Hardening sterling silver

I understand it is possible to harden sterling silver by heat treating it
over a prolonged period. I would be grateful for any information on
temperature, time and how hard the treated silver is likely to be. I havea
small kiln (max 1000 centigrade) which I could use. Any other information
regarding hardening (other than work hardening) would be appreciated

Kendall

"Kendall Davies" wrote in message
...
I understand it is possible to harden sterling silver by heat treating it
over a prolonged period. I would be grateful for any information on
temperature, time and how hard the treated silver is likely to be. I havea
small kiln (max 1000 centigrade) which I could use. Any other information
regarding hardening (other than work hardening) would be appreciated

Kendall

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^

To heat harden Sterling Silver heat to 600 deg F. (316 deg C.) for 30 - 50
minutes in a kiln or furnace. Allow to air cool ( do not quench ) before
pickling. The hardness achieved will be 3/4 hard. Rockwell 83.

--

Don Thompson

There is nothing more frightening than active ignorance.
~Goethe

It is a worthy thing to fight for one's freedom;
it is another sight finer to fight for another man's.
~Mark Twain

Don T wrote:
(snip)
To heat harden Sterling Silver heat to 600 deg F. (316 deg C.) for 30 - 50
minutes in a kiln or furnace. Allow to air cool ( do not quench ) before
pickling. The hardness achieved will be 3/4 hard. Rockwell 83.

Which Rockwell scale? I take it not C.
Todd

Thanks Don,
I sort of had that information. I had 600 deg in the back of my mind but I
was thinking in centigrade which was a bit too hot so thanks again for the
information. Would it be better cooled in the kiln, that is left to cool say
over night?

Kendall

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^

To heat harden Sterling Silver heat to 600 deg F. (316 deg C.) for 30 - 50
minutes in a kiln or furnace. Allow to air cool ( do not quench ) before
pickling. The hardness achieved will be 3/4 hard. Rockwell 83.

--

Don Thompson

There is nothing more frightening than active ignorance.
~Goethe

It is a worthy thing to fight for one's freedom;
it is another sight finer to fight for another man's.
~Mark Twain

On Wed, 05 Apr 2006 00:32:48 -0700, in rec.crafts.jewelry "Kendall Davies"
wrote:

I understand it is possible to harden sterling silver by heat treating it
over a prolonged period. I would be grateful for any information on
temperature, time and how hard the treated silver is likely to be. I have a
small kiln (max 1000 centigrade) which I could use. Any other information
regarding hardening (other than work hardening) would be appreciated

Kendall



Before giving process details, it's useful to also understand how heat treating
differs from work hardening. With work hardening, the crystals in the metal are
deformed, eventually leading to a degree of deformation of the crystals that
then resists further deformation. In addition, partly because sterling silver
is a mix of several solid solution crystals with differing proportions ofsilver
and copper, not only do the different crystals deform and harden at somewhat
different rates, but the boundaries between the crystals become stressed and
also deformed. A very significant amount of the hardening that one gets with
work hardening is due to the grain boundaries resisting further deformation and
stretching. Work hardened metal is characterized by greatly deformed crystals,
often flattened by rolling, stretched to almost fiberous shapes by drawing, or
otherwise deforned.

In heat treating, a process called age hardening or precipitation hardening is
used. In this process, no deformation of the crystals is done. Rather, it
depends on the fact that copper and silver are not all that soluable in each
other at temperatures below the melting points. As the crystals initially
solidify, two types of crystals form. One is nearly pure silver. The other is
a "eutectic" alloy of about 71.9% silver, and 28.1% copper. At the melting
point, this proportion of copper and silver presents the lowest melting point
for a mix of these two metals. Below the melting point, however, the
intersoluablity of copper and silver in each other lessens quite a bit (in gold
alloys, the same is true with gold and copper). The copper in these eutectic
crystals makes them much less deformable than the pure silver crystals, and room
temperature, much of the copper remains dissolved in the solid crystals unly
because it's been trapped there by the solidification and cooling of the alloy.
At temperatures above the annealing temps (which varies some depending onthe
time used), the copper redissolves in the silver. If held at a temperature of
600 F, however, for a time, at this temperature the copper is not all that
soluable in the silver, but the temp is high enough that the copper can become a
bit mobile within the crystal structure. What happens is that at this
temperature, the copper comes out of solution and recrystalizes in copperrich
crystals along the grain boundaries forming a binary structure. The effect is
to make the grain boundaries, which no have to contend with these different
copper rich crystals along them, much less able to deform and stretch. The
result is a significant hardening of the alloy. It differs from work hardened
silver in that though harder and springier, it's not quite as strong, being more
easily fractured. For maximum hardness, an initial over anneaing step can be
used. Annealing the silver at a high enough temperature as to cause grain
growth, rather than just stress relief and crystal reformation, gives the
silver an initial structure of much larger, but fewer, crystals. The effect of
that is to lessen the surface area of the crystal boundaries. So now with
precipitation hardening, the copper migrates to those fewer boundaries resulting
in a high concentration of the copper crystals along the grain boundaries, and
this gives a higher degree of hardness. It can impact the strength of the alloy
to do this, however.

