I'd stick to cold blueing, all that seems an awful lot of trouble to go to, when you can buy a bottle of birchwood casey that'll work just fine.

I've used their super blue and it's worked great, just so simple to do. Degrease, then wipe on and leave it. They say leave it a couple of minutes or whatever, I've left it overnight and it goes a yellow rust, run it under the hot tap and give it a scrub and your done.
No reason why you can't keep coating until you get the effect/depth your after. Once done it's all about the oil.

I've got a cold blacking kit from Frosts that works great too if you want jet black instead of blue-ish black, comes with a great degreaser too. But the dewatering oil doesn't do much.