A very simple method for stripping old seasoning off a cast iron piece is to coat it with oven cleaner spray. Most regular oven cleaner spray is lye-based. Look for lye's chemical name, sodium hydroxide, as the active ingredient. Of the available brands, Easy Off Heavy Duty™ seems to work best, because its thick, foamy consistency coats and sticks better than cheaper store brands. Cleaners that tout reduced odor typically use active ingredients other than lye, so don't use them. Do this procedure in a well-ventilated area outdoors, and use eye and skin protection.
To prevent the spray foam from evaporating and drying up, wrap the piece up in a plastic garbage bag, and place it in a warm spot, away from the reach of children and pets. To protect against leakage, place the bagged piece in something like an old plastic dishpan or a large disposable roasting pan (bearing in mind that, over several uses and leaking bags, the lye can eat the aluminum somewhat).
It will take several days for the oven cleaner to work its magic. Check back in a day or so, and reapply cleaner as necessary until all the crud is softened into a brownish-black goo that can be rinsed off.
As a long term cleaning solution, aerosol oven cleaner is relatively expensive. If you will be cleaning more pans in the future or want to clean several pans at a time, a lye bath is easier and more cost effective.
Aerosol oven cleaner at work:
Basic Rust Removal
Surface rust can often be removed using a simple solution of one part white vinegar and one part water. Soak the piece for 30 minutes in a container large enough to treat the entire pan at once. If not completely submerged in the vinegar solution, the result will be an unevenness of color. Then scrub using a stainless steel scouring pad or steel wool, and rinse well. Additional half hour soaks/scrub sessions may be necessary and are OK, but don't leave the piece soaking for longer periods. Once free of rust, the piece should be thoroughly rinsed, dried, and seasoned to prevent its return.
(If you're not interested in setting up a lye bath or an electrolysis tank, you can now skip ahead to Initial Seasoning.)
Lye works great at removing crud from cast iron without harming it, but is very caustic and can cause skin burns, and blindness if it gets in your eyes.
Proceed with all due caution.
The lye product being used absolutely needs to be 100% sodium hydroxide crystals. Trouble is, illegal drug labs apparently use lye, so some brands like Red Devil 100% Lye™ have been pulled from the market. Crystal Drano™ has lye in it, but it also has other stuff you don't want. Rooto™, however, still sold at Ace Hardware, is 100% lye. Other sources of lye include suppliers of soap making ingredients.
One pound of lye crystals per five gallons of water is the formula. Always add the lye to the water, never the reverse-- it will create a thermal reaction which can cause it to boil up and splash on you. Even when mixing and using lye properly, always use skin and eye protection, and protect clothing or wear clothes that it won't matter if some might drip on them.
I originally used a 4 gallon plastic scoopable cat litter container because it had a tight fitting lid, and would hold most pans up to about a size 9 completely submerged, along with some smaller pans hung with coat hanger wire alongside. I later replaced it with a 20 gallon Brute™ trash can with a locking lid. Any similar, sturdy container capable of holding its volume in water, with a secure cover to keep out inquisitive children or pets will also suffice. Over time, plastic containers not made of UV resistant material, if used outdoors, will become brittle and need to be replaced before they crack and leak.
Depending on how thick the build-up on the piece is, it will take from a few to several days for the lye to soften and dissolve the crud. Be sure to rinse the piece well before proceeding with initial seasoning.
Other things to know about lye: The warmer the lye solution is, the faster it works, so in a sunny spot is best. Keep another container filled with fresh water nearby to rinse the item being processed so you can handle it without fear of lye burns/irritation. You can leave a cast iron pan in the lye bath virtually indefinitely without concern. Even when the solution over time becomes black as coffee from removed crud, it will still be quite effective. I have used the same batch of lye for more than a year to clean dozens of pieces. Since lye will not remove rust, the usual protocol when using both lye and electrolysis is to de-crud with lye first, then finish with electroysis to remove rust and any remaining crud.
A word about the use of lye: I have had at least one person tell me that lye should not be used because it is "toxic" and environmentally irresponsible.
Lye is a caustic substance. To be toxic to humans, it would need to be ingested. Since lye can be easily eliminated from cast iron by rinsing, or neutralized by an acid such as vinegar, it does not present a poisoning hazard. Properly diluted for disposal, a lye solution will not even kill lawn grass.
Lye (sodium hydroxide) is a naturally occuring substance leached from wood ashes. It has been used for centuries in the making of soap. It is said without lye, there is no soap. There is such a thing as food grade lye. If you have consumed pretzels, bagels, hominy, canned mandarin oranges, lutefisk, or green olives, you have eaten a food which used lye in its preparation.
This is not to say that lye is not dangerous. It can be, under various circumstances. But, if handled appropriately and with respect, it is a perfectly acceptable means of cleaning cast iron cookware.
The most common set up for an electrolysis tank involves a plastic storage container or the like, sturdy enough to be capable of holding eight or more gallons of water, and a car battery charger. You'll need a piece of metal that will serve as a "sacrificial anode", to which the electrical current will flow from the piece being cleaned.
You'll also need turn the water in the tank into what's called an electrolyte, making it more conductive so the current will flow more readily through it. For this, we use Arm & Hammer Super Washing Soda™ (not baking soda), available in the laundry additives section (medium size yellow box), at the rate of 1-2 tablespoons per gallon of water. Washing soda is primarily sodium carbonate, whereas baking soda is sodium bicarbonate. Some people use what's called pH+, which is a swimming pool water conditioner consisting of sodium carbonate.
