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Recasting old 18K...nasty alloy?


#1

I took in two old, heavy plain 1/2 round wedding bands, said to come
from the client’s grandparents. They were marked 18K but had no
hallmark. I tried to recast them without adding any new material. The
melted alloy smoked a lot, which I have never seen before. (Yes, I
was wearing a respirator and using positive active ventilation, I’m
glad to say!) I heated it until it looked right to me, but the metal
froze before it filled the mold (mold temperature @ 900 degrees F.).
When I examined the partial casting, and tried to bend part of it, a
brittle crack opened up at one point. I do not want to heat this
metal again, as I am afraid of what might be in it. I am thinking of
offering to make the piece in new gold, taking their old gold as
scrap to be refined. Of course, this will cost more, since I will
have refining fees some day when I send in scrap to my refiner. The
initial estimate I made to the customer did not include materials,
just my labor and overhead. I feel bad about having melted down their
heirloom rings and not producing the cross made of the same metal
that they wanted to give their son. Questions: 1. What might make an
old 18k alloy smoke when melted? I guess it is some metal burning
off, but what? 2. What might cause the brittleness in the casting? 3.
Do you take in old gold to recast? If so, what kind of guidelines do
you use in deciding if it is appropriate for you to accept? These
rings did not seem to have solder on them. 4. What should I tell the
clients to make them feel better about this little disaster? I will
tell them the truth, of course, but in how much detail? 5. Is there
any reason I should not feel badly about this? I thought I could do
it and that it would work ok, but now I’m feeling kind of
incompetent and fearful about trying it again. What if there’s
cadmium in the alloy? Why risk my health just to attempt to please
some client? 6. Is this why some jewelers don’t take in old gold to
recast? – M’lou Brubaker, Jeweler 14015 W. County Road 578
Goodland, MN 55742 phone/fax:(218) 492-4487 www.craftswomen.com
@M_lou_Brubaker


#2
Questions: 1. What might make an old 18k alloy smoke when melted?
I guess it is some metal burning off, but what? 

My guess is a higher zinc content than is normal for 18K alloys.
That, combined perhaps with a higher copper content, if the alloy is
rosier than usual, might easily do what you’ve described.

2. What might cause the brittleness in the casting? 

Too slow a cooling of the metal, if it’s a rose gold, can do that.
Or, more seriously, if the metal is contaminated with iron, lead,
tin, or some solders, you can also get brittleness. I’d suggest
melting the metal with a quite reducing flame (and very good
ventilation), on a standard charcoal block (hollowed out cavity
thereon), and when molten, adding a pinch of ammonium chloride, which
won’t melt, but which will skitter around on the surface causing much
blue fumes. As it does that, stir the melt with a carbon rod.
repeat this, then sprinkle on some boric acid and let the button
cool. The Ammonium Chloride will tend to form chlorides of baser
metals, including iron, tin, lead, etc. These chlorides are
insoluable in the melt, and then slag off with the flux, resulting in
less contamination. It also removes zinc. The downside to this is
mostly the fumes, so do it with good ventilation, or outside. I’d
suggest then trying to recast it. this time try a hotter mold, and
heat the metal a bit hotter too. Sounds like it wasn’t fully liquid.
Be sure to use a casting flux of mixed borax and boric acid, or a
good commercial casting flux. The combination of the two works better
than either one alone.

Also, on the possibility that the casting was brittle from slow
cooling, after you’ver removed it from the investment, before doing
anything else, anneal it. Reheat it to a low red, then at just the
point where it looses that glow, which will be around 900 degrees,
quench it IN ALCOHOL, not water. This is a gentler, slower quench
that water, as some alloys will tend to crack with a water quench.
The alcohol quench is sufficient to keep it from age hardening as it
cools. If it’s still brittle, then you’ll just have to be careful.
In that case, cut off cast jump rings for the cross, and solder on
new ones made with good wire. If the heavier cross is brittle, it
might still survive, but a brittle jump ring or bail is likely to
break off. When you then cast this, again be sure you’ve got a gentle
flame (you’re using natural gas or propane with oxygen, aren’t you?
Not oxy/acetylene, I hope? That can easily overheat your metal, also
causing problems. In golds, acetylene can also cause formation of
carbides if the flame is too reducing, which are hard spots in the
gold…)

3.    Do you take in old gold to recast? If so, what kind of
guidelines do you use in deciding if it is appropriate for you to
accept? These rings did not seem to have solder on them. 

The trouble with old gold is that even if it’s the right alloy,
which you never know, it’s not as likely to give a good casting.
Usually, the cost savings for using old gold don’t make up for the
reduced quality of the finished piece, so the only real reasons to
use old gold like this would be sentimental, not economic. I’d
actually charge the same as if I were supplying the metal, and in some
cases, maybe even more, since sometimes you’ll have to add a bit of
your own to have enough for a sprue, which is then scrap you won’t
want to reuse again, but will have to sell the customer, or scrap
out. Customers should be warned that the finished casting will
almost certainly have more porosity than normal, in some cases it can
be quite serious, more spongy and full of holes than they’d expect.
That’s what you tell em. Along with possible brittleness and other
casting faults. If they then still want to proceed, they’ve been
warned. And though you’ve told them to expect porosity and crappy
castings, as often as not, they turn out somewhat better than that,
and sometimes are just fine. Depends on the alloy and your luck that
day. If they’re told there are risks up front, then no matter how
bad it turns out, they’ve been warned, and any success is better than
they may have been led to expect.

