>>2530284forced patina is what you want, like anon said.
and like anon said all you have to do is expose the knife to something acidic for a while.
how i personally prefer to do the acid etching depends on how i plan to use the knife. really thick patinas last a long time between re-applications but give the metal a sort of matte texture which drags on food.
knives that might contact food: i just stab a banana or apple or something and leave it for a day.
knives that will not contact food: near-boiling apple cider vinegar for a few mins, or cold apple cider vinegar overnight. cheap household product you might have around already that gives near-black super thick patinas that last forever. the patina sheds a bit at first but it goes away, rub it down real good.
people make it more complicated than it is that's all you really need to know.
