Hot Rods Preserving bare metal

You could Blue it like a shotgun but it would take a pretty big pot.

 

My car roof is rusted badly for years, not new metal. The metal color turns black.

 

Thanks to everyone that made recommendations.

 

Yeah, thanks! ^^^^ I need to do something with my '55 F100 NOW. Am seeing a little rust on top, want to arrest it immediately. My new carport makes condensation daily, leaks drops (Big drops) onto the roof, hood, fenders...
My back shop is full of roadster & touring stuff, plus 2 future projects (Aggh!)
Now I can go to work on F100.