Nitre bluing is nothing more than heat or temper bluing. All the Nitre salts do is to provide a bath held to a specific temperature so that the temperature is uniform around the part (no hot spots or cooler spots). But this can be easily accomplished with a flame or in a high temp oven. Potassium nitrate is a good medium because of its working range (300-1000 deg F) and its very soluble in water so its easy to clean up.

Mike Hunter
www.mikehunterrestorations.com