HOME > Chowhound > Cookware >
What are you cooking today? Get great advice
TELL US

Copper Pots w SS Lining

o
oooYUM Nov 2, 2011 03:42 PM

So, I thought I would ask here, just a quick one.
Sorry, but would really like to know....
I promise I did a search, but you can get kind of
side-tracked reading through all these interesting threads....

So please help...
Any utensils are safe to use with SS lined copper, yes ?
Also, ok to place the pans in the oven?
(as long as the oven is not set really really high)
And no high temp searing of meat? *really??*

I have a small Mauviel fry pan (with brass handle)
and just ordered the Try Me Falk (can't wait to get that one)

I love my Mauviel fry pan, but want to treat it right.
I am not afraid of using it, and not afraid of the occasional
mark, but I don't want to do stuff that would potentially hurt it.
Same with my Falk, or any other Copper piece I might add to my collection.

Thanks for any advice anyone can give me....
I do have in my collection lots of Lodge Cast Iron,
a Staub 5 qt DO, a SLT enamel CI oval 7 qt DO (Love !),
and some All-Clad in various shapes and sizes.
Oh and my 2 remaining Revereware pots that I have had since 1970
that my Dad gave me for HS graduation... (I just *can't* give those up)
Oh, and my DeMeyere 11 fry pan *(also Love)

  1. Chemicalkinetics Nov 2, 2011 03:55 PM

    "Any utensils are safe to use with SS lined copper, yes ?"

    Pretty much everything, unless you want to intentionally destroy it and stab it with a hard steel knife or pound it with a hammer....etc

    Also, ok to place the pans in the oven?

    Yes.

    "And no high temp searing of meat? *really??*"

    Who said that? I have to disagree. It should be fine to sear meat. You may not want to get crazy hot though because the cladding can separate.

    "I do have in my collection lots of Lodge Cast Iron,
    a Staub 5 qt DO, a SLT enamel CI oval 7 qt DO (Love !),
    and some All-Clad in various shapes and sizes.
    Oh and my 2 remaining Revereware pots that I have had since 1970
    that my Dad gave me for HS graduation... (I just *can't* give those up)
    Oh, and my DeMeyere 11 fry pan *(also Love)"

    Are you telling us that you own these cookwares? Or are you asking us to give advices for all these cookwares?

    5 Replies
    1. re: Chemicalkinetics
      dcrb Nov 3, 2011 06:49 AM

      Good morning - I thought I would chime in and post this link. It doesn't track with the discussion on SS lined copper, but I thought some of the readers might gain something from it.

      http://www.popularmechanics.com/home/...

      1. re: dcrb
        Chemicalkinetics Nov 3, 2011 06:53 AM

        Thanks. :)

        1. re: Chemicalkinetics
          dcrb Nov 3, 2011 07:10 AM

          You're welcome. I found it interesting and decided we did not need it in a full blown stove top. Sticking with gas. But we did buy a Magnaflux induction single burner hotplate contraption and it works well enough, but doesn't hit the counter very often. Mostly my wife uses it to keep well meaning guests busy doing something on the other side of the kitchen. In that respect, it is worth its weight in gold.

          1. re: dcrb
            Chemicalkinetics Nov 3, 2011 07:15 AM

            "Mostly my wife uses it to keep well meaning guests busy doing something on the other side of the kitchen. In that respect, it is worth its weight in gold."

            Wow. ha ha ha. Seriously, I mean seriously, the moment you wrote those I thought of this please skip to 0:55 min.

            http://www.youtube.com/watch?v=LFZaCM...

            Same idea? :D

            1. re: Chemicalkinetics
              dcrb Nov 3, 2011 07:21 AM

              Absolutely priceless. Thanks.

    2. kaleokahu Nov 2, 2011 04:27 PM

      Hi, oooYUM:

      I'm SO glad you asked these questions, because in looking to answer you I think I've found the answer to an important question I've been after for a LONG time! First, your answers: You should be fine with any utensils in your bimetal pans. Yes, they are fine in the oven, but make sure they have a substantial amount of food in them if you're going to use a high oven. As for searing, you should be able to do that, and well.

      One thing that doesn't always get mentioned is the SS linings and salt. You should not put salt in the pan and just leave it to dissolve in the water, because the grains in contact with the SS lining can cause pitting. Because the lining is only a few tenths of a mm thick, a pit can easily get down to copper, and once that happens, physics and chemistry will work together to kill the pan. Read your Falk warranty carefully--I have heard they specifically exclude pitting which in THEIR opinion was caused by salt.

