T&T: Anchor chain painting

[Arild Jensen]

Faure, Marin wrote:
>> "rust destroys...it doesn't protect.
>> REPLY
>> I believe there is at least one exception to this and that is Core Ten
>> steel (I think that's what it's called).  It's formulated to form a
>> surface oxide ("rust") and then it stops.  No painting ever needed-- the
>> "rust" protects the metal itself.  
The so called Kor-Ten steel was also used extensively for bridge 
building in the seventies and eighties. I  believe it was Dominion 
Bridge that first used it for bridges.

Actually  oxides  have been used to prevent further "rusting"  The old 
browning of gun barrels was a form of controlled rust. 
Several industrial  surface coating processes  also use a form of  
oxidation to  protect   metals.   Mill scale is he iron oxide  that 
forms when hot stel lis extruded in a rilling mill.  Unfortunately  this 
mill scale is often britle and cracks then flakes off, exposing  raw 
iron or steel  to begin the oxidation process once again.
Parkerizing  is the black matte finish  you often see  on non plated  
hardware.  Its a controlled rusting of a uniform nature  but with added 
chemicals to create a barrier coat  of more durabel  characteristics. 
The black finish  you see on blacksmith forged  metal work  is also a 
kind  of rust but with a high level of carbon  from the charcoal  in the 
forge furnace.
Rust as opposed to controlled oxidation of  the surface is  a 
non-controlled form of oxidation that weakens the  metal if deep pits  form.

Arild