I saw some that have the cool purple blue color and wondered how you did it with out screwing up the blade temper.
Looks like this.
(http://i27.photobucket.com/albums/c154/Skullworks02/KNIVES/gallery25-lg.jpg)
I would think the blueing heat has to be no higher than the drawback temps of the blade steel. Lin
I recently read a post where a 20 minute etch in vinegar followed by 2 hours at 320 degrees gave a very nice blue. I plan to try it on a couple of blades I am working on.
I have used some cold blues with varying degrees of success. I have also tryed to heat blue but the temp is too high for a blade. I have used it on damscus bolsters. Knifemaker