Cleaning Cast Iron using Electrolysis
By John Belden
This skillet that was suspended partially out of the tank providing you with a before and after view.
Using Electrolysis is, to me, the easiest and most efficient method of removing all of the corrosion and other built up materials from the surface of the metal that I have found. It is truly a one step, minimum labor, cleaning process. Electrolysis has been in use in science and industry for many years for various processes. There is certainly nothing new or novel about it. In fact, the first law of electrolysis was written by Michael Faraday in 1832. The internet is full of great information about the chemistry involved so I will not be covering any of the science related to how or why it works. Web search engines are great tools for that research. It is always fun to apply science in the backyard when practical, safe, and effective. This process does not require mixing any caustic chemicals. You can dip your hands into the electrolyte and it will just feel soapy. Using lye or oven cleaner exposes you to hazards which don’t exist using electrolysis as I have outlined it.
Disclaimer: I am outlining here a process that I use to clean cast iron hollow ware. I am not in any way advocating that you use this method. You have to make that decision for yourself and by following the method outlined here you accept all risk and responsibility for your use of this information.
What is involved, and what is required, to set up an electrolysis cleaning system?
1. A tank of suitable size to clean the largest piece that you want to clean. This tank needs to be able to hold the “electrolyte” so it must be liquid tight. Depending on whether this tank is conductive itself things change slightly (see 2 below, more on that later.)
. 2. You need a conductive element to act as the anode in the process. This is the electrode that is connected to the positive terminal of your power source. Remember that this is a sacrificial electrode so some loss of this material is to be expected. Depending on the material chosen for this electrode, its lifespan will be different.
3. A power source capable of delivering the necessary current at a suitable voltage to the load circuit and get the job at hand done. In my case, a 12 volt DC manual battery charger capable of delivering 40 amperes on a steady state basis has proven more than adequate.
4. An electrolyte solution that is suitable for the task. I use a solution of Sodium Carbonate (Soda Ash) and Water. Do not confuse Sodium Carbonate with Sodium Bicarbonate (baking soda). Sodium carbonate is available in a number of “packaged forms.” Swimming pool ph+ is one. However the least expensive source, available in small quantities, would be Arm & Hammer Washing Soda found in many laundry detergent aisles in local stores.
5. You will need a method of holding the item to be cleaned keeping it isolated (electrically) from the anode of the system. The item to be cleaned acts as the cathode in this process, you connect the negative lead of your power source to the item being cleaned. You can’t have the anode and cathode touching or you will create a short circuit and the process will not work…at a minimum. If they do touch, depending on the power source used and your circuit breaker, you may also have to reset the circuit breaker.
The above items outline the essential items required to successfully clean something using electrolysis with the electrolyte outlined. Your choice of electrolyte, cathode material, holding tank, may alter what you require. I will cover some accessory items later in this outline that I have found helpful.
Pictured below is my previous tank, made from an old SS pool filter, and is now about used up. It has been used enough that it started seeping which made it necessary put it into a plastic garbage can to keep going.
Notice the lovely color and texture of the electrolyte. Yours too will look like that over time. It really presents no detriment to the cleaning process; it is just not real attractive. To try and reduce the buildup of impurities in my new setup, which is being documented here, I have decided to add a couple more steps. You can read further about that in the tips at the end. When I get around to emptying this tank I will add a picture of it as an update. I expect that we will see some pretty large holes in it. As I mentioned before, the anode material gets used up in the process over time. The particular material will determine how long it will last. This tank was not of a particularly high grade of stainless steel, was well used in its first life, and thin by design. My new tank on the other hand is restaurant grade stainless and quite thick; it should last a long time.
Here is a picture of my new tank. As you can see it is a large stock pot.
With the tank selected we need to mix up some electrolyte. As mentioned above, I use Arm & Hammer washing soda. I mix this with water in a 5 gallon bucket at a rate of 1/3 cup of washing soda to a 5 gallon bucket of water. I get some water going into the bucket from the hose and while it is swirling around I slowly add the washing soda. If you just dump it in, it will tend to clump up…think grains of sand flowing through your fingers. As you add water, make sure to create as much turbulence as possible to help in mixing it into solution with the water.
