Chemistry of Cast Iron Seasoning: A Science-Based How-To

The post after this one on “black rust” describes why you should heat the pan before applying oil for seasoning. This helps the seasoning to adhere and makes the pan pleasantly black.

In a previous post, I illustrated how I cleaned and reseasoned an antique cast iron popover pan. This was my first attempt, and my seasoning technique was somewhat haphazard because I couldn’t find consistent, science-based advice. I used a combination of organic avocado oil and strained drippings from organic bacon. This worked pretty well on the popover pan, which doesn’t have a polished surface. But the smooth inner surface of a skillet showed an unevenness of color and texture, and the seasoning wasn’t hard enough. It was too easily marred by cooking utensils or scraping against oven racks.

I wanted to understand the chemistry behind seasoning so I’d know how to fix this, but there is nothing that addresses this issue directly. A Web page on cast iron posted by someone similarly obsessed with the science gave me two crucial clues, the phrases “polymerized fat” and “drying oil”. From there I was able to find the relevant scientific literature and put the pieces together.

The pictures below are both of the same antique cast iron skillet. The “before” close-up on the left is from a picture of the skillet in my previous blog post on making German Pancakes. I stripped the pan with oven cleaner and reseasoned it based on my new understanding. The “after” close-up on the right shows the result.

Griswold skillet closeups: old seasoning on left, new seasoning on right
Griswold skillet closeups: old seasoning on left, new seasoning on right

Start With the Right Oil (It’s Not What You Think)

I’ve read dozens of Web pages on how to season cast iron, and there is no consensus in the advice. Some say vegetable oils leave a sticky surface and to only use lard. Some say animal fat gives a surface that is too soft and to only use vegetable oils. Some say corn oil is the only fat to use, or Crisco, or olive oil. Some recommend bacon drippings since lard is no longer readily available. Some say you must use a saturated fat – that is, a fat that is solid at room temperature, whether it’s animal or vegetable (palm oil, coconut oil, Crisco, lard). Some say never use butter. Some say butter is fine. Some swear by Pam (spray-on canola oil with additives). Some say the additives in Pam leave a residue at high temperatures and pure canola oil is best. Some say it doesn’t matter what oil you use.

They are all wrong. It does matter what oil you use, and the oil that gives the best results is not in this list. So what is it? Here are some hints: What oil do artists mix with pigment for a high quality oil paint that dries hard and glassy on the canvas? What oil is commonly used by woodturners to give their sculptures a protective, soft-sheen finish? It’s the same oil. Now what is the food-grade equivalent of this oil?

The oil used by artists and woodturners is linseed oil. The food-grade equivalent is called flaxseed oil. This oil is ideal for seasoning cast iron for the same reason it’s an ideal base for oil paint and wood finishes. It’s a “drying oil”, which means it can transform into a hard, tough film. This doesn’t happen through “drying” in the sense of losing moisture through evaporation. The term is actually a misnomer. The transformation is through a chemical process called “polymerization”.

The seasoning on cast iron is formed by fat polymerization, fat polymerization is maximized with a drying oil, and flaxseed oil is the only drying oil that’s edible. From that I deduced that flaxseed oil would be the ideal oil for seasoning cast iron.

As a reality check of this theory, I googled “season cast iron with flaxseed oil” to see what came up. The very first hit is a page written by a guy who seasons his cast iron cookware with linseed oil from the hardware store because it gives the hardest surface of anything he’s tried. (I’m not sure how safe that is; I don’t recommend it.) Below that were several sites selling traditional cast iron cookware from China, which they advertise as being “preseasoned with high quality flax oil”. I don’t know whether they really use food-grade flaxseed oil (which is expensive) or linseed oil from a hardware store. What’s significant is the claim. Seasoning with high quality flaxseed oil is something to brag about.

With this encouragement, I stripped one of my skillets and reseasoned it with flaxseed oil. As you can see in the picture above, the result was a dramatic improvement. The finish is smooth, hard, and evenly colored.

Seasoning Is Not Cooking: Different Principles Apply

The first time I seasoned a pan I chose avocado oil because it’s monounsaturated and doesn’t easily go rancid. It also has the highest smoke point of any edible oil, 520°F, so I could heat it in a 450°F oven without passing the smoke point. I knew that when cooking, you should never heat an oil past its smoke point because that causes the release of “free radicals”, which are carcinogenic. I was careful not to choose a polyunsaturated oil – and especially not an oil high in omega-3 fatty acids – because these are especially vulnerable to breakdown with heat and the release of free radicals.

