Metalergists I am wondering if it is better to work harden or heat
harden jewelry pieces or both. Can you describe the best processes
for doing both.
Thanks so much
You cannot use heat to harden gold or silver (and I would think
ditto with platinum). These metals will work harden only.
John Dach
I have tried heat hardening fine silver (after forming and then
soldering on a jump ring), by heating to annealing temperature and
then quenching. No luck but then again I’m not sure exactly what
temperature the fine silver had reached accept that it was close to
melt down. In the end I had to reform my piece and rework to harden.
I can solve this in future by changing the order of work.
Judy P
You cannot use heat to harden gold or silver (and I would think ditto with platinum). These metals will work harden only.
That’s not actually always true, John. While work hardening gives a
better, stronger, result, some gold and silver and platinum alloys
CAN be made harder via heat treatments. Gold and silver alloys
(sterling, yellow, white, and rose golds, etc) can be hardened by a
process called precipitation or age hardening. This is not generally
the equal of work hardeing, but it can be better than nothing if the
alternative is fully annealed metal. Heating to about 700 F with
these metals, which is below the annealing temperatures, causes
copper to come out of solution and recrystalize as copper rich
crystals along grain boundaries in the metal. That makes those grain
boundaries much less able to stretch and deform, so the metal gets
harder. It gains some strength, but not as much as proper work
hardening would give. Some alloys, the rose golds in particular and
few white golds, can sometimes be made even harder than usually
attained by work hardening. In all these cases, though the effect is
harder metal, more resistant to dents, bending, and scratching, it
doesn’t usually gain as much strength as is gained by work hardening,
and sometimes can be more brittle too. As to platinum, normal
platinum alloys don’t harden this way, but the late Steve Kretchmer
came up with a vew versions of exotic platinum alloys, which he
developed for his tension setting, which were heat treated to
harden. Anneal and quench, and it’s soft. Anneal and allow to slowly
air cool, and it’s hard and stiff. Neat stuff. Hoover and Strong
sells the resulting SK platinum alloys, and several other producers
have come up with related heat treat platinum alloys.
However, back to your comment as it relates to the original posters
question.
Many people are familiar with the way steel handles, being
wonderfully variable in hardness and springiness by means of
hardening and tempering heat treat operations. These of course are
pretty much unique to steel alloys, and part of what makes steel such
an essential part of human industry and history.
The precious metals as a basic rule, harden only by work hardening,
and only soften when heated to annealing temps. Most do not get
harder or softer by a significant degree based on whether one
quenches or not.
But those are the basic rules. As I said at the top, there are major
exceptions that can be exploited. Sterling silver can be heat treated
to harden it to a significant degree (Argentium probably cannot, as
it doesn’t have much copper in it.) Green golds, or golds with mostly
silver in them, also won’t harden. But alloys with significant copper
in them, well, those are the ones with that ability to age harden.
And for the OP, age hardening operations with silver or gold alloys
are not the usual, normal, way these metals are handled. Age
hardening can be a bit tricky, and has it’s own drawbacks. Each alloy
will have it’s own best temperatures and times for the most effective
results. And it’s seldom as controllable as one would be used to
seeing with steel. You cannot, for example, harden and then temper to
a full range of intermediate hardness levels. if you age harden it,
you have what you have, unless you then fully anneal it again. Not
much in between. And often, the hardening is countered to a degree by
increased brittleness, rather than the toughness one would get with
work hardening the metal. If you take a piece of 18K red gold (just
gold and copper), and fully age harden it, what you end up with is
metal with a rather unique “ordered array” structure of layers of
alternating copper and gold atoms. the result is very hard. And it’s
brittle as glass. don’t drop a ring made of this. It will shatter
when it hits the floor… If you’re lucky, you anneal it before you
develop cracks in it…
Hope that helps.
Peter Rowe
John,
You cannot use heat to harden gold or silver (and I would think ditto with platinum). These metals will work harden only.
Not sure about Pt, there are some exotic alloys out there from mr.
k. Regular gold and silver alloys are going to leave you rather
frustrated. Argentium will heat harden, not a lot lot but better than
nothing.
jeffD
Demand Designs
Analog/Digital Modelling & Goldsmithing
http://www.gmavt.net/~jdemand
You cannot use heat to harden gold or silver (and I would think ditto with platinum). These metals will work harden only.
Hmmmm… Interesting… I did it yesterday. Heat hardened a sterling
money clip. Seemed to work.
I have tried heat hardening fine silver (after forming and then soldering on a jump ring), by heating to annealing temperature and then quenching. No luck
There seem to be many jewelers, especially the “self taught” and the
beginners, who are confused about how precious metals can be
hardened. Everyone is at least vaguely familiar with how steel is
heat treated and hardened, and some people just assume all metals can
be treated this way. (they cannot). And it gets more just assume all
metals can be treated this way. (they cannot). And it gets more
confusing when people like me, or others, point out that SOME of our
jewelry metals can actually be heat treated. But it’s important to
know that this is more the exception, than the rule, and the process
is quite different from what goes on with steel.
