problems casting 18k red gold alloy
redsmith-israel
very fragile and slightly crisp ,im casting an 18k yellow green and
white gold,and im using a vibrating-vacuum machine and an electric
centrifuge for my casts.most of the time without any particular
problems,except to rarely a very little porous on small areas but not
allways;(. my casting process are in the same manner for all the above
gold alloys,but only in the red or reddish 18k gold i have this annoing
problem of faglility.
i will appreciate any help with this one.
Peter W.. Rowe,
wrote:
Rose golds can cause problems when allowed to cool slowly, as do most castings
before being quenched. The problem is caused by the ability of a gold/copper
alloy to form an alternate crystal structure, which differs from the usual
structure of the metals. This structure forms generally at temperatures below
about 800 F, and is highly brittle and unworkable. The problem is especially
noticable with 18K rose golds containing only copper and gold, which can be made
so brittle by this problem as to actually shatter if dropped on the floor. There
are two general cures. One is to use an alloy which still contains enough silver,
in addition to the gold and copper. to avoid most of this formation. But the
other is simply properly annealing the metal after casting. Assume that the raw
casting is hard and brittle. Before any working is done, anneal by heating to a
dark red (around 900F). Allow the red glow to just barely disappear and then
quench. And here's the trick. If you quench in water, you run the risk of
sometimes cracking the metal. So instead, quench it in alcohol. Be careful not
to set the alcohol aflame with your annealing torch, and plunge the hot gold into
the alcohol quickly, so it's immediately totally immersed. Done that way, the
alcohol will not ignite. (be sure your alcohol is in a metal or glass container,
not plastic, so hot metal won't damage the container, be sure it's on a firm safe
surface so it won't get knocked over, and have a lid handy. Should it catch fire,
don't panic. Just drop the lid on the jar. ) It cools the gold more gently than
does water, so no cracking, yet fast enough to deny the gold a chance to
recrystalize in that brittle structure. If, during later working of the casting,
such as soldering operations, you are again heating the rose gold, you should
then again quench. Don't ever allow it to slowly air cool, if you can help it,
and your brittleness and cracking problems should go away. Be aware too, that one
danger is that if you work the original casting without annealing, even if it
doesn't appear to fail, you might form micro cracks in small hardened areas of
what may otherwise appear to be a reasonably soft casting. Those cracks don't
then heal if later annealed, but can then open up at a later time. So simply be
sure that you never take the chance of forming such micro cracks, by being sure
that any time you work the metal, it's properly annealed and quenched. If you're
working on a piece that already has stones set or otherwise cannot be quenched,
you may be able to avoid most of the problem by chilling the ring quickly with
compressed air, instead of quenching, but this is likely less reliable.
As to your casting defects, examine the usual suspects of spruing and burnout.
Be sure your melting flame is only slightly reducing, not extremely so, (molten
copper can dissolve some gasses, notably hydrogen, which can lead to annoying
porosity). Use enough flux when melting to keep the metal clean, and be sure not
to overheat the metal when melting. Some rose gold casting alloys have less in
the way of deoxidizers than normal yellow golds, as the deoxidizers can tend to
reduce the red color, so you have to be more careful in how you handle it. And
you may notice that some rose golds tend to melt suddenly, with less of a "slushy"
stage. These alloys, when cast, also solidify more suddenly, which makes proper
sprueing all the more important. If you feel this may be part of the problem, one
thing you may try is to increase the flask temp a hundred degrees or so, then
when getting ready to cast, pull the flask out of the oven a couple minutes
earlier, setting it sprue hole down on an insulating board. That allows the back
end and outer surface of the flask to start chilling, but the center core of the
flask will not loose much heat. When you then cast it, you've set up a
temperature gradient between the center of the flask, where the sprue and button
are, and the outer portion of the flask, into which the models extend. That will
help to increase the degree to which metal solidification occurs progressively
from the end of the model towards the sprue and button, and this may help reduce
shrinkage porosity and sprue related problems. (that bit is true for any aloy,
not just rose golds)
Hope this helps.
Peter Rowe
Sarit Wolfus
Your enlightening replies are always a pleasure to read!
Does the same procedure apply to 14k red gold as well? To working with
red gold sheets?
