For proof of this, check out your aluminum baking sheets. If they’ve been used, they’re almost certainly covered in a shiny black substance that’s a complete pain in the ass to remove, even with abrasives. That’s essentially what’s on your cast iron.
Actually, if you throw it in the oven and set it to self-clean it'll strip the seasoning right off. I've done it with my cast iron pan before. Washes completely clean and ends up gun-metal grey; a non-oxidized pure iron surface. This is a great way to start over with the seasoning process if you're unhappy with it.
Edit: because of course I triggered a storm. Maybe it's common elsewhere. I've lived in few EU countries, rented then owned a few houses, exactly only one of them had an oven with the self cleaning(by heating up to like 500C) feature, I don't think we ever used it. When we bought our current oven none of the ones we looked at had that function. A fancy Candy we looked at had a function where it cleans itself with steam(where you fill up a provided container with water and then it heats it up to fill the oven with steam and in theory that softens the gunk. No idea if that actually works).
If it's common where you live, then my apologies for this comment.
Couldn't find statistics on this with a quick search...
But yes, it is just an element that can go hotter and a shell that can withstand it. Ovens are incredibly overpriced for how rudimentary they are IMO. Ripe for 'disruption' if you had something non-bullshit to compete on but price - sizing is already standardised.
The cleaning module of the one oven I'm aware of that had that option was more than just a heating thing. The manual talked about foam and how to refill it. Different countries, different mechanisms I assume.
Maybe it sounds fancier than it is? Is not like it has a little robot that cleans the oven. It's just a mode where the oven can get the internal temperature very high (up to 1000 degrees F according to that article) that just incinerates any organic material stuck to the oven walls.
Most ovens in the U.S. burn natural gas, which burns at 1000 degrees F (which is the self-cleaning temperature).
Or just use easy off which is a spray on acid.
Most new cast iron cookware now has a raw surface with lots of pits and bumps from the casting process as well, which doesn't seem to get nearly as smooth and non-stick as "vintage" cookware.
For smoothing out the surface, you could just use a flapwheel. You can get them for angle grinders. This will also take off seasoning if necessary (but it's a bit worse for the pan if you're not also trying to smooth it out). Be sure to wear a respirator and googles if you're doing this.
I then used a cheap corded drill and inexpensive flap wheels and similar attachments from the hardware store to make it smooth, wearing an N95 mask to protect my lungs.
As far soap. My experience is that it definitely damages the nonstick coating, depending on how much you use. You can get by with a soapy sponge, but putting detergent directly on it and the nonstick coating will be lost.
The best way to avoid need to avoid soap or scrubbing and re-seasoning is to put hot water in the pan while it's still hot and scrape. Meat is the worst for leaving a coating and this technique removes 99% of it.(If not blackened use that water for a delicious sauce with all the best flavors of your cooking). This routine allows me to use the same pan for months without a deep cleaning.
I have tried to put cold oil on after heaving soaping, but I'm not happy with the pan until I season it with high heat. The only reason I'd do it for rust and still would pan on seasoning it properly later.
Which makes sense. Essentially burnt-to-pan bits are food-pan interface, as opposed to food-oil-pan interface.
Give enough time, heavy food displaces oil and comes in direct contact with pan. Given enough movement, oil is able to reimpose itself between the two.
1: https://www.thekitchn.com/why-you-should-almost-never-use-th...
2: https://lifehacker.com/dont-use-your-ovens-self-cleaning-fun...
Voila - a clean iron surface. Use rubber gloves, and wash off any splash with lots of water - caustic soda is nasty stuff.
I use flaxseed oil. It works. Unless you have an awful lot of pans, your small bottle of flaxseed oil will only be 10% used by the time it goes rancid; swallow the cost.
I've tried this on a goood carbon-steel omelette pan. The result was mixed; a grubby-looking polymer layer that comes off in the wash, but a pan that still works well, and has reasonable non-stick properties. I suspect that with carbon steel, the oil only needs to get into the pores in the metal, and doesn't need to form a layer on the surface at all.
But my best experience has been with cast iron: a mexican comal, to be specfic. I stripped and seasoned my comal about 8 years ago, and the finish is still flawless.
Obviously, do not use on cast iron or carbon steel.
What also helps is simmering something acidic in the pan for about 10-15 minutes (wine, watered-down vinegar, etc). The base then cleans pretty easily. It's the burnt bits of fat that splatter up the walls of the pan that are murder to get out.
Here in the US at least, there tend to be scratch (yellow/green) and non-scratch (blue/darker-blue). Along with straight scratch pad (pure green) and steel wool (silver metal).
You can grind all day with a non-scratch pad, and all you're really polishing with is the harder bits of gunk you've managed to take off.
Same way you can sand with 220 grit all day and barely make a dent, but hit something with 60 grit and make progress in 5 minutes.
Afaik, Barkeeper's Friend is essentially microgrit in some sort of liquid carrier. If you had the right shaped sand, you could probably add that to something and get a similar effect.
Unless your seasoning is flaking off because you followed OP's instructions and you need to start again.
I'd never made this link before, thanks for pointing it out! We have plenty of baking sheets like this and I thought it was a form of black rust or something but your explanation makes so much more sense.
Use dish detergent (commercial dish soap). It's made in a different way, so you can't get un-reacted lye.
It's part of why you had the rubber dishwashing gloves get invented: soap used to be harsher, and one of the reasons why is the fact that soaps were made with lye.
Commercial dish soap can be soap, or it could be detergent. Detergent is made differently, and doesn't necessarily involve lye.
> The production of toilet soaps usually entails saponification of triglycerides, which are vegetable or animal oils and fats. An alkaline solution (often lye or sodium hydroxide) induces saponification [...]
i.e. that's the usual process, and it often involves lye. (It elsewhere mentions potassium hydroxide too.)
Anyway my point really wasn't too disagree about how to make soap, I've never done it, it just seemed weird to me to tell someone how they made something and that it's a problem, vs. 'Did you use lye? If so...' or even 'Assuming you used lye, ...'
For example, I think what you call 'commercial dish soap' I would call 'washing up liquid' (never soap, not would it cross my mind if someone else said 'soap') so a slightly different conversation could easily have been based on a wrong assumption about what the created thing was or was used for.