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While investigating some heat treating issues at work I stumbled on this info. It might be useful to someone. I cut and paste, I know nothing more about it. It sounds like a Shep idea, except there is no used brake fluid in the formula!
Here is a "Practical Plater," solution to your dilemma. Many years ago, a customer approached with motorcycle exhaust parts that had a blue/irridescent color to them. All he wanted to know was how to get this off. Obviously, it was an oxide similar to the one you describe, and was caused by high temperatures on the pipe (without heat sinks or fins).
The cure was rather inelegant. We took some dilute Phosphoric Acid (I remember 10% by volume), and used reverse current gotten from a few flashlight batteries wired together. The part was made anodic and the cathode was a piece of Stainless wrapped in cotton which was saturated with the Phosphoric acid Solution.
In seconds, the blue color came off, and the blue bright color of the chrome was again in evidence.



Here is a "Practical Plater," solution to your dilemma. Many years ago, a customer approached with motorcycle exhaust parts that had a blue/irridescent color to them. All he wanted to know was how to get this off. Obviously, it was an oxide similar to the one you describe, and was caused by high temperatures on the pipe (without heat sinks or fins).
The cure was rather inelegant. We took some dilute Phosphoric Acid (I remember 10% by volume), and used reverse current gotten from a few flashlight batteries wired together. The part was made anodic and the cathode was a piece of Stainless wrapped in cotton which was saturated with the Phosphoric acid Solution.
In seconds, the blue color came off, and the blue bright color of the chrome was again in evidence.