Handy and Harmon describe the process in their "Handy Book of Precious Metals"
as follows:

First heating to 1375-1400F (745-760C) for 15 minutes, then quenching rapidly in
cold water. [[ This results in a structure with larger crystals, and themost
uniform solid solution of the copper in the silver. This is fully annealed, but
with that degree of grain growth which normally one might wish to avoid.]] Now
the silver is heated to 600F (316C) for 30 to 50 minutes, then air cooled. The
resulting hardness is roughly equivalent to what can be obtained by cold working
to a 50% reduction (rolling or drawing, etc.)

It should be assumed that normal precautions against the formation of fire
scale/fire stain will be followed, especially with the initial annealing step.

Remember that hardness obtained by heat treating is not quite the same asthat
obtained by work hardening, in terms of the achievable hardness, and the
resulting strength of the metal. The grain growth caused by the initial anneal,
if used, may also have some affect on finishing operations.

Hope that helps.

Peter Rowe

Thanks for the answers, very helpful as usual.

Best regards - Kendall

On or around Thu, 06 Apr 2006 02:02:18 GMT, a clone named "Peter W..
Rowe," attempted to communicate:

On Wed, 05 Apr 2006 00:32:48 -0700, in rec.crafts.jewelry "Kendall Davies"
wrote:

I understand it is possible to harden sterling silver by heat treatingit
over a prolonged period. I would be grateful for any information on
temperature, time and how hard the treated silver is likely to be. I have a
small kiln (max 1000 centigrade) which I could use. Any other information
regarding hardening (other than work hardening) would be appreciated

Kendall



Before giving process details, it's useful to also understand how heat treating
differs from work hardening. With work hardening, the crystals in the metal are
deformed, eventually leading to a degree of deformation of the crystals that
then resists further deformation. In addition, partly because sterling silver
is a mix of several solid solution crystals with differing proportions of silver
and copper, not only do the different crystals deform and harden at somewhat
different rates, but the boundaries between the crystals become stressedand
also deformed. A very significant amount of the hardening that one getswith
work hardening is due to the grain boundaries resisting further deformation and
stretching. Work hardened metal is characterized by greatly deformed crystals,
often flattened by rolling, stretched to almost fiberous shapes by drawing, or
otherwise deforned.

In heat treating, a process called age hardening or precipitation hardening is
used. In this process, no deformation of the crystals is done. Rather,it
depends on the fact that copper and silver are not all that soluable in each
other at temperatures below the melting points. As the crystals initially
solidify, two types of crystals form. One is nearly pure silver. The other is
a "eutectic" alloy of about 71.9% silver, and 28.1% copper. At the melting
point, this proportion of copper and silver presents the lowest melting point
for a mix of these two metals. Below the melting point, however, the
intersoluablity of copper and silver in each other lessens quite a bit (in gold
alloys, the same is true with gold and copper). The copper in these eutectic
crystals makes them much less deformable than the pure silver crystals, and room
temperature, much of the copper remains dissolved in the solid crystals unly
because it's been trapped there by the solidification and cooling of thealloy.
At temperatures above the annealing temps (which varies some depending on the
time used), the copper redissolves in the silver. If held at a temperature of
600 F, however, for a time, at this temperature the copper is not all that
soluable in the silver, but the temp is high enough that the copper can become a
bit mobile within the crystal structure. What happens is that at this
temperature, the copper comes out of solution and recrystalizes in copper rich
crystals along the grain boundaries forming a binary structure. The effect is
to make the grain boundaries, which no have to contend with these different
copper rich crystals along them, much less able to deform and stretch. The
result is a significant hardening of the alloy. It differs from work hardened
silver in that though harder and springier, it's not quite as strong, being more
easily fractured. For maximum hardness, an initial over anneaing stepcan be
used. Annealing the silver at a high enough temperature as to cause grain
growth, rather than just stress relief and crystal reformation, gives the
silver an initial structure of much larger, but fewer, crystals. The effect of
that is to lessen the surface area of the crystal boundaries. So now with
precipitation hardening, the copper migrates to those fewer boundaries resulting
in a high concentration of the copper crystals along the grain boundaries, and
this gives a higher degree of hardness. It can impact the strength of the alloy
to do this, however.

Handy and Harmon describe the process in their "Handy Book of Precious Metals"
as follows:

First heating to 1375-1400F (745-760C) for 15 minutes, then quenching rapidly in
cold water. [[ This results in a structure with larger crystals, and the most
uniform solid solution of the copper in the silver. This is fully annealed, but
with that degree of grain growth which normally one might wish to avoid.]] Now
the silver is heated to 600F (316C) for 30 to 50 minutes, then air cooled. The
resulting hardness is roughly equivalent to what can be obtained by coldworking
to a 50% reduction (rolling or drawing, etc.)

It should be assumed that normal precautions against the formation of fire
scale/fire stain will be followed, especially with the initial annealingstep.

