A lot of folks use electrolysis for rust removal, which works great and if you are going to do a lot of rust removal, I recommend it. I don’t do a lot of it, and find Evapo-Rust works spectacularly to clean up even pitted parts. The product is reusable, so a gallon jug lasts quite a while. I have some different sized plastic containers depending on the size of parts, and completely submerge the parts. I cover the container to limit evaporation (Saran Wrap works great if you don’t have a lid). Every few hours I take a look. For light rust a few hours can do the trick.
The parts should be cleaned and degreased before being put in the Evapo-Rust. I use a power wire brush on pitted areas, and then wash the parts with dish soap. During rust removal I use a brass or stainless brush, or Scotchbrite pad, to rub the heavy black oxide build up areas, just leaving the parts in the container.
Some have commented they don’t like the gray color the Evapo-Rust leaves. Using a brass or stainless brush, Scotchbrite, or steel wool, while the parts are still in the Evapo-Rust, will remove most, if not all, of the grayish color. A little buffing with Scotchbrite, steel wool, or other abrasive after the parts are dry will brighten the cast iron up further.
When satisfied the rust is gone, I rinse the parts with water with some emulsion type grinding coolant added to prevent flash rust. I fill a container with water/coolant to dip rinse the parts. The first time I used Evapo-Rust, and rinsed with plain water, the parts flash rusted before I could spray something on them.
Rust Prevention
I used Remoil and various waxes for rust prevention with reasonable effectiveness. Wax is difficult to get into every nook and cranny. Remoil works pretty good, but I found an even better solution. Researching rust preventives turned up a product called Alox, a calcium based rust preventive originally developed back around WWII for naval ships. Lee Precision, maker of many ammo reloading products, has a product called Liquid Alox. It’s designed use is lubrication of cast lead bullets, but it is an excellent rust preventive. I reduce it about 20:1 with naptha, and use it in a spray bottle. I spray a little on a part and use fingers or paper towel to spread it around. It dries as a thin, hard film with a bit of a haze. It can be buffed with a cloth if desired. Previously something might get some water overspray on it and get rust spots. The Alox treated parts have had water spots from minerals left behind but no rust. I treat all my hand tools with it, including blades after sharpening. Works well on any cast iron or steel. Part of the Alox will settle out of the mixture when it sets for awhile, so it needs to be shaken before spraying.