My father, who was a chemist, once told me that it was possible to blacken the surface of stainless steel by mixing a few drops of iodine (yes the stuff you get at the drugstore should work fine, and he said that you only need a few drops) in muriatic acid, then suspending the stainless steel item above the liquid. The fumes should blacken the steel over time. I never tried it, and Dad is gone now, so I can't get any more information. I don't recall him saying how the different grades of stainless react to this treatment, or how deep the color goes. You could try it with a piece of the same grade stainless you have by buying a small piece from some place like Online Metals, provided you know what grade stainless you have.