Grab a tool that offends...
I found an old socket chisel up at Dad's house. This thing was a wreck. The handle was missing, the socket had been mushroomed out such that it won't take a new handle, the bevel edge looked like Dad had used it to shave a few 10 penny nails, and the rust had to be 20 years worth. We're going to use electrolysis to clean it up.
The pics don't always translate well, so for contrast, I put the bad one next to one of my good bench chisels and a Stanley Fat Max I use as a beater.
Gather your tool cleaning stuff...
You'll need a D.C. power source, a plastic bucket, a piece of sacrificial steel or iron, some sodium carbonate, and an old coat hanger.
Sodium Carbonate (Na2CO3) is a sodium salt of carbonic acid, blah, blah, blah. It's used as an ingredient in making glass, pH regulator in pools, food additive, and water softener, among others. And, it comes in many names: You may find it listed as driveway cleaner, super washing soda, soda ash, OxiClean, and many others. Odds are high that you have some around the house. Check the HHS Household Products Database to see some of the other product names... OxiClean will work in a pinch, but it's more expensive and less effective. I use either soda ash (I have a pool) or the Arm & Hammer Super Washing Soda... both are ≥85% and they're cheap!
As for the power source, we all have those little plastic bricks from an old piece of electronic equipment, but those typically don't have the horsepower we need. You can use a constant current power supply, but they're kind of pricy. All you need is something that will deliver a couple of amps... I have an old Craftsman light duty 6/12 volt battery charger, and it works just fine.
Set it all up...
Fill your plastic bucket with enough water to immerse the tool you're trying to clean. Use warm water as it will aid in dissolving the sodium carbonate. Now, add the sodium carbonate... there's a formula to determine the correct amount, but I don't know it. The formula I use is just add about four table spoons, and stir it until the soda starts to dissolve.
You may have noticed the old railroad spike in the picture above. That's my sacrificial piece of steel. Rebar is a great alternative! There's also some coat hanger wire with the coating sanded off.
Start off with the power supply UNPLUGGED! Hook the positive lead to the sacrificial steel. Hook the tool to be cleaned to the negative lead. This is where the steel wire may come in handy. If need be, it will conduct to the steel and allow you to keep the clamps out of the water... otherwise, the positive lead clamp will corrode over time.
Start the show...
Plug it in. Within just a few seconds, you should see it begin to bubble. A word of caution here; the bubbles you see are hydrogen and oxygen... no smoking or open flames. Also, it's a good idea to just do this outside.
Now, just let it cook. This isn't a 10 minute job, and depending on the amount of rust, this may take a day... or two. Ultimately, the bubbles will drastically slow down as it approaches the end of the cleaning phase.