Hi Everyone, I have been lurking for a few years and have thoroughly
enjoyed learning from all of you. Your generosity to share knowledge
and experiences so others can learn and experiment is amazing. THANK
YOU.
Now I need your help with a project. My piece will need to have
tension/spring like money clips. I know that money clips get this way
by tempering in a kiln. What I haven’t been able to find out is… at
what temperature, for how long, does it depend on the size and gauge
of the silver? If I decide to do something similar in gold is it the
same process? I will thank you in advance for your wisdom!
I need your help with a project. My piece will need to have
tension/spring like money clips. I know that money clips get this
way by tempering in a kiln.
Tempering is a heat treatment applied to ferrous products. I am sure
you can not use this term to sterling silver.
Just finished a sterling butter knife, and thought it seemed too soft
in its annealed state, so I hardened it, heating to low red,
air-cooling. Not much improvement but some, I guess. Do you routinely
harden sterling work before letting it go to the client?
Only certain, specially formulated, SSs can be hardened by heat
treatment. Most can only be annealed, or softened. All can be work
hardened though, including gold, platinum, etc. Whenever a metal is
deformed, it gets a little harder. Almost everybody has exploited
this property in order to break a wire, or small bar, in the absence
of a suitable cutting tool. You bend it one way, then the other, and
continue bending back and forth until it breaks. Every time you bend
it, it gets a little harder, until it gets so hard that it can no
longer bend without breaking.
This process is called “work hardening”; the bending deforms the
metal which gets a little harder. You don’t have to bend it; you can
twist, hammer, stretch, compress, or deform it in any way you like.
For your money clips you should design the work hardening in from
the beginning. If your metal comes in the annealed (or softened)
state, the easiest way to work harden it is to roll it thinner in a
rolling mill. Even easier is to buy it in the fully hard state to
begin with. By the way, heating a metal to a certain point (usually
around 600C for silver) anneals it and makes it soft again, so avoid
soldering after hardening.
If the metal you want to use has been formulated to be heat treated,
then the suppliers should have full details of the process.
Just finished a sterling butter knife, and thought it seemed too
soft in its annealed state, so I hardened it, heating to low red,
air-cooling. Not much improvement but some, I guess. Do you
routinely harden sterling work before letting it go to the client?
To heat treat (harden) standard sterling you need to solution anneal
it by heating to 1382F and immediately quench followed by a
precipitation hardening (aging) step of heating to 572 F for 30 min.
The problem is silver solders melt at lower temps than 1382 F so you
will not get the full benefit from this process if you have any
solder joints in the work as you will not be able to heat to a high
enough temperature. So if your work is soldered anneal at as high a
temperature as you can and then age the work at 572 F and you will
get some but not the maximum hardness increase.
Joan and Mark- To harden silver your best bet is to work harden it.
This can be done by a variety of means. Hammering, burnishing and
tumbling. Heating silver to red hot and cooling it will anneal it,
thus making it softer. When I’ve had to make money clips, I did all
of my soldering first while it’s flat, then at the last bent it so
that my clip has spring were it was bent. The act of bending it work
hardens it. I also hammer it lightly at the bend to assure extra
spring.
If you have a finished piece that hammer marks would spoil the looks
of, then burnishing or tumbling will work nicely.
Silver can be easily hardened through work-hardening (although it
will never end up as hard as steel, of course). Work-hardening
happens basically two ways:
Manipulating the silver itself so that an area loses its
flexibility (think of bending a strip back and forth until it snaps).
The downside of this is that if you do it TOO much it becomes a bit
weakened and brittle.
Hammering or impacting the silver with steel or a metal harder
than itself. This compacts the lattice structure of the metal (and if
done properly on thin enough metal, the entire structure) and hardens
it. This is the basis of forging techniques, which not only shape the
metal but also harden it. That’s why if you’re hammering away on a
piece of metal you need to stop and anneal periodically.
You can do a good degree of work hardening of relatively thin pieces
in a rotary tumbler with steel shot (use water and dish soap, or
liquid burnishing compound with the steel). Don’t leave them in for
more than about 45 minutes before changing the water or you’ll get a
buildup of “black gunk” that’s a pain to remove. All told, about an
hour is going to get you the maximum work hardening in the tumbler,
anyway (as long as you have a half-decent tumbler that has plenty of
room to move the shot and the piece around. Otherwise, you might
need more time.
