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topic 11776

Do we have to have oil on the BLACK OXIDE?


Our company recently started investigating the use of black oxide as a rust preventative finish on some steel pivot bushings. When we got past the one and two part sample stage, our shipments had a thick sticky oil all over them. From what I can read, the oil is what prevents the rust. Oil is what we don't want because it will attract dirt and promote wear in the steel on plastic pivot.

I'm getting cold feet. I'm wanting an oil free finish that will retard rust while the part is new. A robust long term finish is not required. Is there a black oxide variation that we need to specify? Another finish altogether? (with similar costs).

Bruce Peterson
- Assaria, Kansas


It sounds to me like your vendor used an oily finish oil. Not all oils will leave that tacky residue. Some oils are formulated to leave a dry-to-the-touch finish so as not to attract dirt once the part is in service. You may also want to look at using a water soluble oil that when mixed properly will leave a dry finish. Oh yeah, you do need to put some sort of rust prevent on the black oxide because the coating itself will only give minimal (1-2 hrs) salt spray corrosion resistance. With a good oil, you can easily get in excess of 80 hours salt spray resistance.

Dan Brewer
chemical process supplier - Gurnee, Illinois


Hello Bruce,

I am assuming your parts are steel and yes it is the oil that provides the corrosion resistance on Black oxide coating for this material. Stainless will blacken does not require the oil, and the processing costs are similar to processing black oxide for steel. Other processes (black zinc, nickel etc..) are usually more expensive and alter the part dimensionally.

Good luck,

Bill Grayson
- Santa Cruz, California, USA


Bruce, typically an oil is applied to black oxide coatings to enhance its rust protection. The type of oil and the amount applied will determine if the treated parts are wet or sticky. The parts you received appear to have been treated with a viscous oil that makes them sticky. I suggest you contact the shop that applies the black coating and see if they could apply less of a lower viscosity oil. This type of oil will provide less rust protection than the current material but it help you to meet your performance goal of not allowing dirt to stick.

We typically recommend applying a water dilutible rust preventative oil over black oxide. That way, by increasing or decreasing the concentration of the oil in the water, we can vary the amount of oil deposited on the parts. At low concentrations, the treated parts are dry to the touch and will not collect dirt.

Roy Nuss
Trevose, Pennsylvania, USA

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