815F/825F and you'll get the blue black color. I get excellent results with the Brownells Nitre Blue salts at those temps so I don't know what the problem is supposed to be with them, they work fine for me. Plain potassium nitrate will yield the same but it's hard to get anymore in small quantitys. I've never put mang.dioxide in 'cause I never had any. I use my lead themometer to keep a close check on the temp. A little higher temp than the needed 815/825 and you get a grey cast to it,,or at least that's what I get. To redo any parts, strip in a weak cold acid bath then repolish.
