Back to Ganoksin | FAQ | Contact

Black spots on silver


#1

PLEASE HELP

I have worked with sterling silver for 25 years but recently
encountered a new problem. I ordered a sheet of sterling from a
different supplier as the one I usually use could not deliver before
Xmas. I cut out shapes for earrings and drilled a hole for the
earwire. Domed them in my doming punch and polished and cleaned. I
did not anneal so no heat on the metal. The final cleaning was with
a JCR cleaning system which does a final clean like nothing else.
Everything looked great. I make these earrings regularly and have
had no problems in the past.

PROBLEM

A week after making I noticed black spots on the metal half a mm and
smaller. At first I thought that some how I had cross contaminated
from the doming punch, but on closer inspection the black spots are
also on the edges which did not touch the punch. Also one of the
pieces has a brown tarnish on the back. I re-cleaned them and other
pieces with the JCR as I regularly do with my stock. The black spots
remained and the brown tarnish was still there on one piece.

Are there impurities in the metal? This bullion dealer boasts of
recycling silver and I have been told by those who have used this
supplier (after I purchased the metal) that assay is true but metal
quality is inconsistent.

My solution would be to pickle and polish but am worried the black
spots will return. But I want your advice before I do this as this
knowledge base is greater than any one person, which is why I think
Ganoksin is the best. What do I do if I can’t get the black spots
out?

If I return the metal I loose labour and lemel. I have sold some
pairs, before the black spots appeared, and may have to deal with
returns.

Is this a case of stick with the quality you know or have I stuffed
up somewhere in the making process?

Thanx Richard


#2

Hello,

as far as I can think of, this sounds like “comma-silver”. In other
words a poor quality type of silver with imperfections due to a lack
of good refinning. It, however, can be perfect sterling silver but
with copperfailure.

I’m not a metallurgist so keep in mind that my explanation is not
how it should be. Copper forms copperoxide (CuO) in contact with
oxygene. This is te reason why one need to use a reducing flame (poor
oxygene heat). After reduction copperoxide turns into copperoxydul
(CuO + Cu). That’s what comma-silver exactly is. A grey-blue
substance left behind a silver alloy and seen as little black
comma-like spots. De-oxidizing agents can be use to solve this
copperoxydul. Manganesecopper is one of them, siliciumcopper, cadmium
and a view other ones are also known as de-oxidizers. The main
problem is overheating a silveralloy made with copper. Both metals
attrack oxigene in huge amounts and silver oxides are build very
quickly if you do’nt take care of them by using the correct flame,
boraxwater as an antifirescale or other preps.

Don’t monkey around with this stuff. Refinning this silver takes
knowledge, effort and you need to buy the products in order to have
it refinned. In my opinion toomuch trouble to go for. Refinning it
yourself is adding more products to your alloy changing the
caracteristics of the alloy talking about ductility, workability and
more. Use straight forward two component alloy like silver-copper,
argentiumsilver or other ones. As I alway’s say, keep it stupid
simple (kiss).

Stick to your company with good products or choose for another
backup company is my best advice I can give.

I hope this will help… if I’m correct in my opinion of
clearifying this problem.

Have fun and enjoy
Pedro