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To tarnish or not


#1

Hi to all

A friend wears two 925 silver rings. One oxydizes grey, the other
not. Any clues ? The metal mixed in the silver ?

thanks


#2
A friend wears two 925 silver rings. One oxydizes grey, the other
not. Any clues ? The metal mixed in the silver ? 

I’d bet on one of two possibilities.

First, one is argentium silver (still marked 925) while the other is
standard sterling silver.

Second, One ring has been cleaned up and polished enough so as to
remove any fire stain, so the surface is clean sterling silver, while
the other was not finished that way, so the visible surface is a fire
stained one. Fire stain is not the black scale after heating. That’s
fire scale. Fire stain is a subtle penetrating subsurface layer of a
small percentage of red copper oxide mixed in with the silver. It has
a creamy to slightly pinkish creamy color, slightly dusty looking
compared to the darker cleaner and a bit more reflective look of
clean well polished sterling. Fire stain forms on standard sterling
silver if it’s soldered, annealed, or cast in a manner that does not
protect the surface from exposure to atmospheric oxygen. Normal
soldering fluxes are not very effective at preventing it, and in
casting, most of the time, the long interval between pouring the mold
and when it’s quenched gives the hot casting long exposure to the air
in the plaster, so fire stain in castings can be quite deep and
thick. If the casting is only lightly processed, or polished mostly
by tumbling in steel shot, which does not remove surface metal, then
that surface will be a fire stained one, not a clean silver one. The
fire stained surface will tend to tarnish more quickly than clean
silver will.

Peter Rowe


#3

Does he do different right hand and left chores? Switch hands with
the rings. Maybe his right hand goes in the detergent in the sink
and the left does not. Bill

Reactive Metals


#4

Most likely, the one that is oxidizing was not originally filed and
buffed down to a stable alloy eliminating the near imperceptible film
of fire scale. Try lightly filing and/or sanding and then use a good
buffing compound like grey star compound. Then take a piece of a
white paper and hold it over the piece to get a reflection of white
off the surface. it helps to “disclose” any remaining scale on the
surface.

James F. Conley


#5

The more you explore the world of metalsmithing, the more options
you will find in the metals you can work with.

Traditional sterling silver is pure silver alloyed with copper, and
it oxidizes naturally or with the help of chemicals. However, there
is no reason you can’t use other metals to combine with the pure
silver. So long as you keep the silver content at 925/1000’s of the
total, you could add whatever you wanted and still call it sterling.

Many refiners around the country have alloys they sell which when
added to pure silver, help it to cast cleaner, tarnish less, or
create less fire scale when heated.

If you are curious, why not alloy your own sterling with different
alloys, and see what works easiest or looks best to you? It’s not
rocket science!

One of my students called a refiner back east to ask about these
various kinds of alloys for silver, and they sent her 3 different
types to try. for free!

Personally, I love the S57NA sterling alloy made by United Precious
Metals in NY. It contains germanium, and really controls tarnishing
and fire scale.

Good luck and have fun!
Jay Whaley


#6
Personally, I love the S57NA sterling alloy made by United
Precious Metals in NY. It contains germanium, and really controls
tarnishing and fire scale. 

Jay, How does this compare with the UPM S88 master alloy? I haven’t
tried S57NA. Has it replaced the s88 in your studio or is it just
better for some things and if so what?? Thanks Frank


#7

Frank,

We have shifted over to the S57 NA alloy, mainly because I wanted to
try an alloy with germanium. Many months ago, I interviewed on my
blogtalkradio show a metalurgist from United Metals. He really got me
thinking about the advantages of germanium in sterling, so I wanted
to try the germanium-bearing S57 NA alloy.

Even though I was happy with the S88, which we used for years, I did
notice some fire scale on polished pieces, and thought the S57NA
would control that better. It seems to. My students love working in
the S57 NA sterling, as it does not tend to break when hot, and the
stuff casts so cleanly you don’t even need to pickle it after
casting! It’s a dream to fabricate with. It also stays bright,
without the terrible tarnishing issues traditional sterling has.

Give the S57 NA a try. I think you’ll like it.

I now think of traditional copper alloyed sterling as very
old-fashioned, with lots of inherent problems.

And Frank, that wax injector I bought used from you is still working
perfectly! We are using a carvable injection wax which my students
love because they can modify injected wax models with files and
scrapers much easier than the usual injection waxes.

Jay Whaley


#8

Thanks for the info Jay I will give this new alloy a try. I just got
my boss to switch to the S88, which she is very impressed with. I
will try the new stuff on my own. Also which injection wax are you
using, I always liked the Plasto-wax myself but I am always
interested in new and better stuff… glad to hear the injector is
still working…

Frank