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Oct 7, 2009 10:13 PM

Confused about thermal shock and cast iron?

Hi all, I am planning to buy some preseasoned lodge cast iron skillets and have been researching a lot about cast iron use and care. I have a what I believe to be a cast iron wok already so I am comfortable with cast iron. I understand that you're not suppose to put cold water on a hot cast iron skillet or it'll crack (although the water didn't bother my wok), but what about heating up a skillet with high heat on a gas stove? Is that ok or should I start with low heat/medium heat first and then crank it up to high heat? Any help would be appreciated.

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  1. Broadly speaking, the rate of heat transfer from hot gas (e.g. flame) to cold iron is less than the rate of transfer from hot iron to cold liquid. The main danger lies in putting a hot pan into a basin, or even a puddle, of cold water. The layer of iron in direct contact with the cold water will cool rapidly, and contract more quickly than the inner core of the iron, leading to stress and possibly failure. Same goes for glass, especially thick glass. Manufacturing inconsistencies or faults make all this worse.

    That said, I think that the slow heat-up might be wise if you are worried.

    1 Reply
    1. re: Robin Joy

      See, that's quite similar to what I was thinking when deglazing. But a puddle of cold water will be heated by the pan far more quickly than the heavy pan would be cooled by the water.
      I can't see that it would be a problem with CI, but don't put it in the sink until it's cool.

      Eivuwan; Cast iron warms slowly but retains the heat. I don't use mine on very high heat, more about 3/4 of the dial. It still heats up really hot, hotter than anything else (I use the hand-over-the-pan method) that I've cooked with.

      Also, it retains its heat well enough to cook eggs after being taken off the gas, no problem.

    2. Now I'm confused...
      Having used cast iron for 40+ years and reading CH posts about cast iron thermal shock and high heat it's a revelation to me.
      I've never had a failure of a cast iron pan or pot and I've been taking them from high heat and dropping them into a dish pan of water or putting water into them when finished cooking to help clean them (makes a neat sound). Having inherited some cast iron stuff and having bought a few pieces I've never remembered a warning label on the directions or no one ever told me what you shouldn't do.

      9 Replies
      1. re: monku

        I can imagine it's quite satisfying... Mine is enamelled so I wouldn't dare.

        And now you say it, they used to slake molten iron the same way in sword making. IDK.

        1. re: Soop

          Isn't that how they temper steel and other metals?

          1. re: monku

            If I remember school correctly then controlled tempering of iron is achieved by using oil of some sort at various temperatures. Crude use of plain water......Oh. Off subject a bit!

            1. re: Robin Joy

              Yes, after I posted I remembered something about tempering with oil.
              But, back in the days maybe water was used before there was oil? But, whatever I saw on TV about tempering it looked like they took a red hot piece of steel and whatever they put it into it made some big sizzling sound like I get when I put my hot cast iron pan into the dish pan of water.

              1. re: monku

                Can you check if your pan is flat? Don't know if it would make that much difference at that temp.

                1. re: Soop

                  According to the tips on the Lodge Cast Iron website it says you should pre-heat the pan slowly and avoid thermal shock which will cause cracking or warping.

                  I never saw those directions and as badly as I seem to be abusing my cast iron stuff, I've never had a problem.

                  Why change when it's worked for 40+ years. Flat as a board and I'd challenge anyone who can destroy a cast iron pot or pan.
                  Heck, I've used cast iron frying pans to hammer tent pegs into the ground.

                  1. re: monku

                    It's not a myth, I've come across CI pans that don't sit flat. If its enamelled then you'll really ruin it. Everyone advises against it for a reason.

            2. re: monku

              You temper in different materials and at different temperatures to create different effects, depending on whether you want toughness, hardness, ductility, stress relief, corrosion resistance, resistance to fatigue and so on. etc. You can also preheat oil to temper at a higher temperature. In the aircraft industry we used to temper some stuff in liquid cyanide salts, but I cannot for the life of me remember what that did.

              1. re: Paulustrious

                Cyanide carbarizing is used to surface harden the part by drawing the very hard carbon particles to the surface. It gives the part abrasion resistance while protecting the ductility of the parts interior.

                IMVHO< it's more important to cool the part before submerging it in cold water because the thermal conductivity of water is far greater.

        2. Lodge cast iron skillets are pretty good, I think. Although I only have their two dutch ovens. I preseason my two dutch ovens because sometime they don't do such a good job. I wish they would just sell unseasoned cast iron, so I don't have to work twice (burn off the original seasoning surface and then reapply my own).

          Cast iron woks are different sometime. If you are talking about Lodge cast iron wok, then they are not that different from other Lodge cast iron cookware. However, if you have a traditional cast iron wok, then it is thinner. Traditional cast iron woks are made thinner, so that you can skill more it with one hand when you cook.

          1. Cast iron may be a metal, but it's mechanical properties are more like ceramic:strong in compression, weak and brittle in tension. Because it lacks the crystalline structure of steel or aluminum, heat treatments like quenching in water, oils, or solutions of cyanide (nitriding) don't do much to help cast iron.

            If you have been dunking hot cast iron pans in a sinkful of col water for years, and haven't broken or massively warped one yet, I would chalk it up to dumb luck.

            2 Replies
            1. re: MikeB3542

              Odd though that we have not had anyone say they doused a cast iron skillet and it shattered. I've always used a 'sprinkle' method on my hot CI pans and griddles. Much easier to clean when they are really hot. And I am sure it is to the horror of other CHers, I use steel wool. to clean. It doesn't take the seasoning off my pans. Or at least it is being replaced at the rate it is being abraded.

              1. re: Paulustrious

                I've never seen one "shattered" by being put in cold water, but I think a friend of mine knows someone who did it, and we do have one in our house that is cracked because someone put it in the sink while it was still very hot and ran cold water into it.

                From what I understand, cast iron is like ceramic or glass, it can go *poof* if you do certain things to it, but won't always. The warning to not putting into cold water is because it *can* (but won't always) cause it to crack or shatter. Kinda like the warnings that you sometimes hear about super-heating water in the microwave. I spent years using the micro to boil water for instant rice and such with no problem, and then one day I took water out of the microwave that didn't appear to have even reach boiling, dumped in the rice and had a volcano of water and instant flavored rice. Burned my hand (the one pouring the rice) pretty good and made a huge mess in my dorm room.

                Better safe than sorry. There is no good reason to put a hot pan in contact with much colder water. Plenty of methods for cleaning that won't shock the metal.

            2. This sounds like a good test for Mythbusters. They could heat a cast iron skillet to red hot with welding torches and pour liquid nitrogen on them to make them shatter. I use cast iron for all high temperature cooking and my preferred method to clean them is to put them under a stream of cold water as soon as I remove the food (this removes most of the grease and shocks loose a lot of crud without any scouring but leaves the seasoning intact). This works especially well when searing at very high temperatures.

              I've been using this method for decades on at least 3 different pans, including a rather thin one (no brand marking, made in Taiwan), and they all are intact and sit flat to this day. Theoretically, you might be able break any piece of cast iron if you heat it high enough and cool it fast and unevenly, but I don't think this is something to worry about with cast iron cookware. The pans are just too thick and the cooking temperatures not that high and room temperature water is not that cold. Relax, Eivuwan.

              But the reason you shouldn't be deglazing cast iron pans is they just don't make good fonde. The crusty bits mix with the seasoning and you end up with a nasty looking grey sauce. Stainless is best for that particular task. I have exactly one stainless skillet and the only time I use it is when I need to deglaze.