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This is a method for taking old gold and refining it to
about 23kt. When I do this I regard the gold as 22kt, and I
alloy it accordingly down to 18kt or 14kt. This gives me a
safety margin so the gold is a slightly higher purity than I
stamp it. Safety disclaimers notwithstanding, this process
uses Nitric acid at 70% concentration, and caution must be
used. Generally spoken, when one makes a mistake with strong
nitric acid, one makes that mistake only once..... After that,
the lesson is well learned. Only yellow gold can be refined,
since nitric acid does not dissolve palladium. Nor
platinum, for that matter. I have not tried it with 14kt
white, since I do not work in metals that are derived from
the devils armpit.
The old
gold is weighed out and five times the weight of copper is
added. So for example 40 grams of gold will need 200 grams of pure
copper.
Since I am refining a large
amount of 14kt and since that is more than I can melt at one time with five times
the weight of the copper,
I divide the gold and copper up into four, and for this Hidi
(How I Do It) I shall only be showing a portion of the melt.
I use a
large refuse drum, which I fill up with water to make shot.
A steel one would be better, but hey, I use what I
got.....:)
At the
bottom I use a stainless steel bowl and a plate below that
to catch the shot, just in case it missed the bowl. It does
sometimes.
Then I
melt the copper.
And I
add a portion of the old jewellery to the molten copper.
And
then, when the gold is mixed with the copper, I pour it into
the water. This makes the shot, and the finer the beads are,
the quicker the nitric dissolves the mix. There are better
methods, using steel baffles, but this is a quick method,
without to much added hassle.
This is
the resultant mix of copper and gold.
Then the
fun starts. The bowl of alloy, a bottle of 70% fuming nitric
acid, a bucket of water. The water is there to wash and
spills off quickly, just in case a spill occurs. Much better
that running to a tap screaming, If you dumb, you will not
use safety glasses and gloves, so it's lucky you are clever,
not?
There is a decent reaction when nitric acid hits the
copper/gold solution. A cloud of dangerous gas is released,
so it is better to do this outside and stand up wind at the
same time. And maybe make sure your downwind neighbors are
not at home.....Fun stuff, this.
After
the reaction is finished, and all is calm, more acid is
added, until there is no more reaction. This means that all
the copper, silver, and any other contaminants are dissolved
and only the gold remains.
And
this is the before and after picture. The fine gold looks
just like coffee grounds, and if you take it between your
fingers, is crumbles just like coffee. I doubt very much
that it tastes like coffee, though.
Then I
mix it with alcohol and borax and saltpeter ( potassium
nitrate) all available at your friendly chemist. It is not
really necessary, because one can just melt is as is. The
alcohol dries out the water and the borax and saltpeter
makes melting easier.
This
picture shows the water/alcohol burnt off and the top of the
mix melting. Suddenly, gold appears. This is only one reason
why it cannot be used as a coffee substitute. There are
others.
After the gold it melted in the normal fashion and cast into
an ingot, it looks like this, ready to be alloyed down to
whatever karat is required.
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