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Black Oxide Control

Hot black oxide on steel processes contain caustic soda ⇦liquid caustic soda in bulk on Amazon [affil link] , sodium nitrate ⇦this on Amazon [affil link] and sodium nitrite.
Has anyone proposed what reaction the nitrite/nitrate go through and how they are consumed and therefore how to maintain rather than just using the same ratio as makeup.
Also what role the other additives have.

Geoffrey Whitelaw
- Port Melbourne, Australia
December 7, 2010

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Well for what its worth, in school I was told that caustic soda baths of sodium nitrate, sodium nitrite, ammonium nitrate, or potassium nitrate and sodium hydroxide were NON DEPLETING BATHS. Which means that the combination of the niter's and the heat caused the iron atoms to borrow the oxygen atoms from the water to form Fe3O4. In theory the salts would last forever if one found a way to prevent the introduction of elements that break down the solution such as aluminum etc and found a way to deal with the carryout problem when taking the parts out of the bath. We were also told that the introduction of certain chemicals such as cyanide and a few other less desirable things would felicitate blueing some forms of stainless and nickel steels. We were also told that potassium would enhance the blueing of vanadium base steels and the list goes on. As far as cyanide it does work to some degree but its far to dangerous for some one as stupid as me to tamper with although do use it to poison gophers. As far as potassium and vanadium, it seams to be an old wives tale. I've played with it and it does not work or I did something wrong. Rugers, Weatherbys and HVA actions and some barrels still turn purple. I have come to the conclusion that purple is very pretty. I love purple and so do you! Some gunsmiths believe that you can not start a new batch of salts without a few cups from a bath that is operating to activate the new salts. I have even read this in some old publications. HOGWASH! Also some gunsmiths add a few drops of acid to the bath. Adding acids to base's never made much sense to me unless it was vinegar and baking soda in a bottle with a cork in it. That's all I know but I'm not a chemist so I probably would take what I've just said with a grain of salt. FYI the longest I have ever run a bath without killing it was 5 years. I generally add a cup of mixed salts every 30 hours of running time. More if I have to shock parts repeatedly.

Rod Henrickson
gunsmith - Edmonton, Alberta, Canada
February 4, 2011