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Fissures in ingot


#1

Greetings All!

I’ve got a recent problem that I’m hoping you can help me trouble
shoot. For over 16 years, I’ve alloyed my own 18K and worked from
ingot for most of my work. Recently I started working with sterling
silver and for some reason, have encountered a wall that I just
cannot seem to find my way around.

I’ve been using a standard reversible ingot mold and attempting to
make flat ingots for sheet. The problem is that no matter what I
try, my ingots (a little over an ounce) end up with a whole bunch of
little fissures after about 2 or 3 passes through the mill. Though
they sometimes occur in multiple places around the ingot, they
pretty much ALWAYS appear in the center of the bottom half for some
reason. I have scoured all my books, the forums, the internet in
general and cannot seem to find an answer to this problem.

What I’ve thought and what I’ve tried:

  1. Contamination: I’ve eliminated possible contamination by starting
    with fresh sterling (alloyed myself from .999 silver and copper)
    along with a new crucible. I doubt contamination though because of
    the consistency with the location of the fissures. If it was a
    problem with the alloy it should either be throughout the ingot or
    at least move around each time I re-pour it.

  2. Perhaps the ingot is cooling too fast or too slow resulting in
    either shrinkage-based weakness or large crystalline structure? I’ve
    tried a cold mold, warm, and hot with no effect on the occurrence of
    the fissures. I’ve also tried annealing the ingot immediately after
    the pour before forging to see if that helps. Nope!

  3. Melt temperature too high: I’ve tried pouring just after being
    liquid enough (resulting in incomplete ingots), just a bit after
    this stage resulting in complete ingots with a few bubbles trapped,
    and finally high temperature pours which result in complete ingots,
    but with large crystalline patterns on the surface.

  4. Sterling not properly annealed/worked prior to rolling: I’ve
    forged the ingots (cross-peen and 45 degrees left and right to
    rolling mill direction on both sides of ingot). I’ve tried
    potentially under-annealing and over-annealing to no alteration of
    the occurrence of the cracking. For the heck of it, I’ve also tried
    rolling just after pouring (no forging) which changed nothing for
    me.

  5. Quenching too soon or too late: I’ve tried quenching immediately
    after annealing, giving it a minute to air cool before quenching,
    giving it 5 minutes before quenching, and finally letting it air
    cool. No change in occurrence.

  6. Too turbulent of a pour: I’ve tried pouring slowly, quickly,
    medium. They pretty much all have the same result. My last and only
    idea left is to try tilting the ingot mold a bit to have the silver
    roll down the inside rather than splashing directly on the bottom
    from the top.

For the life of me, I cannot seem to figure out what exactly the
problem is and am pretty much out of things I can think of to try.
What bugs me more than anything is that because the fissures occur
in a consistent spot, it’s got to be something I’m doing or can
control and not the alloy, but after spending the last 2 days and
pouring about 50 variants to attempt to correct the problem, I’m
just stumped. I’ve never had this problem in 16 years of pouring and
rolling 18K gold ingots, but for some reason, sterling has decided
to become my bane.

Has anyone encountered this problem before or have any
thoughts/insights on what I may have overlooked?

Many thanks for help you can offer!
Erich


#2

Eric, Have you per chnce bought “new” metal or casting grains that
you are now having trouble with? One time I bought nearly 2 tons of
Everdur Bronze ingots and that whole lot gave me NOTHING but
problems. Mostly cracks in the piece, but terrible time welding on a
piece without getting cracks and on and on. Bought some more ingots
from a different supplier and there were NO PROBLEMS. Had to be a
problem in the parent metal (copper) or an alloy or ee Jusst a
thought, expecially since you were previously successful. Good luck.
John Dach


#3

I cast sterling all the time. I remove anything magnetic with a
magnet, assemble the mold (wire or flat ingot), melt the metal, stir
with a graphite rod and add a bit of borax from a salt shaker, remelt
and pour.

Once cool, I open the mold and remove the ingot, sand/grind off any
flashing or parting line, forge in several directions, anneal and
roll. I have had it fissure around the edges, but if you grind, sand
or file them clean, they don’t seem to propagate further. Anneal
often and you are good to go. I do get some feathering once I roll
out to very small square wire and have yet to be able to control for
this. In the end, I only roll or draw very small gauge wire if I am
out of it and can’t wait for the next shipment of wire to arrive. I
used to go thru great steps to heat the mold and then drive off any
water that might have condensed from the fuel on the initially cool
mold surface. I don’t do this anymore unless I am having a problem. I
do try to coat the mold surface with gas only soot. If I cast in an
open mold, I rub a light coating of oil on the mold once in a while.

