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Silver casting won't blacken


#1

I’ve been getting my designs cast for about fifteen years with one
casting company. My designs require an “antique” finish, and I use
selenium toner to blacken the castings before they are tumbled.
Periodically, for months at a time, the castings will not blacken. I
tried liver of sulpher, but that was no better. The only solution I
have found is to anneal each piece. But simple annealing doesn’t
always work, in which case I have found that heating with a coat of
Cupronil will work. This adds a time-consuming step to my production,
and is a source of great frustration. The company that does the
castings says that nothing has changed in their process. Can anyone
offer any suggestions?

Thanks,
Virginia


#2

Virginia,

Is the casting company using De-ox Silver which is a.925 Silver, but
not Sterling silver?

If they are that may be your problem. De-ox Silver makes a better
casting Silver since it cuts down on fire scale. I use it all of the
time, but I have never tried patina solutions on it.

Just a thought,

Ken Moore
www.kenworx.com


#3

I use De-Ox silver for casting, and it is just wonderful. I have
been able to successful give it a patina using good old liver of
sulfur. No problem.

Alma


#4

i’ve read that sometimes casting companys will use an alloy with
some Zinc so the casting has a brighter, smother finish. the zinc
oxide on the surface would stop the reaction with sulpher. this would
also explain why you’re annealing (and i guessing pickeling) would
solve the problem. try just pickling the whole batch without
anealing. or you could try tumbling them with a mild abrasive. by the
way, i’ve never had this problem so im only guessing here!

Chris.


#5

Virginia - why don’t you try a short run in your tumbler with a mild
abrasive media? Then immediately rinse, patinate with liver of
sulpher with a bit of ammonia, and run again. Sometimes patina
solutions don’t work well unless the silver is freshly cleaned and
without oxidation.

Judy Hoch


#6
i've read that sometimes casting companys will use an alloy with
some Zinc so the casting has a brighter, smother finish. the zinc
oxide on the surface would stop the reaction with sulpher. 

I wonder if that’s what I have. I have a 20+ year old ring that is
marked “WM STER” with the WM run together. It’s as shiny as the day
I bought it, bright and smooth. It’s also brittle. One prong broke
when I tried to set a cab in it, and another is cracked. I just
tossed it in a drawer and it’s been there since.

Al Balmer
Sun City, AZ


#7

Hi. Thanks to everyone who has responded to my inquiry. I’ve never
heard of De-ox silver (thanks Alma and Ken). The company that does my
castings in not very forthcoming when I ask about the silver they
use, although they say they don’t use zinc. They don’t allow me to
provide my own silver. But the quality of their casting is REALLY
great, so I would hate to change companies.

why don't you try a short run in your tumbler with a mild abrasive
media? Then immediately rinse, patinate with liver of sulpher with
a bit of ammonia, and run again. Sometimes patina solutions don't
work well unless the silver is freshly cleaned and without
oxidation. 

I’ve tried tumbling the castings in abrasive media before oxidizing,
but the media doesn’t get into the recessed areas, which are the
exactly the areas that I want to oxidize. It has been suggested that
I try sandblasting, and that is something to look into.

My liver of sulpher supply has expired, so I tried mixing ammonia
with a silver oxidizing solution that I got from a local jewellery
supply place. Sadly, it didn’t work. In any case, I was a bit leery
of mixing the two together. I really wish I had taken chemistry in
high school!

Thanks again for all your suggestions. This problem with the
castings not blackening seems to come and go as the years go by, so I
will hope that it goes away in the near future.

Virginia


#8

Virginia,

That sounds a bit weird that they won’t be open about what silver
they use. I would ask them by what legal name should you use for a
hallmark, i.e. Sterling or .925.

I have checked my source and on their website they show “Sterling
Silver 57 Fires Scale resistant casting grain. 92.5% Silver,
remainder is Copper, Zinc and Indiom.”

I checked another source of which I might would purchase casting
grain from and they describe their Deox silver as “.925 Silver +
Other.”

Finally I checked a third source of which I would purchase casting
grain from and their catalog describes their Anti-Fire scale casting
silver as, “92.5% with Copper and select deoxidizing elements.”

I don’t think you necessarily need the formulation, but is it
Sterling Silver (92.5% Silver and 7.5% Copper) or is it some form of
an Anti-Fire Scale or Deoxidizing Siler.

If they would not share that with me, I personally would not use
them no matter how good their castings are.

Again, just my opinion,

Ken Moore
www.kenworx.com