      Now, the exciting part (at least for me). When I was researching your "sear" question, I wanted to see how far apart were the "coefficients of linear thermal expansion" of the two metals, copper and SS. I wanted to see because if the coefficients were very far apart, heating cycles of the pan, and especially high heat, can put different stresses on each layer--the greater the difference, the greater the propensity of the bimetal to debond. What I discovered is that the CoLE for *austentitic* SS (actually several alloys) falls in a range of 16-17.3 (10-6 m/m K), which is *very, very* close to copper's (16.6). The small difference bodes well for being able to sear--and for a lifetime--without a delamination problem.

      HOWEVER, the data table had a second line and data for *ferritic* SS, and the number given for that material was substantially less, almost by a factor of 2., at 9.6 10-6 m/m K. I THINK this wider number disparity may explain why bimetal copper cookware DOESN'T WORK ON INDUCTION. If I am right, Falk (who makes all the world's bimetal) *must* use austentitic SS for some reason (maybe debonding, maybe something else or in addition), and that steel simply won't heat in the induction field. Many of us have always wondered how high the effective induction field was, and I think it has been demonstrated (thanks, Politeness) that a I-compatible pan needn't even be in contact with the cooktop to "work". I always believed there was nothing magical about the copper being on the cooktop, and the lining sitting <3mm above.

      To my ears, this is the first plausible explanation of the incompatibility of SS-lined copperware with induction. Looking at it from the opposite end, even if Falk *could* bond copper and ferritic, the bimetal would probably work itself apart in use.

      What say the more scientifically-minded?

      Aloha,
      Kaleo

      29 Replies
      1. re: kaleokahu
        Chemicalkinetics Nov 2, 2011 04:33 PM

        "bimetal copper cookware DOESN'T WORK ON CONDUCTION"

        What? Typo?

        "I always believed there was nothing magical about the copper being on the cooktop, and the lining sitting <3mm above."

        That would be a rather stupid design for induction cooking if I heard you right. The copper is wasted in such a design.

        1. re: Chemicalkinetics
          kaleokahu Nov 2, 2011 05:19 PM

          Hi, Chem:

          Typo corrected I believe.

          "The copper is wasted in such a design." '

          Not a complete waste, and therefore not stupid, because the induced lining will heat the copper as well as the food, which will result in heat being put into the food through the *walls*, at a height above the effective height of the induction field. A thermowell would be a good analogy, I think.

          Kaleo

          1. re: kaleokahu
            Chemicalkinetics Nov 2, 2011 05:54 PM

            "Not a complete waste, and therefore not stupid, because the induced lining will heat the copper as well as the food, which will result in heat being put into the food through the *walls*, at a height above the effective height of the induction field. A thermowell would be a good analogy, I think."

            Actually, the effective height of the induction field is quiet high compare to the stainless steel lining. That I am not worry about it. What cookware design are we talking about? If you are talking about All Clad copper core, yes I agree with you. If we are talking about the typical Mauviel cookwares with copper body and interior stainless steel lining, then no.

            http://s3.hubimg.com/u/2217278_f260.jpg

            Yes, the steel will be magnetically induced by the field and will heat the foods along with the copper, but it is a backward design. It is so ineffective that it is not even funny. I don't mean the induction field is weaker because the steel is a few mm above. That is not what I am getting. What I am getting at is the fact that the copper hardy redistributes the heat. So any heat spots would have remained. It is a design no better than just a straight steel pan.

            In this copper-steel cookware we are talking about, the induction field penetrates/skips the copper and directly heats the steel, and the steel then directly heats the foods. The copper sit on the other side.

            In a conventional cooking, the energy heats the copper first, and so the heat is distributed in the copper before it get to the steel lining. Only then, the food get cooked by the steel surface.

            Let me give an extreme example. Remember these copper heat diffusers?

            http://www.quickshipmetals.com/heat_d...

            Well, instead of putting this diffuser in between the your gas stove and the cooking surface, you put this copper disk below the gas stove. Yes, you put it under your gas stove. That is pretty much what one is doing in the above example.

            The induction field affects the steel lining. In an induction cooking setup, the first heat source is actually the steel, not the stove. So now, you are putting the copper on the bottom of this heat source (steel), while the food is cooking on the other side.

            1. re: kaleokahu
              Chemicalkinetics Nov 2, 2011 06:17 PM

              Continue from above.

              A picture worth a thousand word, so I am giving you this All Clad stainless steel cladded cookware design, and please have the patient for 1 minutes.

              http://a57.foxnews.com/static/managed...

              On an induction cook stove, the magnetic field will affect the exterior "magnetic stainless steel". It will heat up, and the heat will arrive up through the aluminum, and through the 18/10 stainless steel -- no different than heating on a gas stove or an electric stove.