4. What should I tell the clients to make them feel better about
this little disaster? I will tell them the truth, of course, but
in how much detail? 

Tell em the truth. No sense smoothing over it. But you might want
to retry it one more time before telling them it’s a total failure.

 5. Is there any reason I should not feel badly about this? I
thought I could do it and that it would work ok, but now I'm
feeling kind of incompetent and fearful about trying it again. What
if there's cadmium in the alloy? Why risk my health just to attempt
to please some client? 

There’s not likely to be cadmium in the alloy, unless it’s
contaminated with solder manufactured since WW2. Even then, amounts
will be very small, and you probably burned most of it off the first
time, if there was any there. but there may be other metals there,
and even with new good golds there are componants you don’t want to
breath, so you should always melt metal with good ventilation. Zinc
fumes, flux fumes, etc, aren’t good for you. I doubt your metal
presents a special case in this regard. As to feeling bad, well,
that’s normal. But don’t dwell on it. You cannot predict how unknow
metal will react till you try it. Sometimes even supposedly good
metal can “go south”. I recently had a commercially purchased bit of
14K nickel white gold that was just terrible. We’d cast it once,
which was fine, but now attempting to fabricate parts with the sprue
metal, was a total failure. I couldn’t even get the stuff to pour a
good ingot, and I’m not exactly a beginner at this. Hollow
sections, big shrinkage voids into the side, sludgy pouring
characteristics. And the portions I could get to cast wouldn’t roll
into good metal either. I’ve no clue what the hell got into that
melt. Something, I’m sure. But beats me what. The full ounce of
that crap is in our refining bin now… Not worth the time to fool
around with it. I just got another sprue button and used that, with
no problems…

6. Is this why some jewelers don't take in old gold to recast? - 

Yes

Peter Rowe


#3

It is my opinion that you should learn when to say nothing to your
customers. They will not thank you for your honesty in fact they
may just turn out to be your worst nightmare. I have 35 years of
experience in dealing with the public as a jeweller and watchmaker.
All they want is a piece of jewellery, bite the bullet and make this
item from your own stock at your own expense and tell them nothing.
Your problem will be over and they will think you are wonderful.

Some of you will not agree with this I know on an honesty and
ethical basis and when I first started in business I told my
customers everything all my mistake and errors, some were
understanding and some wanted to consult their solicitors.

Save yourself a lot of worry, in this business you win some and you
loose some.

Alan UK

@Alan_Lewis


#4

Some (especially UK) refiners will take in gold scrap and return
your gold - even as carat gold - for a reasonable fee. This
guarantees your clients their original gold.

I suspect cadmium as the pollutant here - but it could be almost
anything.

Tony Konrath


#5

Hi M’Lou, I’m going to take a stab at this, and you will probably get
some more informed responses. Its probably a good thing you were
wearing a respirator. I’m thinking the fumes you observes being
released were zinc being burned off from the original alloy, and
that’s hazardous to breathe. The alloy used in this older 18k
version might not have had the copper and silver content you would
usually find in today’s alloys. Galvanized steel has a zinc coating
and will release it as hazardous fumes when heated.

If I am correct in this supposition, the burning off of alloying
material would result in a metal with different metallurgical
properties than the original material. I would assume that the end
product would have a higher purity, but might not have the ductile
properties or flow properties (for casting) that one might need.
Most vendors recommend adding 50 percent new casting grain to recast
material to maintain the desired properties in the end product.

I would probably end up doing the “right thing” to satisfy the
customer. Educate them on what you went through to deliver the end
product, and they become a partner in the process, and hopefully, a
customer for many years to come.

All the best,
Dave
Dave Sebaste
Sebaste Studio and
Carolina Artisans’ Gallery
Charlotte, NC (USA)
dave@sebaste.com


#6

Greetings All, I haven’t caught all the threads for this subject but
what I have read seems very informative. It’s pretty ironic that I
was reading this months issue of Lapidary Journal and came across an
article that covers this subject as well. The name of the article is
’The Metallurgical Balancing Act’ by Sharon Elaine Thompson. The
article is quite enlightening probably because I am still learning.
The article covers about the alloys and some of the
reasons certain ingredients are used and why the ratios are important.
The dangers of recasting/re melting used gold or silver is also
covered, but with a twist that I didn’t know. Not only do you have
problems due to depleted zinc and possible solder contamination but
it seems that metals alloyed from different vendors can also give way
to problems. If you get a chance read the article, it is very
interesting, at least for me it was. By the way I do not work for
Lapidary Journal nor do I have the pleasure of knowing Sharon Elaine
Thompson.

I’ll be listening
Tom Timms
@Thomas_Timms
USA Arizona


#7

My first reaction when I see white smoke coming off of molten gold
is to assume that the smoke is zinc that is burning off. Some have
suggested that zinc is a toxin and while it is true that the human
body can absorb zinc in such a state and induce a case of “zinc
shakes”, I am not particularly concerned about them. My
understanding is that with some time, them body will recover. What
does concern me today is the unknown quantity of cadmium that may be
involved with melting and remelting scrap golds containing cadmium.
Cadmium is a carcinogen. A lot of us have been ignoring this cact for
a lot of years. At this late date I use cadmium free solders, but if
I am melting someone elses gold, I have no idea what is in it.

Anyone have any thoughts?

Perhaps Dr. Aspler is privy to some data on the possible toxins in
scrap materials?

Bruce Holmgrain
JA Certified Master Bench Jeweler
http://www.goldwerx.com