Thanks, I will try that, I even happen to have flexseed oil on hand. I am surprised that high temperature would remove the seasoning. I thought high temperatures are good for seasoning?

@user1721135 - There's high temperatures that are for cooking, and then there's the cleaning temperature, that is high enough to incinerate everything. Your oven baking temperature is going to max out around 550 F/285 C, which is hot enough to polymerize the oil, over time. Cleaning cycle tops out at 880 F/470 C. A huge difference that takes us to a temperature that will destroy/incinerate the coating.

Oh ok, I do not have that function. Does it make sense to simply apply the flexseed oil over the current, spotty seasoning, or do I absolutely have to get rid of the old seasoning first?

@user1721135 - I'd strip off the existing stuff first. Before ovens had self-cleaning cycles, we had to use regular oven temperatures and chemical "oven cleaner" sprays. I'll edit my answer to include instructions for this.

Does that seasoning method assume the person doing it has 2 ovens (one to pre-heat and one that's cold at the start to bake the oil on), or that the oven will cool down sufficiently during the few minutes it takes to apply the oil?

do people actually do this? all of this is really unnecessary...what difference does the type of oil make(apart from taste)? soap does not leave a residue(how is soap going to interact with iron besides removing anything that isn't iron?). all of this is arcane alchemic weirdness with no basis in science. how does this answer have 13 upvotes?

And for people who neither have a self-cleaning oven nor access to "Easy-Off" brand cleaner... ?

everything @KaranHarshWardhan says is correct. This is totally unscientific nonsense. (open the "pores" in iron? soap "residue" ?)

The black "hole" in the middle of the OP's seasoning isn't a hole so much as a buildup of carbon. You do need to remove that prior to seasoning. @KaranHarshWardhan - the type of oil makes all the difference in the world. Oils that don't polymerize will quickly wear off - it's no different than just adding oil to the pan prior to cooking. Flax and other drying oils basically turn into a solid plastic coating on the pan and will remain more permanent. It's basically a home-made version of the non-stick surface you'd get in a commercial nonstick pan.

@DavidRicherby - you can remove the old seasoning with plain old sand paper, as long as you're thorough in washing it out afterwards. That's what I do with all my new cast iron - I use an orbital sander to remove the existing surface down to bare iron.

@Fattie - do yourself a favor and go read the linked blog post. Soap "residue" and iron pores aside, there's plenty of well-accepted science behind how different oils behave when treating bare iron. I agree, the myths around soap are not well founded. The bit about pre-treating to "open pores" isn't so much about the pores, it's about driving the moisture out of the top layer of iron and getting a clean surface for the new polymer to adhere to.

hi @dwizum - yes, by all means different oils are totally and completely different. Every single other thing mentioned is totally unscientific claptrap :)

"you can remove the old seasoning with plain old sand paper, as long as you're thorough in washing it out afterwards. That's what I do with all my new cast iron - I use an orbital sander to remove the existing surface down to bare iron." Yes, this is a billion percent correct.

Just BTW - I don't know this for sure - simply based on basics, trying to "remove!" old seasoning with heat, say 500C - is just silly. (You remove it by scrubbing it the hell off.) Would you remove some say paint (a polymerized oil) on the pan by heating to 500? I'm not even sure if warming it up a bit (before scrubbing) helps in any way with removing seasoning.

Most people mistake baked-on carbon (caused when you have inadequate seasoning) for "bad" seasoning or "missing" seasoning. A cleaning cycle will absolutely remove baked-on carbon. It will remove many lesser oils, too, so depending on what you seasoned with it may or may not remove the actual seasoning. This is why I sand pans to clean them, there's no doubt that you're down to bare iron.

@Fattie - you really don't know what you're talking about. Are you claiming that cast iron is a perfectly smooth surface? If it was, it would already be non-stick. There are tiny pits and valleys, which they label as "pores" for the sake of making it easier for people to understand. It's also what allows a coating, any kind of coating, to adhere to the surface. Are you claiming that metal does not expand and contract under heat, at all? Really?

@KaranHarshWardhan - And, of course soap leaves a residue. If it didn't, we wouldn't have to rinse it off. You might be able to remove pretty much all that matters, in most contexts, but we're chemically bonding a polymer to bare metal here, so best results would be expected when there are no other substances interfering. Of course oils are different. They are physically and chemically different, which is why oils have different smoke points, flavors, health effects. If you bothered reading, it explains why linseed is ideal, because you are polymerizing the oil, not just putting a layer on.

@DavidRicherby - I don't think the brand of oven cleaner is a limiting factor. Just any lye-based oven cleaning spray. It would be kind of like if someone said "Kleenex" instead of facial tissue.

@DanNeely - I actually address those assumptions just after the quoted passage, starting with "I assume," actually, because that aspect stood out for me, as well.

@PoloHoleSet My point was that just stating the brand name doesn't give much information about what kind of cleaning spray it is, whereas paper tissues are all pretty much alike. (Though the quoted text does describe it as a caustic alkali, which is a pretty strong hint.)

@Fattie - so now you're saying that paints are chemically identical to food oils? If you dispute that the oven's self-cleaning cycle has temperatures high enough to break down food oils or food oil polymers, please explain how the cycle actually works, since the residues that get blasted off include those same chemical components.

@DavidRicherby - What I wrote was "oven cleaner." Since I was taking a direct quote from their article, I did not edit it. Also, the passage states, right off the bat, that "Easy-Off Oven Cleaner is a caustic alkali." If someone is online, looking for advice and has never heard of it, and does not understand "caustic alkali," do you really think they will have much difficulty finding out exactly what "Easy Off" is, via a basic Internet search?

@Fattie - Ah, I see the basis for your odd opposition - cooking.stackexchange.com/a/91212/49684. You are of the belief that there is no scientific basis for this. Both of the links at the bottom of my answer go into detail about the scientific basis. Try not to be so entrenched.

@DavidRicherby - No worries, there were a couple of sloppy shortcuts they made based on assuming everyone would be on the same page, in that article, so I definitely agree that describing the oven cleaning spray in a generic, specific fashion would have been much better.

@user1721135 - comment correction - Oven cleaning cycles max out closer to 1000 degrees Farenheit/538 C. Apparently around 932 degrees is where pretty much any food-based compound is going to incinerate.