Ironically, it’s for exactly these reasons that the best oil for seasoning cast iron is an oil high in omega-3 fatty acids – in particular, alpha-linolenic acid (ALA). Free radicals are actually what enable the polymerization. Drying oils, which produce the hardest polymers, are characterized by high levels of polyunsaturated fatty acids, especially the omega-3 fatty acid ALA.

The lard that was traditionally used for seasoning 100 years ago was much higher in ALA than fat from pigs today, because back then pigs ate their natural diet. Today they are raised on industrial feedlots and forced to eat grain, making their fat low in omega-3s.

Since lard is traditional but no longer readily available, many people substitute bacon drippings, but this is a bad idea. If it’s conventional bacon, you’re baking in carcinogenic nitrates. But even organic bacon is not good for an initial seasoning because it’s filled with salt.

The reason that Pam seems to work well in seasoning is that its main ingredient is canola oil, which is relatively high in ALA (10%), making it a “semi-drying oil”. Flaxseed oil, a drying oil, is 57% ALA. But it’s not a good idea to use a spray oil, no matter what oil it’s made with, because of its additives. You’re doing chemistry here. If you want good results, use pure ingredients.

Fat polymerization can be triggered or accelerated in a variety of ways. As best I can tell from my reading, the cast iron seasoning process is an example of “radical polymerization”. The process is initiated when something causes the release of free radicals in the oil. The free radicals then “crosslink” to form the tough, hard film you see in a well-seasoned pan.

So what is the “something” that initiates the release of free radicals in fat? Iron, for one thing. High heat, light, and oxygen, for some others. To prevent cooking oils from going rancid – i.e., breaking down and releasing free radicals – you need to store them in dark, tightly sealed containers in a cool location. To initiate or accelerate the release of free radicals, put the oil in contact with bare iron and heat it above its smoke point, which will cause even non-drying oils to release free radicals.

I haven’t defined “free radical” or “crosslink” because that gets into details of chemistry that you don’t need to understand to season a cast iron pan. All you need to know is that the molecular structure of the oil changes and becomes something else, something tough and solid. The process is initiated with the release of free radicals, which then become crosslinked, creating a hard surface.

Free radicals are carcinogenic inside your body, and also a cause of aging. So don’t ever heat oil you’re going to eat above its smoke point. If the oil starts to smoke, toss it out and start again. When you’re seasoning a pan, you’re not cooking food. By the time the seasoned pan comes out of the oven, there are no more free radicals.

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 suboptimal 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.

Editorial Note:

Many flax oils contain added ingredients to prevent rancidity, and it’s the tendency of this oil to go rancid that makes it so good for seasoning pans. Flax oil only works if it’s 100% pure flax oil with nothing added, so read the ingredients! People have reported mixed results, and this is probably why.

493 thoughts on “Chemistry of Cast Iron Seasoning: A Science-Based How-To

  1. I followed your instructions to the absolute letter on three cast iron pans – it took many, many hours to do this, $$$ for the expensive oil (not to mention the electricity used) plus the awful stink of the burning oil that got all over the house for 6 rounds of this. My pans stick WORSE than they ever have in the past. I think this might be a complete hoax.

  2. I don’t think it is a hoax if Cooks Illustrated featured this method.

    From comment above:

    “This method is featured on the new 2011 January/February issue of Cooks Illustrated (only available on the website at the moment AFAIK) and credits this article!
    November 21, 2010, 10:40 pm”

  3. I have tried this method with no success. Followed the instructions exactly, and the skillet looked great when done – shiny and black. But as soon as I cooked with it the seasoning came completely off. Tried it again, same thing happened. Has anyone else experienced this? I have to think I’m doing something wrong since Cook’s Illustrated recommended this method, but can’t imagine what it is. Any comments would be appreciated!

  4. I just reseasoned two cast iron skillets, a round griddle and an æbelskiver pan using Sheryl’s method. I am SO thrilled! Just now I made æbelskiver, which are Danish ‘donuts’ that look like New Orleans beignets or Dutch poffertjes, and they turned out perfectly. My picky Dutch husband just kept popping them in his mouth. Thank you, Sheryl, for all your hard work coming up with this system!

