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. As I was finishing unpacking all of my precious cast iron vessels from long term storage I decided to give them all a new “seasoning” before using them in my new home. I followed several steps that I had used in the past:
    1) Completely removing all rust from the pieces, especially lids that had become very rusty, using naval jelly compound. Some had to be wirebrushed several times to get back to raw metal.
    2) Rinsing well and drying in 200ºF oven
    3) Then while warm coating with thin layer of olive oil
    4) “Firing” in 480º oven
    While waiting I decided to read this blog, and discovered that I had used an oil not recommended, and that flaxseed oil would be best. So now I’m in the cooling stage….so will see how well the olive oil and lard works.
    Thanks for the great comments. It is great to have all the good information that all of you have forwarded.

  2. Whew, what an odor!–I would describe it as sardine plus fruity olive oil. Others have made similar comments, and I notice that we all bought our oil from Whole Foods. Perhaps it is just the Whole Foods brand that has this distinctive, um, aroma.

    By the way, you won’t find flaxseed oil with the other cooking oils at Whole Foods. Refrigerated dietary supplements are in the section with grooming products, cosmetics, etc.

  3. > Why does the cooking side need to face down while being heated in the oven?

    > So the oil doesn’t pool.

    Uh-oh–there has not been nearly enough oil to pool up. I wonder if I have been overly diligent in wiping away the oil: After six coats, the pan still seems open-pored. It practically soaked up a few drops of water. I wiped it dry with a towel, but found a new layer of rust less than an hour later.

    Should a properly seasoned pan be able to repel water?

  4. You’re right to wipe it away so it looks like there’s nothing on there. But if you don’t turn it over, then weirdly it will pool. If you don’t believe me, try it.

  5. This may be a silly question, but I would like to know if I am supposed to season both sides of the pan or just the inside cooking surface.

  6. I did not see this question answered above, but I did the process about ten times on a Lodge dutch oven, and it looked great. First thing I tried cooking was a roux (flour and oil) and it came out fine. However, after cleaning and a light coat of olive oil, when I wipe it paper towel comes out black. What is the black? Is it the seasoning coming off? It obviously didn’t come out when cooking the roux because it would have been obvious. I’m reluctant to use it now as every time I wipe it, the towel is black. Thoughts?

  7. As a test, I baked one pan rightside-up, and there was no puddling, which told me I was using even less oil than recommended. But it is still progressing; the cookware will simply need more than six layers of seasoning.

    For those of you who are having trouble finding flaxseed oil: Trader Joe’s carries it, on an unrefrigerated shelf along with coconut and other oils.

    I am using unfiltered flax oil from Whole Foods. In the beginning I would shake the bottle before use. Then I realized that the oil itself is homogeneous, and the other layer contains solids and other residue from the pressing. It may have some dietary value, but I am only using it for seasoning pans, so I started using just the oil layer. It seems to work as well, and with less of the fishy/fruity odor.

  8. Is it common to get what appears to be a rust color on the pan after the first seasoning but have no rust color on the paper when wiping the subsequent coats? Should I re-strip the pan and start over?

  9. > For those of you who are having trouble finding flaxseed oil: Trader Joe’s carries it, on an unrefrigerated shelf along with coconut and other oils.

    Be careful about flaxseed oil that you find in an unrefrigerated section. Look at the ingredients. It surely contains ingredients besides flaxseed oil. I think this is why people are obtaining such widely different results from my instructions. Pure flaxseed oil is what works – the kind that goes rancid (needs refrigeration).

    Buy it online if you need to. Someone asked me to post a link a while back, and I should. I will soon.

  10. Thanks to a link posted earlier in the comments (either on this page, or a related page), I came across the suggestion that grape seed oil (GSO) would work well for seasoning cast iron. Since I happened to have a bottle of grape seed oil in my cupboard, I took a look at the label and noticed that it stated the smoke point was 485 degrees — although it should be noted that some grape seed oils have a much lower smoke point, if they are “virgin” or “cold pressed”, and some others not labeled as such may have a smoke point of just 420 or so — I used San Giuliano Alghero.

    The reason I came across this page in the first place is because my cousin recently returned from a camping trip where someone had left behind a cast iron griddle pan, and she couldn’t keep it because she was returning home on a plane.

