This is my short page about electrolytic derusting.
If you don't know what I'm talking about yet, it's a great way to get red rust off of any iron/steel stuff and it can't hurt the material.
If you search for "electrolytic rust removal", you will get lots of hits. Take a look at some of them if you want more detail.
It consists of a 5 gallon plastic pail filled with water to the height needed to cover up whatever you want to derust,
a battery charger of some sort, some Washing Soda (Baking Soda will work, too, I am told), and a piece of mild steel or
stainless steel plate.
You add several tablespoons of washing soda to the water in the pail. Connect the positive lead from the battery charger to the steel plate that will act as the Anode. Connect the Negative lead to the part that you want derusted(it is called the "Cathode").
Put both the part and the Anode into the pail, making certain that they CAN'T touch. Plug the charger in. In a minute or so you should bubbles fizzing from the part and you should see that the meter on the charger shows that it is working. I generally wait at least several hours before examining the part to check for progress.
I unplug the charger, remove the work and I can see a black film on the affected area. I scrub the black stuff off with Scotch Brite. If the part is all shiny, I immediately oil it or apply car wax so it doesn't rust.
If the part needs more work, I put it back in the pail for several more hours or overnight, maybe.
It seems that the current drops off after a while. It goes up again, somewhat after cleaning the part off. It goes up more when I clean the anode off.
That's my 35 year old home made battery charger on the chair. Since it has both voltage and current meters, it allows me a better picture of what's going on in the pail, but just about any battery charger in the 4 amp to 20 amp range will work.
The lower the current, the longer it will take to get the job done.
1. You can't put back metal that's already rusted away, so if there's a pit in the part, there will still be a pit in the part when you are done. Some of these pits may be deep enough that its hard to get the loosened black stuff out of them. I used scotch brite to get the black stuff off and it worked well on things that simply were rusty. But things that were badly pitted needed a wire brush. Wire brushing a chisel isn't a problem for me, but wire brushing a 12 inch ruler would ruin the apprearance. So, there's a limit on what you can "bring back to life".
2. Too bad, but this process doesn't work on mill scale. I tried. The scientists say the mill scale is a ferrous oxide that doesn't have an "extra" atom of oxygen to give up in THIS process.
3. The first time I tried this process, a few years ago, I was somewhat dissapointed that I didn't get the orange grunge floating on the top of the water that other people had described. That time I had used a stainless steel anode (the positive plate). This time I used a piece of mild steel and I sure did get the grungie goo on the top.
4. This time, it seemed that the current dropped off considerably after several hours. I noticed that the anode had gotten thickly coated with rusty grunge, something that, I think, didn't happen with the stainless steel anode. When I scraped the stuff off the anode, the cureent went right back up.
5. Repeat after me: Negative Lead to the part, Negative Lead to the part, Negative Lead to the part, Negative Lead to the part, Negative Lead to the part.