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Annealing Silver


#1

All,

I was wondering what kind of environment people on this list might
suggest in which to anneal a silver coated specimen. I have read
through several archived posts on HOW people have annealed silver,
but I never came across what the composition of the environment
(air, nitrogen, oxygen, etc) was in which people annealed their
silver. I ask this because I have performed an anneal at 600oC for
about 3 minutes in a nitrogen environment, and when I allowed my
specimen to cool, the pure silver was cloudy and not at all lustrous
as it was before the anneal. It was very disappointing, and I am
trying to figure out the reason behind the cloudiness. Any help or
input would be greatly appreciated. If it helps at all, the silver
was 100nm thick over a layer of titanium that was 20nm thick.

Thanks in advance,
brian


#2

Brian,

Whenever I heat silver (sterling or fine) to annealing temperatures,
I do it in a regular “room” atmosphere using a torch.

You didn’t say whether you’re using sterling or fine silver, so I’m
assuming sterling.

However, any time you heat sterling silver to annealing temps, you
will get a change in the surface structure that will “cloud” it
(bringing the fine silver toward the surface by depleting the copper
in the alloy) – and likely outright oxidation. Pickling following
annealing is always required, in my experience.

I can’t think of any case where annealing would be the final
finishing step for a piece; you’ll always be pickling and doing final
polishing after annealing and shaping. Am I missing something in
what you’re trying to do?

Karen Goeller
@Karen_Goeller


#3

I can’t really speak to your actual problem but hot titanium is a
getter for oxygen and nitrogen even as low as 350 C. Titanium
would be properly heated in a very pure argon or helium atmosphere
or under a very good vacuum. Silver is not considered to be
adversely affected by nitrogen .

I would suspect this is the origin of your problem --but???

jesse


#4
I ask this because I have performed an anneal at 600oC for about 3
minutes in a nitrogen environment, and when I allowed my specimen
to cool, the pure silver was cloudy and not at all lustrous as it
was before the anneal. 

It sounds as though you have cooked up a layer of Silver Nitrate…
In all probability, oxygen either from an oxide layer already on the
metal or residual in the atmosphere has combined with the nitrogen to
form silver nitrate which is white but darkens in the presence of
light. Annealing is best done in air but with a thin layer of flux
melted onto the metal. This completely excludes the effects of any
atmospheric gases and also removes by chemical means any oxides.

Best Wishes,

Ian
Ian W. Wright
Sheffield UK


#5

Hello Ian:

I was very interested in your post replying to the question about
annealing silver. You suggested that possibly nitrogen was fixed in
the annealing procedure cited. That would be very interesting
because fixing nitrogen by chemical means usually requires a
catalyst, high temperatures and high pressure (the Haber process
producing ammonia). Some fairly recent work using unusual metal
complexes showed the promise of greatly lowering temperatures and
pressures, but I have not heard anything more about it. If you have
a reference for the process you suggested, I would appreciate your
sharing it.

Captain Blood
"Marlinespike Seamanship in Precious Metals"
@Alden_Glenda_Blood