Back to Ganoksin | FAQ | Contact

HELP! - How do I get the zinc out?


#1

Hi everyone, Here’s a mess I got myself into which may amuse you.

In my own defense let me explain that I’m about 99 44/100 percent
self-taught. This means that very often I’m re-inventing the wheel
when I make something. This can be instructive, where "instructive"
usually means that you’ve just learnt at first hand why they don’t
normally do it that way.

Now here’s my mess. Part one is, I’m making a set of wedding rings
for two very good friends; cut a really bright pink Maine tourmaline
for hers and a green oval one for his. His will be bezel set. No
problem there. Hers is about a 3 mm square emerald cut for which I
built a set of prongs. Prong settings give me grey hair anyway. These
prongs aren’t as pretty as I’d like 'em to be so I want to do a
re-cast (in cuttle fish bone) to file out new ones from.

That’s part one. Part two is, I’m using unorthodox metal. It’s the
result of an experiment in quartation (when you alloy gold scrap down
to less than 25% gold prior to subjecting it to acid). The low-gold
quartation alloy had a really subtle attractive moon-glow sort of
soft yellow, much more to my liking than the standard 14 or 18K
"shopping mall" gold. My friends also liked it. Guesswise it would be
about 80% sterling silver, the rest gold.

(One of its other interesting aspects is it melts at below the
melting temperature of medium 14K solder. “Hers” Mark I bit the dust
that way. Oh well I knew about that and I do have some extra low
temperature gold solder. Just forgot to use it the first time.)

Now here comes the real problem. What I’ve been doing is casting
this stuff into ingots in cuttle bone and then rolling it down. That
worked well for a while but recently the cast has come out unsound,
bubbly. I tried re-melting in charcoal; I tried “poling” the melt - a
semi-medieval procedure in which molten metal is stirred with twigs
of green wood to de-oxidize it. Neither cured the bubbles.

So as a last resort just now I added about 1/2 gram of zinc (to
about 25 grams of the alloy). I’d heard that the zinc would help make
for sound metal for casting and that it would burn off if you kept
the heat on it. Unfortunately either my memory is flawed or the
itself is suspect. Probably the latter.

What I’ve got now after adding the zinc is essentially what the old
goldsmiths called spelter, and used for solder. It is excessively!!!
low melting. So low that there’s no way it can be soldered at all
(short of lead solder, and that’s out).

So my question is, using the kitchen table melting technology I have
available to me (acetylene torch, borax, charcoal, graphite
crucible, and a kiln that goes up to 1800 F) can anyone suggest a way
I can de-zinc this stuff?

Cheers,
Hans Durstling
Moncton, Canada


#2

Hans First place do not stir the melt, you are getting gassing, try
some of the borax, and another thing to try, put some clear broken up
glass in the metal as it melts, do not stir. This will help the metal
from oxidizing on you and the glass will help to trap all the gunk
coming out once the metal is hot enough to pour skim this off the top
quickly and pour. You might try a melt first with out the glass, just
use the Borax, and do not stir, skim the gunk and pour Clint


#3

Dear Hans, Have no idea how to help with zinc, just wanted to let you
know that I’m concerned about the tourmaline for wedding bands. I
have a beautiful sea green tourmaline in my engagement ring - in fact
it’s the second one in there, neither of them have lasted more than
1-2 years without being scratched and abrated badly. I’m sure there
are lots of gemologists who know more about the ‘hardness’ etc., I
just know mine didn’t last, and I won’t use anything less than
sapphire in a ring I wear all the time. And I am not a laborer -
just a regular housewife. Sincerely, Dina in muggy Maryland


#4

Dear Hans,

Here is an OPINION on what to do short of send the stuff to a
refinery. In an open crucible take and melt everything. Make sure you
have adequate ventilation. Several times take a pinch of table salt
and use it as you would flux. Keep doing it until it doesn’t smoke.
It will smoke a lot at first and less as you progress. As far as I
can determine the zinc is being removed by this process. For the last
cleaning use a pinch of 100% borax. This can be an 20 Mule Team Borax
Laundry Soap. Make sure you use a neutral flame and not an oxidizing
or reducing flame. The flame can also act as a wind to blow the
impurities off the surface of the melt. Pour into an open ingot or
ingot frame. When pouring an ingot make sure you oil the ingot mold
prior to pouring. Three in One oil will do. Preheat the ingot frame
until the oil starts to smoke. Don’t burn it off. This will help
lubricate the surface for the molten metal. Let it cool for about
four or five minutes and quench. This process I will use mostly for
the customer who insists on melting old chains into something. PLEASE
use adequate ventilation. Having not worked with your mix of metals I
would treat the project like I had to use junk gold. Your advantage
is not haiving any of the odd alloys to deal with at the same time.
Again good luck.

Best Regards,

Todd Hawkinson
TR the Teacher


#5

Hello Hans Your metal alloy is of a contains that the melting point
is very low already (eutectic), buy adding the zinc it went further
down as I read in your story. Normally you use the zinc as an
deoxidiser to get rid of unwanted oxides. These oxide make the alloy
fast work hardening and make it brittle. You only have melted under
reducing conditions. This will leave the zinc in the alloy

What you can do is heating the alloy again, but than with a
oxidizing flame (overdose of oxygen) and overheat the melt. (up to
Boiling) and use no borax What will happen is that the metal of
lowest melting temperature will evaporate, and burn away. White smoky
clouds will come of. and an oxide layer will form on the melt. Takes
depending on the amount at least 2-5 minutes after this, let the
alloy cool down again.

Now remelt with some borax and sugar on top with reducing flame
stir the alloy good to remove the oxides and cast again. when you are
lucky the problem is solved

And people, never use a lead containing solder on gold. Above 250
degrees Celsius it will amalgam like mercury with the gold and make
the material at the joint brittle and even eat it away.

Let me know the result
Greetings
Martin Niemeijer