Sarit.
http://sarit-jewelry.com
Heinrich Butschal
> On Tue, 30 Aug 2005 18:10:05 -0700, in =1C=08=F5 "redsmith-israel" <fil=
ig...@walla.com>
> wrote:
>=20
>=20
>>>my 18k red gold casting (lost wax) are allmost allways has defects,its=
>>>very fragile and slightly crisp ,im casting an 18k yellow green and
>>>white gold,and im using a vibrating-vacuum machine and an electric
>>>centrifuge for my casts.most of the time without any particular
>>>problems,except to rarely a very little porous on small areas but not
>>>allways;(. my casting process are in the same manner for all the above=
>>>gold alloys,but only in the red or reddish 18k gold i have this annoin=
g
>>>problem of faglility.
>>>i will appreciate any help with this one.
>>>
>=20
>=20
> Rose golds can cause problems when allowed to cool slowly, as do most c=
astings
> before being quenched. The problem is caused by the ability of a gold/=
copper
> alloy to form an alternate crystal structure, which differs from the u=
sual
> structure of the metals. This structure forms generally at temperature=
s below
> about 800 F, and is highly brittle and unworkable. The problem is esp=
ecially
> noticable with 18K rose golds containing only copper and gold, which ca=
n be made
> so brittle by this problem as to actually shatter if dropped on the flo=
or. There
> are two general cures. One is to use an alloy which still contains eno=
ugh silver,
> in addition to the gold and copper. to avoid most of this formation. B=
ut the
> other is simply properly annealing the metal after casting. Assume tha=
t the raw
> casting is hard and brittle. Before any working is done, anneal by hea=
ting to a
> dark red (around 900F). Allow the red glow to just barely disappear an=
d then
> quench. And here's the trick. If you quench in water, you run the ris=
k of
> sometimes cracking the metal. So instead, quench it in alcohol. Be c=
areful not
> to set the alcohol aflame with your annealing torch, and plunge the hot=
gold into
> the alcohol quickly, so it's immediately totally immersed. Done that w=
ay, the
> alcohol will not ignite. (be sure your alcohol is in a metal or glass =
container,
> not plastic, so hot metal won't damage the container, be sure it's on a=
firm safe
> surface so it won't get knocked over, and have a lid handy. Should it =
catch fire,
> don't panic. Just drop the lid on the jar. ) It cools the gold more g=
ently than
> does water, so no cracking, yet fast enough to deny the gold a chance t=
o
> recrystalize in that brittle structure. If, during later working of t=
he casting,
> such as soldering operations, you are again heating the rose gold, you=
should
> then again quench. Don't ever allow it to slowly air cool, if you can =
help it,
> and your brittleness and cracking problems should go away. Be aware to=
o, that one
> danger is that if you work the original casting without annealing, even=
if it
> doesn't appear to fail, you might form micro cracks in small hardened a=
reas of
> what may otherwise appear to be a reasonably soft casting. Those crack=
s don't
> then heal if later annealed, but can then open up at a later time. So =
simply be
> sure that you never take the chance of forming such micro cracks, by be=
ing sure
> that any time you work the metal, it's properly annealed and quenched. =
If you're
> working on a piece that already has stones set or otherwise cannot be q=
uenched,
> you may be able to avoid most of the problem by chilling the ring quick=
ly with
> compressed air, instead of quenching, but this is likely less reliable.=
>=20
> As to your casting defects, examine the usual suspects of spruing and =
burnout.
> Be sure your melting flame is only slightly reducing, not extremely so,=
(molten
> copper can dissolve some gasses, notably hydrogen, which can lead to an=
noying
> porosity). Use enough flux when melting to keep the metal clean, and b=
e sure not
> to overheat the metal when melting. Some rose gold casting alloys have=
less in
> the way of deoxidizers than normal yellow golds, as the deoxidizers can=
tend to
> reduce the red color, so you have to be more careful in how you handle =
it. And
> you may notice that some rose golds tend to melt suddenly, with less of=
a "slushy"
> stage. These alloys, when cast, also solidify more suddenly, which mak=
es proper
> sprueing all the more important. If you feel this may be part of the p=
roblem, one
> thing you may try is to increase the flask temp a hundred degrees or so=
, then
> when getting ready to cast, pull the flask out of the oven a couple min=
utes
> earlier, setting it sprue hole down on an insulating board. That allow=
s the back
> end and outer surface of the flask to start chilling, but the center co=
re of the
> flask will not loose much heat. When you then cast it, you've set up a=
> temperature gradient between the center of the flask, where the sprue a=
nd button
> are, and the outer portion of the flask, into which the models extend. =
That will
> help to increase the degree to which metal solidification occurs progre=
ssively
> from the end of the model towards the sprue and button, and this may he=
lp reduce
> shrinkage porosity and sprue related problems. (that bit is true for =
any aloy,
> not just rose golds)
>=20
> Hope this helps.
