In addition to what Ccass said, the vast majority of polished ceramic coatings also have superior chip resistance and (ironically) corrosion protection.
From the pictures crustysarge provided, the headers were not properly polished and the unpolished surface absorbed moisture. A vibratory tumbler, which is what most companies use to polish headers, will not completely polish a pair of headers. The hard-to-reach areas need to be hand polished and wiped clean prior to the tumbler.
Feel free to PM me with any more questions. I'd be happy to answer them. Advice is free.
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Don't tell people how to do things. tell them what needs to be done and be surprised by their ingenuity. -- Gen. George S. Patton
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