What is the Grey Coating

[Curti]

Some steel comes from the foundry with an almost ultra thin ceramic coating that resists rust. It varies from a light to a dark grey. Can this coating be reproduced? I have found in the past that I have summarily painted parts black, when in reality the factory never did paint them.

[Bhigdog]

When steel is heated to red or higher heat in the atmosphere the surface oxidizes. It's called scale. That's what it looks like to me.......Bob

[nearchoclatetown]

Bhigdog is right, it is the carbon scale from being heated when made.

[Curti]

Thanks fellas. Now I know how it got there, all I have to do is figure out how to reproduce it. Maybe bead blast then parkerize fowllowed by a thin coat of dull clear. I am always trying to achive the original look.

[Roger Walling]

It could be a heavy coating of phosphate that will not allow the steel to rust. I had a truck that all the paint peeled of the roof once and there was not a spot of rust on it.

I was told that if steel is left in a phosphate solution too long that occurs.

[Curti]

That begs the question, what is phosphate? Is it oxide of phospherous?

[Mark Shaw]

Phosphate is a mined mineral that can be used to produce phosphoric acic. This acid can be used to prepare bare steel for painting. It etches the metal to provide excellent adhesion and also serves as an excellent rust inhibitor. (See OSPHO)

http://www.ospho.com/

[bkazmer]

and yes, it is a salt that is an oxide of phosphorus.

[rickomo1]

Read this a week or two ago and low and behold was in home depot and saw a product by Klean strip called Phosphoric Prep & Etch might be worth a try it states removes rust and prevents flash rust so it must leave a film or residew of some kind. about 6 bucks a quart.

[Mark Shaw]

Rick,
Much less expensive than OSPHO...particularly when they charge extra for shipments west of the Rockies.....

P.S.
I see you are just across the river from me....