It was rust blued using Neideners formula, not cold blued with the selenium crap. I don't recall the exact formula but it was essentially nitric acid, hydrochloric acid, and pure iron filings. Some of the misc parts - like the lever blued beautifully in just a couple applications. The bbl turned a dull gray and stayed that way. I must have made 15 passes on the thing. It would rust, but then carding it off took off everything.
It's been a while but IIRC, The bbl was swabbed with clean cloth wetted with the bluing solution, placed in a warm box (wooden box with a light bulb and a pan of water for humidity) allowed to rust overnight, set by pouring boiling water over it, then carded off. It worked wonderfully for everything but the bbl.
ETA: Didn't / Don't mean to distract from your post op. Your Model 12's look great! - and rust bluing is the right way to do it.