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Melting gold


#21
Yes, and if you want the best quality you should scalp (remove)
the outer surface to get rid of any metal/mold reaction products. 

Hey James,

Do you use a steel mould?

I used Delft clay because it was just easier to reset the mould in
case of operator errors.

When I picked up a copy of Mark Grimwade’s book “Introduction to
Precious Metals”, it confirmed that it’s a good idea to use sand or
clay for making ingots… well if you’re interested in an even grain
structure throughout the ingot. So of course I use it all the time
to make ingots.

I was wondering if the use of steel moulds today is due to the
expense of the clay or because “it’s always been done that way”.

Regards Charles A.

P.S. Just traded away some of my ingot moulds, and gave away a few
to people in need.


#22
I used Delft clay because it was just easier to reset the mould in
case of operator errors. 

I gave up my steel molds a couple of years ago after reading about
using delft clay for ingot molds here on Orchid. It was one of those
slap the forehead, why didn’t I think of that moments and I have
never cast ingots in steel since.

James Binnion
James Binnion Metal Arts


#23
You can achieve this by building a micro furnace body to accept
your torch, and you do have to use bilge type crucibles. Open
crucibles are too inefficient for melting gold. 

Thank you for your advice Charles. I will try that.

Best regards,
Jennifer


#24

I read these statements of the superiority of metal forged before
being milled to sheet form and still wonder why do it. That it is
denser, stronger and can be polished to a fine finish (more than the
usual fine finish?) may be true, but, what exactly do these
adjectives mean in quantitative terms. How much stronger and how
much denser? How much longer will a piece of jewelry last that is
made by your milling method than one made without forging the metal
before milling. How hard a blow is a “small hit” and why will large
blows not work? Is work that Paf does inferior? How can a customer,
dealer, or I determine this. His stuff looks excellent as I have seen
it. Perhaps his customers return pieces of his work because of
density lack or because the jewelry wears out too quickly, but I
doubt it.

I am not willing to say the the pre-milling forging is bogus because
it is probably not. However, I have not seen the research literature
supporting your position. I am now tempted now to look for it At
this point in the discussion I am left with the impression that,
though it can be done, the forging you describe is not necessary to
the production of fine jewelry. I wish I could get a show of hands
from people who do and those who don’t employ the forging prior to
milling. It might be interesting but it wouldn’t tell us anything
about the superiority of the method.

Gerald Vaughan


#25
I read these statements of the superiority of metal forged before
being milled to sheet form and still wonder why do it. That it is
denser, stronger and can be polished to a fine finish (more than
the usual fine finish?) may be true, but, what exactly do these
adjectives mean in quantitative terms. 

Primary benefit is ability to obtain complex structures with minimal
amount of metal. Take a look at my Eternity Ring video.

http://www.ganoksin.com/gnkurl/1f0

At size 8, in 18k gold - it only weighs 7 grams, and I guarantee it
for 25 years. Do you think you can do it in casting? I know some
people tried, so far none succeeded. If you want to give it a try, I
have a model of the ring on my website

http://www.ganoksin.com/gnkurl/10o

It shows structure of the ring quite clearly. To see the model java
must be enable in browser. Model is interactive. Angle of view can be
changed simply by using mouse, as well as position, and rotation.

Leonid Surpin
www.studioarete.com


#26
I read these statements of the superiority of metal forged before
being milled to sheet form and still wonder why do it. That it is
denser, stronger and can be polished to a fine finish (more than
the usual fine finish?) may be true, but, what exactly do these
adjectives mean in quantitative terms. How much stronger and how
much denser? 

Thanx Doc.

Nobody has ever returned a piece of jewelry to me for any reason. My
stones don’t fall out (and they are guaranteed not to) and I’ve never
had anyone complain about the density or length of time a piece
remained highly polished.

You won’t say the forging thing is bogus, but I will. (Until of
course someone can prove me wrong.)


#27

When I read this, I laugh. I would prefer a show of hands of those
who have rolled out metal only to have it crack. Forging changes the
grain structure to preclude the possibility of the ingot cracking.

Most of the people on this forum probably work in sterling, less
likely to crack while rolling. If you graduate to gold, more likely
to have more problems with cracking.

Reminds me of the story, a woman buys a pot roast, cuts both ends
off and puts it in a pan that the whole roast would fit in. Husband
notices and asks why she cuts the ends off when it will obviously
will fit. Wife says, that is the way my mother does it. Daughter
asks mother why she cuts the ends off, mother says my pan was too
small for the whole thing…

Sometimes there is a reason to do it according to the way it has
been traditionally done, sometimes, not. It seems to me, sometimes the
traditional way of doing something in metal smithing is for a reason
that is not mentioned clearly, they say changes the grain structure,
but not the reason why, ingot might crack while rolling.

There are metals that are more prone to crack while rolling, like
white gold.

Now the question would be, why not take a few minutes to follow in
the footsteps for prior masters assuming they know something you
don’t and you gain the benefit even if you do not have all the
scientific explanation. Sometimes the quest for knowledge is
relational to experience not concepts.

Richard Hart G.G.
Denver, Co.


#28
I wish I could get a show of hands from people who do and those who
don't employ the forging prior to milling. It might be interesting
but it wouldn't tell us anything about the superiority of the
method. 

