Nick, depends on how anti rust you want the coating but gun blueing/blacking may be appropiate. gThis finish is resistans to rust but will not prevent it completely. I am not talkinh about the cold compounds but either the hot rusting process or the high temperature caustic blacking process.

Neither of these processes make any dimensional change to the component and are resistant to rusting in "normal" conditions but if left wet for a long time rust will take over !

John

Tuftriding.

Low temperature hardening process that puts about 10 microns of case on a steel product. It's black and the upshot is that it very rust resistant.

Local heat treat plant has a bucket of salt water in the passage way with some steel bars sticking out. Where they enter / leave the salt water there is a big rusty scab attached to the bar, but remove it and it wipes off leaving the bar pristine. This bucket has been there for about 8 or 9 years.

The scab is caused by all the crap and dust in the air settling on the top of the salt water and rusting

Sounds more liek you need powder coating or something like that

J

Nick, why not research Zinc Electroplating, it comes out very smooth and clean and is a common industrial process.

Clive

JD, the one I know is POR 15, another of my mates uses it when rebuilding trucks, and cars. Ian S C