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Gold & silver scrap, property change


#1

Hello David Valentine, A problem with a lot of times melting of gold
alloys is that copper oxides will form into the cristal structure. A
solution is to remelt it with some Auro Purifax to get rid of these
oxides. What also can help is the use of an desoxidiser, some
magnesium (dangerous if you don’t know what you are doing),or some
zinc Melt the gold under a reducing flame (overdose of gas) and stirr
some small pieces of zinc in it ( 1-5% in weight) Stirr this trough the
melt. The zinc is less nobel as the copper, and will react with the
copper oxide. Do this under a borax layer. And you will end with
ductile gold.

Martin Niemeijer


#2

Many thanks Martin. Both Auro Purifax and other melting/casting
compounds don’t seem to exist in the UK. I have tried all the major
bullion suppliers to the trade with no luck. Having said that,
there’s an awful lot of other things not available here too!

Zinc shouldn’t be a problem. What exactly do sodium Carbonate and
ammonium chloride do by the way?

david


#3

Hello david, If purchasing these melting casting compounds I can help
given you an address: Due to your rather high pond prices towards the
Euro it would be not expensive for you.

In the Netherlands it is available at “Bijou Moderne” in Bleiswijk tel
+31 10 5296600 Fax +31 10 5290088 Mail info@bijou-moderne.nl The Dutch
price for Auro purifax is Fl 19.20 incl tax. for 45 gram Normal
melting compound Fl 20,- for 500 gram.

It is also available in Germany at Karl Fischer GmbH Pforzheim tel:
+46 7231 31 0 31 Fax: +46 7231 31 0 300 Mail info@fischer-phorzheim.de
And : www.fischer-phorzheim.de German price is DM 12.00 excluding tax
(I think 19%) for 40 gram and DM 219 for 1 Kg.

What do you mean, what does Sodium carbonate (Na2CO3) do? If you mean
in melting, I do not now I think it will only burn away, I know it is
sometime used as a soot solver in heat exchangers. This would mean it
will react with carbons and will work as a very light oxidiser. The use
I have for Sodium carbonate is, neutralising the jewellery after
pickling.

Ammonium Chloride is a I know NH4CL, This does need a lot of oxygen
for burning. The heat will break it up in I think NH3 and HCL again.
This means it will react with copper oxides and will build chlorides.
It should work than as a deoxidiser of the copper in the melt. But may
be this salt it will melt to fast I think I will try it for some
experiments. I know that we can buy this stuff as salmiac stones for
cleaning soft soldering irons tips.

Greetings
Martin Niemeijer


#4

Hi Martin, Thanks for the info. I have now tried everywhere in the UK
with no joy! Goodness knows what people here use? There are no
melting/casting fluxes/compunds of any sort at all here. I do have
the Fischer catalogue but they lay on the agony with extra charges
which I was hoping to avoid.

I spotted Sod Carb etc in Oppi Untrachts book where there are a few
formulas. I was in fact wondering whether Auropurifax and Argoflux
were just a combination of these and something else, which would mean
I could just make it up.

david


#5

Hello David,

If you find out what’s in the Auro Purifax and Argo Flux, let me now.
I haven’t found it out. and the stuff is expensive enough. Maybe I can
try to get a product safety sheet. These sheets often reveals the or
at least some of the compounds in the fluxes.

But if it is really trouble to get Auro purifax I can help purchase
it for you.

Martin Niemeijer


#6

Hello Martin Sodium carbonate is used in fluxes mainly to remove silica
and sulphur compounds. On heating the sodium carbonate "breaks up"
into carbon dioxide and sodium oxide. The latter forms new compounds
during the melting process.

It is important that the flux used for melting jewellers precious
metal waste, does the following:-

  1. Removes all the magnetic particles ( contamination by the iron
    files used by the jeweller).

  2. Removes base metal oxides ( oxides of copper, zinc etc.)

  3. Removes the carbonaceious matter.

  4. Allows the alloy to be homogenious.

Here in South Africa the jewellers flux FILUX retails at US$ 4.50 per
500 grams tax included. Regards, (groete van ons almal in Suid Afrika)
Twain Manufacturers (Pty) Ltd. E. Wocke.