    The pan was extremely dirty & rusty, but not very well seasoned. I cleaned it up with oven cleaner, plus steel wool & copper pads with comet. Then when I figured it was as clean as I was going to get it, I did a final wash with dish soap and rinsed very well in hot water, then put it in the oven at about 450 for a few hours.

    Once it had cooled down enough to handle, I slathered it in the GSO, wiped it off with a paper towel until it looked pretty dry, then back in the oven, kicking it up to 450.

    I ended up doing this 6 or 7 more times, with a few amendments to the procedure: after “cooking” it for an hour at 450, I then turned the oven up to 550 and continued for another hour, thinking that it couldn’t hurt as far as “curing” that layer; also, for the last couple of runs, I decided to leave on a bit more of the GSO, since it seemed to be a bit slower going than I’d anticipated — thus, I left just enough oil on the pan so that it was a little shiny, no more.

    I’m left now with a nice black and smooth finish on the pan. The only minor flaws are a few spots on the surface (under the layers of black, it looks like) that are a little lighter-colored, almost like water spots — it could be due to me not cleaning it well enough initially, although I can’t think of anything more I could have done in that initial process — but as I said, that’s a minor issue, and really not even noticeable unless you’re looking at it the right way under the light.

    Overall, it went so well, I’ve dug out an old cast iron kettle that I had stowed away, unused, and have started the cleaning process on that. This piece will take a lot longer to prepare, since the seasoning is hard and flaky, with much of it falling away on the inside of the kettle. But I’m looking forward to doing the same process on it, using my GSO again. (And I just have to remember not to try to cook tomato sauce in the kettle once it’s finished.)

    Just passing along another option that worked well for me, for those people who may want to try it. Following your techniques as closely as possible yielded great results.

  11. By the way, Sheryl, I kept getting my previous post rejected with the note: “Hmmm… your comment seems a bit spammy. We’re not real big on spam around here.” After trying a half-dozen different things, I did a web search on that phrase, and somebody mentioned that (on apparently the same brand of spam filter) if you mentioned the word “sex” too often, you got that error message. So I thought, well, I used “oil” a lot in my post… thus I changed the repeat uses to “GSO”, and voila — the post went through! Maybe, just maybe, that spam filter is set a little high? 😉

  12. DJ – thanks for sharing your experience with the grape seed oil, and your method. The problem I’ve had when I’ve put the oil on too thick is that it comes off with cooking. When I use very thin layers, that doesn’t happen. Patience was the key for me – that and very pure flaxseed oil, the kind that goes rancid, in the refrigerator section, without the additives that prevent rancidity.

    >By the way, Sheryl, I kept getting my previous post rejected with the note: “Hmmm… your comment seems a bit spammy. We’re not real big on spam around here.” After trying a half-dozen different things, I did a web search on that phrase, and somebody mentioned that (on apparently the same brand of spam filter) if you mentioned the word “sex” too often, you got that error message. So I thought, well, I used “oil” a lot in my post… thus I changed the repeat uses to “GSO”, and voila — the post went through! Maybe, just maybe, that spam filter is set a little high? 😉

    Oh no! Very sorry for the inconvenience, and thank you for your research. Sadly, I don’t have the first clue how to fix this. There are actually two spam filters on the blog, and I don’t even know which this is coming from, let alone if I can adjust the settings and if I can, how to do it. There is a bunch of maintenance I need to do on this blog and I haven’t been able to find the time. I want to add a link to the right kind of flax oil and add a “Share” button (people have requested both). These changes require a bunch of other upgrades. I’ll see if I can put aside time this weekend to do it all. You didn’t happen to make a note of which spam filter it was, did you?

  13. David wrote:
    > Is it common to get what appears to be a rust color on the pan after the first seasoning but have no rust color on the paper when wiping the subsequent coats? Should I re-strip the pan and start over?

    It sounds like your stripped pan may have been slightly rusty, like the stripped popover pan in this post:

    I describe how to clean off rust in the popover post, but follow the instructions in this post you’re commenting on and the one that came after about black rust for the seasoning. The popover post is an earlier post, so the seasoning instructions aren’t the latest and greatest – it’s before I discovered flaxseed oil.

    You aren’t seeing rust after subsequent coats of seasoning because you locked it into the seasoning. The first coat is still permeable.