    Recipe for Æbelskiver: Heat pan on medium flame. 2/3 cup sourdough starter, 1 egg, 2 T sugar, 1/4 tsp each soda, baking powder and salt, 1/2 tsp cardamom (or more), several grinds of nutmeg, 1 T vegetable oil. Whisk all together, drop about 1/4 tsp butter into each depression on the pan, and then fill each almost to brim with dough. Add a couple berries or apple bits in the middle of each if you’d like. When the edges start to look cooked, use a long wooden skewer to pull the cooked bottom part up and over the uncooked part. Let the bottom brown and then turn each a bit more to even out the cooking. Place the æbelskiver on a warm plate and cover with cloth while the rest are cooking. Before serving, sprinkle with confectioner’s sugar. Nothing else is needed to serve, well, besides lots of good, strong coffee.

  5. Could it be there is some kind of cast iron that doesn’t season in this manner? Mine all did fine, but it’s odd that several people have had the same problem although they have followed the instructions to the letter.

  6. I have a problem! I just spent a week following these directions on my Griswold #6 and, for some reason, it all came off the first time a cooked on it. I stripped my Griswold skillet with oven cleaner for three days, then I scrubbed and scrubbed it to get it nice and clean, then I dried it and put it in the oven for a while to dry completely and blacken. Then, I began the seasoning.

    I followed the directions above, using flax seed oil; I would warm the skillet, apply the oil, completely wipe it down with paper towels, bake it for 1 to 1&1/2 hours @ 500 degrees, then leaving it to cool in the oven for at least 2 hours, before repeating the process again (I actually did 10 frikkin coats). At the end, the skillet looked gorgeous, but here comes the problem.

    After cooking on it for the first time (using only silicone tongs), I went to scrub it lightly with water and a natural fiber brush, and ALL 10 layers of seasoning came off on the bottom of the skillet. Most of the bottom was stripped all the way to the bare metal. I was SO bummed.

    I know I followed the directions, so I don’t know what could have gone wrong. If anyone has any ideas as to why this would have happened and what I need to do differently, they would be much appreciated. Otherwise, I guess I will be going to the store for some Crisco tomorrow and doing this the old-fashioned way. Thanks.

  7. Yeah, I too followed these instructions to the letter and after six rounds my pans are good and black but there is no slick surface and water just soaks in. I haven’t tried washing them.

  8. I’ll provide some more data points. One of my more-use small cast-iron pans was in need of seasoning. Previously, I could fry an egg in a bit of oil and the egg would not stick. Now the egg sticks, so I figure I’d have a look on the internet to see if I could improve my seasoning technique. I had been using the method as described on Lodge’s website- a thin coating of oil, one hour in an oven 350-400 degrees, cooldown with the oven off. This time, I used the method described, only with canola oil. After three coats and most of an afternoon shot, the pans are basically what I would describe as “unseasoned.” The egg sticks. Sure, maybe with the linseed oil. And maybe if I’d wasted TWO afternoons and gone for six coats. Life is too short. I’m going back to the old way. It gets bonus points for:
    1- taking less time
    2- using readily available materials
    3- using less energy
    4- providing a more non-stick surface!

  9. I just bought a very old cast iron skillet which appears to be coated with nickel or a similar substance. Would that skillet be a candidate for your seasoning method? Jim

  10. Out of curiosity, to everyone that this didn’t work at all for… did you use food grade flax-seed oil? The kind that needs to be refrigerated? Also, I hear a lot of people saying that they are boiling water to get black rust, and I am pretty sure Sheryl does not do that. I think she is putting the bare cast iron pan straight into the oven at 450-500 for an hour to blacken it. Maybe the boiling water thing is throwing everything else off?

    Would be cool if we could figure out why its not working for some people.

  11. Cheryl, I like the way you think (: I just got my grandma’s old cast iron pans from Canada. I have stripped, cleaned and seasoned them one time with animal fat. Can I continue to season them with flaxseed oil? Or do I have to start all over again. Thanks for all your posts!

  12. I’ve just started the seasoning process, and am following it verbatim 🙂 I have one niggling question, though: the ‘fumes’ coming from the oven- are they bad for you at all? It’s not smoke, just that hot oil smell. It’s very strong and I’ve had to open all the windows.

    Many thanks!

  13. Hi Sheryl,

    I had a cast iron pan that just would not season correctly. Tried this technique and it worked great. Last week I cooked some meat and did not clean the pan afterward. There was only grease in the bottom of the pan and I didn’t see any issue with leaving it for a day. Well, that turned into two days. When I did clean the pan I noticed that much of my seasoning came off. The pan was blotchy and appear to have bare cast iron in a few spots.

