I use a product called bio-deruster, sounds a very similar product to the above sugestion. Uses a chelation process.

Doesn’t burn and removes all the oxidisation right into the pits. Great for seized assemblies and doesn’t harm plastics, rubber or even touch paint or chrome. Cast iron emerges from an overnight soaking a nice uniform grey.

Blasting is pretty agresssive.

If you can find a company that does soda blasting (as in bi-carb), then you’ll find that is an extremely gentle medium. It is possible to take paint off layer by layer, and it’s good for the environment.

I’ve used it on various classic car and motorcycles panels etc, and it’s very impressive.