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Cracking


#1

We do an awful lot of melting down of clients own gold (broken
chains, odd ear rings etc), and make up bangles, chains etc.

On the odd occasion when rolling out the ingot we repeatedly get
cracks apearing not just on the edges but on the surface.

Filing them out helps to remove them but sometimes even if we
remelt the ingot it still cracks after only a couple of passes
through the rolling mill.

You read about people saying never to remelt gold but we do a
lot of business with it.

Is it possible to remelt including with it some alloys or
anything, or is it best to refine it.

Does anyone know of a way of refining that can be carried out in
the workshop that is not too dangerous?

Thanks again

Andrew


#2

You need a very good ventilation (draft, suction) system for
this crude method but it often works. Remelt, when molten add a
heaping tablespoon of potassium nitrate (saltpeter). It will puff
up into a crusty, spongy mass and then collapse down into a melt
again. Avoid the fumes. REALLY avoid the fumes. Then pour it into
an ingot, as usual using a slightly gassy flame coverint the
metal to avoid oxygen access. This will often fix such problems.
Charles

Brain Press
Box 1624, Ste M, Calgary, Alberta, T2P 2L7, Canada
Tel: 403-263-3955 Fax: 403-283-9053 Email: @Charles_Lewton-Brain

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#3

On the odd occasion when rolling out the ingot we repeatedly get
cracks apearing not just on the edges but on the surface Is it
possible to remelt including with it some alloys

Hi Andrew I do a bit of this also my cracking problems are
usually with 9ct. here are some tips I use that seem to work for
me.

1 stir with a carbon rod, pencil or chopstick to keep oxygen
down.

2 add more clean gold of the same carat weight if possible. I
tell my customers its like cutting out gingerbread men I will
account for all their gold and definitely use it but I have to
add more to get a big enough bit of pastry so to speak. 3 use
a flame not to high in oxygen.

4 anneal after pouring before rolling. (being careful not to
quench the gold until it is a black heat. quenching red hot gold
does hell to it.

5 anneal often while rolling.

                Best wishes Gerald.
                Arrowtown opals & Jewellery
               ph 64 3 4421288 fax 64 3 4421488
 trade site
 http://www.angelfire.com/biz/wholesaleopals/index.html

#4

Hi again Andrew

I do quite alot of this as well, maybe I can lend some advice…

Mixing different gold alloys together is a crap shoot, I have
had trouble with cracking mixing 2 different alloys of virgin 18
yellow gold, which surprised the heck our of me. Apparently it
has to do with the silicon additive that so many manufacturers
use today.

Is it possible to remelt including with it some alloys or
anything, or is it best to refine it.

I suggest refining is the best practice.

Does anyone know of a way of refining that can be carried out in
the workshop that is not too dangerous?

I highly recommend the salt water refining system from Shor
Comany. For about $700 US and a few dollars per ounce of gold for
materials you can safely refine your gold to an acceptable
purity.If nothing else you could then send the produced gold
ingot to a refiner in trade for casting grain or whatever your
needs are. In this manner you could greatly reduce your refining
costs.

         Jeffrey Everett

Handmade 18K, 22K, and platinum gemstone fine jewelry.
Diamond setting, rubber/metal molds, casting, lapidary
Die and mold engraving, plastic patterns for casting.
Cad jewelry design, cad/cam milling scroll filigree…
P O Box 2057 Fairfield IA 52556 515-469-6250


#5

We never use old gold for anything other than a “nugget”.Chains
and other types of jewelry can have a large percentage of
solder. They may also have been exposed to chemicals that can
dammage the alloys.Either of these problems can cause the
cracking you describe. They can also cause problems in
casting.Speaking from experience, we avoid using old gold at all
costs.


#6

hi
I too have had that cracking problem. Just recently I started
adding a pinch of a flux that comes from germany called argoflux
and argopuroflx it comes in very small bottles and you use only a
pinch to your regular flux. I don’t know if its a coincidence or
not but the product does seem to give me better casts a well as
ingots. You can get it from Frei in the states or Fischer in
germany

steve ross