    Is this a known issue? Was my seasoning possibly not done correctly? And I need to strip it down with over cleaner again or can I just add a few more coats of baked on flaxseed oil?

  14. I seasoned a cast iron pan using your approach…I probably put on 8-10 very thin coats, warmed the pan before, 500deg etc…and the seasoning just seems to be gradually coming off. It’s like there’s dark dusty seasoning coming off each time I clean the pan with a paper towel. Not sure why that would happen, but it sure doesn’t seem to be a durable, hard coating.

  15. Followed the directions exactly. As stated above, the first time I used the pan, the seasoning came off. Epic failure. Will strip it again and this time I will use crisco and hopefully will end up with a seasoned pan that didn’t take a week to fix up and who knows how much electricity running my oven at 500 degrees. I highly recommend NOT to use this method.

  16. Hi, I wonder if anyone here has experience with a very smooth cast iron pan, and stovetop seasoning. I bought this pan ( here in Germany. The instructions said to just clean of the wax coating and then fry potato wedges in it for an hour. Eventually, the pan was getting too much gunk on it, and cleaning that (paper towel and salt) eventually wore off whatever seasoning (if you can call it that) there was.
    I then found this method, and using organic, food grade linseed oil, applied about 5 coats. Note, the first coat turned the pan bluish around the edges and I could not wash that off. I continued in any case, with more coats, each time noticing that rubbing with a paper towel afterward, a bit of orange film would come off — this looked like extra oil, and not rust, since i noticed that just leaving it out for a few days would not lead to more of the orange film. But like some others here, the seasoning wore off after a few uses. I have to admit, I did the seasoning on an electric stovetop — the pan does not fit in my oven — at the maximum setting. I am trying now to scrub the pan down but cannot get it back to the original silver sheen all around, as in the photo linked above. Any suggestions?

  17. Thanks for the article. As I write this, my favourite cast-iron frypan is getting its third layer of flaxseed-oil seasoning, and so far it looks and feels better than ever.

    I noticed a few people having trouble with eggs sticking badly to freshly-seasoned pans, and I’ve also experienced this. Somehow I found a solution to this frustrating problem, which is to let the eggs reach room temperature before frying them. (For me, that means either taking the eggs out the night before, or running warm water over them while the pan heats up.)

    Somehow, and I wish I knew why, this trick seems to reduce the likelihood of sticking by quite a bit.

  18. I’m happy to have found your site. I’m not sure what I’ve done wrong, but food still sticks the surface of my 4 cast iron pans. I’m not sure what I’ve done wrong in the past. I never wash with soap. One think I neglected to do is to oil the pan after cleaning it. I’d always wait to oil the next time I used the pan.

    Here is what happened so far.

    There does not appear to be any rust on them so I did not do any stripping.

    Round 1 >> Sunday, I started to re-season them. I accidentally left the pans in the oven at 500 for about 3 hours. They came out dark gray.

    My husband used 2 pans that day to fry some potatoes. They stuck badly.

    Round 2 >> 1) made sure they were clean and dry; 2) heated on stovetop to insure dryness;
    3) coat with flax seed oil, and wipe dry; 4) put in oven, turn to 500, leave for an hour, then cool in the oven

    Round 3 >> Today when I put more flax oil in and was rubbing it around for this 3rd “round” of seasoning, one of my pans was getting a LOT of black residue on the paper towel. Is this the black rust you speak of?

    One thing I’ve never been sure of is what I should do between seasoning steps. After the pans have cooled and come out of the oven, should I just put on the next coat of oil? If my paper towel gets black, should I just rub it around and get a new towel if needed, but basically ignore the black dust? Thanks so much for your help.

  19. Hi Sheryl,
    I would like to add my thanks to all the others here for your clear and methodical explanation of the science behind the seasoning process. I noted others have asked my question but I have not found an answer from the posts listed so far: can your seasoning for cast iron be used on a carbon steel wok? Are there any modifications that one must make from a technique appropriate to cast iron because of the carbon steel?


  20. Loved reading this! My mother in law gave me my skillet 30 years ago as a wedding gift. i still use good ole Lard to season. Do you think that is okay? Where do you find flaxseed oil? Thanks so much for all the research and information. Good to know. I’ve had people say they threw their skillet away cause it was rusty! AHHHHH…… I about died. Wish everyone knew about seasoning these wonderful pieces of cookware!!

