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I've always seasoned my cast iron pans with vegetable oil because that was what I was taught. I'd done some research before, and even came across this StackExchange post on asking the best oil for the job.

To my dismay however, when I tried doing some research myself, all sources pointed to blog posts, particularly the Sheryl Canter one. There is not a single source on her post and she doesn't seem to be very near a materials scientist. The closest paper I could find to the topic was this one. Other than that, it was all anecdotal evidence, many people claiming many different things.

It felt almost absurd that I couldn't find a paper on something that seemed relatively common to me. This will bug me till the end of time unless I figure it out, so I need to know - does anybody have any real sources on cast iron seasoning or what factors play a part in the polymerization of different oils? Thanks in advance.

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    $\begingroup$ Interesting applied chemistry question... $\endgroup$ – MaxW Aug 20 '20 at 4:41
  • $\begingroup$ Google "Thermal Polymerization of Drying Oils" which should get you started. Most of the papers are behind firewalls and I don't have access. $\endgroup$ – MaxW Aug 20 '20 at 19:24
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There is this research on Chinese equivalent of seasoning process called "Kitchen God's Blessing" [1].

They argue that the non-stick property of seasoning comes by iron oxide $(\ce{Fe3O4})$ nanoballs.

If they are correct then the oil or its polymers is not exactly what is causing the non-stick property but the those nanoballs on the surface. Their seasoning method is somewhat different however. It uses temperatures up to 450 °C.

Reference

  1. Gao, C.; Yang, N.; Li, C.; Wang, X.; Yu, X.; Zhang, L.; Wei, Z. Seasoning Chinese Cooking Pans: The Nanoscience behind the Kitchen God’s Blessing. Nano Materials Science 2020. DOI: 10.1016/j.nanoms.2020.06.001.
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There is 'seasoning' to protect the pan, but on heating the pan, the chemical breakdown products are 'some' things I would not recommend to anyone for continuing good health for yourself or your family (see, for example, Genotoxic and carcinogenic risks associated with the dietary consumption of repeatedly heated coconut oil).

Unfortunately, many oils do breakdown even at low heat, and some at high temperatures, which includes even my favorite healthy (especially when acquired fresh from its harvest) Olive Oil!

However, a safer alternative path may yet exist to resurrect ourselves (but not likely literally).

Electrochemistry to the rescue!

In particular, try employing a sacrificial anode, like a small piece of zinc metal sitting in distilled water plus sea salt, covering your entire pan. Yes, to be explicit, my recommendation on how to best season your iron pan to guard it from future corrosion is zinc metal and saltwater free of oxygen, which unlike an oil coating, is not easily subject to removal or chemical disruption (from air/light exposure).

On the mechanics, your iron metal will no longer be the most anodic metal present, and the zinc may undergo limited anodic corrosion resulting in white ZnO/Zn(OH)2 product. However, even the latter can be consumed in low doses daily whereas, one must be more mindful of iron intake especially with small children. One has also, at low cost and safely, eschewed the dangers of associated heat generated cariogenics from various organics.

Aesthetically, I would also challenge you to compare the results from two iron pans, one stored in the manner I have suggested, to the other pan that was coated in whatever oil-based seasoning formulation you may believe is suitable, after washing both pans.

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    $\begingroup$ I think you miss the point. First the seasoning isn't mainly to protect the iron from rusting but rather to get a non-stick coating. Second, the oil polymerizes on the pan, thus it isn't the same as whatever oil you started with. $\endgroup$ – MaxW Aug 22 '20 at 17:10
  • $\begingroup$ MaxW: Is that the same, to quote per my source, "polycyclic aromatic hydrocarbons (PAH), some of which have been reported to have carcinogenic potential. Consumption of these repeatedly heated oils can pose a serious health hazard. ", which sort of makes my point! $\endgroup$ – AJKOER Aug 23 '20 at 1:39
  • $\begingroup$ Interesting, I've seen conflicting evidence on the breakdown of oils. I have seen that repeatedly heating oil does release carcinogens, but this study and this one both suggest olive oil is one of the safer oils at high heats. $\endgroup$ – Subhasish Mukherjee Aug 24 '20 at 19:11
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    $\begingroup$ The dangers of cooking are greatly exaggerated and irrelevant to this question. Most every theoretical worry (PAH, nitrosamines, acrylamide...) has proved irrelevant in the real world. And the oil used in "seasoning" the pan is polymerised to an extent that means it does not contaminate anything (this is very different to repeatedly reusing the same oil to cook). $\endgroup$ – matt_black Sep 21 '20 at 15:36

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