Causes for Off-Colored Black Oxide Finishes

A consistent black oxide conversion coating is always desirable, but when the finish is not satisfactory here are issues that might be the cause. If a black oxide bath drops below boiling for longer than two minutes when a load of parts is immersed the parts may have a loose red oxide film over the black oxide.  The same type of loose red oxide {which wipes off) can be developed over the black oxide if
electric heaters or hot gas flues are used which scorch the solution.

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Excerpt: A consistent black oxide conversion coating is always desirable, but when the finish is not satisfactory here are issues that might be the cause.

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