  21. So I attempted your re-seasoning method on a Lodge cast-iron skillet twice, and I’m not sure what I’m doing wrong.

    The first time I didn’t oven clean/lye/etc. really clean it. I attempted the 6 cycles of cooking it with Flax oil, as suggested. The oil basically didn’t stick.

    I tried again, putting the pan in a garbage bag in the sun and overnight (~18 hours) soaking with oven cleaner. I then scrubbed the crap out of it. I did 5-6 cycles in the oven. I used it this morning with a little bit of bacon grease in it to cook some bacon. The bacon stuck a little bit, but nothing terrible. I figured I’d use a little scrub with a soft nylon brush while the pan was still hot to get the bits out.

    And the coating came off.

    The oven is getting to well over 400 degrees, I made sure to heat the pan for 10 minutes at the lowest temp to make sure it was dry before applying the first coat. I made sure to wipe off as much oil as reasonably possible with paper towels before throwing the pan in for another cycle.

    I basically gave up and am just going to buy another one for $20. I spent more in labor and personal time trying to “fix” it than it would’ve cost to buy a new one. I’m not sure if it’s the factory seasoning that’s somehow interfering, or something in the Lodge iron itself. I’m glad this method has been working for others… I unfortunately didn’t have luck, but I don’t think it’s the method that’s the problem.

  22. i wonder if it has to do with the material Lodge uses, or the coating they put on, because i have a similar story to what i’ve read a few times in the comments here. brand new lodge skillet, used oven cleaner to strip it, applied 6 coats of organic cold pressed flax oil, and food stuck worse than the skillet i seasoned with bacon drippings.
    any thoughts?

  23. Thanks.

    Traditional method of cleaning off old cast iron: put it through a wood fire. The crud turns to ash. The science: the carbon burns off leaving just the other elements (silicon?).

    If you try the above, you might want to ease your skillet into the fire. Cast iron will break, for example when thermally stressed. Cast iron is brittle: not resistant to impacts.

    Cast iron CAN be welded or brazed. To do so, you must preheat the cast iron so the welding arc doesn’t thermally stress the cast iron and break it. Welding cast iron is difficult and will not restore it completely, because the weld itself is usually different from the iron, for example mild steel or bronze. You would not want to weld cast iron cookware unless it is very special, that is, you would rather have it repaired and functioning.

    Carbon nanotubes are sometimes grown using iron molecules as catalysts. The tubes or whiskers grow and lift the iron molecules off the substrate.

    If iron is catalyzing the flaxseed oil reaction, how does it still work as a catalyst on the second coats, if the first coat covers the iron?

    Are you sure that linseed oil is refined and flaxseed oil not? What comes out during the refining? Does refining mean distilling or centrifuging in this case? If it is like olive oil, people would prefer to eat “virgin” flaxseed oil: from the first pressing, pressed without heat, because it has more flavor. If the heat used to season cast iron also refines the oil (drives off nasty components) why not use linseed oil?

    What do you oil your knife handles and wooden spoons with?

    You took the lid off Pandora’s dutch oven.

  24. Justin,
    I’m not sure. Just took a brand new Lodge and seemed to have the same issue. I wonder if it’s just my electric stove that’s the problem (glass top range).

    Heated up the cast iron slowly on med-low. Put a ton of bacon grease into it. Put some bacon in it. Tried to even keep it moving, but the bacon still stuck a little bit. Ended up having to scrub a little bit and it seems like there are spots now that are either burnt on bacon grease or scrubbed off Lodge seasoning.

    For cookware that is supposed to be so idiot proof, durable and non-stick, I am somehow having nothing but bad luck. If using cast iron means that you have to practically deep fry your food to keep it from sticking, I’m not sure what the non-stick value is 🙂

  25. I’m still frustrated with my pans. They look great after I pull them out of the oven… but I just can’t figure out why they still stick. I’ve done at least 8 coats. Any ideas?

  26. I had two cast iron skillets that were actually working pretty well. Thought I could improve them with this seasoning process. It did not work. After using, I got tons of black crap that I have not been able to completely remove. I am afraid the skillets are ruined now. I even scrubbed the pans with SOS pads to try and get all the black residue off of them. They are better, but now unseasoned and basically back to square one. I’ gonna re-season them like grandma did–by cooking bacon…

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  28. Okay, I have to say, I read this and was very impressed by all the chemistry and science-based approach, but I have to say, this did not work at all for me. Maybe I am doing something wrong. Here were my issues:

    1. first off, my oven goes up to 500 degrees. 500 degrees for one hour times six times?? Really?? I am sorry, I like cooking and food, but this is a hell of an investment in time and energy costs.