              Now imagine this following *awesome* design. Imagine, the magnetic steel and 18/10 steel are switched -- magnetic steel becomes the interior surface and 18/10 becomes the exterior. What will happen? Now, the magnetic field will heat up the interior magnetic steel (not exterior now), and it will directly heat the food. The aluminum and the 18/10 steel are sitting on the other side.

              Would you call this design stupid for induction cooking?

              1. re: Chemicalkinetics
                kaleokahu Nov 2, 2011 11:20 PM

                Hi, Chem:

                Seems I caught you in an argumentative mood...

                I didn't say that having the induction-capable layer *inside* the pan was the best or even smart. And it might be decidedly LESS than smart if *all* we were talking about was cooking on induction. But even so, it's not, IMO, stupid. If this design, already in production (and excellent on all other hobs) could ALSO work on induction simply by changing the alloy of the liner, that would be an improvement, yes? Would that "fits all" quality disqualify it from being stupid? IMHO, the answer has to be yes.

                Now then, IMHO, you are about 70% right that having the heated layer directly against the food won't reduce hot-spotting. Personally, I think it *will*--a little--simply by conducting the heat away from the pan's bottom. But until we have some empirical data (on a pan that's not yet made), your and my opinions aren't worth a whole lot.

                About the field extending "quiet high", I think it drops off exceedingly quickly, something like the inverse of the square root. This means that there is effectively no heating being induced in the ferritic liner on the walls of the pan. The copper, even though it's on the wrong side, will conduct more heat higher than would otherwise be induced and flow through SS alone.

                While we're at it, the "quiet high" analysis you give this concept can be directed with equal force against... clad. If the liner layer of clad generates heat from induction, are the copper or aluminum layers "wasted"? Would we be better off putting these layers "under the stove"? I think not, and wonder how you can think so.

                Perhaps the best design to put copper on induction would be magnetic steel disk under thick copper, with [name your liner]. This is basically what deBuyer has done with Prima Matera. Is this better than putting the magnetic layer inside? I think so. But is Prima Matera as good on non-induction hobs as bimetal copper on the rest of the choices? Don't bet on it. When you take all hobs into account, i.e., that people do change all the time to/from/between electrical-based and gas, having a highly-conductive pan that works on induction would mean people wouldn't have to downgrade their pans (if they like copper--or upgrade their pans when they learn to hate ECI) when they move to induction. They could buy ONCE.

                Aloha,
                Kaleo

                1. re: kaleokahu
                  Chemicalkinetics Nov 3, 2011 06:29 AM

                  "Seems I caught you in an argumentative mood"

                  No, not really actually. From my angle, it seems you are are in an argumentative mood. :)

                  "But even so, it's not, IMO, stupid. If this design, already in production (and excellent on all other hobs) could ALSO work on induction simply by changing the alloy of the liner, that would be an improvement, yes?"

                  I didn't say that it won't heat up. I said it would be a very bad design for induction cooking.

                  "Personally, I think it *will*--a little--simply by conducting the heat away from the pan's bottom. But until we have some empirical data (on a pan that's not yet made), your and my opinions aren't worth a whole lot."

                  That is the point. There would be heat drawing on the opposite side. I didn't ignore that part, but it is a poor design. Why put a very expensive material, copper, out of the way of the design heat path? Worse, the copper is drawing the heat away. It effectively slow down the steel from heating up. So the design is really using the copper more like a heat sink. It decreases the overall heat response compare to a straight steel pan, and it barely provides any heat evenness if any. Very bad design for induction cooking. This case is so obvious that empirical data is not needed to form some opinions. Think of it this way. Think of a gas stove with a copper pot and a stainless steel lid. Now, think of a stainless steel pot and a copper lid. Do we really need empirical data to know that a copper lid is not as good as a copper body (the lid is in contact isn't going to do a whole lot of good)? I think having the copper on the other side is clearly a worse set up than having the copper in between the magnetic steel and food.

                  "If the liner layer of clad generates heat from induction, are the copper or aluminum layers "wasted"? Would we be better off putting these layers "under the stove"? I think not, and wonder how you can think so. "

                  I actually have no idea what you are saying. I was thinking of an electric stove at that moment. You can put copper underneath the electric coil just like you put a copper layer underneath the inducted steel layer. In the electric stove, the coil is the heat source. In the induction cooking, the magnetic steel is the first heat source. In both case, you are putting the copper underneath the heat source. If you don't like the under the stove example, then there are plenty other examples like the All Clad triply example I gave. Or think of putting a copper handle or copper lid on a steel cookware. It is attached to the steel right? But it is obviously a very poor design.

