[TheForge] pitted rust

Wed Oct 1 13:41:00 2003

My limited understanding of pitting is that it occurs because (1) rust =
catalyzes further rusting and (2) the "pit" acts as the cathode where the =
oxidation Fe-->Fe+++, and the rest of the steel acts as the anode, where =
the corresponding reduction of oxygen or whatever takes place.  Conceivably=
 you could artificially duplicate this natural process, but it could take =
considerable experimentation to do so.
=20
You could cheat by painting the entire surface and then blasting this with =
sand or beads to create pits in the paint.  Now simply etch in strong acid =
(muriatic) and maybe you'll get what you are looking for.
=20
The sawdust idea ain't half bad, except that if the acid is strong enough =
to etch quickly, it's gonna dissolve the sawdust.  Maybe something besides =
sawdust could be used.  Large-grained quartz sand, perhaps?
=20
Another idea would be hammer in scale.  Scale is harder than iron, so can =
easily be hammered into the hot iron, producing an all-too-familiar =
pattern.
=20
Hope this helps,
=20
Bruce
NJ

>>> [email protected] 10/1/2003 10:48:52 AM >>>

Hello all,
    I have a bit if a problem on a project and thought I should see =
what=20
the collective wisdom of the forge might have to offer.

I have a client who would like me to duplicate the rust finish found on=20
an old piece of ~ 2" pipe.
This guy is very picky and I've tried several textures which have been=20
rejected.
The difficulty is that this is some serious rust. I think this sample=20
of pipe was buried in  the ground for many years. Its surface is=20
covered with small pits maybe 3/23" average diameter and about 1/32=20
deep. i.e. it's a fairly heavily pitted rusty surface. I am imagining=20
the corrosion process could develop this way when grains of varying=20
composition and size sand/minerals of the ground being pressed against=20
the pipe.

Typically when I do a rust finish, I treat the item with muriatic acid=20
to remove any black forging oxide and to chemically clean the surface=20
of oils/junk/etc. I then warm the metal with a small torch and sprits=20
it with bleach solution. This gets a powdery red oxide almost=20
instantly. I do several treatments with bleach solution, then switch to=20
a saline solution and heat for several days. I've found using only the=20
bleach solution will develop streaks in the patina and it can for white=20
residues. The salt water keeps the patina even, and has some nice=20
subtle color variations such as brown and black spots speckling the=20
surface.

The main fault with my 'artificial' rusting, is that it would take me=20
years to develop any kind of deep pits on a surface. Someone suggested=20
packing the pipe in a box of sawdust permeated with muriatic acid, but=20
this seems like a fire hazard to me, and I bet it would still take=20
years.

My current best idea is to braze a lot of small diameter ball bearing=20
balls to a set of die plates and texture the pipe in the hammer before=20
the rusting.

Anyone have any clever tricks for getting deep rust?

Seems like there should be a way to do this electrochemically, perhaps=20
using a plastic sponge/foam as an irregular electrode against the pipe.

Thanks for any advice.

                Cameron Stoker
                [email protected]
                "May you run like a vicu=F1a!"
                pgp key @ http://keys.stoker.net

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