Ed- I've seen many videos related to heat treating. Larry P. jigs up everything he puts in the crucible. As many companies have consistent patterns on their colored parts, I'm pretty sure they shield their parts the same way every time, to get the color pattern they desire.
My only real curiosity about this anymore is "Can patterned oxides (and other films) be created at the surface of a previously case hardened part, without the carbon atoms beneath the film migrating out?" I'd need to see sections from a sacrificial part to develop my opinion.
Please read the MSDS, Kasenit is a mixture of Carbon black, and Ferro Cyanide compounds.