In the case of silver, with sterling silver, you take advantage of
the fact that copper is not completely soluable in silver, or vice
versa. So careful heating, below the annealing temperatures, allows a
sort of seperation to take place, with copper moving to the crystal
boundaries between the silver crystals (actually it’s crystals of
mostly copper with a tad of silver, and crystals of mostly silver
with a tad of remaining copper, but that’s being picky), and this
structural change makes the metal harder. Not as much harder as can
be attained by work hardening, but enough so sometimes it’s worth
doing.
But it’s the interaction between the silver and the copper in the
alloy that does this. You need both to be there.
In the case of fine silver, there is nothing there but silver. In
that case, the only possible way to harden it is with cold working,
to work hardening. There are no heating processes which will increase
the hardness of fine silver.
This is true, by the way, of all the pure metals, including gold,
platinum, silver, copper, and yes, even iron. Pure iron cannot be
heat treated and hardened. You can anneal it, or work harden it, but
no heat hardening or tempering. For that to happen, you need an
alloy. In the case of iron, it’s an alloy of iron and carbon, rather
than an alloy of iron and another metal, but again, it’s the
structural interactions between the two different componants that
make the heat treatments possible.
As well, just because you may have an alloy of two metals, does not
mean you can get heat treatability out of it. In the case of silver
and gold, both of them can be hardened if they have enough copper
mixed into their alloys, and in both cases, it’s because copper’s
ability to fully dissolve into the other metal varies with the
temprature. Molten, it’s fully soluable, but in the solid form,
niether gold or silver are completely soluable in copper, or copper
in them, thus the ability to induce useful structural changes.
But gold and silver themselves, are completely soluable in each
other. So no matter what ratio of gold and silver you have, that
alloy will not be able to heat treat for increased hardness. You can
only anneal them, or work harden them. They won’t harden if it’s just
an alloy of gold and silver, without copper or other elements.
Hope that helps.
Peter Rowe
You cannot use heat to harden gold or silver (and I would think ditto with platinum). These metals will work harden only.
Except Argentium. That is the only silver I know of that will
actually heat harden.
Michele
Hi John,
You cannot use heat to harden gold or silver (and I would think ditto with platinum). These metals will work harden only.
Actually you can use some heat treating techniques (precipitation
hardening, or ordering) to harden some alloys of silver and gold.
Sterling silver precipitation hardens nicely and gold alloys with
enough copper or palladium will order and can get quite hard from
this. There are others like Argentium silver which will also
precipitation harden or order. Heat treatable platinum alloys are
available from at least 2 vendors (Hoover and Strong, Imperial
Smelting and Refining)
Regards,
Jim
James Binnion
James Binnion Metal Arts
Except Argentium. That is the only silver I know of that will actually heat harden.
Standard sterling silver does the same thing. Fine silver is the one
that will not harden with suitable heat treatment.
Peter Rowe
Except Argentium. That is the only silver I know of that will actually heat harden.
Actually you can harden standard sterling (92.5 silver, 7.5 copper)
the same way you harden Argentium and acheive a very similar result.
The Argentium folks have just been rather good at marketing the
process. The differences between how much hardness you can achieve
between standard sterling and Argentium using the same temperatures
and times is fairly minimal.
Jim
James Binnion
James Binnion Metal Arts
Except Argentium. That is the only silver I know of that will actually heat harden.
But it is not just silver… I really liked Peter’s explanation…
Thanks Peter, I have passed it on to a few other folks.
John Dach
Hi Jim,
Does fine silver harden? I was considering raising a vessel with
fine silver and chasing it.
Jennifer Friedman
Does fine silver harden? I was considering raising a vessel with fine silver and chasing it.
Yes it does but it is by work hardening only. So you must plan your
annealing and soldering so that you will be able to work the vessel
sufficiently after final annealing and soldering to leave it in a
hardened state.
James Binnion
James Binnion Metal Arts
Peter,
thank you for your (always) complete and concise answers. I was
pretty sure fine silver can only be work hardened, but it never gets
as hard sterling silver when work hardening.
Jennifer Friedman
Ventura, CA
thank you for your (always) complete and concise answers.
You’re welcome, of course. But be aware of a couple things, please.
I’m only human. I make mistakes too. Just because I tend to type
long posts doesn’t mean I’m more likely to be right. Almost 40 years
of experience in this stuff, an MFA, and a few other credentials may
help the odds, but they’re no guarantee. Sometimes I’m just plain
wrong, and other times, just too stubborn to admit it till too late.
And just because some people think I’m often right, does not mean any
one single post of mine is right, or complete. Like anything on the
internet, be cautious of unverified info. In the case of my posts,
be aware that I only occasionally reach for the bookshelf (or google)
to verify what’s bouncing around my memory. Sometimes that’s
unfortunate. And I really should learn to proofread more. But darn.
My posts are too long to bother proofreading, and spell checkers seem
to sometimes just make it worse… (grin)
By the way, that whole bit about being aware of, and evaluating the
source of has a name. The field is called media literacy.
