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"Testing quality of blackening coating"

Current question:

July 15, 2021 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. How can we test blackodising chemical from the bath? Is there any standard process for that?

Prasad Mohan kasar
- Pune maharashtra

July 2021

A. Hi Prasad. We appended your inquiry to a thread where I have asserted that such questions are just slightly 'backwards'. The better question is "what specification/standard should I be blackening in accord with?" Once you have made that decision/determination, the specification/standard will tell you what is required of you in terms of testing the finish and the bath.

ISO 11408 [affil. link to spec at Techstreet] is a specification and list of test methods, SAE AMS2485 [affil. link to spec at Techstreet] is a black oxide standard, so are MIL-DTL-13924 [link is to free spec at Defense Logistics Agency / dla.mil] and DIN 50938 [affil. link to spec at Techstreet]. Look them over, as well as perhaps Indian standards, then pick one if your customer hasn't (Nissan, GM, Boeing, and probably many other companies have their own black oxide specifications). Because, until you do that, your question can be thought of as "how should I test an unspecified finish for compliance with unspecified requirements?" :-)

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

Closely related historical postings, oldest first:


Q. We are using blackening process for our components (forgings). I want to know whether salt spray test is applicable for checking the quality of blackening. If not what is the test to be conducted to check the quality of blackening.

- India


A. I have tested blackened parts last up to 6 hours in a SST only. This is too fine to be rated as a conclusive go - no go test. I would rate a good jet black appearance as a better guide. If you want to go further, then cut a cross section and measure it out on a magnifying microscope.

Khozem Vahaanwala
Khozem Vahaanwala
Saify Ind
supporting advertiser
Bengaluru, Karnataka, India

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A. If your blackening process is a black oxide process, the corrosion resistance is given by the post treatment applied over it, for example oil, wax, etc. The black oxide by itself has almost no protection value. General Motors tests these coatings in a Humidity Test, not SS test. Carlos

Carlos Cielak
plating shop - Mexico City, DF, Mexico

July 17, 2009

Q. Hi to all,
How to test the surface treatment of Blackening coating.
Is there any procedure for testing?

medical - Bangalore, Karnataka

A. Hi cousin Jebaraj.

Although the responses to the original poster are valid in response to your question as well, the subject cannot actually start with "how to test an unspecified finish for compliance with unspecified requirements?"   :-)

Rather, the essential starting point must be "what specification are you blackening these parts in accord with?" If none, no one can authoritatively suggest applicable requirements.

Decide whether you are trying to do cold blackening, hot black oxiding, salt bath nitriding, or whatever and then find an ISO, ASTM, AMS, IS or some accepted standard for it. Then you've got a starting point. Good luck!


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

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