I do not know the details of this process, but I have been told that the best way to remove rust while removing the least possible amount of metal is to blast the surface with ground walnut shells, in a process similar to sandblasting. This is how historic cast iron machinery at the Slater Mill in Pawtucket, Rhode Island (the birthplace of manufacturing in America) is conserved.

Our back storm door is painted wrought iron. When a rust spot develops, I sand it a bit with the dremel. There is actually a tool you can buy to remove the rust.

Sorry, I've never heard of using vinegar.

I ended up soaking the frame in white vinegar just under 2 days and the rust just rubbed right off with a very worn scotch brite pad. I was amazed how clean the frame came out and there was no pitting in the finish.

I know this is late and you solved your problem but I wanted to add my 2 cents. I use a commercial white vinegar to remove rust on many of the parts for my found object sculptures. When that doesn't work I use a product gunsmiths use to remove rust and bluing. You can buy it at most sporting goods stores like Cabela's.

Robert

Robert