I usually use whatever food grade oil I have then I put it a cold oven set it for 475 let it reach that and stay there for at least an hour then shut the oven off and take it out the next morning.

We use the lard rendered from the hogs we butcher ever year.

Tallow has a higher smoke point than lard, believe lard is around 350 degrees and tallow 400 + degrees.
I like my tallow for any deep frying I want to do.
Has to be 350 degrees at the lowest ,so 400 degrees allows me to stay around 375 degrees once something in put in the pot.
That way, there's less grease left once drained, on the fried food.
Now that people are going back to tallow and lard , which are a lot better for you.
It's getting hard to find a good source of good fat of either.

Bear fat

Crisco is cotton SEED oil.

My question is how do you clean cast iron. I get some stuck on stuff and just scrape off as good as possible.

When pan is still hot after cooking, pour little water in it. It will bubble - scrape the pan of unwanted stuff. Then add some oil to re-season

I do like black spot. Let the pan cool a little then add hot water. Adding water, especially cold water to a hot pan can crack it. I turn on the heat and let it boil awhile. Scrape it with a plastic or wood spatula while its boiling. Sometimes have to scrub a bit with one of those non metallic dish scrubbers. Dry and heat it back up with a good coating of tallow or lard or olive oil. Let it smoke a bit. If you burn something in one and its real bad put your skillet in a self cleaning oven. Then reseason. You can put one in a fire too. Use a low heat wood like pine construction scraps. Put your skillet on top the wood before you light. Just leave it till the fire is gone and skillet cool. Scrub it good with dish soap and steel wool or something. Rinse it good, dry, and reseason.

Olive oil. But I cook in butter.

If ya want a deep somewhat scary rabbit hole, dive into the harmful effects of seed oils and the myths about them…I don’t use anything with them if possible.

Any oil will work. You’re literally filling the crevices in the iron with carbon. All oils are made of hydrocarbons and as they heat up and smoke, they break down into eventually just carbon. There is no oil that’s better for seasoning than any other oil. Unless it’s contaminated with heavy metals or something, if it’s edible oil it’s just going to turn into carbon. You won’t contaminate your food with the seasoning unless you allow it to build up and then it starts flaking off. Even then, it would just be almost all carbon.

First ..I get the pan hot...then run it under the hottest water you sink can produce.

Always Hot to Hot...while scraping with a wooden spoon.

Use the rough side of a spong ..to lightly scrub some more.

Then wipe dry....and if there are some stubborn areas left...

Pour some kosher salt in the pan..and take a pepee towel and start scrubbing

With that salt....it's abrasive as sand blasting media..

That will get it smooth and clean.

Dump salt out ...heat pan..and apply a coat of bacon grease...and wipe dry..

Let it heat up until the top edge of the pan is hot...then remove from heat

Its cast iron for crying out loud, why are you guys being so dainty with it? Use a hatchet to clean out the tough spots if you have to, add more oil and cook away.

Mobil 15w-40 for me.