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Surface contamination of silver plated wire

I am an engineer in a wire manufacturing plant. We plate silver over copper wire to be drawn down in other processes. We use a standard high speed silver bath with 8-12 oz/gal silver and 16-20 oz/gal free cyanide. We have been having problems with "white spots" appearing on the silver-plated wire after a few hours. It only happens in one plant; if we place the reels in another plant, the spotting does not occur. The spots occur all year round, but are more prevalent in the summer months. The spots seem to be an oxidation of the silver plate. It does not rub off, but will come off in a cyanide solution or strong acid. They are not light sensitive, as they do not turn black in the light. We have had different labs perform SEM analyses of samples, but do not find really anything. The spot are too thin for an SEM analysis and we are having the samples sent off for an ESCA analysis. Has anyone else had this problem? Does anyone have a theory on what this white spot might be and where it is coming from?

David Murphy
- Charlotte, North Carolina

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