I have a technique of wetting the rust and rubbing the alum foil over the rust... Then using items such as soft toothbrushes, dental tools, handsoap/dishsoap, more and smaller pieces of alum foil... Over and over until most if not all the rust is neutralized.... It is a technique that I have used for 5+ decades.
It is a technique that is not the easiest to master; so before one tried it on one of their items? I suggest they practice, practice and practice over and over..... Multiple times on old cheap large 5 gal square cans... When you can neutralize rust and not remove graphics on the cans... Then start practicing on smaller and smaller cans... Always working to neutralize rust without removing graphics.. (much harder than it sounds, but oh so worthwhile when you are able to either save and/or make a very marginal can into something you can display)...
Of course the more you practice; the less time and energy it takes to make an item more presentable... The technique, is not fool proof and it will not bring any item back to NOS.... But, I've have had some great success with the technique and I know that others have also had some very striking success in the last 10 years or so since I first shared what I do and how I do it here on Oldgas....