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Yeah it's black patina from the citric acid in that product. Autosol should clear it up your just going to have to test it as it might remove the gold if it's not a very deep etch.

You should be...

The dovo gentle man is carbon steel not stainless :D The spots you originally saw are what happens to carbon steel if you leave it moist for too long. And the Black color you have now is called the...