Interesting. It’s been around a lot longer than the internet, but the
internet and cable news and similar changes in the way we get our
info these days makes it all the more pertinant…
I was pretty sure fine silver can only be work hardened, but it never gets as hard sterling silver when work hardening.
True. Sterling silver doesn’t heat treat to as hard as it does when
work hardened either. Proper heat treating of sterling is
problematic, since for best results, you have to anneal first at
around 1350F for ten or 15 minutes, then quench. That’s hot enough
that some pieces will have significant problems. Fire stain for one,
if you don’t have an atmosphere controlled furnace or take proper
steps to coat the metal. And for another, at that temp, the easier
solder grades might remelt. Doing this gives you the best end result,
which can get sterling silver to about the hardness of a 50 percent
reduction by rolling or drawing. Not bad, but still not full hard.
Skipping that problematic anneal and only heat treating (600F for 39
to 50 minutes) avoids some of the problems, but doesn’t then give you
as much hardening. And either way, precipitation hardening results in
metal that is less workable and can be somewhat brittle, compared to
metal that’s hardened to the same degree via work hardening.
(and those numbers I actually verified, from the Handy and Harmon
Metals Book…)
Peter Rowe
Fine silver requires far more working then sterling. You might take a
piece of fine silver and hammer it to see how far you have to work it
before you get to the potential hardness of sterling. And of course,
it will never really produce the same rigidity and strength that
sterling will simply because it isn’t alloyed with copper. You will
find that you have to work fine well beyond the point that the
addition of.075 of copper will effect the work hardening of sterling.
Definitely play with some fine silver before you invest time and
money into raising a vessel out of pure silver. When I worked at ONC
( http://www.silvercrafters.com/custom.htm ) we never would use fine
sterling for flatware or holloware. It would never produce the
strength that we would want in the tea or coffee services that we
spun (or I handraised after leaving to work on my own) and then
fluted or chased, etc.
What is the reason behind wanting to use fine over sterling, fire
scale from all the annealing, you prefer the whiteness of the
sterling, you feel it will be easier to chase? As far as heat vs.
hammering to harden, heat can be used to harden and temper by
changing the molecular and or chemical structure of differnt metals
where hammering will increase density making sterling harder AND
stronger.
James F. Conley
I do want to say that fine silver has a beautiful color. so am not
saying don’t use it, just be sure to practice so you can be
comfortable with it’s working characteristics when undertaking your
project. That way you will have a better chance of achieving the
results that you want.
Jim
James F. Conley
Proper heat treating of sterling is problematic, since for best results, you have to anneal first at around 1350F for ten or 15 minutes, then quench. That's hot enough that some pieces will have significant problems.
I agree about having problems. It is possible to skip the annealing
under the right circumstances. The requirement for annealing before
heat treatment is generally only followed if the piece has been
substantially work-hardened (usually just some small local
hardening; if the whole piece was work-hardened then why heat treat?)
since any previous soldering with medium solder or above. The purpose
of the annealing before heat treatment is to prevent cracking in the
metal that would result from stresses present by work-hardening that
are released. Some experience and judgement is required, but if the
piece has only moderate to no work-hardening since the last soldering
operation at or near the 1350F mark, then annealing before heat
treatment can be skipped. Since the amount of work-hardening is a
subjective measurement, only experience and experiment can show the
way.
Dan Culver
I agree about having problems. It is possible to skip the annealing under the right circumstances. The requirement for annealing before heat treatment is generally only followed if the piece has been substantially work-hardened (usually just some small local hardening; if the whole piece was work-hardened then why heat treat?) since any previous soldering with medium solder or above. The purpose of the annealing before heat treatment is to prevent cracking in the metal that would result from stresses present by work-hardening that are released.
My understanding of the need to anneal at that unusually high
temperature prior to heat treating, is a bit different. Normally
handled, cooled, annealed, etc, sterling silver is a mix of crystals
with two distinct compositions. One is a silver rich composition with
very little copper, while the other is the eutectic alloy of silver
and copper. That means the bulk of the copper in sterling silver is
in those eutectic crystals. My understanding of the pre-hardening
anneal is that at that high temperature, with subsequent quench, the
composition becomes one of all uniform crystals having roughly the
same percentage of copper, rather than those two distinct forms.
Then, when age hardening, because the copper starts out uniformly
distributed, the end result (caused by copper migrating to the
crystal boundaries) is more uniform, and more of the copper will
have migrated to the crystal boundaries. Age hardening the original
formula moves less of the copper, because the eutectic crystals are
not as unstable as the uniform “sterling” mix, plus the resulting
distribution of copper at grain boundaries is less uniform, giving
inferior results.
That’s what I believe is happening, but this may not be fully
correct. Perhaps Jim Binnion would care to verify or correct my
notions on this. I think he’s the one whose Orchid posts originally
planted those thoughts in my poor ol brain. What I’m not sure of is
whether those seeds grew straight or not… (grin)
So, Jim, how far off am I?
Cheers
Peter Rowe