I have found the old rust comes off on its own as long as its well lubed. ATF works wonders for this. The best resurrection of a heavily rusted chain I have seen was my neighbor. He put it in a Rock Tumbler with light sand for a few hours.
Over the past years I have come to consider chains an expendable item when it comes to rust and wear...
__________________
No matter where you're at... There you are... Δf:=f(1/2)-f(-1/2)