Back to Ganoksin | FAQ | Contact

Metal surface cracking


#1

Hi every one, I have been melting some scrap gold down and forging it
out in to another piece and have had some problems with the metal
surface cracking. I cleaned the scrap metal over night in a pickle
then covered it in a flux solution before melting. I then proceeded
to forged the metal in to the desired shape - annealing regularly.
When I tried to form the metal in to a curve i noticed cracking on
the surface, the cracks weren’t on the edges as you would normally
get from over working the metal. The integrity of the metal seemed
compromised in some way. Does any one know what could be causing
this - could it be due to impurities on the surface of the metal as
the cracking was only on one side the other side of the metal seemed
good. if any one has any ideas it would be very much appreciated as
I have a job to complete for a customer and I am running out of
time!! thank you ness


#2

Ness,

When you’re working with scrap metals, you really don’t what kind of
working characteristics you are going to have.

With gold, there are 2 basic types of alloys that are used. One is a
rolling alloy, which is soft, and designed to be rolled and drawn.
The other alloy, designed for casting, flows well for casting
purposes, but is generally too brittle to roll out well without
cracking.

I never use a casting alloy, because it is too brittle for my uses.
I need an alloy that will not only cast well, but will roll out and
draw well, too. Rolling-type alloys are more versatile this way.

I suspect you have a casting alloy in your scrap gold, and that is
what your problem is. If you knew exactly what alloy you were working
with, the alloy manufacturer would have a tech person who could give
you all the info. you’d need regarding recommended annealing,
fabricating tips, casting temperatures, etc. But if your alloy is
unknown, well, good luck with your efforts!

Jay Whaley


#3
When I tried to form the metal in to a curve i noticed cracking on
the surface, the cracks weren't on the edges as you would normally
get from over working the metal. The integrity of the metal seemed
compromised in some way. 

Gold and silver can form compounds with organics and other metals
which can render alloy brittle. It could happened because of scrap
contamination, or even wrong type of flame used for melting. You may
be able to repair alloy by remelting it with small amount of
potassium nitrate. It works sometime, but not always. If you go that
route, you will increase carat value of the alloy, and crucible will
be damaged as well. So it is method of last resort.

If you do not have experience with scrap alloying, it is a bad idea
to try to melt with potassium nitrate. Ask someone with experience to
alloy it for you.

Leonid Surpin
studioarete.com


#4
I have been melting some scrap gold down and forging it out in to
another piece and have had some problems with the metal 

Ness, I can think of a few reasons this could happen. First, perhaps
the gold did not blend well when melted together and you have hard &
soft places in the piece. Second, perhaps you overheated the metal
and simply boiled away some of the gold content…gold will vaporize.
(had a guy that worked for me once do that) Lastly, perhaps the
annealing process is not just quite right… Do you know what gold
content the mixture should be??? Test is in a few places and see if
it is the same throughout.

Hope this helps. Dan
DeArmond Tool
dearmondtool.com


#5

When you say contamination of the scrap is there someway of
decontaminating the scrap before heating or would the contamination
be integral to the material. Thanks ness


#6
When I tried to form the metal in to a curve i noticed cracking on
the surface, the cracks weren't on the edges as you would normally
get from over working the metal. The integrity of the metal seemed
compromised in some way. 

I gave a course once teaching beginning jewelry. Every student had a
problem with soldering their 2 pieces together. I contacted the
supplier of the solder. Their pieces either came up with a split in
the flat sheet in the center or straight through and the split was
equivalent to a tear in the silver. The suppler told me it was due
to bad solder and took back the bad solder and gave my students good
solder. He told me this happens more often than not.

Hope this helps.
Jennifer Friedman
Ventura, CA


#7

This is such a complex question - there are so many variables in
this sort of situation. The most likely explanation is that the scrap
gold contains material that isn’t good for forging - that’s not to
say that its necessarily “bad” metal; it might just be that it’s a
casting alloy rather than a forging alloy.Of course, it could be a
genuine dodgy alloy - just this morning, I was resizing a horrible
ring from Dubai, which partially melted before I’d reached a normal
annealing temperature, and cracked as soon as it was tapped with a
hammer.As well as rejecting the metal, you might want to discard the
crucible too, as there could be trace amounts of contaminants there,
which could mess up future jobs.If you’re really desperate to use
the metal you’ve been given by the customer, you could try doing the
melt-up with lots and lots of borax and charcoal, but this isn’t a
very scientific method, and the alternative options are that you
perform a proper chemical refining process and re-alloy the gold, or
you contact the customer and explain the problem - this might not be
that much of an issue; we often encounter this situation, and the
customer is generally happy to accept fresh gold, so long as they
are given a full explanation of why this is necessary.

Jamie Hall
http://primitive.ganoksin.com


#8
When you say contamination of the scrap is there someway of
decontaminating the scrap before heating or would the
contamination be integral to the material. 

Refine it.

James Binnion
James Binnion Metal Arts


#9
When you say contamination of the scrap is there someway of
decontaminating the scrap before heating or would the
contamination be integral to the material. 

The simple answer is not to contaminate in the first place. If you
want to reuse your own scrap here are some basic rules:

Clean your bench first thing in the morning, and every time you
change metal.

There should be no food, coffee, and etc., on your bench. Maintain
clean hands throughout the day.

Throw away all fancy abrasive wheels. When wheel is used up, most of
it winds up in you fillings, and it is impossible to predict what
effect it would have on your metal.

Learn to do you work with files, scrapers, gravers, burnishers.
Rubber wheels, preferably pumice, should be your last resort and
very limited one.

Provided all of the above is followed:

Separate fillings from scrap pieces.

Boil out pieces in strong detergent, calcium carbonate is the best.

Using iron pan burn out organics from fillings.

When cool, spread on piece of cardboard and work over with strong
magnet to remove everything magnetic.

Mix fillings with fair amount of smelting flux.

Many recipes exists. Try one part of borax, one part of boric acid,
and one part of powdered charcoal. There are recipes of limestone,
ground glass, and etc. The simpler, the better. Do not complicate the
recipe unless you have a reason for doing so.

Wrap the mixture of fillings and flux in paper napkin making a neat
package. Slowly pour water on your package until it stop absorbing
it, and let it alone overnight. Water will dissolve borax and will
form binding to hold fillings together while melting.

Melt your fillings package separately and cast it in water. It is
more difficult to melt fillings than pieces. You would need to use
neutral flame. That is the reason for using a lot of flux to protect
the metal. After casting, collect all the pieces and melt it together
with other scrap pieces. Use only a little flux and reducing flame.

It may sounds like a lot of trouble, but it isn’t. It quickly
becomes a second nature. Besides, once the discipline is imposed, the
quality of you work will improve by itself.

Leonid Surpin
www.studioarete.com


#10

hi, but i feel solder should not be not te be bought from the
market, but made in the lab only according to the article, we are
working with.

solder must hav a lowermeltig point, by adding zinc and to reduce
brittleness silver should be added. it must a combination of lower
melting point, malleable, and same color. like for silver (sterling)
it can be 50:35:10 sil, copper and zinc respectively


#11

Leonid,

There should be no food, coffee, and etc., on your bench. Maintain
clean hands throughout the day. 

Now you have things backwards. Food and coffee at the bench are much
more of a problem with contaminating the jeweller than the metal.

jeffD
Demand Designs
Analog/Digital Modelling & Goldsmithing
http://www.gmavt.net/~jdemand