    2. did anyone else have issues where their house becomes inhabitable during this process?? My smoke alarm went off both times I tried this. And, my house filled with a mustard-gas-like vapor. Not impressed by this.

    I think my crappy skillet will likely be used as an anchor for my canoe. God bless teflon. Thanks for nuthin.

  29. Just in the middle of seasoning my cast, and after having read a few articles regarding less than satisfactory results was really hoping that I did not have the same issues. When people experience problems with bonding and having ‘it all come off’, just thought that maybe the problem was with the initial prep that did not allow whatever type of oil you may be using to become one with your pan. In my opinion it matters not what you are applying and are wont to have it bond to the application surface, it is the attention to details that will save the day. By this I mean that you must not skip any steps in the prep stage because if the first seasoning step does not bond, then it does not matter how many coats you apply. Please take the time and effort to pay attention to the itty bitty details when you start out and I would hope that your results would prove worth the effort.

  30. Sheryl or anyone knowledgeable,

    I am very new to cast iron and I could use a lot of advice. I purchased a small Le Cruset enameled cast iron skillet and filled it up with lots of corn oil and put it in the oven at 450 degrees for about 3 hours. When I opened the oven, I noticed the grease had splattered all over the beautiful enamel and on the inside sides of the pan and the only way to get it off was to use oven cleaner. I tried this again but I used a lot less corn oil and put it in the oven and got great results maybe 1 or 2 times when I cooked afterwards. But around the 3rd time, the potatoes stuck and basically coated the bottom surface of the pan, and did not get fried. I read your article and will now do the 6 coats with flaxseed oil because I really want to get this seasoning business nailed down correctly. But my question is how long is this seasoning supposed to last? Will it last the lifetime of the pan (forever), or will I need to season it again sometime in the future? If so, is there a way to tell if there is not enough seasoning in the pan before I start cooking so I don’t waste ingredients and get terrible results?

    Thank you,

  31. Igor, the seasoning methods described here, both flaxseed and others, are for use with “bare” cast iron — iron pots without enamel, such as the kind you get from Lodge, Heuck, Old Mountain, or others. You don’t have to season an enameled iron pan; in fact, as you saw, the seasoning method doesn’t work well with it. It will be necessary to use cooking oil every time you cook with an enameled cast iron pan, because it is meant to be used without seasoning.

  32. I recently picked up a Second Series “ERIE” 9 Griswold griddle for $10 off craigslist 🙂 It was rusted pretty bad, after using some hardcore sand paper and a fine sandpaper with palm sander I got a smooth surface. I bought some of the Flora brand Flax oil, it says it is High lignan. After putting on many coats using the articles process I can see tiny little speck on the surface. I have decided that these specks are actually tiny bits of flax seed which are present in the oil, much like High pulp Orange Juice. I am going to have to strip the pans again and buy some “filtered” flax oil. I believe that this will make a perfect surface. Or is there any way to filter it myself? Coffee filter?


  33. First read about this in Cooks I., then found this online. Sheryl, thank you for the well-reasoned article.

    I’m currently 4 coats in on a small dutch oven, a small Wagner #3, and some other frying pan. The technique works very well. I’m mostly adding to the seasoning in the fry pans but doing a brand new seasoning on the dutch oven. It appears to be great for both uses (new seasoning and adding to old).

    Some comments on various bits above.
    – Couldn’t find flaxseed oil in Whole Foods, but it was on Amazon.
    – Dang. This takes a while. I’ve got my fan blowing full bore during the process. My tiny apartment doesn’t stink too bad, which was a fear of mine. *knock on wood* no fire alarms have gone off yet.
    – Chaining the seasoning together (waiting 2 hours for the cooldown, then applying new oil, and starting to heat back to 500) shaves off precious time. Important since this is a 20+ hour process to get on six coats.
    – Cast iron is far from foolproof to cook in. But, once you learn how, it is a joy. (I hope most people reading this would agree).

    I can’t wait to see how the pans actually come out after another two coats.

  34. I recently came into possession of two old Griswold skillets. I stripped one using the oven cleaner method, and it came out nice and gray, no rust. Scrubbed it well and dried it in the oven.

    Over the next two days I did six coats of flax oil. After the sixth coat, it came out of the oven dark, though not black and not glassy. Attempting to fry an egg in it resulted in some mild sticking. What really ruined it was when I tried to wash it out using some hot water, just like several others here, all the seasoning came off, leaving the gray iron behind.