  14. > This may be a silly question, but I would like to know if I am supposed to season both sides of the pan or just the inside cooking surface.

    Yes. You don’t want the outside of the pan to rust.

  15. Sheryl,
    Wanted to thank you for clearing up my issues with my cast iron. I have used the pop-up links pointing to electrolysis cleaning of the cast iron and have started the process of re-seasoning all my cast iron now that I know what I did wrong (too thick on the oil and not using flaxseed in the first place).

    My first attempt was with my Lodge reversible griddle. It looks better than it did the day I bought it!

    It took me more time at Home Depot finding what I needed to set up the electrolysis bath than it did to actually get it all together and start the process.

    Really appreciate the detailed look at how to do it right!
    Happy Campfire Cooking

  16. > thanks for sharing your experience with the grape seed oil, and your method.
    > The problem I’ve had when I’ve put the oil on too thick is that it comes off
    > with cooking. When I use very thin layers, that doesn’t happen.

    Hi again, Sheryl — yeah, that part of the process seemed to make sense to me, since from my days in construction, I know how important it is when painting or applying varnish to use several thin coats rather than trying to do it all in one thick one. Therefore, I only started leaving just a bit more oil on the pan after I’d already laid down several layers on it with the method you proscribe — it was a calculated risk which I took only because I felt the process was happening more slowly than I’d thought it would, and wanted to see if a layer with a bit more oil would still come out smooth, hard, and not sticky at all. And since it worked the first time that I added more GSO, I continued doing that for the rest of the layers. Granted, though, it was definitely not enough GSO to pool, nor would it likely even get your hands very greasy when touching it — just a hint of shininess on the pan was all I was going for.

    Now, it could be that the difference here is due to the qualities of Grapeseed Oil. GSO is said to be the kind of oil that will get gunky after leaving it out for a while, so it shares that property with Flaxseed Oil (FSO)… but I’ve cooked with FSO in the past and once, when I didn’t wash the pan right away, I noticed that it hardened on the bottom of the pot, almost like I’d left shellac in there — it was a beast to scrub away — and when I looked at that, I thought that I didn’t want that same kind of hardening to happen inside my body, so I stopped cooking with it. 😉 But GSO doesn’t seem to be nearly as “sticky” as FSO, so maybe it doesn’t grab on to the cast iron as well, thus causing my process with the GSO to go a lot slower. I don’t know. It’s only a theory.

    Right now I’m having a heckuva time cleaning my other cast iron piece in preparation for this process. The oven cleaner I have didn’t get rid of much (it’s one of those no-fumes cleaners), so I may have to try a different brand and see if it’s more “aggressive” with the flaky gunk on this kettle. Right now I’m boiling water with vinegar in it, to see what that does. Hopefully I don’t have to resort to the power tools. 🙂

    > You didn’t happen to make a note of which spam filter it was, did you?

    No, sorry — there wasn’t much info at all on it, other than several people commenting on other blogs who had gotten that message. If you Google that phrase, you will probably find the same references I did to it.

  17. Hi Sheryl,

    Excellent Article! Concerning use of vinegar, I prefer to just use plain yellow mustard. The vinegar percentage plus the “grit” of the mustard is perfect for removing heavy rust. There are numerous methods of use… from preheating pan and adding mustard while stirring it around (messy, smelly, possibly dangerous if inhaled, etc) to application of mustard, then placing in oven or charcoal fire, and even a method of adding hot coals on top of the mustard. I’ve found that they all work, to varying degrees, and with varying degrees of effort required. I prefer the apply mustard and bake method.

    When it comes out, I use COPPER wool and scrub it. Steel wool is too prone to scratch and damage the actual iron. Copper is softer and less prone to scratching, only removing the rust and leaving the iron.

  18. Regarding your recommendation of flax seed oil seasoning, will I get the same results as yours if I seasoned my iron skillet with flax seed oil OVER my (smooth)accumulated seasoning (canola, bacon fat) of 5 uses,or do you recommend flax seed from the get go? Thanks.

  19. Hi Sheryl
    Thanks for this much needed and detailed explanation of the process of seasoning. I’m not sure if you’ve answered this question, I know one one previous poster asked a similar question – can this process be used for seasoning a steel wok? Is flaxseed oil still the best oil in this case?
    Thanks 🙂

  20. Hi Sheryl,
    Thank you for the great explanation, I’m using walnut oil to season my cast iron skillet, but that’s not my question: do I have to season all at once, or can I split, like do the process once a day until I get my 6+ layers?