                  "Perhaps the best design to put copper on induction would be magnetic steel disk under thick copper, with [name your liner]. This is basically what deBuyer has done with Prima Matera"

                  That is what I said

                  ____

                  So to get back to my original point or where this first started. I think to simply make the steel surface magnetic on the Mauviel to accommodate induction cooking is not even a half-hearted attempt to do the correct design.

                  "But is Prima Matera as good on non-induction hobs as bimetal copper on the rest of the choices? "

                  I was not talking about the best design for all cooking heat sources. I was saying that putting a magnetic steel surface above the copper to make it induction compatible is really stupid. I specifically wrote "That would be a rather stupid design for induction cooking..." I certainly wasn't talking about gas cooking or electric cooking. Otherwise, I would have said that in the very beginning. I only mention it is a stupid design after induction cooking was bought up.

                  "having a highly-conductive pan that works on induction would mean people wouldn't have to downgrade their pans"

                  With that design of copper body, magnetic steel lining, it would be a downgrade for sure on an induction cooktop. The design is completely reversed from what a inductive pan should be. Little use of the copper for spreading the heat out, but big use for the copper as a heat sink to slow down the thermal response.

                  1. re: Chemicalkinetics
                    kaleokahu Nov 3, 2011 08:16 AM

                    Hi, Chem:

                    We disagree. Repeating the arguments ad nauseam is unconvincing; in fact, it makes an argument less so. But we may disagree about that, too.

                    All clad pan designs with a magnetic lining are "stupid" under your analysis, you realize that, right?

                    But returning to the MAIN point--which your long replies never addressed--do you think the CoLE differential between austentitic and ferritic SS explains why the latter is not used in copper bimetal?

                    Cheers,
                    Kaleo

                    1. re: kaleokahu
                      Chemicalkinetics Nov 3, 2011 08:40 AM

                      kaleo,

                      "Repeating the arguments ad nauseam is unconvincing"

                      I stepped through my argument very carefully and describe the overall heating pattern and heating mechanicsm. I cannot make you believe it, but if you want to provide your point, then you have to provide more evidence and describe your thinking process more. You have never stepped through your argument. In a previous post, you have done the same. On the copper pan in oven, you have talked about thermal conductivity about how copper cookware act in an oven. "... I'm wondering, since copper's conductivity is dramatically superior to CI, AND the specific heat (heat holding capacity) is better by weight, wouldn't very thick copper both: (a) hold the heat better when dehors the oven; and (b) more quickly regain the heat when put back in?"

                      No, thermal conductivity has a secondary effect in an oven. It is the photo adsorption matters most in the oven. As for the specifically heat, it acts both as pro and as a con for reheating, so it even out. In this current post, I think you have something mixed up. Like I said, it is like to putting a copper plate underneath an electric coil vs on top of an electric coil. If they seem the same to you, then I dont' know what to say.

                      "All clad pans with a magnetic lining is "stupid" under your analysis, you realize that, right?"

                      No, I don't realize the All Clad scheme is stupid under my analysis. If anything, I argued it is the correct cladding order. I wrote "Now imagine this following *awesome [opposite to All Clad]* design. Imagine, the magnetic steel and 18/10 steel are switched....Would you call this design stupid for induction cooking?" Please read carefully, I argued FOR the current All Clad scheme, and argued AGAINST the opposite cladding scheme -- which would have been the same as the copper case.

                      "But returning to the MAIN point..."

                      Sorry, that was never my main point which is probably why I did not address it, and I am pretty sure that was not the orignal poster's main point neither.

                      1. re: Chemicalkinetics
                        kaleokahu Nov 3, 2011 09:43 AM

                        Hi, Chem:

                        I'm missing why you're so personally invested in this as to dig up out-of-context old posts. I have been reading (and "stepping") carefully. Have you?

                        I'm going to give this one more little steppy try. I like your latest analogy about the copper plate under the coil better (before, you said under the stove). But to be apt, this analogy must be with *placing the coil at the bottom of a copper pan*. If the coil is in solid, fused contact with the pan's bottom (as is the case with SS linings), heat from the coil is going to flow up the copper sides of the pan, and put at least a part of it into the contents. This is exactly what happens with all full clad (not All-Clad as you misread) on induction which has a ferritic lining--the heat induced at the bottom of the pan is also going elsewhere, namely up the walls.

                        Let's say, 100 years from now, we're all dumbed down enough to buy WidgetCo's 27-layer fully-clad ware. Layer 27 is the liner in contact with the food, and it is ferritic and in the induction field. Are layers 1-26 wasted?

