One of my customers is covering the plating on some small electronic connectors with a black oxide coating. This is the specific plating process that they are using: Caswell Inc. - Black Oxide Kit

The problem is that our parts are already pre-plated with a shiny nickel finish over brass. The customer is finding that the black oxide plating is not adhering well over the nickel plated surface.

Drawing on my car and homeowner experience, my feeling is that the customer will have to break the finish before applying the black oxide. In the past, I've used Duplicolor Self Etching Primer on some of the metal parts I've painted. For my customer's project, I would think something similar might work. The parts would probably have to be dipped, so a canned liquid might be better - there will be hundreds of small parts, so sanding isn't an option.

Any suggestions?

Thanks,
Al

The instructions indicate that it can only be used for steel or iron, and that they sell a separate product for stainless steel. They also mention prepping the surface using one of several abrasive processes.

Without knowing more, I wouldn't jump to the conclusion that it's a "plating" at all - maybe something that performs a chemical conversion?

Black oxide is a chemical change. To be able to achieve it, those parts will have to have the current plating stripped.

__________________
1987 560SL
85,000 miles

Black oxide is utilized on plain steel or iron. It will not work on nickel very well and it will certainly not work if you stripped the nickel and tried to use it on brass.

The use of nickel effectively eliminates any need for black oxide. Both provide corrosion protection, although the brass hardly needs it.

Brian is correct about brass.

Read the following for information on the process of Black Oxidizing. Black Oxide Basics

__________________
1987 560SL
85,000 miles

From your linked article-
Black Oxides on Stainless steel and/or brass alloys will yield excellent corrosion protection, primarily due to their inherent properties.

I personally have never had good luck with black oxiding brass. In my experience it doesn't come back in looking like it should, and the oxide doesn't have the same visual aesthetics as that of steel after the process. As for corrosion protection of brass...it's the last process I would ever use, as there are many, better ones on the market.

__________________
1987 560SL
85,000 miles

Thanks everyone. I really appreciate the help.

Do you know of anything that would produce a black finish - similar to black oxide appearance - on a nickel plated black surface?

I thought that if you applied too much current when nickle plating the finish would burn and darken. Nickle is inactive or inert till activated but you might experiment a little. Activate it and add a few microns of overcurrent nickle.

It almost sounds though that if the customer wants the finish black he might have to supply it that way. Black chrome is also a finish for example. I still have a partial roll of copper with it as the final finish left over from construction of my solar panels years ago. It is an electroplating process.

The issue is to do these things reliably is not really cheap in my opinion.
Maintaining long term conductivity has to be a consideration as well. I assume the customer desires this for esthtic reasons as I can not visualise any other neccesity.

Barry what you are saying is true about over current to electro plated nickel, it is called frosting. However most nickel plating being done now is electroless, so therefore there is no current applied.

There is black nickel out there if you can find it.

I did not know that there was black nickle out there. If so it is a real pain in some ways but is a potential viable answer. The customers quantity had better be very high to justify gettinginto this or subcontracting it out. Plating work tends to be pricy if farmed out in low volumes.

How about $600. for nickle plating:

I had all the special steel hardware for a race car electroless nickel plated and it was cheaper than paint. It wasn't black, but black can be done electrolessly.

Don't quote me on this but you may be able to do a black zinc plating on brass, but this may require an undercoat plating which would drive the cost up. I guess we should ask, how much are you willing to spend? Most plating shops have steep minimums and less and less are willing to work with the public. What would be wrong with painting or powder coating the heads (visible areas?) the nickel on the thread should provide corrosion resistance....

I mentioned black nickel earlier, but I guess I should have said it is neither cheap or readily available. Sorry 'bout that.

Another option ould be to have the screws made out of stainless material and then black oxide coated, but you really want to keep oil on black oxide to keep it nice and this isnt always desirable. Yet another option: Replace the screws with a zinc plated steel screw (assuming it is a standard screw and the difference in material would be acceptable), strip the zinc (this is easy) and send for black zinc, parkerizing or so on.