  21. Hi Sheryl,
    I seasoned my cast iron frying pan using your method and was really happy with the results. However, I roasted a chicken in the pan – the chicken was stuffed with lemon and basil – and a lot of the baked on flaxseed oil came away from the pan’s surface. Is this due to the acids in the lemons do you think? Or perhaps the seasoning layer doesn’t stand up to roasting? What are your thoughts?
    Best wishes,

  22. Any acidic food will remove the seasoning from a cast iron pan. That’s why you’re not supposed to use cast iron to cook tomato sauces, etc.

  23. As person who loves using cast iron, your article is interesting.
    As a chemistry specialist, I find a lot of what you said to be inaccurate, and I can back this up with reliable sources.
    If you are going to claim “they are all wrong”, please site some credible sources, from scientific journals (JACS). To give such a bold statement and back it up with Google, anecdotes or simply “something I read” is hearsay. I could take any oil/fat and write a convincing article on how it should be the best for seasoning.
    Needless to say, the scientist inside me experimented, along with many of my friends. I must say right off the bat after seasoning a bare cast iron pan, it gives an extremely photogenic glossy pan, which I expected since it is a drying oil used for paint. However its non-stick capability are similar to other oils/fats. One common problem that came up, no matter what method of seasoning was used, is that this seasoning has a tendency to chip especially at higher temps. My speculation as to why this chipping occurs is as follows….
    although linseed/flaxseed oil is a drying oil and can dry hard, you have to remember that these applications are not often subjected to the same temperatures, and fluctuations as a cast iron pan. Since it forms such a hard polymer the expansion of the metal and the hard polymer layer will expand and contract at different rates. Since it dries so hard, the probability of chipping is much higher. In contrast a polymer that does not form as hard is more “flexible” so to speak, so it is less likely to chip.
    Think of an object that has been painted outdoors, after years of heating and cooling it will start to chip. It is the same concept.

    Also I would like everyone to keep in mind that although many oils and fats are different, the mechanism that provides this non-stick surface is similar for ALL oils. However each oil will increase the “non-stick” capability in different proportions due to the chemical structures of the oil as well as its contents. This proportion maybe observed as the amount of times needed for seasoning in order to get a non stick surface. This is why it is generally agreed that the longer you use cast iron the more non-stick it becomes. I do not believe that there will be much of a difference between most oils. This speculation comes purely from the fact that there is really no consensus on what the best oil/fat for seasoning cast iron is. It depends on your method of seasoning, some oils may work better for certain methods, other might not.

    I would love to see the outcome of different oils, using different seasoning processes and temps, before anyone can claim that a certain oil “gives the best results”.

    sorry for the wall of text

  24. Kevin,

    Your theory doesn’t make logical sense to me, and also doesn’t match my experience:

    (1) Cast iron is very rigid and brittle. The proof is how easily it breaks – like glass. When you buy cast iron on eBay, you have to make sure the seller packs it really well. If you buy a skillet that is not packed well, it could easily arrive with the handle cracked off. Cast iron is not flexible like plastic so that a rigid coating would flake off it.

    (2) In my experience, the only time seasoning has flaked off cast iron is when it was put on too thickly, and that goes for any kind of oil – my own early attempts with flaxseed oil, and a small skillet I bought on eBay that was seasoned with Crisco. On the pans that I heated first (see this post for why) and then applied the flaxseed oil very thinly, I have not had any flaking.

    – Sheryl

  25. just because it doesnt match your experience doesnt mean its wrong, flax seed oil hasnt worked for a lot of people. If you carefully read what i wrote again you will realize what im actually trying to say.
    firtly, that flax seed oil is the “be all end all” oil for cast iron seasoning. There isnt really a best oil, Its the oil and the corresponding method and conditions of seasoning that matter.
    Secondly i was just speculating as to why flax seed oil has a tendency to chip off. Even if you apply it very very thinly, after the coats start to build up it always seems to flake. This is based of the idea that linseed/flaxseed oil is a drying oil and it dries really hard

    also i dont understand your first point and how it relates to what i said. I was trying to say that Cast iron and the patina layer doesnt expand and contract at the same rate, like a layer of paint on any object. This is what speeds up the flaking process, as compared to other oils/fats that dont form as hard a layer as flaxseed does. it has really nothing to do with cast iron being brittle or rigid. If you also noticed i said flaking was a “common problem” meaning some of my friends have had this work quite well for them and have yet to experience flaking. You shouldn’t make judgements based solely on your own observations.

