JDW,
No offense meant, 'cause I don't know the difference; but I thought the cyanide process provided the same kind of surface hardening as the bone charcol process, but usually throws a different coloring style as C-man mentioned the P-gun type tiger striping (Philistine that I am, I like it).

And I do know that many steel parts are case hardened without coloring. Browning SP recievers were case hardened with no coloring.

There's folks here that really do know and we'll get the skinny soon enough.