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  for Metal Finishing since 1989
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Late developing white stain on black oxide

I have an issue with some black oxide parts that came back from my black oxider. The problem is a white residue, which I believe is from not being rinsed properly.At first inspection they are fine and then in a day or two the white starts to show up. My problem is how do I prevent this from happening here at my shop and when it arrive at my customer .We currently spray with crc or WD-40 ⇦this on eBay or Amazon [affil links] and wrap in kraft paper and all this seems to do is slow it down.Is it a problem I need to fix at the black oxider or can I do some thing at my shop?

Joe Zalek Sr
QA inspector - Whitehall, Pennsylvania
2006

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There are 2 salt problems that come from black oxide: red iron oxide salts from the sludge that builds up in the black oxide bath and white caustic salts resulting from alkalinity in the bath that hasn't been sufficiently rinsed away or neutralized. The red sludge salts are generally insoluble, are a nuisance since they're the same color as rust, but are readily rinsed away. The white salts, usually found in holes or crevices (weld seams, cracks, etc.) are best attacked during the rinse following the black oxide. An air/water pressure gun works wonders for this or there are proprietary post-black oxide "neutralizers" that remove the salts before they form. If you're talking about sintered metal components, they're the biggest challenge for any black oxide house - can they be impregnated to seal the porosity rather than allowed to adsorb the oxide salts? Send me some parts and I'll give them a try!

Milt Stevenson, Jr.
Syracuse, New York
2006