    One thing I noticed is that during the 500F baking cycles, there was absolutely no smoke coming from the pan. Oven temperature did get to about 500F according to the oven thermometer I used. I can’t help but think that perhaps this is the reason that it’s not working for some of us. Maybe a problem with the type oil used, or the oven (mine’s electric). I might try this again using the broiler to see if I can get the pan to smoke as I bake it.

  35. How do one rectify the grey color of leg of lamb after it was cooked with red wine in a cast iron pot? Thank you.

  36. Thank you so much for taking the time to do this! I pinned your article. I am calling it, “Everything you wanted to know about seasoning cast iron but didn’t know who to ask.”

  37. Hi Sheryl,

    Thanks for all the great info. I went out and bought a brand new pre-seasoned Lodge cast iron skillet. After reading your entire post several times I scrubbed off the thin lay of pre-seasoning they put on at the factory and went out and bought some organic flax seed oil from Trader Joes.

    I seasoned the cast iron 8 times exactly as in your instructions. It looked great, but then after the first use and washing, I noticed much of the seasoning came off in little black flakes. Not sure why? Do you have any advice on how to fix this?

    Warm Regards!

  38. Sheryl,
    Been usin cast iron for years and tried everything on the inet.Thanks for the detail.You have answered every ? I have ever had.Can’t wait to get started.

    I have a rust removal process that utilizes a battery charger and washing soda.When the rust is removed a black coating is left on the iron/steel part.I have researched this and it appears to be black iron/magnetite.
    My question is will it be safe to do this prior to apply your seasoning procedure?

  39. Last night I did the self-cleaning oven cycle twice, and this morning I heated the pan at 200 deg. F before applying oil, but I get lint in the oil coating just as I did when I used paper towels to apply iol.

    May I ask what type of cloth you and otters successfully use to apply oil?



  40. Update: I’ve done 5 coats on my pans and dutch oven. I’ve used the pans about a half dozen times since.

    I’ve found this method to be quite excellent (even though I skimped…). The seasoning is now being built on perfectly from the fats and oils rendered from each dish cooked.

    Thanks again for the great technique!

  41. I had never heard of using flaxseed oil. I just received a new cast iron skillet for Christmas this year and have been searching for some information on how to properly care for it. Thank you for sharing this information!

  42. Sheryl, thanks so much for this. The pragmatist in me says 6 cycles * 3 hours = a lost weekend. The amateur chef in me says it might just be worth it. (But not more than once.)

  43. @ Doug, perhaps the surface of your pan is just too rough. I sanded mine down with a palm sander (!) as it was a very basic “pre-seasoned” pan made by Red Stone (available form Tractor Supply Company, if that is any hint).
    I’m now going down the agonizing seasoning path laid down in this article and expect great results. I hope the silica doesn’t plug the pores too much as it would with racing brake rotors… but I digress.

  44. @BJ: Thanks!
    Does the fact that I now end up with what, fir lack of a better term, appear on the surface like spires, maybe half millimeter tall?

    Like you have suggested, this is ONE LONG PROCESS, so likely I won’t be doing anything more until I am certain what direction to head.

    Thanks for your interest, BJ, and your suggestion!

    P.S. – Instead of “wasting” a day, you can do a coat in the morning, and a coat at bedtime, or any other timing that might be more convenient for you.

  45. Hi Sheryl,
    I know this article has been debated and discussed ad nauseum, but after having tried this science-based process, I didn’t get a very good result. The theory seems very sound though, so I wanted to find out what I did wrong.

    The short answer: Too much heat! Your how-to suggests 500 degrees or as high as the over will go. As it so happens, mine goes to 550. Anything over about 460 will actually INHIBIT the cross-linking process that we’re relying on!

    I dug through a lot of the comments on this thread as well as the “black rust” thread and it seems other people were having my same problem.

    As it turns out, the cross-linking and polymerization of linseed(flaxseed) oil starts at about 392 Degrees Fahrenheit (200 degrees Celsius) according to a scientific article I found that I will link to at the end of this post. HOWEVER! At around 464 Degrees Fahrenheit (240 degrees Celsius), “heat bodying” begins to take the place of the cross-linking, producing a softer, flakier polymer. So as it turns out, the fact your oven only goes to 450 was a blessing in disguise, as that would be a wonderfully ideal temperature; right on the high side of cross-linking temp but below heat-bodying temp.

