Does anyone know any good sources of info online for hot-blueing formulas, etc? Or, recommend any exceptionally good books?
The best source for chemicals, equipment and info is Brownell's Gunsmith Supply
Some of their literature on bluing is free.
One great book is the all-time classic "Firearms Bluing & Browning" by R. H. Angier.
There's also a video, "Hot Bluing Firearms" by Steve Acker.