Angier page 123 H 2
""At Springfield armory a mixture of Saltpeter (Potassium Nitrate) and 8 to 10% manganese peroxide is thorughly mixed & heated to about 200°C (390°F), at which temperature a pinch of sawdust dropped onto it briskly burns off. The degreeased parts are stirred about in it for 5 minutes or until the desired color is obtained, freed from adherent saltpeter with hot water, darkened in hot whale oil, cleaned with gasoline and finally oiled.
According to Hartmann, a temperature of 315°C (600°F), that is about the melting popint of saltpeter, is necessary for producing a deep blue colour: the same author (and many others) state that the addition of manganese peroxide is of no special advantage, safe a slight quickening of the process.""
The only times I ever tried it I simply used straight saltpeter & immeresed the parts as soon as it melted & was quite pleased with the results. No doubt results (Color) can be varied some by the exact temp used. Also I have no idea what the difference in effect would be between using the Manganese Peroxide Angier mentions & the Mangenese Dioxide Oscar used would be.
