A dilemma. I am about to mix up another batch of 22 karat gold and
happened to read this contribution from Ronda Coryell on alloying 22
karat gold.
Specifically what is stated below.
Forging Ingots
Ingots are somewhat like a sponge and should be compressed before
rolling ordrawing down. Stress lines and blisters will form on your
sheet if the ingot is not forged down properly. Forge the ingot down
to one half the originaldiameter in order to break down the
crystalline structure of the metal before reducing through the
rolling mill.
I studied for many years at the school founded by Robert Kulicke and
was only taught to press the gold down with a piece of charcoal and
then continue to roll to sheet or form a rod for wire.
Should I hammer the 22 karat disk and rod before rolling? The hammer
used in the article looks very specific and intimidating. Any
thoughts or leads on the process and the hammer used would be
greatly appreciated.
I’ve been making jewelry since before the beginning and have never
forged anything.
I do all sorts of custom made stuff, make my own sheet and wire, in
various karats and metals, and you can’t prove to me that beating on
my ingot will make anything any better.
Lois-Tim and I always forge our ingots before rolling. We do this
with gold, silver, and platinum. It’s what we were taught by the old
timers back in the day. I’m not sure if it’s a science based
technique. However when the old European masters who learned their
chops before WWII tell you to do it, I’m happy to oblige.
We use a smallish sledge hammer that we polished the face on.
The hammer she was using is just a generic Sears cross-pein sledge.
2 pounds, picked up at the hardware store. The only reason for using
something that heavy is to smash the metal down fast.
As far as forging on the material goes, yes, that’s a good idea. A
hammer with a very faintly rounded end will work just fine. (Like a
heavy planishing hammer, or a goldsmithing hammer.) Break it down to
at least 2/3 of original thickness before you start to roll. (if it
started out at 1’ thick, forge down to.66 inches, then roll.) (Yeah,
stupidly large. Just to make the math obvious.)
The first few passes through the mill, rotate the blank 90 degrees
between passes. After the first few it doesn’t matter so much.
Don’tbe intimidated. Try it with silver first. Silver’s actually
harder to ingot, so if you can make that work, then you’re golden.
Ingots are somewhat like a sponge and should be compressed before
rolling ordrawing down. Stress lines and blisters will form on
your sheet if the ingot is not forged down properly. Forge the
ingot down to one half the originaldiameter in order to break down
the crystalline structure of the metal before reducing through the
rolling mill.
This is a kind of confused description.
Yes you want to forge ingots for maximum quality final product.
However they are not like a sponge unless you have a lot of gas in
your pour in which case all the cold forging in the world will not
help.
When metal cools from its molten state it forms rather large
crystals which are less strong by nature than the desired small
crystal for wrought material. If you don’t forge them you can end up
with cracking along the grain boundaries as you roll the ingot. With
careful forging of about a 50% reduction in section followed by
annealing you will get recrystallization and smaller resulting
crystals that tend to produce better material.
Do you have to forge? No, but properly forged material will yield a
better resulting piece of wrought material. Improper forging will
either not make any difference or make it worse.
I share your view Paf. Forging must be akin to rolling of metal
stock between platens except that in the rolling mill metal is
compressed smoothly, uniformly and directionally as it traverses the
rollers. Just a thought. Warmest regards, Kofi.
There is a lot of in the archives regarding this topic
that says to forge your ingots first before rolling. It all makes
sense when you read it. I started doing it for a practical reason. I
couldn’tfit the ingot thru my mill to start rolling it without
forging it thinner. I now have a larger mill and still forge first.
I also sand off any irregularities as well as that pesky parting
line flashing. This all seems to work for me, so I don’t mess with
success. I would still like to know why my wire ingots all crack up
close to the button. I suspect that it has to do with shrinkage and
tensional forces caused by the button pulling back as the wire
shrinks. Any thoughts would be appreciated. Thanks. Rob
I normally don’t cast wire ingots with much of a button. (I have a
big wire mold) But before I made that one, I used to get buttons on
occasion. I’d trim them down enough to make them more-or-less
squarish in cross section, then forge them down to roughly the same
diameter as the ingot. Then roll the whole thing. Never had any
trouble with them.
Brian, my understanding is that you can not rotate the ingot
without annealing it first. Is that correct?