The care and feeding of your electrolyte is not a complicated issue. As you use this process, none of the sodium carbonate is consumed. You will see the level go down in your tank due to evaporation of the water. This evaporation concentrates the sodium carbonate in the mixture which will cause the operating current of the system to increase over time, wasting electricity. To rebalance the mixture just add water to bring the electrolyte level back to your original fill level. That is all that would be required to keep things in balance and working as described. I am not overly concerned with doing this all the time. When I see the level go down an inch or two, or three I add some water.
Note: The only time that you may want to replace your electrolyte is if, due to your decorator sense, you can't stand the color anymore. Additionally the impurities that will be in the electrolyte after use are made up of many things. You will have carbon, polymerized fats and other organic matter, maybe even paint or other things that the piece was exposed to. None of these present a risk to the process working. One thing that will, is the spent iron that will come off by converting the rust. Over time (related to how much you use it but, a long time) a conductive silt could accumulate to a point where your piece would touch that. This would cause a short circuit, stopping the process and perhaps causing your circuit breaker to trip.
In this case, the tank is the anode which simplifies things a little. I selected a Stainless Steel tank since it will be much less reactive and last longer. You could use most anything for a tank as long as it holds water. If you use a plain steel drum it will be perforated quickly (depending on how thick it is). The advantage of using a metal tank as the anode is that the electrical field created between the anode and cathode (item being cleaned) is uniformly created around the entire piece. You could just as easily use a plastic tank (think garbage can, rubber maid container or similar) and a piece or sheet of steel, stainless steel, fence wire, for your anode. The choice should be made by deciding whatever is best given your circumstances and quantity of items you wish to clean.
If you use a single flat sheet you will notice that one side of the piece you are cleaning is much cleaner that the other. Since the electrical field that develops is stronger on the side facing the anode, that side will get clean faster. Turning the piece around will get the other side cleaned up easier. You could also use a flat sheet on each side, making sure that they are wired together creating an anode electrode on both sides of the piece. You could bend a single sheet in to the shape of a “U” so that the sides and bottom are all exposed to the field in closer proximity. You really have to decide how much you are going to use it and how much money or effort you want to put into it.
Now I have a tank, mixed up some electrolyte, I need a way to hold the item in the electrolyte suspended so that it does not come in contact with the tank (anode).
Being a simple country boy, I generally subscribe to the KISS principle (Keep It Simple Stupid). I used a length of closet rod long enough to span the tank. Since the wood is electrically a good enough insulator to hold off 12 volts DC, I can hang the item being cleaned from that. I simply cut up steel coat hangers, bent a fairly tight hook on one end that will go through an available hole in the item and a bend of the radius of the closet pole on the top. I took a chisel and made two flat sections in the pole so that it won’t roll around. A stone axe approach - but it works. If you are a fabricator, let your imagination run wild with clamps, platforms and such. Just don’t violate the electrical insulation requirements.
Let’s look at a couple of items set up without the electrolyte first; it makes it a bit clearer to see.
Normally I clean just one thing at a time. With the new tank, there is enough space to clean multiple items if I choose. In the picture above, there is a #12 skillet and a #3 skillet cover. If doing multiple pieces, you want to try and make sure that you have them at different elevations in the electrolyte. Again the electrical field will develop more uniformly around the item that way. You also need to connect all of the pieces being cleaned to the cathode (negative terminal of the power source) in some way. You can make up clip leads using large alligator clips and stranded wire. I would probably look for clips suitable for 12 gauge stranded wire. I would not rely on the “hangers” for this electrical connection. That is why you see me connecting the negative lead of the power source directly to the item being cleaned.
Next let’s get the electrolyte solution in the tank and wire it up.
Notice in the picture that the positive (red) lead of the power source is connected to the anode (tank) and the negative (black) lead (cathode) is connected to the item being cleaned.
NOTE: In this arrangement, the tank is electrically at a positive 12 volts DC and depending on how the battery charger is set, capable of delivering 20, 40, or even 240 amperes in my case. Although it is not necessarily something to be “afraid” of, it is certainly something to be respectful of. You could get hurt if you are not careful. Do not grab the tank with your power source operating. Do not stick your hands into the electrolyte solution when the power source is running. My standard method of removing an item from the tank is to switch off the battery charger, lift the item out of the tank by picking up the wooden bar near the point the hanger is located, disconnect the negative lead and clamp that onto the tank, finally remove the item from the hanger.