This can be frustrating, but I have found a way that works for me
most of the time. You might try casting in delft clay. It is a lot of
fun and you can get surprisingly good results. I have made my own
casting frames as the little ones that come with the clay are, well
little. You might also try adding a little new casting grain to your
mix. That’s all I know. Good luck. Rob


#4

Try a little Sal Ammoniac and crushed charcoal as a refining agent-
it yields a bright, tough ingot. If there is any contamination you
have overlooked somehow this will pull it out of your rolling, molten
’ball’ of metal in the crucible, and look like flaky bits on the
surface you can dip off with a carbon or graphite rod. Mix about 1:4
and keep very tightly covered -the sal ammoniac is highly humectant
and draws moisture from the atmosphere-quite readily!! Pure Sal
ammoniac is the tinning block you find at stained glass supply
stores, (or occasionally where soldering irons are sold).

Another thing to consider is ambient temperature and humidity in
this season ; perhaps it is less humid than ordinarily in your
studio- or wherever you melt-n-pour! heat the mould thoroughly as you
are melting the metals- We were taught years ago to “fume” the mould
’s interior with lampblack (easily accomplished with an acetylene/ O2
torch right before turning the O2 up) while heating the outside of
the mould by hitting it with the torch to maintain a more than warm
temp as you melt your metals or lampblack with a candle before you
heat the mould: just hold the assembled mould over the candle to give
it an even interior coating of lampblack then pour into the preheated
mould.

When using copper you may want to sand it /abrade it first when
alloying into sterling (or anything you use copper for) and use the
same ‘new’ copper each time, instead of tossing in portions of
pennies to make the weight in Cu you need in an alloy.

It sounds like you have tried everything! I hope this isn’t
redundant I presume you have inspected the mould -(perhaps with a
microscope from the sound of it!!!) to make sure the manufacturer
gave you evenly rolled plates, alternatively, if it’s one of those
reversible moulds that has a flat side and cylinders for wire on the
reverse of that side the ‘ribbing’ created by that design could
affect the metal you are pouring- it sounds like the atoms aren’t
packing uniformly nor crystallizing properly when cooling in that
area if it’s consistently defective in the exact same place at the
exact same gauge when you are rolling it out- which is a bit bizarre
to have occurred in 50 pours of the same alloy! Try using fine silver
for one single run (you can always add the Cu back to the alloy)-
just to rule out any copper (you may be using) problem entirely. and
use at least 60% new casting grain to scrap- it could be a problem in
the scrap you thought was.925 but was fake. you would be amazed at
the amount of stuff turning up in the past 5-10 years that is stamped
sterling but can be almost anything. Another thing to watch for when
using scrap is “Taxco” silver- it can be more like 850 if that much
silver at all! hope you found at least one thing you haven’t thought
of- yet- in this… rer


#5

Hi Erich.

Looks like you’ve given lots of things a try. It can be really
frustrating trying to sort out what is going wrong. I had trouble
with cracking of gold a couple of years ago and I spoke to my
refiner. I melt using a flame or torch. The problem turned out to be
oxygen from the atmosphere getting into the metal when I would remove
the flame from the metal periodically to let the flux run up over the
melt. I was told to keep the flame on the metal at all times even
when pouring and this solved the problem for me. The flame needed to
be neutral as well which required me to fit a larger tip size as I
had been using a slightly oxidising flame to generate the heat I
needed. Whilst the problem was originally with 18 carat Palladian
metals this technique has improved all of the metals that I use.

Dean


#6

Hi Erich,

I have had that problem in the past and I am certain I shall in the
future. I have started doing two things that seem to help me.

I forge the ingot with a cross peen, both directions, both sides.

How ever much scrap I am melting I add some new wire of the roll and
a pinch of Boric acid.

I heat the ingot mold a little more than is usual I think. Something
my Dad showed me years ago.

And I stir the melt with a graphite rod to pick up crap in the melt.
Something my brother Rob suggested.

Where I would have annealed the ingot twice I now do it three times.
And I air cool until the color is gone before I toss it in the
pickle.

And I take much smaller bites with the mill than I used too.

Probably all stuff you are doing and it isn’t always perfect for me.
But I get good results more often than I used to.

Don Meixner


#7

Thank you very much everyone for the various ideas!

I think I’ve ruled out an issue with the alloy because the problem
consistently occurs in the center of the bottom-half of the ingot.
In fact, I’ve noticed that the area there seems slightly indented
right after the pour as though it perhaps shrunk in that location.
Sure enough, even after forging with a cross-peen (plus and minus 45
degrees to the rolling direction) on both sides, that area is the
one that seems to always create the fissures. To boot, they look
similar to dough or clay that’s too dry after rolling in that the
fissures are usually tightly packed and parallel to each other like
waves and are always oriented parallel to the rolling direction. You
would think that if it was a problem with the alloy that the
fissures would occur with no predictability after each pour. I’ve
also noticed that whether I pour a tall narrow ingot or a wide short
one, this center location seems to always be where the fissure shows
up about 90%+ of the time. It’s got to be something I’m doing (or
not doing), but I just haven’t been able to zero in on it.

