Although technically all brown or blues are oxides the term Black Oxide most often references the hot salt method rather than rust bluing/browning. I can't say for positive if this was what Baker used on the Black Beauty or not. They would not have used it on the barrels unless they had the ribs & all brazed rather than soft soldered.
Most cyanide hardening I have seen has more of a "Zebra" stripe appearance to it than this Folsom Leader but perhaps they were able to get a different effect using it.
I have a 16 gauge Black Beauty, though not as nice as this one. It has 28" barrels, tight chokes & @ 6 3/4 lbs is not a lightweight but a nice shooting gun never-the-less.