>=20
> Peter Rowe
Hallo Peter,
You gave a perfect description. :-)
Only some of my remarks:
My father had alway a box with alkohol at his working bench, to cool all =
his=20
soldered items. First i found its a bad idea, for yellow gold items get=20
completey red when they where thrown hot into alkohol. I thought it cause=
s=20
more work to polish them as if they are put in sulfur acid (so they get p=
ale=20
yellow) - however in the meantime I use also alkohol for standard cooling=
=20
after soldering. Its very practic and the the items don=B4t suck any acid=
if=20
there are small cleaves.
Since that time I have also less problems with brittle alloys.
The other thing is, that an alloy of 75% weight percent gold and 25% weig=
ht=20
percent copper might result in a perfect eutectic alloy of 50% percent go=
ld=20
atoms and 50% copper atoms.
This crystal is hard and brittle if the crystals are grown big, so it wou=
ld be=20
a good idea to add some zink in form of brass and some special=20
cristallisazion kernels and/ore some other alloy additives like AC 9.105 =
to=20
reduce the risk to get big cristals by casting process.
I think Hafner in Germany developed a powder of Iridium/titan wich is mix=
ed=20
into the wax.
When the wax is burned out a small amount of it is staying in the flask a=
nd=20
will be mixed into the alloy during the casting process.
I have had good results wiht the following process:
First I take a very thin sheet of brass. Then I measure the time until my=
=20
rhodium bath will secrete a visible white layer on it.
For my "fine grain additive sheet" I divide this time by 5 and put the sh=
eet=20
exactly this time into the bath (mostly 7 to 10 seconds).
So I habe a thin brass sheet (0,05mm) with approximately 50-100 atomic la=
yers=20
of rhodium.
Then I roll a small part of it (1 square cm per 200 grams of Gold) and p=
ush=20
it (1 to 2 minutes before casting)into the melted gold, it will melt=20
immediatly and destroy the layers of rhodium to small units of some hundr=
ed=20
atoms of rhodium.
This units don=B4t melt and act as cristalisation units.
So the grain gets much finer and the gold get more smooth and ductile.
This works with all gold alloys.
Mit freundlichem Gru=DF,
Heinrich Butschal
--=20
Aktuelle News =FCber Schmuck http://www.schmuck-boerse.com/blog
Historischer Schmuck und ber=FChmte Juwelen http://www.royal-magazin.de
Schmuck nach Ma=DF http://www.meister-atelier.de
Firmengeschenke http://www.schmuckfabrik.de
redsmith-israel
what can i say !!? you have stunt me with this one!!!
thank you very much,after reading your reply many cloudy things become
clear,as you say "Don't ever allow it to slowly air cool" this was
exactly the problem,(can i use the alcohol method also for 18k white
gold ?,now im cooling it in the open air with a satisfying results).
Regards
Redsmith.
Peter W.. Rowe,
wrote:
White golds do not form the same type of structural anomoly that rose golds do,
so you don't have that specific danger. Some white golds anneal better with a
quench, and others anneal just fine with air cooling. Stress cracking CAN be a
problem with some white golds if water quenched from too hot, so in those cases,
the alcohol quench is a good way to deal with it.
By the way, if you can find a phase diagram for gold/copper alloys, you can
clearly see on the diagram, two smallish zones, one located at around the 18K
proportion, the other lower down a bit, that look a little like a couple gothic
arches in the midst of the diagram (if 100 percent gold is at the right side of
the diagram, these two zones are close to the right side). Those two areas
indicate the metal/alloy proportions and temperature ranges at which this
alternative crystal structure is stable and can form. These are the temp ranges
you then need to avoid with rose golds, and chilling the metal quickly through
those ranges then denies it the chance to reform in that structure while passing
through those temperature ranges. The structures involved are called ordered
array structres where the gold and copper atoms segregate out into a multilayered
affair quite different from the usual face centered cubic atomic arrangement of
the usual crystal structure
Hope that helps.
