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  for Metal Finishing since 1989
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Black oxide coverage

August 31, 2009

I am evaluating product that has a nice even black coating on most surfaces of the steel part. However, one surface has a water like stain. An area was not covered by the blackoxide process to the same uniform degree. It is not just a variance in shade it actually looks like water/oil remained on the location which caused the blackoxide to process differently.

In your expert opinion, would this be an acceptable black oxide condition? If not, how many times could the part be reprocessed? Do you have specs on acceptable and rejectable blackoxide conditions?

Thank you in advance for your opinion.

Alicia Hodnett
Quality Control Engineer - Falconer, NY, USA

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September 2, 2009

Unfortunately, what is acceptable is dependent on the specification in the work order or contract.
Several people could give you a better idea of the problem cause if they could actually see the part(s).

From your description, it sounds like the part was not properly cleaned on that surface for some unknown reason. It could actually be that there is an air bubble from the way that it is racked that is preventing proper cleaning or the black oxide solution contact.

Can your company live with it-Only the boss can make that decision. Can they be reprocessed-Generally- yes. There might be a gradual roughening of the surface, but virtually no loss of dimention. There are always exceptions.

James Watts
- Navarre, Florida

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Well you have not said what black oxide process it was. Different types demonstrate different problems. Also the types of polishes can give erratic shades of blue. In a nut shell it sounds like you do indeed have a cleanliness problem. Either oil or wax that was not completely removed. The best description I was ever given for a well done blue job was made by a woman who's over and under shotgun I had blued. She simply asked me if it was bluing or black chrome? The finish and color should be as even as a good automotive paint job. :o)

Rod Henrickson
gunsmith - Edmonton, Alberta, Canada
September 4, 2009