    Regardless if you agree with my speculation or not, your chemical explanations are still wrong. If you would like to disprove me about the chemical natures of heating oils, please add some links to scholarly articles that agree with the chemistry you speak of because it really doesn’t make sense.

    i hope this clears up a few things

  26. sorry i meant to say
    “firtly, that flax seed oil ISN’T the “be all end all” oil for cast iron seasoning.”

  27. It’s incorrect that flaxseed oil seasonings have a tendency to chip off more than seasonings with other oils. Your premise is wrong. The reports here of flaxseed oil seasonings coming off have to do with various mistakes people have made:

    * Using flaxseed oil that has other ingredients in it to slow rancidity (which defeats the whole purpose of using flaxseed oil).

    * Putting the oil on too thickly (which will cause any seasoning to come off, regardless of the oil).

    * Cooking with acidic ingredients such as lemon, tomato, vinegar (which will cause any seasoning to come off, regardless of the oil).

    I have many cast iron pans seasoned properly with flaxseed oil where the seasoning did not come off. That empirical experience is highly relevant. The burden of proof is on you to show that flaxseed oil seasonings come off properly seasoned cast iron pans. I know they do not. I’ll bet you haven’t tried it.

  28. …ok, im tired of this…
    you are just saying im wrong, no explanations, or theories or speculations as to why. Im not talking about thing like “you’re doing it wrong” because im not, seasoning cast iron isnt brain surgery i have many well seasoned pans.
    I love hearing reasons to why i am wrong so i can further explore these types of topics. I love to do research and study different sides of the coin and explore, but you’re literally giving me nothing.
    You are saying im wrong because you said so or im doing something wrong.

    one person’s observations even a handful of peoples is still hearsay
    -i use high quality flax oil from the health food store sealed and refrigerated, its 100% food grade
    -You MUST always put on oil in thin layers when seasoning, i put it on as thin as possible, and so did my parents and grand parents. I usually rub a thin layer on and wipe down with paper towel
    in my test, after striping the initial patina layer i applied 6 layers first, and got flaking after a period of 1.5 months use (mostly cooking eggs, bacon, grilled cheese). then i did 11 layers and still flaking. each time i did another experiment i noted the duration of time before flaking the extent of flaking on a scale of 1-10, i also striped the patina before each trial. I tried different methods for seasoning too doing about 6-11 layers, this has been a long experiment but those are my results. I always had flaking.
    -I never cook with acidic ingredients in cast iron, low pH values react with iron.

    There are many people who have tried this method and did not get good results. Im merely trying to explain why their results may not be working. People like me who have owned cast iron pans their whole life, and know how to season, tried this method, but not with the glowing results that you claim. Im sure it works great for some people, but how do you explain experiences with flaxseed oil that doesn’t work?

    basically i’m saying flaxseed oil isn’t the best and isn’t for everyone. It works for you and that’s great, it works for some people and it doesn’t work for others. This is how it is for all oils/fats that people use on their cast iron, there isn’t one oil to rule them all. I feel like im arguing about religion, i tried to start a more scientific factual debate but that didn’t work. There isn’t one best religion, just different religions, which generally have the same overall teachings. This is how i feel about different types of oils/fats and methods for seasoning.

    regardless your ramblings on the chemical aspects of fats/oils and heating them are incorrect. please fix it so people aren’t mislead. I’ll assume you know how to find these types of scholarly articles and journals, to get the proper info. good luck. Shoot me an email if you want me to review the chemistry section.

    im starting a new experiment today, which involves mixing oils/fats to produce the most efficient and effective way to season.
    my first mixture will be 1 part lard, 1 part canola and 1/2 part flaxseed oil.
    I have striped and applied it to my Dutch oven today. Wish me luck 🙂

  29. If you want to post where you think I got the chemistry wrong in my article, go ahead. I’m interested to hear objective facts. Please include links to references.

