That looks great Fred. I need to give this process a try.
I believe this is a variation of the Charcoal Blue process that was used by Colt. But in the Colt process, the parts were held stationary in a rotating drum oven. The charcoal was heated along with the parts to the correct temperature. As the drum rotated, the tumbling of the hot charcoal over the steel surfaces provided the burnishing. Another variation was called the Carbonia Blue process, which was used by Smith & Wesson. It also utilized a rotating drum oven, but instead of wood charcoal, they used bone charcoal that was treated with a proprietary product called Carbonia Oil that contained pine tar.
Both of these processes replaced the earlier hot, dirty, and labor intensive hand burnishing described by Kutter