Here is a picture of the power source that I use. It is a manual type battery charger. That feature is important. The newer automatic battery chargers won’t work. The electronic control circuitry will not allow them to start into this load. As long as your battery charger is one of the transformer types you will be just fine. This model has been sold at Sam’s Club for $89.00 in the past. I know that there are other brands around too.
What was in the tank in the above picture you ask? Why a #7 Erie that is as cruddy as I could
find. I saved it specifically for this “how to” write up.
The buildup is very heavy, and no rust visible, just grease and carbon buildup. It is not just for rust. It will clean these impurities off too, with time.
Let’s hook it up and get it in the tank.
The skillet is in the tank now with the power on. You want the electrolyte to provide enough conductivity to be drawing between 15 and 20 amps. There are a few variables that will determine the operating current. The electrolyte mixture ratio, the size of the item, how clean it is to start with, and the temperature of the electrolyte all contribute to what the load current is; the electrolyte being the biggest contributor in the matrix of variables. Once power is applied and the process starts, you will see bubbles coming up from the item being cleaned. These are hydrogen gas bubbles. This will produce a small amount of hydrogen, which is a flammable gas. Make sure that you have adequate ventilation and don’t use open flames around the tank. Although the amount produced is small, an ounce of prevention as they say would be warranted.
A few hours later, how are we doing? Starting to work, still long way to go.
Fast forward now to 24 hours
As you can see in the pictures above and the couple that follow it is really working now. The buildup is starting to dislodge in large areas.
Experience has taught me to keep going. Although good progress has been made the amount of carbon buildup on this piece is substantial. Carbon is quite inert so the process takes much longer to get it to separate.
After two days in the tank and a quick rinse it is ready to scrub up and season.
I saved a nice rusty specimen for you to see how this works on rust.
The Griddle is in the tank now and the current is just where it should be. This piece will clean up much faster since there is a lot of rust and not much carbon.
A mere 4 hours later and we are ready to scrub this one up.
The brown color you see are impurities that are now floating on the top of the tank. The black is the residue of the converted rust. The oxygen molecule is consumed leaving the spent iron as a sort of black/gray powdery silt. This is easily removed with a stainless steel scrubbing pad and some dish detergent.
In my experience when the soap beads up on the surface it is as clean as it is going to be.
Here it is now scrubbed up and ready to season. Start to finish less than 5 hours.
Here are after shots of the two pieces now that they have been seasoned.
A few tips from my experience using this system so far.
I have decided to do a little tank maintenance as I go with this new tank. I bought a strainer to scoop the solids off the top of the tank as it is working. I am hoping that this keeps the electrolyte a lot cleaner and reduces the sludge build up on the bottom of the tank. One other benefit to this is agitating the electrolyte. At a molecular level, as the process occurs, the faster you can get the spent molecules in the process away from the piece you are cleaning, replacing them with fresh molecules, the more efficient the process will be. Additionally, this agitation moves the hydrogen bubbles away from the surface of the item being cleaned quicker helping to speed things up. This is all a bit new in my thinking and I have yet to find a low pressure pump to do this on a continuous basis. I will probably be investigating aquarium pumps. Since there is some amount of solids in suspension in the electrolyte you need something that can deal with those.
I am cleaning the inside walls of the tank with a deck brush between pieces. This is to dislodge anything that may be clinging to the tank. I believe that keeping the walls clean will improve the efficiency of the process.
Deep pieces take a lot longer to clean than shallow pieces. Deep skillets, Dutch Ovens and the like take much longer. It goes back to the way the process works. An electrical field is developed between the anode and cathode. The farther a surface is from the anode, the weaker the field is. In this picture you can see that I have added a “helper” to the anode. I simply took a piece of fence wire and wound it into a coil on the end, keeping it flat and concentric. Then determine the distance between the tank and the inside bottom of the piece (in this case a Dutch Oven) bend the wire at a right angle the distance from the tank wall, keeping the coil you made on the end about an inch from the inside bottom. Affix the wire to the tank with a clamp making the electrical connection creating an anode deep inside the Dutch Oven. Of course one is only limited by their imagination. When I get some time I will pick up one of the long metal bendable funnels, put a stainless steel piece (maybe a can) on the end, and clamp that onto the tank instead. It should make things a bit quicker to set up since it will be easier to bend into the proper position than just plain wire.
