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Black Passivation and Black Trivalent Plating

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Q. Find a formula of trivalent chromium black zinc.

Liu Alice
- Taiwan
October 21, 2023

A. Hello Liu,
Please introduce yourself -- it's hard to frame an answer without knowing whether you are you from a plating shop, or an established supplier of metal finishing processes, or you are doing research for your PhD at a university.

If you are from a plating shop, please don't try to formulate such complicated chemistry yourself; instead, find a supplier who offers it and will provide help when things don't work well. That's what virtually every other plating shop in the world is doing.

If you are from a supplier, no one will give you the secrets to black trivalent chromium passivation of zinc on the internet; but offers some rather good leads, and a patent search will give a good idea of what has been done.

If you are a student, please give us a general idea of your thinking; you probably have a good idea where you're headed. Thanks. Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

⇩ Related postings, oldest first ⇩

Q. Hi,
We are a trading company that deals with fasteners. We have encountered some cases of 'Black Passivation'. Is this the same process to Trivalent Black plating? Will appreciate your good advises.

Thanks & Best Regards,

Shawn Wong
manufacturing - Singapore

A. These are ambiguous terms. Add some language and/or specifications to define the substrate, coating (type & thickness) and the process.
'Black passivation' perhaps means a black chromating (either trivalent or hexavalent chromium unless specified) of zinc plating on steel, e.g., per ASTM B633, Type II (Black). Or, perhaps black oxidation of steel per MIL-DTL-13924 [on DLA] or alternatively, by high-temperature heating in air or steam.

'Trivalent Black plating' is confusing.
'Trivalent Black' is probably black chromating using Cr+3 as mentioned above. Trivalent black chromated, zinc-plated steel is more explicit. The zinc thickness or service class (SC) should also be specified.
'Trivalent plating' could be bright chromium electroplating from Cr+3 (rather than Cr+6) plating solution. Metallic chromium is produced; no +3 or +6 remains.
'Black plating' could be black chromium, black nickel, a plating subsequently blackened, black oxide or maybe even anodized aluminum dyed black.

Ken Vlach [deceased]
- Goleta, California
contributor of the year honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at, continue to benefit from.

Q. I also am interested in learning what options are available for a consistent, high quality black electroplating. I currently use black/zinc with hex-chrome and my customers are needing tri-chrome that is RoHS compliant. I have high volume small parts for OEM applications.

Thanks in advance.

Shane Lee
- N. Augusta, South Carolina

Q. How to get a black colour over zinc plating from trivalent passivation?

keerthi p s
- Bangalore Karnataka, India
February 17, 2010

A. Hi, Keerthi. I do not know any shop which is attempting to formulate their own trivalent chromate in these days where compliance with specifications and RoHS certification is necessary. Your only realistic choice is to go to the plating process supply houses, of which there are many in Bangalore, and tell them of your needs.

You may wish to consider switching to zinc-iron plating, as a consistent and stable black color is perhaps easier to achieve. Good luck.


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

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