                        I take it you have no interest in answering my question posed above: Do you think the CoLE differential between austentitic and ferritic SS explains why the latter is not used in copper bimetal? That was the main point of my original post on this thread, to which you responded.

                        Aloha,
                        Kaleo

                        1. re: kaleokahu
                          Chemicalkinetics Nov 3, 2011 11:01 AM

                          "I'm missing why you're so personally invested in this as to dig up out-of-context old posts. I have been reading (and "stepping") carefully"

                          I brought it up as an example, that sometime you misinterpret people's statements and debate on something else. I support the All Clad design for induction, but you wrote 'All clad pan designs with a magnetic lining are "stupid" under your analysis', which I promise you that it is not true.

                          "If the coil is in solid, fused contact with the pan's bottom (as is the case with SS linings), heat from the coil is going to flow UP the copper sides of the pan, and put at least a part of it into the contents."

                          If we are discussing my example, then the copper is on the bottom not on the top, so heat won't be flowing up to the copper, and there is no copper side to speak of. Are you talking about a different example? The attached photo is what I was talking about. The two designs are vastly different.

                          "This is exactly what happens with all full clad (not All-Clad as you misread) on induction which has a ferritic lining--the heat induced at the bottom of the pan is also going elsewhere, namely up the walls."

                          I am not entirely following, so I will just say that I don't know.

                          "I take it you have no interest in answering my question posed above: Do you think the CoLE differential between austentitic and ferritic SS explains why the latter is not used in copper bimetal? That was the main point of my original post on this thread, to which you responded."

                          Not really interested.

                           
                          1. re: Chemicalkinetics
                            dcrb Nov 3, 2011 11:34 AM

                            I think I can explain this. If you take one of those business card sized flexible fridge magnets, and place a few sheets of paper under it and attempt to stick it on the fridge door, it becomes difficult, Each successive layer of a non-magnetic medium reduces the effect of the magnetic field. True, these magnets are not very strong, but it does illustrate the need to put the actual target of the magnetic field, measures in Gauss, as close to the source of the magnetism as possible.

                            Introducing a barrier is counterproductive. While it may work, there has to be some trade of in efficiency, and I understand that the reason induction is desirable is because it is efficient. I may have oversimplified this but that is my take. The copper may look good, be impressive, and be a top performer, but I would view is as a wet blanket on induction. Just my 2 cents worth on this.

                            1. re: Chemicalkinetics
                              kaleokahu Nov 3, 2011 04:17 PM

                              Hi, Chem:

                              "...an example, that sometime you misinterpret people's statements and debate on something else."

                              If I had a dollar for every time you've done that, I'd have every piece of cookware made. Are you sure you want to go there?

                              Let's look at your bottom schematic. Heat generated in the top layer will go both up into the food *and* down into the copper (and thence up the walls). This *actually happens* to some degree in all full clad that has a magnetic interior lining above one or more conductive ones.

                              This may not be an ideal configuration if ALL you're ever going to be cooking on is induction, but it would not be "stupid" in the sense that you'd be better off putting the copper "under the stove".

                              Aloha,
                              Kaleo

                              1. re: kaleokahu
                                Chemicalkinetics Nov 3, 2011 05:26 PM

                                kaleo

                                "If I had a dollar for every time you've done that, I'd have every piece of cookware made. Are you sure you want to go there?"

                                I am ok if you want to go through everything we have said between the two of us.

                                "Let's look at your bottom schematic. Heat generated in the top layer will go both up into the food *and* down into the copper (and thence up the walls)"

                                You know. To be really honest, I understand you until up the walls part. What walls? I draw two discs. There is no wall.

                                "This *actually happens* to some degree in all full clad that has a magnetic interior lining above one or more conductive ones. "

                                Yes, this is true for some of the cladded cookware, but rarely happen to the very top layer. For All Clad stainless steel line, the magnetic layer is the most outer layer. In Debuyer Affinity cookware, it is not. Affinity has the magnetic layer in the 6th layer of the total 7 layers, but there are 5 layers above it before reaching the cooking surface, so it is definitely on the lower bottom. Moreover the 7th layer is really to provide stainless inert ability, not for conductivity even for traditional cooking. If you find another cladded cookware where the magnetic layer is up on top, then I will call it stupid for induction cooking as well.

                                "This may not be an ideal configuration if ALL you're ever going to be cooking on is induction"

                                Although it is technically "not ideal", it is an understatement. It is like saying lead poisoning is "not good" instead of saying it is "bad". This copper design is the opposite of an ideal induction cookware design. I wrote it the very first time: "That would be a rather stupid design for induction cooking" I said induction cooking. I didn't say this design is stupid for gas cooking.