Electrolysis cleaning works like chrome plating in reverse. By connecting the positive and negative wires the opposite of the plating process, you get crud and rust removal. You just have to remember the blacK (negative) wire goes on the sKillet. Also, the battery charger you use must be a manual one, or have a manual charge mode. An automatic charger will see the electro tank as a charged battery and shut itself down.
I use a 2amp/10amp switchable manual Die Hard™ Charger from Sears. I understand Sam's Club has some inexpensive manual chargers as well. I place a length of 2x2 wood across the top of my container, and suspend the pans in the water from it with coat hanger wire. The other, red connector goes to a piece of central air conditioner cabinet steel sheet metal I get from an HVAC guy who often has panels of new, unpainted metal left over from his installations.
For best results, make sure the connectors make good electrical contact with both the piece being cleaned and the sacrificial metal. Use your wire brush or stainless steel scrubber to remove some of the rust and/or crud at the spot on your piece to which you will be attaching the charger connector. You'll know you have good current flowing when you see a mist of fine bubbles forming around the piece and your charger's amp meter reads towards the maximum end of its scale.
The process of electrolysis both coats and rots the "sacrificial" piece of metal over time, so it needs to be scraped down occasionally and eventually replaced.
A byproduct of the electrolytic process is the formation of potentially flammable hydrogen gas. It may be prudent, therefore, to insure the area around the setup is well-ventilated, or to consider doing it outdoors.
Electrolysis is a line-of-sight process, meaning the side of the piece closest to the sacrificial metal will become cleaner first. If you put something between the piece and the metal, a "shadow" of crud will be left on the piece where the object blocked the flow of current from the piece. Some people's set-ups have metal on both sides, or surrounding the piece for faster action. I just turn the piece around from time to time. Visually, the crud loosens and peels and flakes off like old paint. In some places, it sticks tighter, and takes longer to come off. Rust will turn into a fine black residue that easily wipes or scrubs off. The process is finished when the metal is bare and gray. Some darker staining may remain in spots that were particularly rusty, but that's OK, it can be dealt with.
How long does the electrolysis take? Before I started using lye, cleaning an average piece using electrolysis alone might have taken a couple of sessions, maybe 8 hours each. Softening things up with the lye first reduces that to about one afternoon session of a few hours. Hanging the piece to be cleaned as close as possible without touching the sacrificial metal also tends to speed up the process.
Two identically rusted Lodge #7s, before and after electrolysis:
Next, you go to the hand tools. I use a variety of things for the final touches before seasoning, and only items that will not mar the iron.
Items I find useful include stainless steel Chore Boy™ scrubbers (never brass or copper, they will transfer their color to the iron), and a medium stainless steel bristled brush. Popsicle sticks and expired credit/gift cards cut into shapes are great for getting into crannies to scrape and chip away at stubborn bits. Bamboo skewers work well for deep cleaning loosened crud from fine details in pieces like corn stick pans. Use 0000 steel wool for a final once-over on smooth surfaces.
Sometimes, there are some stubborn dark stains left behind, and that's not unusual. The thinking is don't use anything harsh to try to remove them or you risk damaging metal. And by damage, I mean leaving any kind of marks, either scraping, grinding, or even polishing swirl marks. The consensus among collectors, though, is it's normal to have some staining and cooking utensil marks on vintage cast iron because people didn't buy pans back-when to display, they bought them to use. You can try to remove or at least minimize residual stains by soaking the piece in a solution of 50/50 white vinegar and water for 30 minutes at a time, followed by a buffing with 0000 steel wool. An alternate method is to wet the piece and then apply white vinegar full strength with a sprayer bottle, let stand a few minutes, and scrub with a stainless steel scrubber or steel wool. With repeated cooking use, however, layers of new seasoning will continue to darken the piece, and any stains that did not yield to the vinegar treatment will blend in.
Which is better, lye or electrolysis? Lye (and lye-based oven cleaner) melts the crud in to a black goo that rinses off. Electro makes the crud release from the metal. Both still require a little elbow grease afterwards. The lye tank is a real workhorse, since you can throw multiple pieces in it and forget them for a week (or more). The electro removes the rust lye can't, but you can also use a simple white vinegar solution to remove rust.
Some people use electro exclusively, because they think lye is not good to use on an item you will be cooking food in, or that it will damage the metal. I have to date not found any reliable information to support either of those concerns. After proper cleaning and rinsing, no lye residue remains.
The best results actually come from using both lye and electrolysis. First, because lye won't affect rust, and second, because lye can do most of the hard work unattended, letting the electrolysis more quickly and easily handle what it does best.
Bottom line: You can be successful using either lye or electrolysis. Or both.
As you delve more into the subject, you'll likely hear or read about various other "quick and easy" methods for cleaning cast iron. From a collector's standpoint, anything that alters the appearance of the metal is to be strictly avoided.
Cleaning pieces by burning them in a fire, or using a self-cleaning oven both have the potential to ruin if not outright destroy a piece. Fire may heat the iron to the point it turns the metal flaky and irreversibly red in color. Pieces so-damaged will never season properly again.
Self-cleaning ovens may vary in their working temperatures by hundreds of degrees-- one may work fine, another may overheat the piece to the point of warping or cracking. The best advice is don't try it unless you can easily replace the piece if something should go awry.
The use of power tools also risks leaving permanent grinding marks or swirls in the metal. Even sand or bead blasting will subtly alter the original surface texture.
Two pieces that were cleaned using a combination of lye and electrolysis. The small skillet at right is the same one as in the electrolysis photos above. Residual black stains on the inside of the small skillet were reduced using the vinegar/water solution.
And here's one of the rusty Lodge #7s above, after electrolysis alone.