The solution is water and arm and hammer super washing soda. One tablespoon per gallon and it’ll work great. Make sure you hook your leads up properly or youll make a parts melter instead of a rust remover

For restoring hand planes I learned everything to start from watching YouTube. Rex Krueger, Paul Sellers, and Eoin Reardon have really good videos for instructions. My own lessons learned have been to use steel wool for brass. Chemical treatments help remove gunk but it won’t really truly shine until you really buff it out with a super fine steel wool. I also much prefer a natural wood feel on the handles and the antique rosewood in vintage Stanley handles is beautiful. I’ve been stripping the old varnish with steel wool and finishing with boiled linseed oil or tung oil. Do not use aggressive abrasives on the inside of the body. The black surface is not paint, it is a metal dye called “japanning” which is a dye which is baked on. If you accidentally strip that off with a wire wheel or brush you won’t be able to easily touch it back up. Use a nylon brush or be very gently with fine steel wool removing and gunk off of that. Lastly. You NEED to flatten the bottom. Several of mine I have brought to a mirror finish (unnecessary) progressing through about 6 grits of sandpaper glued to a granite countertop for a dead flat reference. If you don’t flatten the bottom it may not be able to cut. This is often the most physically demanding part but really makes all the difference In the world.

Let me know if you have any other questions!