I would be very interested in seeing your results. I have used potassium nitrate for various things before, one of which was growing tobacco. Which is leagal in certain amounts and for personal use. I am not talking about wacky tabacy either, just plain old burley tobacco.
Anyway, I have seen the Nitre Blue salt on the Brownells website and was curious on how they work. From what I understand about "fire bluing" steel, is that it is the oxidation of the steel at that temp is what causes the color. By submerging your steel piece into a melted salt bath or melted lead, how does it allow the oxygen to get to the steel? I gues I can see it with salt peter, there is probably enough O2 in the salt to allow the color to happen, but I would not think that lead would work.
Definitely post your results, I would really like to see how it turns out.
Also, do you think fertilizer grade KNO3 would work as a Nitre Blue salt, or would it have to be pure? If you are looking for a source of salt peter, check out eBay (of course) and also do a search for firework supplies (
Skylighter ). Potassiumm nitrate is a key ingrediant in making black powder. Fertilizer grade is cheaper than pure, but not sure how the "conditioners" that they put into the fertilizer would affect the steel.
Edited to add: I agree that liquid KNO3 can be very dangerous. It is a molten salt which will burn and probably stick to you. Plus potassium nitrate is an oxydizer and will facilitate the burning of a fuel like wood, paper, charcoal, etc. It is some wickedly fast stuff that makes up 75% of black powder. Use caution!!