I tried the pickle juice years ago. Yes it does turn the blade dark, but also blotchy. Some of this may be due to oil left in the steel. Tried several times more and gave up. Each time I rubbed off the oxidation with 1000 grit non woven grey Scotchbright pad, it came right off down to original finish.
So last year I started using a little 21 for boning out a turkey carcass and don't you know it's now got a nice patina and it's part of my turkey disassemble kit.