                                "but it would not be "stupid" in the sense that you'd be better off putting the copper "under the stove". "

                                No, but very close because it is a very bad use of the copper. I made many example from "under the stove" to "under the coil" to "reversing All Clad design" to "copper lid" to "copper handle" to the drawing I just made. Of course, it is not actually under the stove, just like the fact that it is not really the same as having a copper lid or copper handle or underneath a heating coil or really reversing the All Clad cladding scheme, but it is a stupid design for induction cooking. It is using the copper in an inefficient manner. You are more than welcome to say this copper design is also not as stupid as putting an extra copper handle along with all the other examples. I agree. None of my examples is the same as the actual case. They are merely illustrating different aspects.

                                Like I said, I am not trying to make you believe it is a stupid design. If you think this is a smart design for induction cooking, fine. I am still believing what I first said, "it (That) would be a rather stupid design for induction cooking." I think it is rather stupid for induction cooking, and you think it is rather smart. Fair?

                                1. re: Chemicalkinetics
                                  kaleokahu Nov 3, 2011 06:53 PM

                                  Hi, Chem:

                                  Well then, let's just start with *this* thread before we move on to others.

                                  "If you think this is a smart design for induction cooking, fine."
                                  "...you think it is rather smart. Fair?"

                                  Who's "misinterpret[ing] people's statements and debate on something else" here? Where in this thread have I opined that this design is smart? I've actually said the *opposite*, and more than once *in this thread*.

                                  The funny part (that would be the opposite of "not even funny") is that this design you call stupid over and over doesn't yet exist. Neither of us knows for sure how it would perform, except I think we're in agreement that the magnetic liner in a copper bimetal pan would indeed cook food, i.e., it would *work*.

                                  How high do you think "quiet high" is for the effective (cooking) height of the induction field? 6mm? An inch? 6 inches? You seem to know about all these things. I'm curious to hear your expert opinion, rather than read more attempts to score points and skew the discussion.

                                  Aloha,
                                  Kaleo

                                  1. re: kaleokahu
                                    dcrb Nov 3, 2011 07:17 PM

                                    If I may: Having read thru all the above several times, I believe that the point to be made is that for induction to work, the cooking vessel must react to the magnetic field. To generate the heat necessary to cook, there must be great resistance to wit there is very little resistance in copper and aluminum, therefore, little to no heat. That is why placing the copper between the cooking surface of the cooker and the metal that must supply the resistance is a poor design, such as placing a copper disc below the cooking element Chem was referring to. Poor resistance equals poor performance.

                                    I attempted with a couple of links to illustrate this process for those of use with little to no first hand experience. We have an induction hotplate/single burner, what ever. It works. Basically, manufacturers say if a magnet sticks, the pan will work on induction. Magnets supplied with these hotplates are very weak, which is why I used the fridge magnet as an example.

                                    Not taking sides here, just trying to simplify things.

                                    1. re: dcrb
                                      kaleokahu Nov 3, 2011 08:54 PM

                                      Hi, dcrb:

                                      With respect, I don't think electrical resistance or a lack thereof plays a part in this. If it did, Visions glass cookware would be the champ.

                                      Nor do I think that things placed between the induction coil and the ferritic "heating: layer (e.g., the ceran cooktop surface, air, paper towels, parchment, enamel, aluminum, copper, scads of clad, etc., etc.) do much to moderate or interfere with the field. I suppose by sheer dint of *elevation* you could shim up the heating layer(s) to the point where the field drops off (it does drop off very fast with distance), but I think the propagated field just does what it does, regardless of what cookware is placed in it.

                                      But hey, I'm sure I'll be corrected soon.

                                      Aloha,
                                      Kaleo

                                      1. re: kaleokahu
                                        dcrb Nov 3, 2011 10:00 PM

                                        The heating layer you are referring to is the resistance layer. It is the resistance that generates the heat. Any object contained in contact with the resistance will get warm or hot. And you are correct in that the items you mentioned above have little to no resistance. I read somewhere and cannot remember where, that the induction burner is technically off until a pan with magnetic properties comes in contact with it. In other words, no heat, just a hum. But since I cannot recall where I read it, I will call it an unsubstantiated opinion.

                                        "With respect, I don't think electrical resistance or a lack thereof plays a part in this. If it did, Visions glass cookware would be the champ." I'm not sure what you meant by this. Resistance produces heat in induction cooking. And I don't understand the reference to Visions cookware. It isn't even pertinent to the discussion. If you hadn't looked at it yet, here is a link posted earlier. It explains induction methodology ;

                                        http://www.popularmechanics.com/home/...

