Seasoning method from the following article (worth a read a there is good chemistry info behind using flaxseed oil over other forms of fat): http://sherylcanter.com/wordpress/2010/01/a-science-based-technique-for-seasoning-cast-iron/
The Recipe for Perfect Cast Iron Seasoning
The basic idea is this: Smear a food-grade drying oil onto a cast iron pan, and then bake it above the oil’s smoke point. This will initiate the release of free radicals and polymerization. The more drying the oil, the harder the polymer. So start with the right oil.
Go to your local health food store or organic grocery and buy a bottle of flaxseed oil. It’s sold as an omega-3 supplement and it’s in the refrigeration section because it goes rancid so easily. Check the expiration date to make sure it’s not already rancid. Buy an organic flaxseed oil. You don’t want to burn toxic chemicals into your cookware to leach out forever more. It’s a fairly expensive oil. I paid $17 for a 17 ounce bottle of cold-pressed, unrefined, organic flaxseed oil. As it says on the bottle, shake it before you use it.
Strip your pan down to the iron using the techniques I describe in my popover post. Heat the pan in a 200°F oven to be sure it’s bone dry and to open the pores of the iron a little. Then put it on a paper towel, pour a little flaxseed oil on it (don’t forget to shake the bottle), and rub the oil all over the pan with your hands, making sure to get into every nook and cranny. Your hands and the pan will be nice and oily.
Now rub it all off. Yup – all. All. Rub it off with paper towels or a cotton cloth until it looks like there is nothing left on the surface. There actually is oil left on the surface, it’s just very thin. The pan should look dry, not glistening with oil. Put the pan upside down in a cold oven. Most instructions say to put aluminum foil under it to catch any drips, but if your oil coating is as thin as it should be, there won’t be any drips.
Turn the oven to a baking temperature of 500°F (or as high as your oven goes – mine only goes to 450°F) and let the pan preheat with the oven. When it reaches temperature, set the timer for an hour. After an hour, turn off the oven but do not open the oven door. Let it cool off with the pan inside for two hours, at which point it’s cool enough to handle.
The pan will come out of the oven a little darker, but matte in texture – not the semi-gloss you’re aiming for. It needs more coats. In fact, it needs at least six coats. So again rub on the oil, wipe it off, put it in the cold oven, let it preheat, bake for an hour, and let it cool in the oven for two hours. The picture above was taken after six coats of seasoning. At that point it starts to develop a bit of a sheen and the pan is ready for use.
If you try this, you will be tempted to use a thicker coat of oil to speed up the process. Don’t do it. It just gets you an uneven surface – or worse, baked on drips. Been there, done that. You can’t speed up the process. If you try, you’ll mess up the pan and have to start over.
The reason for the very hot oven is to be sure the temperature is above the oil’s smoke point, and to maximally accelerate the release of free radicals. Unrefined flaxseed oil actually has the lowest smoke point of any oil (see this table). But the higher the temperature the more it will smoke, and that’s good for seasoning (though bad for eating – do not let oils smoke during cooking).
I mentioned earlier there’s a myth floating around that vegetable oils leave a sticky residue. If the pan comes out of the oven sticky, the cause is one of three things:
- You put the oil on too thick.
- Your oven temperature was too low.
- Your baking time was too short.
It’s possible to use a sub-optimal oil for seasoning, like Crisco or bacon drippings, and still end up with a usable pan. Many (most) people do this. But the seasoning will be relatively soft, not as nonstick, and will tend to wear off. If you want the hardest, slickest seasoning possible, use the right oil: flaxseed oil.
Cast iron stripping method from the following article (ignore the “seasoning” section as the above method is her updated process): http://sherylcanter.com/wordpress/2010/01/perfect-popovers-and-how-to-clean-reseason-cast-iron/
How to Strip Off an Old Cast Iron Finish
Removing the Crud
A good method is a self-cleaning oven, but there are some risks. There have been reports of the crud catching on fire inside the oven, which is locked during the cleaning cycle so you can’t open it and put out the fire. There is also a risk of warping the pan at self-cleaning temperatures, which are 900-950°F. Most of the time, neither of these bad things happen and it works great, but I don’t have a self-cleaning oven.
Next best is a lye bath, which cleans off crud and old seasoning, but not rust (that requires a second step). That was also a no-go for me due to the lack of a plastic tub, and my general fear of substances that could explode and kill me. But oven cleaner usually contains lye, and I thought I could handle oven cleaner.
Oven Cleaner Method
I put some cardboard down in the bathtub and laid the pan on the cardboard. Before spraying thoroughly on both sides, I suited up like an astronaut – long rubber gloves (double, thin latex underneath, in case there was a tear), double mask over my nose and mouth (one isn’t enough – you still breath vapors), and goggles over my eyes. This is not excessive precaution. I somehow got a drip of oven cleaner on my upper arm and it burned right through my skin. I flushed it very thoroughly in water and then dabbed on some yogurt since lye is base and yogurt is acid – that soothed it.
After thoroughly spraying the pan with oven cleaner, I popped it into a large, thick plastic bag, closed the bag tightly, and put it in a small plastic wash tub in the general vicinity of my radiator so heat could help it along (not on the radiator, of course, just near it). I waited 24 hours, then donned the gloves again and took a look. A rinse and a scrub told me it needed another dose. I again suited up like an astronaut, sprayed it down again, and put it back in the sealed plastic bag near the radiator.
Twenty-four hours later I looked again, and this time all the crud was gone. But the pan was covered in thick rust that went way beyond my scrubbing ability. I didn’t take a picture of the bottom of the pan, but even the letters on the bottom were encrusted with rust.
Removing the Rust
Removing crud from the pan is dangerous to you but not to the pan. Lye does not damage iron. Removing the rust is just the opposite. You remove rust with a 50/50 solution of distilled white vinegar and water. This is safe for you but can destroy iron if you leave it in there too long. (Electrolysis is a safer method for the pan because it removes rust as well as crud so you can skip this step.)
When you put a pan in a vinegar and water solution, it sort of simultaneously rusts and derusts. The vinegar will cause the excess rust to lift off the pan and bubble up, but when you take it out of the solution it instantly starts rusting because the iron is utterly unprotected. A very thin film of rust is unavoidable – you just oil the pan and wipe it off that way. Don’t leave the pan in the vinegar indefinitely waiting for it to come out perfectly gray. It never will.
You want to leave the pan in the vinegar for the shortest time possible, so check it frequently, and never leave it in the vinegar solution for more than 24 hours. I checked the pan every couple of hours. At about the 12 hour mark I dumped out the rusty solution and put in new, clean solution. A few hours later, no more rust was bubbling up from the pan so I figured it was done.
I removed it from the vinegar solution and scrubbed it down with washing soda (like baking soda, but much stronger) to make sure the vinegar was complete neutralized. Washing soda is base; vinegar is acid. Then I put it in a 200 degree oven to make sure it was bone dry. When I took it out, I oiled it all over with avocado oil. I’ll explain the reason for avocado oil in the next section.
I want to emphasize how important it is at this point to rinse all the vinegar off using washing soda to neutralize, thoroughly dry the pan, and then thoroughly oil it. Do not wait even 10 minutes to do this because the pan is already rusting and you must stop the process.