Remember that hardness obtained by heat treating is not quite the same as that
obtained by work hardening, in terms of the achievable hardness, and the
resulting strength of the metal. The grain growth caused by the initialanneal,
if used, may also have some affect on finishing operations.

Hope that helps.

Peter Rowe

Wow!

Hey, how about using a "sub-zero quench?"**
I've used this to harden 24k.
(Never had any luck finding *any* method to harden fine silver.)
Will it work with sterling?

**soaking the jewelry in liquid nitrogen for a few minutes, then
removing it and allowing the piece to warm to room temperature.


Doc

--

Real debates, no bull****.
http://groups.yahoo.com/group/Hale_Bobb/

See also http://www.halebobb.com

On Wed, 10 May 2006 23:53:27 -0700, in rec.crafts.jewelry "Dr. Memory"
wrote:


Hey, how about using a "sub-zero quench?"**
I've used this to harden 24k.
(Never had any luck finding *any* method to harden fine silver.)
Will it work with sterling?

**soaking the jewelry in liquid nitrogen for a few minutes, then
removing it and allowing the piece to warm to room temperature.


Doc

And did you find this process gives you any additional hardness to the 24K
(after it again warms up, of course)? I'd not expect it to do so.

Remember that this type of very cold quench, commonly used with steels, works by
better preserving the high temeprature structure of the metal, chilling the
metal more quickly so as to allow less chance for any rearrangement of structure
as it cools.

This is fine with steel, since hardening of steels relies on the high
temperature structure of steel, which is very hard and brittle, as opposed to
the low temperature structure. If you freeze the metal or quench it froma high
enough temperature, then it traps that high temp structure, leaving it hard.

But gold does not exhibit this dual structure where a high temp structure is
harder. So rapidly cooling it doesn't preserve much of anything other than the
fully annealed state. This is especially true with pure gold or silver (and
for that matter, pure iron too, if you could find such a thing...) . Once it's
annealed, allowing crystals to reform in a "relaxed" state, they're capable of
maximum working again, and thus soft. Chilling it, at any speed, doesn'taffect
this at all in any way that would make it any harder.

With karat golds that contain copper, or some other alloys, heating to a
certain temp range BELOW the annealing temperature, allows copper to precipitate
out of the alloy crystals, increasing the hardness. And quenching from above
the annealing temp prevents this from happening even slightly (It doesn'thappen
quickly enough to fully occur with just normal air cooling) , if the metal is
slowly cooled. So slow cooling of some of these alloys, (white golds androse
golds especially, but any gold alloys with copper in them, or silver alloys with
copper like sterling) can give results after annealing that is harder than if
you quench it (just the opposite of steel, where slow cooling makes the metal
softer). A more rapid quench would increase the softness of the metal after
annealing, but might, with some of these alloys, present a risk of cracking if
the thermal shock is too great. with those alloys that could withstand the
shock, a super cooled quench might give you greater softness. But not harden
the metal. .

A very cold cryo bath would of course harden the metal, but only while it's
cold. Once it warms up again to normal room temp, it would again be it'ssame
soft and annealed self.

You say you're hardening your 24K this way. I'd love to see some hard data
documenting this, or explaining metalurgically what changes are being induced in
the metal to harden it. For the life of me, i cannot think of any way this
would make a difference at all.

Peter Rowe

Dr. Memory wrote:



Wow!

Hey, how about using a "sub-zero quench?"**
I've used this to harden 24k.
(Never had any luck finding *any* method to harden fine silver.)
Will it work with sterling?

**soaking the jewelry in liquid nitrogen for a few minutes, then
removing it and allowing the piece to warm to room temperature.


Doc


Oh yeah, I knew I was missing something. Now I realize, that I forgot topick
up some liquid nitrogen at the corner grocery store the other day.

And BTW, this does not work for a variety of reasons. I am sure Peter will
explain in length.

--
Abrasha
http://www.abrasha.com

On or around Thu, 11 May 2006 07:15:38 GMT, a poster allegedly named
"Peter W.. Rowe," drooled

On Wed, 10 May 2006 23:53:27 -0700, in rec.crafts.jewelry "Dr. Memory"
wrote:


Hey, how about using a "sub-zero quench?"**
I've used this to harden 24k.
(Never had any luck finding *any* method to harden fine silver.)
Will it work with sterling?

**soaking the jewelry in liquid nitrogen for a few minutes, then
removing it and allowing the piece to warm to room temperature.


Doc

And did you find this process gives you any additional hardness to the 24K
(after it again warms up, of course)? I'd not expect it to do so.

snip for brevity

You say you're hardening your 24K this way. I'd love to see some hard data
Pun?
documenting this, or explaining metalurgically what changes are being induced in
the metal to harden it. For the life of me, i cannot think of any way this
would make a difference at all.

Peter Rowe

I've used this to harden my wedding band which is made from .9999
I made the band (constructed not cast, and fused together).
I made it like 5 sizes too small, sub-zero quenched it, then stretched
it up on a ring stretcher.
It's VERY hard, just like a 14k band.
I guess YMMV.

Doc