                                        1. re: dcrb
                                          kaleokahu Nov 4, 2011 10:04 AM

                                          Hi, dcrb:

                                          Again with respect, you and Popular Mechanics are leaving out the most important parts of the picture. Yes, the heat is generated within what you call the resistance layer. But that material's overall resistance isn't what makes induction work in the kitchen. The field and its eddy currents can make current flow in most metals (witness induction furnaces and the coming Japanese "all metal" cooktops). However, without magnetic permeability, almost no heat is generated on a home hob. So, in the kitchen, two "resistance layers" of equal electrical resistance, one with magnetic permeability (say 432 SS) and one without (say 304 SS), are going to heat differently.

                                          The reason underlying this is that the greater a metal's magnetic permeability, the thinner its skin depth. It is the skin depth in which the heat-generating friction takes place, and the thinner the depth (of the skin, not the metal) the better for cookware. To continue the above SS examples using a real cooking induction frequency (24kHz), The very permeable 432 SS has a skin depth of 0.009 inches. 304 SS, being 200 times less permeable, has a skin depth of 0.112 inches. This equates with a *surface resistance* differential between the two of 3.5 vs 0.25 10-3 ohms/sq inch, respectively. The thin one heats, the other won't very much (should read "won't at all, because the hob's detection circuit prevents the coil from switching on).

                                          My reference to Visions was to disprove that resistivity in and of itself means anything.

                                          Aloha,
                                          Kaleo

                                          1. re: kaleokahu
                                            Chemicalkinetics Nov 4, 2011 10:28 AM

                                            "The field and its eddy currents can make current flow in most metals "

                                            Electric current alone cannot heat up a metal. It has to have resistance. It is wrong to say resistance plays no role. Your argument is that there is current (which is true). But what is after current? How does current turns into heat?

                                            In short, the pan heats up because of RESISTIVE heating (Joule heating).

                                            Q = I x R^2

                                            where Q is heat, I is current, and R is resistance.

                                            There are more than resistivity in an induction cooking sytem, but that is not to say resistance is not part of the equations. It is a very important part. Without resistance, no heat can generate. Minerals alone cannot sustain a human life, but that is not to say mineral is not essential. Your argument of Visions is like saying "I cannot just eat mineals and stay alive, so this disproves minerals mean anything important". It does not disprove resistivity means anything. What it disproves is that resistivity is not the ONLY thing. At the end, resistance plays an important role.

                                            1. re: kaleokahu
                                              dcrb Nov 4, 2011 11:43 AM

                                              Hi Kaleo,

                                              I am cancelling my PM subscription. All these years I thought they knew what they were writing about. Who knew PM would leave out the important stuff.

                                              Thanks for clearing that up.

                                              1. re: dcrb
                                                kaleokahu Nov 4, 2011 12:25 PM

                                                Hi, dcrb:

                                                I'm not sure you're tongue-in-cheek or not. Despite how others might twist what I've written, I was just trying to explain to you why electrical resistance is meaningless without also taking into account other things like frequency, permeability, and the skin depth.

                                                Now, according to some authors (and the theory makes sense to me), you can thin the skin depth and thereby raise the surface resistance enough to generate cooking heat another way. How? By *thinning the metal gauge*. IF, IF, IF you could thin copper enough (I am not saying you could or that it would be "smart"; I even stipulate it would be "stupid")), the surface resistance could be heightened to the point where it would work. It would require thinning the copper down to 1/59 the thickness of an equivalent in ferritic steel. This principle is the explanation for how, sometimes, aluminum foil melts on an indiction cooktop.

                                                Consider keeping your PM subscription--they have such nice drawings.

                                                Aloha,
                                                Kaleo

                                          2. re: kaleokahu
                                            Chemicalkinetics Nov 3, 2011 10:10 PM

                                            "With respect, I don't think electrical resistance or a lack thereof plays a part in this"

                                            dcrb is correct. Electrical resistive heating is the reason why a pan can heat up on an induction stove. Otherwise, why "induction"?

                                            " If it did, Visions glass cookware would be the champ. "

                                            ........All I am going to say is that this is a rather poor argument.

                                            "I think the propagated field just does what it does, regardless of what cookware is placed in it"

                                            No, this is not true. The magnetic field can definitely be changed based on a cookware which interacts with it.

                                        2. re: kaleokahu
                                          Chemicalkinetics Nov 3, 2011 09:33 PM

                                          "Where in this thread have I opined that this design is smart? I've actually said the *opposite*, and more than once *in this thread*."