I have only used this process with black iron. Different metals have different characteristics. For instance, Aluminum is highly reactive and will be consumed by both acids and bases chemically. Never put aluminum into your electrolysis tank (or lye tank for that matter), it will be etched and ultimately be completely consumed if left in long enough. I suppose you could use electrolysis for other metals but that would require researching different electrolytes, power levels, and cleaning times to optimize the process for those applications. My interest, at this point, is not in studying electrolysis per se, but how to use it for cleaning cast iron.
I have never tried this with plated pieces. I do have one skillet that was given to me that is in such bad condition that I will do that piece at some point just to observe for myself what effect this process has on the plating. When I do that piece I will update this writing with those results and pictures if they prove of value. I doubt that this process is good enough to remove plating where the bond to the cast iron is still sound. However, I will be researching that further at some point.
Accessories that can make your life better and easier using this process.
Good gloves. Although you do not have the same concerns with the electrolyte used here that you do with a lye solution (see cautions associated with using the lye cleaning method elsewhere on this website), you can keep yourself a bit tidier if you use gloves.
Keep a garden hose handy. I remove the piece from the tank and rinse it off, long enough that I also cool the piece down. I do this to reduce the propensity for flash rust, especially helpful in the summer months. Heat is a natural byproduct of the electrolysis process. You are dissipating a bit of power in the solution with 12 volts and 20 amps. Pieces shouldn’t get hot enough that you can’t handle them but the electrolyte will evaporate fairly quickly on a warm piece after you remove the item from the tank.
Stainless steel “chor-boy” to use for scrubbing. I do not like the “polished look” that wire wheels and the like produce. I limit my cleaning to using one of these chor-boys and some dish soap and cold water. I do keep a small, hand operated, soft stainless steel wire brush handy for getting into crevices where you really have no other option. This is used sparingly and with very light pressure.
A strainer to scoop the solids off of the top of the tank during cleaning. Take care if your strainer is metal. Don’t cause a short circuit by touching the anode and cathode simultaneously with the strainer.
A long handled brush to wipe the side walls of your tank (or anode material depending on your design) keeping them clean from debris and keeping the metal exposed to the electrolyte.
Since my tank is the anode it is electrically charged. I didn’t want to set it directly on the concrete floor. When the floor is dry it may not allow much leakage current to flow from the tank to ground through the concrete. However, if it were to get wet it may. I put a small rubber mat on the floor between the tank and the floor insuring adequate insulation to hold off the 12 VDC that my battery charger is providing.
In closing I would like to mention that I am by no means a chemist, writer, or inventor. Some of the above is my interpretation of material I have read, some is based on my observations over time using this method. It is certainly not the definitive text on the subject, even perhaps containing misunderstanding on my part. I would hope that anyone reading, who has experience in this area, will feel free to add to, correct, or otherwise educate our club with their experience using our forum bulletin board located at www.gcica.org Thank you for taking the time to read through this. I hope that you found it helpful and provided you with some insight into what is involved in this simple process.
This was prepared, in part, for the use by the G&CICA. The G&CICA have been granted free use of the copyright, both of text and pictures, to publish in any manner they deem beneficial to the club at large. No others have been granted any copyrights’ in part or in whole. The text and pictures herein are not to be copied or redistributed without the express written consent of the author.
© John Belden November 2008
A NOTE FROM STEVE STEPHENS REGARDING HIS EXPERIENCE WITH ELECTROLYSIS
Want to put these photos and info on your website? Might be interesting to those using electrolysis to clean iron.
This is a food grade 304 SS 55 gal. drum I used for electrolysis cleaning of my iron for several years. The barrel itself was the anode and the iron was the cathode. As you can see the barrel has gotten pitted in many areas with tiny but deep pits. I cleaned it out to sell and and discovered the pitting which was not there when I started to use the barrel. It will be going to the scrap dealers on my next trip.
Match is a standard kitchen size. Top photo is of the bottom where, in several areas, the metal appears to have been pitted enough for some corrosion to come through although it hasn't yet leaked. I bet I could prick out some crud from these areas and it might leak. The other two photos are of the inside near the top water level. I used common swimming pool PH+ in the barrel and probably cleaned well under 100 pieces of iron in several years. The inside pitting seems to be in certain areas, not all over, but in quite large areas. I'll be going back to using lye if I can find any at a reasonable price for any iron cookware cleaning in the future. I actually prefer that method to what I had set up anyway. I found the pieces took quite a long time in my barrel and would not always clean pieces as much as I though it should. I could have had the barrel set up incorrectly though. Steve