Magnesia cupels are small, shallow, and porous containers used in assaying precious metals, such as gold and silver. Cupels are made from a special type of refractory material known as magnesium oxide (MgO). You can find below the general overview of how magnesia cupels are made:

Materials and Equipment:

- Magnesium oxide (MgO) powder

- Water: To mix with the magnesium oxide and create a paste.

- Molding equipment: Cupel molds or cupel trays are used to shape the magnesia paste into the desired cupel shape.

- Drying and firing equipment: A kiln or furnace is required to dry and fire the cupels.

The manufacturing process typically involves the following steps:

- Mixing and molding: Magnesium oxide powder is mixed with an appropriate amount of water to create a thick, paste-like consistency. The precise ratio of water to magnesium oxide may vary depending on the specific cupel design and manufacturer's preferences. The magnesia paste is then shaped into cupels using cupel molds or trays. These molds are typically made of metal and have a concave cupel shape. The paste is pressed into these molds to create the cupel's shape and structure.

- Drying and firing: The molded cupels are allowed to air dry for a period of time. This step removes excess moisture from the cupel, making it ready for firing. The cupels are placed in a kiln or furnace and subjected to high temperatures. During this firing process, the magnesia undergoes a chemical transformation, becoming a rigid, porous structure. This porous structure is essential for cupels to absorb and remove impurities from precious metal samples during the assay process.

- After firing, the cupels are allowed to cool down slowly to room temperature. Rapid cooling can cause cracks or other defects in the cupel. Cupels are carefully inspected for defects, such as cracks or irregularities in their structure, before they are used in precious metal assaying. Once magnesia cupels are produced, they are used in laboratories and refineries to carry out fire assays.