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topic 59024

Rust Bluing problem: the work turns brown instead of black after boiling

November 6, 2012

Q. Hi everyone, I have been trying to blue a handgun barrel as an experiment. I made a solution from HNO3 and HCl. After applying this solution, a thin layer of brown rust forms within an hour and a good one after 12 hours. Now when I put the piece into boiling water it turns brown/bronze in colour. Why not black?

Amazingly when I clean the piece and re-apply the solution, it turns dark gray after a while without boiling. Can anyone help explain what is going on actually?

Amer Khalil
Hobbyist - Peshawar, KPK, Pakistan

November 29, 2012

A. You are creating Fe203 which is ferric oxide, which is reddish brown. You want to make Fe3O4 which is magnetite which is black. Its a different solution. There is a book sold by stackpole called "Firearm Blueing and Browning" [affil. link to book on Amazon] by RH Angier. It has several of the formulas for slow process bluing. It's sort of redundant in North America as a lot of the chemicals used are now very tightly controlled and no longer available.

rod henrickson
Rod Henrickson
Edmonton, Alberta, Canada

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