Zinc Plated Brass turns black in some environments

A. Hi Mack. I don't understand why the zinc plating of brass, but there's a lot in the world I don't understand :-)

It really isn't clear if all of these parts are plated by the same vendor or they are plated around the world, and it's therefore pretty difficult to guess whether the plating is consistent. But certainly corrosion is more of a problem in hot, humid, salty areas than in cool, dry, unsalty areas. Good luck.

A. Perhaps...

If your problem is in an area where there are oil fields there is likely considerable amounts of sulfur ⇦ this on eBay or Amazon [affil links] contaminants in the environment. Much of that sulfur contaminate has no doubt become sulfuric acid which can be floating around the air in it's gaseous state or when the air has a high moisture content as a liquid (acid rain contains high levels of sulfuric acid).

Highly corrosive, the sulfuric acid will attack the zinc plating to create zinc sulphate and hydrogen. Zinc sulphate (water soluble) in contact with copper (remember brass is a combination of copper and zinc) creates copper sulphate.

Zinc will displace the copper in copper sulphate ⇦ this on eBay or Amazon [affil links] and cause the surface of the zinc to go black...

A solution might be to add one more step to the plating process by plating a layer of Nickel or Chrome onto the zinc layer. The extra step is because Nickel or Chrome will not plate directly to brass, but they will plate to zinc.

Hi Max. I appreciate the input, but I can't fully agree with it. Nickel can be plated directly onto brass, although it may be better to copper plate the brass first.

A system solution if zinc plating doesn't hold up may be to substitute electroless nickel plating, which is very well suited to sulfide-rich environments -- but it's usually significantly more expensive.

Regards,

And thank you for the input Ted. I'm not a pro and just plate as part of a hobby. Tried nickel plating over copper on steel a couple weeks ago without the zinc layer. Can get the nickel to stick to steel and to zinc but it would NOT stick to the copper. Looks like it's time for me to do some more research!