Tomorrow I’m going to try the combination of really heating up the
mold and using an even greater reducing flame. I’ve usually had
issues with casting using a large reducing flame as it seems to take
a very inordinate amount of time to bring the melt up to temp, but
at this point I’ve got nothing to lose.

R. E. Rourke, thank you very much for the ideas, particularly sal
ammoniac. I’ve never used it before, but it seems like a handy arrow
to put in my quiver. I know that humidity isn’t the issue around
here as we are in mid-winter (Michigan) and the house is dry as can
be (cracked hands and knuckles bleeding. oh the joys of winter).
However, you raised an interesting question regarding my mold. I’ve
had this mold for 15+ years and used them flawlessly for 18K. I
realize though the 18K is much more forgiving with this kind of
stuff than sterling and since I never officially “seasoned” the
ingot, I’m going to try stripping and cleaning it and treating it
like a brand new one to see if proper seasoning helps. I’d think
after all this time that it is already seasoned well, but again,
I’ve got nothing to lose and since it was never officially done in
the first place I might as well give it a go. I’ll also take the
opportunity to inspect it under a loupe just to double-check any
issues that might be at play. Also, I think I’lltry a run of.999
silver just to see what happens. I started with.999 bullion and
added in copper myself to create the sterling so there’s no scrap
that should be at issue, but still, it never hurts to try something
else.

Thank again for the ideas everyone. I’ll keep you posted as to if I
make any progress and, if so, what on earth I determined the problem
to be!

I don’t think I’ve ever had such a vexing issue in all my years of
jewelry work (about 20 now). Talk about frustrating.

Thanks all!
Erich


#8

I wonder if you are over-annealing. I usually anneal my ingots after
reducing the thickness by 50%. I learned this from Jim Binnion. It
really helps.

I pour ingots several times a day for wire and sheet. I fabricate
and forgealmost everything from ingots, including tube. In sterling,
14k white and yellow and rose and 18k.

Some edge cracking seems inevitable but rarely progresses. I’m
anxious to read what others suggest.

Take care,
Andy


#9

DON’T FORGET, , most all pennies in circulation these days are
actually copper coated zinc!!! using stripped wire is a
potentialproblem as it is usually not PURE, has alloys added to
allow for better drawing and to keep it flexable. John


#10

How about the direction of the rolling, I’ve found that rolling in
the direction the ingot was cast is most helpful, and doing very
small increments ata time 1/4 of a spin (if it is to thick) still not
annealing till it’s almost 50% of its original whit.


#11

Hi Andy,

You mentioned over annealing. Like a lot of us I anneal by torch and
color. I would imagine that while this is an historic method it can’t
be overly accurate. I would wonder if those who anneal in an oven
have similar problems with consistency and rolling plate.

Don Meixner


#12
using stripped wire is a potentialproblem as it is usually not
PURE, has alloys added to allow for better drawing and to keep it
flexable. 

My understanding is just the opposite, that the copper used for
electrical conductors is likely to be purer than that used for a
number of other things, like plumbing pipe and fittings, etc. Wonder
who’s right…

Peter


#13
I've noticed that the area there seems slightly indented right
after the pour as though it perhaps shrunk in that location. 

That’s a fairly important clue. The metal did in fact shrink there.
The cause is that this is apparently the last part of the ingot to
solidify, so thermal shrinkage is trapped there, with surrounding
areas already solid, the metal must shrink in the middle. The problem
with that can be that in shrinking, it can literally be tearing
itself apart. Silver, when hot, has very little strength, so as it
cools, it cannot easily actually stretch the way it can do when
cold.

Although you cannot see them in the raw ingot, it will already have
micro cracks and porosity in that area it was shrinking in. Some at
the surface, more inside the ingot. This is the reason why forging
before rolling doesn’t help much. The metal already has the cracks
that will expand to visible size when you roll.

What you need to do here is a concept familiar to those who do lost
wax casting in order to get complete fills with minimum porosity
(which can be caused by the same shrinkage situations). Progressive
solidification. As you’re doing now, the mold is preheated. But
you’ve got the ingot mold currently heated evenly.