Peter Rowe
Peter W.. Rowe,
Yes, on both counts. 14K rose gold tends to be less prone to forming that
annoying brittle structure, in part because many 14K rose alloys are not only
copper and gold. And 14K doesn't correspond as closely to the gold/copper
ratios at which these structures most easily form. But it CAN still be a
problem, and quenching when annealing is also the cure if it does. As with
18K, the main thing is to be aware that if the metal has formed this structure
(which will make it very hard to work, as well as brittle), you can salvage the
situation by annealing and quencing, IF you've not done things to the metal that
have caused it to crack already, since of course annealing does not heal cracks
that have already formed. Rolled sheet and drawn wire are less prone to
cracking because their smaller grain size is simply stronger. But it can still
be a problem, and they are handled the same way.
Peter
redsmith-israel
after the casting process is done,is it a good idea to quench the hole
flask in alcohol ? ,let it cool to room temprature or cooling it down
slowly in the kiln before breaking down the investment and start
working with the precious ?.
thank you in advanced,
Peter W.. Rowe,
wrote:
Please do NOT quench the whole flask in alcohol!!! Very poor idea. Unlike
simply quenching a single casting or two in a jar of alcohol, I can imagine
several ways in which quenching a whole flask could create several types of
hazards
No, just treat the flask the same as you'd treat any other casting flask. Let
it cool enough so the button no longer glows at all (ie, below about 900
degrees, or lower if you like. then quench in water. The investment itself is
protecting the enclosed casting during the quenching process, so it's not as
suddenly cooled.
Or, if you like, don't quench the flask at all, but let it air cool. The
investment is then best removed with water jet equipment. Probably, if you
completely air cool the flask, the rose gold will then be very brittle, so do
not remove the investment by hammering it out, which could crack the castings.
So do this if you have water jet devesting equipment. Then, anneal the castings
and THEN quench in alcohol. I'd recommend annealing and alcohol quenching the
castings even if quenched in water to remove the investment, just to be sure
it's properly annealed before you start to work it, but you can easily test a
bit of the sprue material after removing the investment, and decide then, if the
metal seems hard or not. If you quenched from above about 800 degrees, the
casting won't have hardened.
The whole thing about quenching in alcohol is that alcohol forms a vapor layer
around the hot metal much more easily than does water, absorbing less heat from
the metal as it does so. As such, it cools the metal more slowly/gently, the
whole reason for it's use, so as to avoid stress cracking from too rapid a
quench. When you quench a cast flask, the water has to make it through hot
investment before it reaches the metal, so the metal is being cooled by steam
long before it is contacted by liquid water, and when the liquid water does
reach the metal, it's likely quite well heated already, which also lessens the
heat shock. If you quench the casting when it's still very hot, of course, you
can still crack it, but if you let the sprue button cool to the point where it's
no longer glowing in dim light, you should be safe enough.
Peter
redsmith-israel
Thank you so much .
i think i have got the idea about the alcohol quenching benefits.i have
try it and the results are sensed, i didnt understand the annealing
process,if i quench it in alcohol before working with the cast, is the
metal is not properly annealed ? how do i need to anneal the metal
before quenching in alcohol ? heat and let it it cool on air, reheat
and quenche ? or doing it by heating the metal and then quench in
alcohol before it go below the 800 F ? is it all about rose gold and
the crystal structure that happened in about 800 F and passing threw it
by conventional annealing and quenching ?
(hope i didnt mess up anything)
regards
Redsmith
Peter W.. Rowe,
Well, I'm frankly having a little trouble understanding just what you're not
clear on, so here's the simple description again.
Cast your flasks in the same way you would normally cast any other gold, which
means after casting, wait until the sprue button has cooled enough that it does
not glow red, then quench in water to remove the investment.
clean the investment off the castings, and pickle them clean. If you like, saw
them off the sprues.
At this point, depending on the temperature of the castings when you quenched,
them to remove the investment, they MIGHT be workable and soft, or they MIGHT
be hardened. Do not test too much, since if the metal is hard, you can crack
it. So to ensure that the metal is soft and workable, we now anneal the
castings properly.
Anneal the castings by dipping them in a slurry of alcohol and boric acid, in
order to protect the metal from fire scale and oxidation while annealing. Burn
off the alcohol leaving a boric acid coating. (this is all normal procedure,
nothing unusual yet). Heat the castings until they just barely glow red, which
will be around 900 degrees F. Allow them to cool slightly until they no longer
glow, and then quench in alcohol. When quenched, and cool, you are then ready
to pickle the castings again (to clean off the boric acid fire coat), and you
should now have a nice soft workable casting.
If you need to solder or otherwise heat the work while turning the casting into
finished jewelry, just remember to quench it in alcohol in the same way, rather
than letting it air cool.
I hope this was clearer.
Peter Rowe