I do forge and then anneal my ingots prior to rolling and if you
will read my reply to Paf you will find reference to two books that
will provide you with the reasons to forge ingots into billets. This
is not just a precious metals thing. Steel ingots are forged into
billets before rolling for the same reason.

James Binnion
James Binnion Metal Arts


#29
I am not willing to say the the pre-milling forging is bogus
because it is probably not. 

It’s not bogus, but it’s probably only necessary if you use a steel
ingot mould, where the grain size in the ingot is inconsistent.

The grain size is consistent in sand cast ingots, so I don’t think
there’s a need to break up grains by cold forging. I could be
totally wrong with this assumption, but time will tell :slight_smile:

Regards Charles A.


#30
When I read this, I laugh. I would prefer a show of hands of those
who have rolled out metal only to have it crack. Forging changes
the grain structure to preclude the possibility of the ingot
cracking. 

Sure I’ve had metal crack on the edges, I’ve had alloys shatter, and
I’ve had alloys break.

A custom silver based alloy broke when forming jump rings, properly
annealed, still broke. A standard bell metal, accidentally dropped
it, and it shattered, straight after casting. A custom gold alloy
(that I’m a little proud of), rolls well, and has a lot of promise.

No amount of cold forging would have saved the failed experiments.

I played with “deep” red gold recently, and it was awful, you would
assume that with the amount of copper in the mix it would be very
ductile, but this was not the case. I did some calculations and
converted it to red gold, and am having much more success.

When you cast an ingot in sand, it’s ready to roll, it’s a joy to
roll. However if you play with non-spec alloys then be prepared for a
few failures :wink:

Richard, have you use delft clay or sand to make ingots? Seriously
it’s a joy.

Regards Charles A.


#31
Primary benefit is ability to obtain complex structures with
minimal amount of metal. 

He wants research documents, I can provide some, but maybe there’s a
place on the web? CIA


#32

Gerald, to repeat, “Introduction to Precious Metals”, by Mark
Grimwade. “Metallography and Microstructure of Ancient and Historic
Metals”, by David A Scott. Also worth looking through the back
issues of Gold Bulletin, it’s available for free online - a bit too
technical for me, but it’s all out there.

Jamie Hall
primitivemethod.org


#33
The grain size is consistent in sand cast ingots, so I don't think
there's a need to break up grains by cold forging. I could be
totally wrong with this assumption, but time will tell :-) 

As cast grain structure is very large. The slower it cools the larger
the grains. So forging followed by annealing produces a small
equiaxed grain structure that is best for rolling. Also due to the
way alloys solidify the chemistry varies within the grain so the
annealing helps to homogenize the distribution of the elements in the
alloy.

James Binnion
James Binnion Metal Arts


#34

The grain size is consistent in sand cast ingots, so I don’t think
there’s a need to break up grains by cold forging.

You’re still dealing with the big grainsize in delft clay casting.
Forging is still desirable.

Grainsize is more concistent with delfts clay but still to large.

Have fun and enjoy.

Pedro


#35

Thank you, i will try that out. i remember years ago having no prob
pouring it into the iron bars, but amazingly, I have forgotten the
technique. I had been thinking about using cuttlefish, but it’s so
messy.


#36
When I read this, I laugh. I would prefer a show of hands of those
who have rolled out metal only to have it crack. Forging changes
the grain structure to preclude the possibility of the ingot
cracking. 

This is interesting. Can you please post a link that explains why
forging before rolling prevents cracking?

There are metals that are more prone to crack while rolling, like
white gold. 

I used to have cracking issues with white gold until the
metallurgist at Stuller explained how to prevent it.

Now the question would be, why not take a few minutes to follow in
the footsteps for prior masters assuming they know something you
don't and you gain the benefit even if you do not have all the
scientific explanation. 

I would still like to see a scientific explanation.


#37
This is interesting. Can you please post a link that explains why
forging before rolling prevents cracking? 

Get the Brephol book, it has to do with the distribution of stress on
the billet or ingot as it is being rolled. He covers this in chapter
4. Rolling is almost the most stressful thing you can do to metal.

James Binnion
James Binnion Metal Arts


#38
I played with "deep" red gold recently, and it was awful, you
would assume that with the amount of copper in the mix it would be
very ductile, but this was not the case. 

You need to learn to read phase diagrams. This would have shown that
there are areas of ordering that occur in copper gold alloys. Ordered
structures resemble intermetallics, in that they are not at all
ductile. But with ordered structures you can heat treat them in such
a way as to preclude the ordering from occurring and end up with
ductile metal. But you need to do the proper heat treating every
time you heat the metal up to or above the ordering temperature. In
the case of red gold the heat treatment is to heat to above the
ordering temperature and quench. Look in your Grimwade book he talks
about this.

James Binnion
James Binnion Metal Arts


#39
I used to have cracking issues with white gold until the
metallurgist at Stuller explained how to prevent it. 

Please share this info.


#40

Charles,

Richard, have you use delft clay or sand to make ingots? Seriously
it's a joy. 

I guess old habits die hard. I have been pouring ingots in metal
mol= ds for 30 years. No problems, no need to try something different.
I make a lot of my own sheet and wire, sterling, white, yellow and
red gold in 14kt and 18kt, and 22kt.

Richard Hart G.G.
Denver, Co.