I am new to cast iron skillet. I have cooked with it several times and found the Lodge 12" cast iron skillet has a convex surface which is not observable unless you pour oil on it.

When I cook, the oil move to rim of the skillet and makes the center short of oil. Is it normal?

EDIT: I added the photo of the stove and skillet for reference



  • 3
    Are you sure that it's truly convex? I've noticed that oil is much more likely to stay around the edge of the pan when the bottom of the pan's hot, but the sides aren't. (or maybe that's a sign that my pan's slightly convex, too)
    – Joe
    Sep 23, 2017 at 14:01
  • @Joe I haven't measured it, I guess this is related to the induction heater I use. Obviously, the center would get hot quicker than the edge. Sep 30, 2017 at 6:16
  • Lot of pans has its center higher than the sides, it is made that way because of physics. Manufacture say due to heating of the pan, the metal will expand and when heated the pan is supposed to become flat. In present time, I get the korean stone surface pans with flat bottom heated or not.
    – Huangism
    Oct 2, 2021 at 2:19

2 Answers 2


Pans should be completely flat, and producers are usually very good at getting it right. Even very cheaply made pans are usually sold properly flat.

What you describe sounds like you warped your pan. When you heat a pan on a burner that is too small, it becomes convex when viewed from above, if you heat it on a burner that is too large, it becomes concave. I have also seen lots of claims that heat shock (too quick heating by placing on an already hot plate, plunging into cold water right after cooking) increases warping. With thinner materials, you usually can see the warp easily with the naked eye.

I have never seen this happen in cast iron pans before (I assume here that it is really cast iron - some people call all iron pans "cast iron" although forged iron behaves differently and warps easily). Combined with you saying that you only notice it when heated, I wonder if it could be that your pan is not really warped, but only temporary developes a hump on the burner. Just try it on a fslightly large burner (which is supposed to bend the metal in the other direction) and see if it changes something.

If the pan continues to be warped when used on a different size burner, it has to be hammered flat. I have never done it myself, but the Internet is full of suggestions. They say that it can get "very flat", I have no idea if that means enough that there is no pooling, or simply much flatter than at the beginning.

  • Thank you for your suggestion, I might try it later but it is not convenient to try it on another burner because we only have one induction stove. I haven't measured whether my pan is really convex. Sep 30, 2017 at 6:18
  • I'm not sure what you found on the internet, but I'd strongly recommend against trying to hammer a cast iron skillet flat, unless you're ready to destroy the skillet. Cast iron is brittle and easy to crack if hammered cold. And if you heat it to cherry red to work it, you can easily cause various damage that will make it less useful as a cooking vessel, if it even survives cooling without cracking after working. I've heard of people sanding down a minor warp in a pan. (And yes, cast iron can be warped; I have a pan I've abused that proves it.)
    – Athanasius
    Jan 26, 2018 at 22:51

You should always use a hotplate at least as big as your pan in order to prevent warping. It's analogous to washing wooden cutting boards, you should always wet them on both sides, otherwise they will get warped as well.

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