Black Marks on AB Black Nickel after Salt Spray

A. Hi Kamlesh. I confess to being pretty unsure regarding your posting :-)

The only thing I can find about "AB Finish" is that it's an acronym for Aurora Borealis (a 'rainbow' colored interference finish) --but you describe it as "black nickel". In some cases people specify their aesthetic needs for "A" surfaces (primary) vs "B" surfaces (not prominent during normal use), and maybe that's what you mean with your photos of top side and bottom side :-)

Your pics seem to me to show some sort of scratch brush finish of poor uniformity, but which don't seem to extend under the black marks. So I think the 'black' areas are not corroded areas but the last remnants of lacquer & black plating :-)

I don't know if you are from the plating shop, such that your description of the finishing process would be accurate, or if you are the supplier of the castings, or the ultimate customer of the finished product, such that the problem might be that you are not actually getting the finish you are told. So I don't really know where to begin regarding trying to explain what black nickel plating is or might be in your case, it's usual low corrosion resistance but sometimes high corrosion resistance, whether it needs lacquer, etc. But generally black nickel plating is a finish of low corrosion resistance because it is very thin and goes on top of another layer of plating, usually bright or dull nickel plating. You don't mention an underlayer but it looks like there is one.

Please tell us what you personally do, and where the company you work for fits into the supply chain, and try to offer more detail of what this finish is supposed to be and how it is obtained. My overall feeling is that your "lacquer" is not as good as it could be and, if it were better, then 24 hours or 48 hours of salt spray probably wouldn't even reach the black nickel layer. Thanks!

Luck & Regards,