When most people hear “borax” they think about laundry. But at Manhattan Gold & Silver, we think about gold refining. That’s because this mineral does more than wash clothes – it’s an important flux in metallurgy for separating gold from slag.
You’ve probably seen borax in the detergent aisle, but it has several uses spanning multiple industries. Not only is borax a detergent, but it’s also used to make water softeners, buffering agents, anti-fungal products and much more. It also plays an important role during the gold refining process as a flux.
In metal refining, a flux is sort of like a cleaning agent because it helps remove impurities from a sample. With some borax, heat, and a little know-how, it’s possible to extract pure gold from a sample of ore. This is because using borax as the flux reduces the melting point of all the elements in a piece of ore, including gold.
While out in the field, a gold prospector can grind and wash a piece of ore, then mix it with borax in a plastic bag. The bag is then placed in a bowl or crucible and heated. The heating action is what triggers the borax to go to work. Once the borax melts, it lowers the melting temperatures of everything in the ore. As all of the minerals melt down, they separate from one another. As the process continues, the borax causes the other minerals to oxidize and breakdown even further. Gold is unaffected by this reaction and sinks to the bottom of the mixture, intact.
The mixture of oxidized impurities and flux becomes slag, which is scraped away to reveal the pure gold at the bottom of the crucible. Because borax is so cheap and effective at extracting gold, borax-based refining techniques were very popular during the 19th century gold rushes. It still continues today among individual prospectors and small-scale mining operations.