cupellation is a metallurgical process used to separate precious metals, such as gold and silver, from base metals, such as lead. It involves heating the metal alloy in a cupel, which is a porous container made of bone ash or a similar material. As the metal is heated, the base metals oxidize and are absorbed by the cupel, leaving behind the precious metals in a pure form. Cupellation is commonly used in the refining of precious metals and in assaying to determine the purity of a metal sample.

Cupellation is a metallurgical process used to separate precious metals, such as gold and silver, from base metals, such as lead or copper. The process involves heating the impure metal in a porous clay vessel called a cupel.

Steps of Cupellation:

1. Preparation: The impure metal is mixed with lead oxide (PbO). Lead oxide acts as a flux that forms a low-melting point slag with the base metals.

2. Heating: The mixture is placed in a cupel and heated in a furnace. The temperature is gradually increased to around 1,000°C (1,832°F).

3. Oxidation: As the mixture heats, the lead oxide reacts with the oxygen in the furnace to form lead monoxide (PbO). Lead monoxide is a molten slag that flows out of the cupel, carrying the base metals with it.

4. Separation: The precious metals, such as gold and silver, do not form oxides and remain in the molten lead until it is fully oxidized. The gold and silver then form a bead that solidifies at the bottom of the cupel.

Uses of Cupellation:

- Extraction of gold and silver from ores
- Refining of precious metals
- Determination of the purity of gold and silver alloys

Advantages of Cupellation:

- Efficient separation of precious metals from base metals
- Relatively inexpensive process
- Can be used to determine the purity of precious metals