What you need to do is heat the top upper section of the mold hotter
than the bottom, so that when you pour metal in, that bottom of the
mold solidifies first, and solidification proceeds upwards, only
solidifying at the top of the mold/ingot after the lower parts of the
ingot have solidified, rather than solidifying last in the center of
the ingot. That way, as the metal cools, the shrinkage proceeds at
the boundary between lower solid metal and still molten upper parts
of the ingto, rather than being trapped in the middle with nowhere
to pull still molten metal from. You’ll know you’re getting this in
some cases when after you pour, the top edge of the ingot has a
sometimes fairly deep depression in the top edge. Sometimes it’s
quite distinct, with an actual little hollow cavity in the top edge.
This can be annoying, since it ruins the very top of the ingot. But
that’s OK. It means the rest of the ingot was able to solidify in a
progressive manner from bottom to top, so it did not trap
solidifying and shrinking metal in the middle. You can always (and
should) lop off that top edge anyway, since it will also be where any
impurities, flux inclusions, oxides, etc, will concentrate. When your
ingots do not have that shrinkage depression in the side, you won’t
have those micro cracks to expand, which should help. So when you’re
preheating the ingot mold prior to pouring, concentrate the flame on
the top of the mold more than the bottom, especially at the end of
the preheating operation. That will control when the metal solidifies
in each portion of the mold.

R. E. Rourkes suggestion of a refining flux like sal ammoniac
(ammonium chloride) is a good one for removing traces of other
metals, especially iron or lead or tin that may have accidentally
gotten into the melt. Be sure to use very good ventillation when
using the stuff though, as it releases chlorine gas during use.

The chlorine is what makes it work, combining with the baser metals
to form chlorides of those metals, which are then not soluable in the
molten silver, so rise as slag to the top, where they can be skimmed
off.

Another comment, which is probably not your problem, but worth
mentioning, would be your source of copper. Some commercially
produced copper items (some plumbing fittings) include traces of
lead. That can be disastrous for your silver. Be sure to use a copper
source that is free of any lead. Electrical wire is one such source
of high purity copper, if you’re not already using such a source.

Your melting flame should be reducing, but not highly so. Only
slightly to the reducing side of neutral. You need the heat, and
relatively shorter melting time is more useful to preventing
impurities and oxides etc, than using a more reducing softer but
cooler flame which then can take a lot longer. Also, too reducing can
end up increasing gas absorbtion by the molten metal, which is the
opposite of what you want.

Peter


#14

Hi Don,

I just torch anneal. According to what I was told (Jim Binnion?)
metal needs a certain amount of cold working to properly anneal.
Larger crystals need to be broken up.

A


#15

Hi Erich.

My understanding is that copper wire has additives in it and it?s
not pure. I bought some pure copper foil from a chemical supplier
which is 99.9% pure that I use in alloying. Recently though I just
buy master alloys from my metal supplier as they are not that
expensive when bought in bulk.

Have you tried buying some sterling silver from a metal supplier and
trying to melt this in a new crucible. If this pours and rolls well
it will tell you that it?s something wrong with your alloy and not
your melting process. The extra cost of buying the new metal as a
test would be cheap compared to the time you?re spending now trying
to get this metal to roll.

Good luck
Dean


#16

I was told that electrical wire had more oxygen in it, and that
copper tube was oxygen free, someone must know for sure?

Tim


#17

Thank you Peter. Well written and a good clear explanation. I so
love science.

Jo Haemer
timothywgreen.com


#18
My understanding is just the opposite, that the copper used for
electrical conductors is likely to be purer than that used for a
number of other things, like plumbing pipe and fittings, etc.
Wonder who's right... 

Wikipedia says that both electrical wire and plumbing material are
99.9% pure copper. In special applications, oxygen-free wire may be
used, and it’s up to 99.99%.

Al Balmer


#19

Copper electrical wire (household circuits) and plumbing pipe are
99.9% pure.


#20

Greetings All!

I wanted to thank you for all your help and suggestions. I decided
to try to get to the bottom of this issue one way or another and so I
completely wasted the entirety of this last week casting and
recasting ingots trying to figure out what on earth was going wrong.

Aside from epically putting me behind schedule and wasting a week of
work, I at least learned some important things about casting silver.
I don’t have an exact tally, but I suspect I cast something like
200-250 ingots and used up an entire 80 cu. ft. oxygen tank!
Unfortunately, I still wasn’t able to get a totally satisfactory
ingot poured. There were always some sort of problems that needed to
be cut out or worked around, but I was able to minimize them quite a
bit. I’m so far behind that I don’t have the time to elaborate at the
moment, but over the weekend I’ll try to put together a
trouble-shooting sheet for others that encounter these problems with
answers based on my experimentation and would welcome and
input/changes/corrections that any of you may see once I’ve got it
put together. There is just so much out there from so
many different people that all have their system that works (“I use a
cold mold”, “I only slightly warm mine”, “I get mine smoking hot”, “I
heat mine to a nearly dull red”) and it would be helpful for others
to understand exact why/what works with these things.

I’m hoping that since I still wasn’t able to completely eliminate
either cracking or bubbles (seems to be the trade-off) someone here
can see what I may have overlooked once I have compiled the sheet.

Thanks again everyone!
Erich C. Shoemaker
ErichCDesigns.com