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Heat hardening in a kiln?


#1

This may be a silly question, and a simplistic strategy, but I have
to ask. On page 35 of Rio’s Gems & Findings catalog there’s a
"Heat-Harding Sterling Silver" tip. I currently do not have a torch
other than a small butane typeI use for jump rings and very small
work. The tip suggests heating the sterling to 1292-1346 degrees F
for 30-60 minutes. I’d run out of butane long before I’d have any
effect on the sterling. However, I do have a PMC kiln in whichI could
easily heat and hold at these temps. Would this be feasible?? The
tip goes on to suggest quenching and then heating it again at 572
degrees F for another 30-60 minutes. In the opening paragraph the tip
also suggests you “cover the metal with flux contained in a stainless
steel pan.” I find myself wondering what would happen if I put this
little sterling “pie” into my kiln. Has anyone with a kiln every
tried this?? I’d like to harden some dead soft wire (I don’t have a
draw plate), so I’m not concerned about protecting solder joints.

(Tip courtesy Jorg Fisher-Buhner; Sante Fe Symposium, 2003)


#2

If you are starting with dead soft standard sterling and you have a
kiln than skip step one as you described. That step of heating the
metal to 1292 - 1346 degrees F is to anneal the metal. To heat harden
dead soft standard sterling the only thing you need to do is place it
in your kiln at 600 degrees F for 60 minutes then pickle and rinse.

Greg DeMark
www.demarkjewelry.com


#3

I’m not a frequent contributor here but I find myself with some time
and I do happen to have some experience with your topic. I hope my
response helps some. And remember, there are, on occasion, silly
answers, there are no real silly questions if you are honestly
seeking

First, using a kiln for heat treatment is pretty standard practice
for many people so your idea of using your kiln is completely valid.
The initial heating parameters that Jorg describes is called
"solution treatment" and is the first step of the annealing process
and, if followed by the second step of immediate quenching, should
produce dead soft (or fully annealed) material. Taking your material
to its fully annealed state is the first process necessary in
successful heat treatment or “age hardening”.

I note that you mentioned your material was already dead soft and if
this is the case you may forego the annealing process and move into
the second heating parameters described which are sometimes
referenced as “aging”. The neat thing about this for you is that the
heat required for aging or “age hardening” is usually below that
which may produce fire scale so you win twice by not having to do the
anneal process. Not only do you get to skip the first (annealing)
process but flux may be unnecessary for the age hardening stage that
will accomplish your goal of hardening your already dead soft
material. Air cool after the aging step, quenching not necessary.

Best Regards,
G
Gary Dawson
http://www.goldworksart.com


#4
I currently do not have a torch other than a small butane type
[snip]... I'd like to harden some dead soft wire 

Under the heading of “That may be OK in practice but it’ll never
work in theory…”

I’m going to risk correction from some of the more pure-minded and
scientific members of the group, and go ahead and say that I use
just the “second half” of this tip with some regularity, with good
results. That is to say, I heat annealed sterling in a kiln to 600
or so for a half hour or thereabouts to harden it.

I have used this pretty much just on finished pieces, which I assume
are pretty-well annealed by the time I’m done soldering them, plus I
often “bring up the fine silver” (which shouldn’t really be at
annealing temp, but…). Heat, and voila! And the great thing is,
this doesn’t work on fine silver, so any bezels are still nice and
soft. I don’t use flux.

Noel