Understanding Fire Assay: The Oldest Method of Gold Purity Testing
Did you know Fire Assay (also know as Cupellation) is one of the oldest and most trusted methods for determining gold purity? Watch our video below to see each step in action!
Here’s how Fire Assay works:
STEP 1: Sampling
We begin by sampling to ensure an accurate representation. A small piece of the object goes through the entire assay process, representing the whole. Although It’s small, but don’t let the size fool you – the information we gather from it is incredibly detailed!
STEP 2: WEIGHING
Next, we weigh the sample accurately using a sensitive balance.
STEP 3: ADDITION
We inquart the gold alloy with silver and compound it with lead. This helps bind the base metals and impurities when we heat the sample. Think of it as a purification step—it allows us to separate the good from the bad!
STEP 4: HEATING THE SAMPLE
Then, we heat the sample in a porous cupel at 1100°C. As it heats, the lead oxidizes and absorbs into the cupel along with the base metal oxides. Meanwhile, the precious metal remains unabsorbed and forms a bead in the cupel.
STEP 5: ROLLING AND FLATTENING
After cooling, we carefully remove the bead from the cupel and flatten it into a thin strip. Rolling the bead increases its surface area for the next step, ensuring the acid treatment is effective and removing all traces of non-gold metals.
STEP 6: PARTING
Next, we place the rolled metal in Nitric acid, which dissolves any leftover silver, leaving only pure gold. This critical step, called parting, isolates the gold completely, ensuring an accurate result. After the acid treatment, we rinse and carefully dry the pure gold cornet, which is now free of impurities.
STEP 7: Final Weighing
Finally, we weigh the cornet with a high-precision balance to determine the exact amount of gold present, giving us the sample’s purity and overall gold quantity
Why Fire Assay? This method is trusted for its accuracy and reliability in determining gold purity.
Find out more about our Fire Assay testing services on our Analytical Laboratory pages.
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