Something I have been tinkering with is a Scottish Sgian Dubh for a friend. Blade is AISI 1084 3/16" thick. Heat treated with a high temperature silicon on the blade to create a pattern. Lightly sanded the blade after quenching then popped in the furnace for tempering. The color variation is from the exposure to oxygen, variation is from well sanded portion with 400 grit to only steel wool buffed. Colors are from blue to purple and almost to black in some areas depending on the angle of light. Just hoping the color will hang around, a few more experiments are in order and testing to see how well the surface holds up. Thinking the cutting edge will get a light acid bath then cold blued and buffed. It should blend in nicely afterwards.