It is most likely that there is a build up of impurities (including copper) in the bath.

You give the analysis for the initial solution make up, but not of the anaysis of any residual fe or cu or cl in the uused bath.

I'm not sure how "rust" couldbe the cause of the black coating.

How could is your preplate clean on the copper item? has water chemistry or cleaning method changed on the rinse ahead of plate?

My best guess is chemicals are contaminated, exhausted. My next isthat the preclean is insufficient.

milo

Thanks for the insight. I also thought impurities in the solution and/or chemicals that is exhausted is the cause. You can go to this link... : http://www.finishing.com/285/32.shtml

...to see her original post (by Jillian Ross) on that site and maybe contact her directly. Or I will e-mail her all the solutions when this thread is full. Thanks again. Oom Sarel.

I would say you have a peice of steel with too low a temper for what your doing. I can;t remember the name of the black surface but caustic comes to minds and dead acid.

Maybe your solution is slowely contaminated by the air surrounding it? The black spots reminds me about sulfur spots on silver spoons when eating egg, an old chemestry experiment from elementary school

Could you explain how the temper of the steel affects its Reactivity?

This is a new concept to me.

milo

Geeeh! I dont know how that may happening but after seen some of couples of differents metals rubbing each other for a while you can tell is some kind of electrochemical reaction or so. Some how like a galvanic reaction stuff which are be the cause of such corrosion effect down the road, who know's? Plus then if you are running some voltage around these metals this also will be part of that condition eventually. I guess it may happening that way too..

No big deal but at least you'll get a clue somehow, perhaps metals tend to have some magnetics properties that may also caused some of such condition eventually after been in contact at some point in time.

IronMan Time,

MC

different metals do indeed set up galvanic cells.

Temper offers no explanation for plating, save if a temper oxide scale is present.

All tempering does is relax (not even move) the molecules already present.

Now "perhaps metals tend to have some magnetics properties that may also caused some of such condition eventually after been in contact at some point in time." ???? Again what is the mechanism? which metals?

milo "iron city time- I'll have an IC Lite"