Hot Bluing at home

[RetiredFAE]

Great video.
That blackening is more akin to seasoning a cast iron frying pan, it blackens the part, doesn't blue it.
In 60+ years of gunsmithing, I have hot blued thousands of guns, hot bluing is a rusting process involving the use of salts heated to about 280 degrees, plus or minus, depending on the bluing salts being used.
This blackening process will give some rust protection, and is far less labor intensive, and less expensive, than actual hot salt bluing using corrosive salts, and is more useful to the home machinist I think.