[ColinTheAmpMan1]

This doesn't really answer your question, but I know from experience that rust-resisting finishes do exist. When at secondary school, I was quite good at metalwork and had finished all of the required stuff. The metalwork teacher asked me if I'd like to make something using the forge and gave me a catalogue of items. I chose a particularly complex table-lamp. After it was all made, the teacher gave me some satin-finish black paint to complete it. Don't forger that this had been in and out of the forge several times and I don't remember wire-brushing it at all. This was over 50 years ago and I still have it as a bedside lamp.The paint is still fine and there is no sign of rust. I wonder what that paint was and if it is still available? Maybe for forge-made items?

I vaguely recall recently seeing a programme on TV about painting and maintenance of the Firth of Forth (I am often tempted to add "of Fifth of Sixth") railway bridge with some new-fangled paint. There was always the comment that as soon as the team of painters had got to the end, they had to go back to start the job all over again, but this new paint is supposedly going to last much longer. Bear in mind that the bridge is in a particularly salty water environment, too.
Colin.