I would be interested in knowing for certain what this guy's chemical is, and just how much heat he applies.

To get the heat colors with a torch, you are getting into pretty high heats, and you don't need any chemicals, just a clean surface.

On the other hand, a guy I know has done some pretty reasonable looking faux color case, using IIRC clove oil, and light heat, just enough to heat up the oil on the surface.

I'll have to consult and see what his process is.

I've used the hot part/cold blue solution on some model engine parts that were to look case hardened, and it won't come out looking anything like that shotgun.

Cheers
Trev