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Ancient gold refining 5 BC


I was just reading how archaeologists have fairly recently turned up
a very ancient gold refinery and thought y’all might be interested.
This exists in the Mediterranean town of Sardis, capital of the
legendary kings of Lydia - of which Croesus was one - and the site
has been dated to the 5th century BC. To shorten a long and
interesting story, all gold as found contains silver even up to about
40% in some cases. Money was invented about this time, and when they
minted gold coins, a high standard of purity was needed. So to remove
the silver debasing the gold the metalsmiths placed fine gold
particles and lumps hammered into foil in layers with common sea salt
in a clay pot, sealed it with a clay lid, and placed it in a furnace;
controlling the temperature carefully to around 800C. Any lower, and
it doesn’t work, and if the gold melts it doesn’t work either. At the
end of about 5 days the pot is broken open and the pure gold removed.
What occurs is that chlorine gas is produced from reactions with the
salt and moisture in the pot, and from iron catalysts in the clay of
the pot. The chlorine goes for the silver and converts it to silver
chloride but gold is inert to it. This silver chloride is fairly
liquid at 800C and finds it’s way through pores in the pot and
volatilises. Thus the silver is nearly all removed, down to about 2%,
so considerably purifying the gold. Which of course would still
contain small amounts of copper, platinum and traces of other metals.
But it was a remarkable bit of chemistry for the times.

Thousands of gold coins etc were made from this process, but Croesus’
unparalleled wealth didn’t do him much good. He wanted more and
started a war with the Persians when the Oracle at Delphi foretold
the destruction of a great empire. Unfortunately it was his. I’d like
to ‘do a Benjamin’ on you and refer you to a picture, but there isn’t
one! For the full story, see ‘The New Scientist’, (a British journal),
19th August 2000 copy. Cheers for now, – John Burgess;
@John_Burgess2 of Mapua Nelson NZ