Here 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 1100°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.
