[TheForge] Re: Rust Patina Finish

Wed Aug 13 00:18:01 2003

Read about it years ago and can' t remember for sure but seems like
phophoric acid is part of the parkerized finish on military firearms.
Randy Mundt
----- Original Message -----
From: "Mike Spencer" <[email protected]>
To: <[email protected]>
Sent: Tuesday, August 12, 2003 11:32 AM
Subject: [TheForge] Re: Rust Patina Finish


>
> >>  The untested answer is a phosphoric acid pickle.
> >
> > ...I thought of nasty acids, which never stop eating through the
> > steel. But Phosporic, now that could be something else again.
>
> Very much so. Depending on what you do after pickling, phosphoric acid
> leaves more or less of a tightly adhereing coat of iron phosphate on
> the metal.  Experimenting with different concentrations of acid and
> with flushing, light rinsing, wiping, steel wooling etc. after the
> pickle will be enlightening.  The comercial product is a thick
> liquid and should be diluted with water.  In a chilly shop, an
> immersion heater will help to keep it up in tepid-to-kinda-warm range.
>
> One test piece -- a repouse experiment in 16 ga m/s -- I pickled in
> phosphoric and only wiped dry, resulting in a uniform matte grey
> finish.  No wash/rinse, no wax or other coating.  It lay on a shelf in
> a damp shop for over a decade.  After a few years, neighboring pieces
> of sheet metal and bar had turned all rusty.  When I moved my shop and
> this piece had been there well over 10 years, it had a few small rust
> spots on it.
>
> I've finished several pieces with phosphoric acid pickle, light rinse,
> wipe dry, light rub with 4/0 steel wool, Brownell's Oxpho-blue,
> carnauba wax.  These have resisted rust (indoors) better than pieces
> finished the same but without the phosphoric pickling step.
>
> And phosphoric acid is wayyyy less dangerous to work with than
> HCl/muriatic, battery acid/H2SO4 or nitric.  Of course you don't drink
> it (er, well, actually, you may, in dilute form in some cola-type soft
> drinks :-), nor put it your eyes or nor soak your hands in it.  But if
> you get a bit on your skin, you *don't* get instant blisters or have body
> parts slough off while you're running to the sink or shower.
>
>
> - Mike
>
> --
> Michael Spencer                  Nova Scotia, Canada       .~.
>                                     /V\
> [email protected]              /( )\
> http://home.tallships.ca/mspencer/   ^^-^^
>
> --
>
>
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