[Boatanchors] Rust, Coatings, etc.

[Bill Carns]

Certainly, and you have too. It is called Gun Blue. Gun Blue is nothing more
or less than carefully applied rust - applied to a very well polished
surface in a very controlled way to produce a layer thickness that refracts
light and makes it look Blue.

Rust is a great passivation for steel and it is a very misunderstood process
and situation.

By the way, the US Navy uses Ospho on their rusty surfaces to terminate the
rust process before they paint and it works well.

The problem with rust is that if you try and paint over it without
terminating the oxidation process, then you get way worse pitting and
potential structural damage.  I use Ospho on my tower components and it
works very well.  I Ospho and then use a Zinc rich paint over that and it
works well and holds up well.

Bill

-----Original Message-----
From: boatanchors-bounces at mailman.qth.net
[mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of Michael D. Harmon
Sent: Sunday, April 07, 2013 9:39 PM
To: boatanchors at mailman.qth.net
Subject: [Boatanchors] Rust, Coatings, etc.

I've been reading the thread about rust converting coatings, and I
remembered something from about 35+ years ago that I've always wondered
about.

Westinghouse built a factory back in the Seventies in Jefferson City, MO
when I lived there (later bought by ABB).  They manufactured big industrial
transformers and switchgear, as I recall.

Once they had the exterior of the building completed, they treated it with
something that made it rust.  Yes, that's right - as in the reddish-brown
iron oxide.  As first it looked pretty bad but after a while it settled into
a deep red-brown color and actually looked sort of unobtrusive.  Not what
you'd expect from a big steel building covering several acres.  I asked
someone why they did that and was told that the rust was only surface deep
and permanently protected the underlying steel from further corrosion.

I'm wondering if any of you have ever heard of a similar situation where
rust was used as a protective coating?  Does the process have a name?  
Does it work somewhat like gun blue?  Gun blue uses phosphoric acid and
creates a deep blackish-blue protective coating (iron phosphate?), but can
rust if you leave salty fingerprints on the surface and don't keep the
surface protected with a light film of oil.  You don't find many shops that
do hot-dip bluing any more, because the salts and solutions (and fumes) used
in the process are pretty noxious.

Mike, WB0LDJ
mharmon at att dot net
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