Ed;
The Torch Coloring I am referring to is where one takes an acetylene torch adjusted to a hot flame & holds it in one spot on the metal until it changes color.
This will of course produce mottled Temper colors, but it also will destroy/draw the hardness of the original case hardening & in my opinion should never be done.
Even though a torch can be used in the chemical method I described it is not held in a manner to concentrate the heat to heat a spot enough to change the color of the metal. In fact no "Tempering" is done, the metal is simply warmed uniformly until it attains an all over temp of around 200°F. This does absolutely no damage to the original heat-treatment of the part.
I would think the part could just as easily be heated in an oven, I just described the way Ithaca wrote it up in their Service Manual, & they suggested a propane torch for the heating.
