I used Evapo-Rust for a while but it was so expensive that I started looking for an alternative. I finally settled on citric acid because it was cheap. Turned out that it worked well also. I always used it in a plastic container such as one of the wife's old Tupperware containers.
I left most things in overnight, which was usually long enough for most items. Wash them off with a garden hose to get rid of most of the "stuff" that was left on the surface. Dry the surface as good as you can and then use 0000 steel wool to clean the balance of the crud off. After all the crud is off, spray it with your favorite potion. I used Remoil(Remington gun oil) to keep the piece from rusting again. I used this on plane irons, wrenches and even plane bodies and frogs. It didn't affect the Japanning on either one.
I did leave a plane body in too long and managed to ruined it. The acid etched the bottom badly. As was mentioned above, make sure your item is completely covered. If you don't you will get a line across the part that is virtually impossible to remove...ask me how I know:).
I used a cup of acid and poured that into a gallon of hot water. It dissolves quicker with the hot water, and if you use it while it's still warm it works faster.
My only problem was that I didn't like the color of the metal after it was done. It was a rather unnatural looking gray. Also it seemed like it made the surface rough. Maybe I left it in the acid too long, but I noticed this on many different items left in for different amounts of time.
Like most things, you need to try it for yourself , you may have different results.
Mike
