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Ted Mooney, P.E. RET
Pine Beach, NJ
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for Metal Finishing since 1989
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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?
Hobbyist - Peshawar, KPK, Pakistan
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 [on eBay , Amazon, AbeBooks affil links] 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
gunsmith - Edmonton, Alberta, Canada
November 29, 2012
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