Getting black iron oxide out of a pit?

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gomipile

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Apr 17, 2010
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A friend of mine wants one of his carbon steel knives mirror polished. It has some pitting, with black iron oxide in the pits. He wants the pits emptied of black oxide and mirror polished as well. To be clear: he wants to leave the pits there, but have the mirror finish extend into each pit. The blade will of course then be stored with a rust preventative sprayed over it.

I can do the polishing, but I was wondering if there is a good way to quickly remove the oxide without hurting the underlying steel.
 
Polishing pastes containing aluminum oxide, like Simichrome or Flitz, can remove the black oxide. Will also need to do some scrubbing, most likely. Not sure how easy that'll be, getting into the pits to scrub them. Something like a toothbrush might help with that.
 
My suggestion would be to remove the rust completely, prior to any polishing. First option would be ScotchBrite. If the pits are too deep, use a brass wire brush.
 
+1 for wire brush, it'll strip scale and such out of pitting without taking off much material
 
My experience is that anything other than media blasting will leave traces of the oxide behind. I'd suggest using a very fine garnet since you're going to be polishing the metal anyways.
 
The black oxide isn't doing any harm to the blade anyway, and there's no mention of rust (red oxide) in the OP. With that in mind, I'll repeat what I recommended earlier and recommend the polishing paste (Flitz/Simichrome). Removing the oxide layer (also known as 'tarnish' or 'patina') is exactly what they were made to do.

There will always be some re-formation of the black oxide anyway (produced from reaction of oxygen with the iron in the steel), but it'll take a little time to become readily visible again. Even longer, if the blade is polished to a high degree. Unless the blade is immediately sealed or coated with wax or something similar, the black oxide will always come back. It's a natural process.
 
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