Cleaning a well-used cast iron pan can be a challenge, to put it mildly. If you purchase a crusty, rusty old pan, you've got your work cut out for you. Before you can season it, you've got to clean it!
There are a variety of options available to clean your cast iron pan. Commonly recommended options include: elbow grease with steel wool, self-cleaning oven, oven cleaner and plastic bags, lye bath, and electrolysis. Sometimes used but not recommended options include using mechanical means such as an angle grinder to get to the bare iron, and sandblasting. This article will give a brief overview of each.
1. Elbow grease and steel wool and/or brass brushes:
This method can work great if your pan is not a holy nightmare. If you just have a small amount of crud, roll up your sleeves and get to work. I like to use Dawn Powerscrub with a sink full of hot water. Let your pan soak for at least 5 minutes, then get it out and scrub it (wear rubber gloves!) with stainless steel scrubbie balls and a coarse steel wool pad (you can get them at your local hardware store in the paint section). A brass brush (you can get these at the auto store - they are often used for detailing) can be helpful to get into any smaller areas. Once you've got the pan cleaned, rinse it well and thoroughly dry it immediately. Without seasoning, the pan will rust very quickly - this is called "flash rust." I use a big terry towel to dry the pan, along with paper towels. You may also wish to put the pan into a warm oven to thoroughly dry.
2. Self-cleaning oven:
Some people swear by this method; others claim it can warp the pans, and still others refute that. I don't know the answer. If you want to give this method a try, stick your pans in your self cleaning oven, and run the cycle. When the cycle is done, LET THE PANS COOL (this will take several hours). Then, pull the pans out and use the elbow grease option detailed in #1. This option works, but it will smoke your house to kingdom come. It also uses a lot of energy, and can discolor your oven racks since you need to leave the racks in so that you have something to set your pans on during the cleaning cycle.
3. Oven cleaner and jumbo plastic bags:
Get yourself some heavy duty oven cleaner, jumbo or extra-large plastic bags (you can get these at Walmart or Target - Hefty and Ziplock both make them) and good plastic gloves. Spray your pan liberally with the cleaner, then put it in the jumbo bag, seal it, and let it sit for a few days. The bags keep the liquid from evaporating. After a few days, put your gloves back on and take the pans out and revert to the elbow grease method to scrub the crud off. It should come off pretty easily, though if you have a really cruddy pan it can be difficult and you may have to repeat once or twice.
4. Lye bath:
Some folks are opposed to the lye bath method because of the use of chemicals. In my opinion, it works about as well as the oven cleaner/plastic bag method at getting crud off of your pans (probably because the oven cleaner contains lye, too!) For the lye bath, get yourself a big plastic container and fill it with hot water. Carefully add 1lb. lye for every gallon of water, and let dissolve. Put a piece of twine through the handle of your skillet and place the skillet in the container with the twine hanging out so that you can easily grab it to get the skillet out without having to put your hand into the lye bath. Lye is very caustic, so you will want to be very careful so that you don't get splashed or get the solution on your skin. You also need to be very careful to cover your container (when I've used this method, I put a piece of wood over the container and put a brick on it to keep it on) so that it's not accessible to children and pets. If you can't find lye at your local hardware store, you can order it online. Look for the "Red Devil" brand. Let the pans sit for a day or two (I've left them up to a week), then pull them out and rinse them off well. Then, revert to the elbow grease method.
I love this method and it works the best of any method I've tried. Do a little googling to find the instructions - the instructions are too lengthy for this little guide. When I do the electrolysis method, I let the pan "cook" at least overnight and up to a few days. I take it out, rinse it off, and revert to the elbow grease method. I don't typically have to use much elbow grease, as the crud is all lifted off the pan, and any rust is removed.
Here are some photos of a Griswold griddle #18 that I recently cleaned using the electrolysis method.
Immediately after being taken out of the electrolysis bath; before cleaning with steel wool:
After scrubbing with steel wool, drying carefully, and "cooking" for an hour at 450 degrees:
After seasoning with Crisco:
6. Angle grinder or other mechanical methods:
If you are desperate and have tried everything with no luck, and are willing to risk ruining the patina of your pan, you can use an angle grinder with a brass brush or a dremel to get to the bare iron. I do not recommend this except as a last resort, as it will change the surface of the pan. It can also result in a mottled or uneven appearance and finish.
Sandblasting will certainly get any and all crud off of your pan, but it will totally remove the lovely patina that you expect with a vintage pan. It also leaves a rough surface instead of the satin surface that you want on your great vintage skillet. Most collectors will not buy a pan that has been sandblasted. The pan will come out a light grey instead of the lovely black you want. If you must try this method, after sandblasting you can use a very light touch with an angle grinder with a brass brush to smooth out the surface. After the surface is smooth, if the pan is properly re-seasoned, it should again revert to black with a nice patina. If the surface is not smoothed, you will not likely be able to get the pan black with a satin patina.
Good luck - Hope you have found this guide helpful!