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Improving black on zinc

2006

I have a need to improve the colour of our finished Black Zinc.

This is mainly in reference to blacking work that has been plated in a barrel in an acid zinc bath where I have plated the work, but also refers to work that comes in already plated silver.

In some cases the blacking is done where the work has already been passivated silver, in others it is where the work has not been passivated. In all cases the results are about the same.

The black that we use is "Black Macro" from MacDermid (components 8665 and 8667). We run it at a pH of 1.4-1.8 normally, and a temperature between 20 and 30 deg C (we have found that this works better than room temperature).

Often our finish comes out with more of a dark blue tint to it than a proper black. I have seen black from other firms, and theirs is a lot closer to true black than ours is. I would like to know how we can improve the colour of our black.

We have dried a nitric pre-dip (0.25% nitric acid), but that has only made an improvement on work that has been heat-treated post zincing, and then it only brings it up to about the same level of our normal zinc plating.

Any help greatly appreciated.

David Chord
- Lower Hutt, New Zealand

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Good luck with this, David, but I don't think you'll find much help in the forum. It's vaguely possible that another reader has a lot of broad experience using this particular proprietary product and will be willing to offer tips on more consistent blackening, but it's probably not likely.

These kinds of products are so proprietary that you will probably need to either get help from Macdermid directly or use a different proprietary product and get help directly from that supplier. Best of luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2006

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2006

Hi Ted, long time no see :-)

Anyway.. With regards to McD's and this product, there's been a few discoveries that I've made about it that they weren't aware of (at least locally). I've also been told by other plating firms that they don't recommend it themselves.

Could someone suggest some alternative blacking processes that I could look into? McD's only seems to do the one in NZ.

Thanks again,

David Chord
- Lower Hutt, New Zealand

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Welcome back, David.

I just got back from Sur/Fin 2006 in Milwaukee, and Macdermid seemed to have a half dozen product managers on hand for discussions. You need to visit the USA physically some time as well as virtually :-)

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2006

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2006

Dear David,
Best is to call the tech-service department of MacDermid or call for the tech-data.

Please try this: increase the working temperature to 35+ °C.
Try a pre dip of Chromic acid @ 5 grm/ltr prior to black passivation dip
Increase the concentration of one of the two products which is colourless.
applying oil will blacken the surface.
Best of luck!
Regards,

T.K. Mohan
plating process supplier - Mumbai, India