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Ask MGS: More Refinery Lingo

Customers who have sold precious metals before, but are doing business with MGS for the first time, are surprised to learn that we are one of the few refineries with completely transparent operations. Customers are allowed to watch the entire process of their lots being weighed, assayed, melted, and poured – like an episode of “How it’s Made.” Naturally, we get lots of comments about how fun it is to watch. We also get questions about different tools, processes, and lingo we use in the shop every day, such as:

Induction furnace

Although our furnace can exceed the platinum’s melting point of 3220°F, it doesn’t use any fire or combustible fuel. The furnace itself is essentially a box built around a coil of high conductivity copper tubing that is magnetically shielded and water-cooled. High frequency AC electricity is generated by an electromagnet and passed through the precious metal. The metal’s resistance to the electric current generates heat – the level of which can be increased or decreased by changing the flow of electricity.


This is the technical term for our fire assay service. The cupellation process produces extremely accurate assay results because it fully separates gold from impurities.


During cupellation, a sample of alloyed precious metal and pure lead are melted together in a bowl called a cupel (pictured). The cupel must be made of porous, calcified material so it can absorb impurities without causing a reaction.


As the precious metal alloy and lead are melted during the cupellation process, hot air is blown across the cupel, which causes the lead to oxidize. The newly formed lead oxide, or litharge, is absorbed by the cupel, leaving only precious metals behind.


In metal refining, flux is an additive that lowers the melting point of impurities – making them easier to separate from precious metals.


Crucibles are the furnace-proof containers that hold the metal as it melts.


Slag is a mixture of leftover impurities and waste materials that didn’t burn away during the refining process.

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