Hope this helps!
Karen Goeller
No Limitations Designs
Hand-made, one-of-a-kind jewelry www.nolimitations.com
Only certain, specially formulated, SSs can be hardened by heat
treatment.
Nope, standard sterling (silver,copper) is definitely heat treatable
by precipitation also known as aging. Gold alloys with enough copper
in them also can be hardened by heat treatment.
James Binnion @James_Binnion
James Binnion Metal Arts
Much has been posted on the generic parts of “tempering” sterling
silver, along with the obvious that you can’t “temper” sterling…
As to the real question asked - that of making knives - well, that’s
different. People may have noticed that sterling knives in
traditional sets have steel blades. That’s the best solution mostly
because silver makes a horrible knife blade - even for peanut
butter, which will tarnish it, too. If someone just has to make a
silver blade, do what the knifemakers do. Make your blade and then
mount it like a stone. People who make custom knives and people who
sell blades -http://www.texasknife.com/vcom is one of the oldest and
best for “normal” stuff - make the blade complete and then fit it
with a handle or whatever is to be done. In sterling I would (and
have) run the blade through the rolling mill a couple of times,
which is better and much neater than hammering, and then shape it
into a blade and mount it, without ever heating it again. That’s
about the best way to get any kind of blade with a uniform hardness,
good grain, etc. But using steel blades on silver handles will give
the best knife, in a utilitarian sense…
Sterling is not something that you can temper. Tempering is a term
used for steel.
However, you can harden regular sterling. To harden either flatware
or money clips, run them in stainless steel shot for about 8 hours.
If the finish is a bit orange-peel like, you can smooth it with a bit
more tumbling. Run the hardened sterling for three or four hours in a
fine abrasive media in a vibratory tumbler, Then return to the rotary
tumbler for about 30 minutes. If you want a bright shiny rouge-like
finish, do a final tumbling pass in a vibratory tumbler with dry
media charged with simichrome for 24 hours.
This all presumes that you have tumblers large enough to permit the
pieces to move freely in the tumblers.
When running money clips, I have them bent to about 90 degrees when
tumbling. This polishes the inside. The final closing adds even more
hardness.
Nope, standard sterling (silver,copper) is definitely heat
treatable by precipitation also known as aging. Gold alloys with
enough copper in them also can be hardened by heat treatment.
Tell me more. I’m aware that certain gold alloys are age hardenable,
but didn’t know about standard sterling silver. How effective is it
compared to work hardening?
Tell me more. I'm aware that certain gold alloys are age
hardenable, but didn't know about standard sterling silver. How
effective is it compared to work hardening?
It is called precipitation or age hardening. Standard sterling is
what is called a two phase alloy, This is because silver cannot hold
more than about 2% copper in solution at room temperature and the
alloy has 7.5% copper in it. So there are two separate structures in
it, a silver rich phase that contains about 2% copper and a copper
rich phase that contains about 2% silver. If you were to carefully
polish and etch the surface of the sterling you can actually see the
two phase structure with an optical microscope. If you raise the
temperature of the silver it can hold more copper in solution, when
you get to 1382 F it can hold 7.5% copper. If you rapidly quench it
from this temperature you lock the coper into solution and this
makes the alloy very soft as there is only on type of crystal in the
matrix and that allows for more ductility. If you then raise the
temperature to 572 F the copper will precipitate out of solution as
very finely distributed pure copper at the grain boundaries of the
sterling matrix. This acts like throwing a handful of sand into a
ball bearing. The crystals now have a much harder time sliding across
each other resulting in an increased hardness. Sterling in its
annealed state is about 60 HV hardness when precipitation hardened it
can reach 125 HV For comparison a piece of sterling reduced in
thickness 70% will be about 145 HV, about the only time we will see
sterling that hard is in hard drawn wire. It would be difficult to
put that much work into it otherwise with out cracking it.
Jim
James Binnion @James_Binnion
James Binnion Metal Arts