    It just didn’t seem relevant to me when you were approaching it as an explanation of a premise that I see as invalid (I do not think it’s true that flaxseed oil seasonings flake more than seasonings with other oils). So are you correcting my science or making a religious argument yourself? 😉

  30. All your mistakes are outlined multiple times in many of these articles, have fun.

    Article 1: “The determination of combined carbon in cast iron by means of the spekker photo-electric absorptiometer”Journal of the Society of Chemical Industry
    Volume 68, Issue 2, pages 49–52, February 1949

    Article 2: The Growth of Thin Lubricating Films of Plant Oils
    Tribology Letters (February 2011), 41 (2), pg. 451-462

    Willis G. Routson (patent 2 411 593)

    artivle 4:Impact of high-temperature food processing on fats and oils
    Advances in Experimental Medicine and Biology
    Volume 459, 1999, Pages 67-77

    Article 5: JAOCS, Journal of the American Oil Chemists’ Society
    Volume 80, Issue 2, February 2003, Pages 163-166
    JAOCS, Journal of the American Oil Chemists’ Society
    Volume 80, Issue 2, February 2003, Pages 163-166

    I dont know if flaxseed oil flakes more than other oils, i havent tried them all. All i can say is that it does flake. I have used lard, canola/crisco, and safflower oil, they do not flake the way that flax does, but this is just my experience, so take it with a grain of salt.

    Anyways you still shouldn’t say things like “they are all wrong”, when you have so little to back up your theories and most of it is backed up by incorrect explanations. I hope you have learned this valuable life lesson.

    Thanks for your creative article, it made me think a little. My quest for finding the most efficient and effective oil/fat/combination for seasoning continues…

  31. Kevin, that doesn’t tell me anything. First, I don’t have access to those articles, so I don’t know what they say. More important, you have not told me what is in MY article that is contradicted in those journal articles. What did I say that is incorrect (besides the hyperbole of writing style “they are all wrong”)?

    If you have anything substantive to say ABOUT THE SCIENCE, I’m interested. But so far, all you’ve done is complain that you didn’t have a good result on your pan (n=1) and you didn’t like my writing style (that sentence “they are all wrong” irked you).

  32. Hi Sheryl,
    I want to add my thanks to the others who have benefited from the information you’ve shared about seasoning cast iron. There still isn’t too much on the web about it, even 2 1/2 years after you first wrote this post!
    I’m new to using cast iron in the house, and while I’ve had a bbq plate for ages I haven’t really cared for it. So I have a newby question that I’d be so grateful if you, or someone else can answer.

    Recently I bought a cheap cast iron pan that is coated on the outside with enamel and on the inside with a black finish. The inside of the pan is quite poor (aka cheap) and I’d like to “fix it up” the best I can to use while I bide by time and wait for something old and beautiful to come my way.

    Should I strip the manufacturers finish off and start again? I’m also concerned about damaging the enamel finish by heating it long and hot in the oven. The instructions for the pan provide a “minimal” seasoning suggestion (on the stove for a few minutes) and warn against heating the pan with nothing in it and at too high a temp.

    I don’t know anything about enamel, and would really value an opinion on this if you have time.

    Thanks again, Missy.

  33. Hi, I am just about to try this but I was wondering if I can use this method to better season an already seasoned pan. I have used olive oil and it is seasoned but admittedly it is not the best. I can use it but it sticks sometimes. I was hoping that I could use this method to “top it up” and make it a better season. Can I do this and has anyone tried this?


  34. Demi – As you use the pan, more and more seasoning will build up slowly over time and it will get better and better. Flaxseed oil is not something you should ever cook with, so if you wanted to add a layer of seasoning from flaxseed oil on top of what you already have, you’d do it in the oven as described.

    Missy – I only know about seasoning antique cast iron. I can’t advise you on your pan.

  35. Hi, Sheryl, and Sheryl’s readers! Above I posted my stepwise redaction of Sheryl’s method, with one little change: I strip the excess oil under running hot water, instead of wiping with paper towels. I found you really, really need to scrub the inside bottom edges very well, as oil loves to puddle there (in hindsight, baking them upside-down will probably help, too).

    Anyway, I’m back to report that my safflower-coated pots are holding up beautifully, after 6 months of (sloppy, careless) use.