    I’m loving the science here and have enjoyed your articles immensely!

    Here’s the link to that study. It’s EXTREMELY technical, but the “Bottom Line” can be found on page 4 of the .pdf. Our case would be conclusion (iii). The “metallic catalyst” in our case is the very iron we’re trying to season and since we’re not purging our ovens with nitrogen or anything, we are using a “dry-air purge.”

  46. I am getting ready to bring my mother’s cast iron “back online”.
    It appears to already be extremely well seasoned.
    Do i really need to reseason it, or just mild wash and really good dry??
    (and then oil for between uses)

    By the way, they are Wagner.

  47. OK, readers seem to be having problems parsing the steps you took, so I will lay out step-by-step how I resurfaced my 12″ black iron stockpot, following your guide as closely as I could. My local grocery sold 12 oz of flaxseed oil for about $9; I used about a third of a cup on this extremely large piece of cookware.

    It began unevenly coated, with a lot of rust areas underneath the coating I had.

    1. Sent the pot through the oven’s cleaning cycle for 90 minutes (the minimum time it would program for), burning off the existing coating and rusting the outside thoroughly. At this point, it was covered fairly evenly in red rust.

    2. Scrubbed as much off as possible, using warm soapy water and a plastic scrubbie & brush. The pot still retained a red coating at this point.

    3. Conversion of red rust to “black rust”: Submerged the pot in a larger pot, covered completely in water. Boiled it vigorously for 30 minutes. At the end of this conversion, the pot was much darker: a vaguely reddish brown, instead of rust-colored. The top 3/4″ or so of the pot, both inside & out, were lighter colored, so I suspect that too much oxygen penetrated to this depth. If I had to do it over, I’d try to make sure there was 1-2″ of water covering the top of the pot (but that would require a bigger “bath” pot than I had).

    4. Immediately dumped all the water, so that the pot self-dried, and set it in a 350-F oven for 15 minutes to force off all residual water. Rubbed it with flaxseed oil immediately, to prevent re-rusting. As with all oil rubs, I made sure to get it into the crevices around the handles, in the holes for the handle bales, into the maker’s marks on the bottom, etc.

    5. Here’s where I deviated slightly from your method. Instead of scrubbing excess oil off with loads of paper towels, I rinsed under hot water (with a sprayer, on full pressure) while srubbing with a soap-free plastic brush. I reasoned that this would carry away excess oils, while leaving a thin coating. Seems to have worked well, except for some buildup at the bottom inside edges, so if I do this again, I’ll try to scrub harder there.

    6. Baked on this coating at 500-F for 60 minutes, followed by 1-2 hr cooldown (with the oven door kept closed). The first two times this produced a must-open-doors level of acrid, eye-burning smoke. In later reps the outgassing became much less.

    7. Repeat Steps 5 & 6 for a total of 5 heating cycles… Might have actually been 6 cycles, as some days I did two cycles, and I lost count.

    End result: an even, VERY dark almost-black coating. Further use is deepening the black. The inside of my pot, which has undergone at least three separate reseasonings in its life, is still vaguely nubbly, but the inside bottom is pretty smooth, and the edges (with the thicker buildup) are downright glossy-smooth. Clearly, more seasoning (from gentle use) will improve on this.

    The second through fourth coatings took noticeably more oil, probably because the polymerized coating had lots of tiny pores to fill. The last coating seemed less “thirsty”; perhaps the coating was smoothing out by then.

    Frankly, I think it might even be counter-productive to polish the casting marks off the pot. I suspect the surface roughness of the iron helps to hold the coating in place. Two to three reps of burning it down to bare iron (rust) have admittedly probably smoothed the surface somewhat, since very small bumps are attacked on all sides by rust. Red rust causing pitting, of course, so this isn’t a way to get a polish on the iron.

    End result: A very nice blackening. Thank you!

  48. Hi Sheryl. Unfortunately, I found your article after I had already cleaned my Griswold pan with the self cleaning oven method and then wiped out the remaining rust with Canola oil. I would like to try your method, but am not sure how to proceed.

    1. Should I start from scratch and do the self cleaning oven method again?

    2. Or, should I clean the pan with soapy water to remove the canola oil and then dry it over a medium heat to get out the moisture? If so, should I use steel wool (Brillo?) or something less abrasive? Then start your flax seed oil process?

    3. Or, should I just leave the coat of canola oil on and apply the flax seed oil?

    I think I am inclined to use my second idea. I was wondering if you had any thoughts on this?


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