The following rust removal setup works great for those pots that are really rusted up. I use this setup a couple of times a year when friends bring me their neglected cast iron and when I find a D.O at a yard sale or a thrift shop. This info is from a site that I sometimes visit, especially when I think I have found a really old piece of cast iron-mostly though it turns out the the piece just "looks" really old.
Rust Reduction Electrolysis Setup
Rust reduction via electrolysis is almost harder to say than it is to set up. While it appears to be a way to remove rust, it is actually a rust reduction method whereby hard red rust (ferrous oxide) is reduced to soft black rust (ferric oxide). There is not much to setting up an electrolysis bath and this simple process will produce spectacular results on rustiest, crustiest, carbon-caked cast iron utensils you can find. There are only four components necessary for the entire setup...
1. A Battery Charger.
While any charger will work, a 12-volt charger capable of 35 to 40 amps is ideal. A 6-volt charger or a trickle charger will work, but will be extremely slow.
2. A non-conductive tub or container.
This is to hold the solution and must be non-metallic. A five gallon bucket, an old cooler, a Rubber-Maid tub, a plastic 55 gallon barrel, anything that will hold the rusty utensil will work.
3. A non-conductive rack to hold the cast iron away from the anode. A plastic parts bin or dish rack will work nicely.
4. A supply of Sodium Carbonate. This is to create an electrolyte solution that is capable of carrying the current created by the battery charger. Two readily available sources are "PH+" (a swimming pool additive available at Wal-Mart or any pool supply house), or "ARM and HAMMER WASHING SODA" (Not Baking SODA). This is a laundry detergent available at most grocery stores. It's in a big yellow box just like the baking soda and is found with the Tide, Oxi-Clean, Clorox, etc... Use 1 Tablespoon per gallon of water in your container. This does not have to be an exact measurement. Another measurement is two handfuls per every five gallons. Make sure the soda is well dissolved in the water.
5. Two chunks of metal. The one you want to clean and another you don't. Any cast iron cooking utensil can be cleaned. Cooked on carbon, rusty, and the worse it is the better it will look. The other piece is technically called the anode. It is what we will be electroplating with the rust from our good piece. Just about anything metallic can be used for your anode. Re-bar, angle iron, coffee cans, shovels, cultivator sweeps, whatever you have handy. The ultimate is stainless steel as it will be less affected by the process, but don't use your wife's stainless steel potato masher without permission (voice of experience here). The larger the surface area of the anode and the more it surrounds the article to be cleaned the better. Try a coffee can with the lid flipped up and the side split and spread out. It makes an easy one to start with. Now comes the fun part.
You must rig your setup in such a way so as to suspend the article to be cleaned next to but not touching the anode. Old dishwasher racks, bolts, c-clamps, bar clamps, duct tape, baling wire, let your imagination run wild. The desired result will have the anode secured and the part to be cleaned next to, above, or below it but again not touching. If something doesn't look right, stick your hand in the water and straighten it out. The solution is harmless. Make sure it is secure enough so that a bump won't tip something over. Now for the critical part... the red (positive) battery clamp must be attached to the anode (scrap piece), and the black (negative) clamp MUST be attached to the part to be cleaned!!!
Now hook your red clamp to your scrap iron and the black clamp to your griddle. Make sure you have a good connection. Use copper wire and more clamps if you need to completely submerge your piece. If it will only partially fit in the tub, you can turn it over and do it in two or more sessions. There will be no lap marks. Try not to allow the red clamp to come into contact with the solution as it will be attacked by the process. The other (black lead) may come in contact with the solution but will have to be cleaned frequently.
Now turn the charger on! If equipped the charger amp gauge will jump slightly. Bubbles should immediately start coming from around the iron pan. If not, check your connections. Make sure you have good metal to metal contact at all points. Let it run for an hour or so and check your results. Always turn off the charger before playing in the solution. If you don't it will let you know. You will see a black coating on the cleaned part. This can be removed by an air compressor or by washing. Bare metal will lie underneath. The bubbling action is what cleans the cooked on carbon off. Sometimes it needs a little more time to clean. But this method is self-correcting in that you cannot over cook it. The clean metal will stay just the way it is and the crud will be removed. Let it cook for 6 or 8 hours and come back to it. The carbon will fall off. Polish it a bit with your favorite method if you want, but it is not necessary. Season it soon as it is extremely susceptible to rusting at this point. Now go show it off to your spouse.
JUST A COUPLE WORDS OF CAUTION. The bubbles coming from the process are pure hydrogen. It is extremely flammable. Do not set it up by an open pilot light, and make sure you have some ventilation. Failure to do so will probably wind you up on the Darwin List.
The solution will become rather horrible looking in just a short time. But the solution will last forever. Only add water for whatever evaporates, as the sodium carbonate will stay suspended. When you can't take the look anymore, simply dump it out in the yard. It is iron enriched laundry water at this point.
Be ingenious with your setup. Try whatever seems right. Hook two anodes together with a copper wire and do two sides at once. Find something plastic to set your part in. Resurrect that old cooler with no lid and set it up. Hit the brakes hard and have your spouse grab that great looking piece of stainless in the barrow pit. Start buying those really rusty pieces of iron because you love the challenge. Try it once and you'll never go back. And all that old iron will love you for it...
Here are a couple of pics of the cast iron fry pan that is used in the above post. They are a "Before" and "After" pics.
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