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Seeking Black Oxide Provider

My company manufactures special automotive test equipment. We have been using black oxide with light oil on some of the small machined parts on the testers. This has worked well but unfortunately our black oxide provider recently got shut down by the EPA.

We send the parts to a new provider with a specification of "black oxide, with light oil". The parts came back with a dark grey zinc chromate treatment, with no oil. We aren't familiar with this treatment, so if anyone could answer the following questions it would help us out.

Is the zinc chromate treatment better or worse than black oxide for rust resistance? Which treatment is better for wear resistance? Does it help the zinc treatment to also apply a light oil and is this a common procedure? Can the zinc chromate plating be put on to appear as dark as black oxide?

Does anyone know of a black oxide provider in the San Francisco bay area (including San Jose and Oakland) that does smaller lot sizes at reasonable prices?

Thanks,

Paul T [surname deleted for privacy by Editor]
Brisbane, California, USA
2001