    I think that, aside from stripping all the red rust off the iron (and/or converting it to brown rust, per your instructions on the other page), NOT making sure the first 1-2 layers of blackening start with extremely thin oil layers is probably the failure point for most people. If the surface is oily feeling, people, it’s too oily!

    Thanks, and tah-tah, Sheryl!
    Thanks again!

  36. Hi Sheryl,

    Thanks for your reply. I did just are you said and then tried to fry an egg this morning with a TON of oil just incase. I heated up the pan well enough but it still stuck like crazy! What am I doing wrong? The cast iron that I have is a newer one so it has tons of “hills and valleys” and is not smooth. I know this doesn’t mean that things should stick if it is seasoned so I have no idea what to do now. Thanks.

  37. oh, and what can I cook in my cast iron right now (ie when it is not yet nonstick and won’t stick too badly)?

  38. May have been asked before, but… With a brand-new Lodge ( 8-inch ) frypan, should I remove the pre-seasoning before beginning the flax seasoning? And a comment — I read somewhere that using a stainless steel spatula helps to smooth out the seasoning. I’ve been using one (wooden handle, blade about 2” wide) and I do believe it helps to smooth out the hills and valleys in the bottom of the pan.

  39. Why bother? A brand new Lodge pan is pre-seasoned and ready to use. This blog post is about seasoning antique cast iron, which is smooth bare metal and not pre-seasoned.

  40. I have to re-season from time to time all my cast iron EXCEPT one Grishwold#8 big logo skillet which was completely rusted when I bought it on e-bay. It looked like no one cooked in it, and it was rusting for the last 80 years. After cleaning and removing rust I was not surprised but disappointed to find that metal was not glass-smooth, looking slightly like the texture of modern Lodge, but dimples were much smaller, like very tiny dimples without spikes. It absorbed a surprising amount of oil during seasoning and absolutely nothing sticks to it afterwords, seasoning stays like it is unseparatable fixture of the skillet, no matter what I put on it. I know that the roughness of the surface is not the reason because Lodge and a skillet with milling marks also need periodical re-seasoning. It looks for me that the rusting made the surface more absorbing. I plan to experiment in a future with my two less valuable skillets(lodge and Taiwanese one with milling marks) by stripping it first, then keeping them for some time in diluted vinegar and let it stay dry for one day before re-seasoning. I think it is possible to make a surface to be more absorbing without looking like an orange peel. My skillets cook great, but I sort of got tired of the seasoning on all but one being so fragile. Any food that releases juices damages the delicate layers to some degree. It shouldn’t be these way.

  41. Hi Sheryl. Thank you to the 100th power for the Wonderful blog.

    Do you know, or have an opinion, on whether the seasoning technique you developed can also be used on carbon steel? For example, DeBuyer frypans, carbon steel woks, and steel griddles?

  42. Sheryl –thanks for all the great additional info-

    I’m using oven cleaner this week so I can start over—Had great results last year with flaxseed oil but seasoning started to flake because I used thick coats (didn’t find your blog until now) – Would there be any reason I couldn’t use my gas grill instead of oven?—I could adjust grill to maintain 450-550 temps

    Kids don’t like the smell and with the Indiana weather I would like to keep all the heat outside

  43. Thank you so much for this blog! I purchased a Lodge 12″ pan less than a year ago and managed to jack up the finish real good. My attempts at re-seasoning ended up with a sticky uneven pan. I had been using corn oil and lathering it on thick and just about every other no-no you listed. I stripped it down to the bare metal (self-cleaning oven method, no warping!) and started over following your instructions to the letter. My pan now has a darker, more non-stick finish than when I bought it pre-seasoned! Awesome awesome info!

  44. P.S. I noticed no weird smell from the flaxseed oil while seasoning, and no strange taste after cooking with it.

  45. Worked well for me. Fortunately I have an oven that goes to 550º, which I knew from prior experience with lesser oils gives best results. I put on the oil a little thicker than described and the reason I think that worked was the higher temperature.

    New Lodge pans have a very rough as-cast finish, so I sand them smoother and need to re-season. Do others also feel that Lodge pans are to rough to ever get the satin smooth feeling of a really well-seasoned pan?

  46. Man does that oil smoke, it smells soooo bad! I hope this works, is it ok if the pan has a bit of rust before putting the layer of flax oil on it?

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