Where the
world gathers for metal finishing
Q&As since 1989


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Cold black oxide

I see a company advertising in different machinist publications for their black oxide process. They say they use their product at about 200°F. Is this considered a cold process? I also have read in several posts that its the "coating" or oil treatment that causes black oxide products to pass the salt spray tests. So if this black oxide process produces a uniform black color and is covered with a "good" oil would this be considered a good "black oxide" part? Has anyone had any experience with this product?

Gary Collins
shop employee - Alpena, Michigan
2007

Ed. note: We appreciate your trying to put flesh on the bones by naming the specific proprietary product, Gary, but we deleted it. As soon as you ask whether anyone has experience in a proprietary, people will name other products that they think are better or worse. With the anonymity of the internet such testimonials are sometimes from "plants" anyway, and it's not fair to the advertisers on an advertiser-supported site to have to pay for postings that recommend their competitors product over their own, while postings that recommend their product over the competitors' are viewed as suspect :-)

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2007

Technically black oxide is just that, black iron oxide. It is obtained by the hot (290F) process and not by other means. The lower temperature processes produce a black coating, but is based on oxides of other metals such as selenium or copper. In either case the coating is very thin, and it's protective value is primarily from the wax, oil or other organic topcoat.

Can you substitute the low temperature processes? Depends. If it's for your own use, you may find it acceptable. If for a customer, you should get their approval. The low temp processes are sometimes not quite black - "there are different shades of black", as a salesman for a low temp process once told me. In addition some of them will rub-off on hands.

Jeffrey Holmes, CEF
Spartanburg, South Carolina