News to me. When you anneal has more to do with how much you’ve
compressed the metal, rather than which orientation it was in. Roll
down about 50%, then anneal. Some metals like to be rolled more. Jim
Binnion’s been following this thread, and I’m sure he can give you
much more technically accurate than I can.
Thank you for responding to my question. I would like to read the
archived comments on this subject. Attempting to find the past
debate was unsuccessful. Can you recall the year?
I never used to forge ingots, wire or sheet. But I recently started
doing so. I can definitely tell the difference: they seem top roll a
little easier and “smoother” and there is less checking (small
cracks) on the edges. But I the difference is not huge and doesn’t
seem to effect the final product to any huge degree…
I should say that I pour and roll ingots pretty much every day…
When I roll out a sheet ingot (reducing the ingot by about 50%
before I anneal), I have found that if I do NOT anneal before
reorienting 90 degrees, I am guaranteed to be left with a large crack
on the first reoriented pass.
So with sheet ingots, I always anneal before changing the
orientation.
(The reason, of course, that I change orientation is to increase a
specific dimension, as in width or length.)
I always turn my wire ingots 90 degrees. Making at least two passes
through each wire notch on the lower rolls on my Durston mill. Always
being careful to trim any fins that appear on the corners.
Personally, I find pouring an ingot and beating the hell out of it
with alarge hammer before rolling it therapeutic… makes me want
to sing elfin songs I always forge before rolling - but I have no
idea if it makes a better ingot. Peddinghaus makes a couple of big
hammers they call “locksmith hammers” that work well if you polish
the faces.
Trying to stay on topic. at least this is related to ingots,
forging, etc… How do you keep the oxygen of of sterling silver to
prevent those pesky bubbles and firescale? I know the big boys do it
in a oxygen free atmosphere, but I don’t seem to have one of those
handy. I’ve tried to put a layer of charcoal on top of the scrap,
but that just blows off when I hit it with the torch and makes one
big mess. I am assuming those directions involve having a melt
furnace. Is there any way to protect sterling from oxygen
contamination during the pour using a torch? I don’t seem to have
the issue with wire ingots as bad, or at least can cut out the bad
spots before drawing. Normally, I’ll only cast sheet ingots for
reticulation alloy, so the bubbles are not as big of a deal as I can
justwork around them. because they are sure going to show up when
you start rolling.
I never rotate sheet going through the mill without annealing first,
with the possible exception of 18K yellow which is only going
through two rolls (on the same bite) after annealing. I sometimes do
that to get the sheet perfectly flat.
Trying to stay on topic. at least this is related to ingots, forging,
etc… How do you keep the oxygen of of sterling silver to prevent
those pesky bubbles and firescale? I know the big boys do it in a
oxygen free atmosphere, but I don’t seem to have one of those handy.
I’ve tried to put a layer of charcoal on top of the scrap, but that
just blows off when I hit it with the torch and makes one big mess.
There is no real rocket science in reducing the oxygen content of
your molten silver alloys.
Prevention; melt with a good melt cover of charcoal or graphite. Do
not use the small brick type charcoal which is compressed dust, use
good quality lump wood charcoal.
Deoxidise; this can be as simple as immersing a graphite rod into
your molten metal and stirring. The commercial casters use
controlled additions of deoxidants such as copper-phosphorus, red
amorphous phosphorus or lithium. However you must be very careful
with this and an excess of phosphorus can make your silver alloy
hot-short and lithium is a highly reactive metal which requires
special handling.
Protect; make sure that your molten metal passes through a lazy, gas
rich flame when casting to minimise any oxygen pick up during the
pour.
If you are having a problem with the charcoal flying everywhere when
you apply the heat from a torch then see if you can source some
graphite pieces which should be more robust.
Following is a link to some archived about what happens
to metal when it is rolled vs forged. It is a bit in depth, but
makes sense.
I learned to listen to metallurgists while working for a company
that made large industrial gas compressors and natural gas engines.
They could explain to me why a failure at the microscopic level of a
small piece of metal could bring one of these machines to its knees.
I would often see them in the foundry covered with casting sand
trying to figure out what small dimension in a sand cast mold needed
to be changed to avoid a failure in the future. It was all very
fascinating to me and has helped me to understand a little better
what I do when I work precious metal. Thanks. Rob
I always forge before rolling - but I have no