Following is a short visual summary of how we process the gold. Fire Assay procedure remained the same through out centuries. The process has improved with additional evaluation methods, but its essential steps have not changed. For example in addition to Fire Assay we also implement an X-Ray Fluorescence Spectrometer (XRF) to determine the exact value of gold in question.
Metal scooper is used to place scrap gold into the graphite crucible for melting.
Borax is used to separate gold from stones and other non-metal elements. After a few minutes the borax will pull the non-metal content to the bottom in order to provide for more precise purity evaluation.
Note: Borax is a mineral also known as a salt of boric acid. It is usually a white powder consisting of soft colorless crystals that dissolve easily in water.
Gold is left to melt in a hot furnace (~ 2060° Fahrenheit) for approximately 20 to 25 minutes.
As the metal begins to ball up and swirl, stirring with a graphite rod assures an even and homogeneous spread in a gold content. Furthermore, it allows for more precise purity measurement.
We dip a vacuum glass tube attached to the tongs into the molten gold to take a sample of a bar at approximately 2000 F.
Molten gold is poured into a mold. All metals but gold will float to the surface to form a slag of molten chloride (Step 2).
We drill the gold bar to extract a sample for testing to determine the precious metal content.
We perform Fire Assay to measure the gold content. This involves taking a small scraping from the article, typically about 250 mg, weighing it accurately, wrapping it in lead foil with some added silver, cupelling it in a furnace at about 1100Â°C to remove all base metals.Then placing the resulting gold-silver alloy button in nitric acid to dissolve out the silver (known as ‘parting’) and re-weighing the resulting pure gold.
As a final step we place the sample from liquid (Step 5) and solid (Step 7) stages of the bar under the X-Ray Fluorescent Spectrometer to ascertain its purity. If the difference in purity data exceeds 1% the process must be repeated.
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