                                          I asked a question. I didn't actually said you said that, but I do wonder. Let's take one step back, I believe this design is stupid. You said earlier that I am being argumentative. If so, then at least I wasn't being argumentative for the sake of arguing. From the beginning, you told me this design is not stupid at all. You said "Not a complete waste, and therefore not stupid" More importantly, you have been debating with me for several posts now, so it is natural to believe you don’t think poorly of this design. Otherwise, why debate me? So I asked.

                                          Now, you are telling me that you have argued the opposite many times (?!) and that you don't think it is smart. So I wonder who is being argumentative. I really believe it is stupid, and said so. Now, you said you don’t think it is smart, yet you argued against my position. So who is being argumentative here? :D

                                          "this design you call stupid over and over doesn't yet exist"

                                          I don't think a manufacturer would adverstised such a design as induction compatiable, but I can see this actully exists. All it takes is to use a magentic stainless steel lining. So I can imagine it exists in an accidential way.

                                          "How high do you think "quiet high" is for the effective (cooking) height of the induction field? 6mm? An inch? 6 inches? You seem to know about all these things. I'm curious to hear your expert opinion.”

                                          What I wrote is that “the effective height of the induction field is quiet high compare to the stainless steel lining”. A 2-3 mm of copper lifting the steel lining is not going stop the field. Let's face it, you are not really curious in hearing my expert opinion.

                                          “I think it drops off exceedingly quickly, something like the inverse of the square root”.

                                          1/r^2? Is that not magnetic monopole? You think the hob acts like a magnetic monopole? Please explain.

                                          1. re: Chemicalkinetics
                                            kaleokahu Nov 4, 2011 10:25 AM

                                            Hi, Chem:

                                            No you didn't ask. You wrote that I believed the design was smart. It's right there for everyone to see. So is the wide and deep context that proves I don't believe that. You can't rationalize away putting those words in my mouth.

                                            As for the resistance issue, please refer to my answer to dcrb above.

                                            I will not be responding to you directly again on CH. You picked this fight by jumping on a typo (which was fixed before you jumped) and then distorting every point you could, just to argue. Don't believe me? Go back to my first response to the OP and try to find where I advocated *anything*, said any design was "smart". Hell, I was just excited to have a plausible theory for why the bimetal hadn't used ferritic SS. Then you cut in just to argue and score points.

                                            I've counted coup.

                                            Aloha,
                                            Kaleo

                                            1. re: kaleokahu
                                              Chemicalkinetics Nov 4, 2011 10:47 AM

                                              I wrote " I think it is rather stupid for induction cooking, and you think it is rather smart. Fair?" I have a question mark as in a question. Apparently, you have a huge problem when I said the design is stupid. Am I wrong about it?

                                              I certainly did not pick this fight for a typo about the induction vs conduction, and that certainly never came up after the initial suggestion. I said the design is inefficient and stupid for induction. I took a very clear stance. You are the one who picked the fight, and said no to my stance. You didn't annouced your position prior to me making that statement, so how can I pick a fight with "nothing".

                                              I said what I believe. I believe it is stupid for induction and said so. You.. I don't even know what you believe. First, you said it is definitely not stupid. Then, now you said you have argued against it all the time. I don't think most people reading this really know where you stand.

                                              P.S.: As for your resistance point, it is not correct. You just don't like people disagree with you even when it is obvious that you are wrong. You just keep digging in. Like this resistance heating thing. Of course, resistance matters.

                                              1. re: kaleokahu
                                                f
                                                freia Nov 4, 2011 10:49 AM

                                                Hey Kaleokahu!
                                                I've been watching this thread with interest, just to see how long it would take you to arrive at your final conclusion. I got there myself some time ago LOL, based on my participation on different (2) threads. Please keep contributing to CH, your input is always graceful and well intentioned. :)

                                                1. re: Chemicalkinetics
                                                  dcrb Nov 4, 2011 11:50 AM

                                                  Hi Chem,

                                                  Do you think maybe this topic (induction cooking in theory and in practice) needs a post of it's own or has it run its course?

                                                  I believe I am finished.

                                                  dcrb

                                                  1. re: dcrb
                                                    Chemicalkinetics Nov 4, 2011 11:58 AM

                                                    I think it has run its course. I don't know if you are joking about the popular mechanics subscription. It isn't really wrong. It is a bit quick, so people who read it may miss some of the descriptions. If I really think it is very wrong, then I would have said it when you first showed me. Even if you think it is wrong on this topic, it is just one single article. Induction cooking as its name suggested induced current for heating.

                                                    In a traditional resistance coil stove, the electric current generates resistive heating, and then this heat travels to pan.

                                                    In an induction cooking system.

                                                    1) the electric current on the stove generates a magentic field

                                                    2) the magnetic field then generates an electric current on the pan -- which is why it calle "induced"

                                                    3) the induced current in the pan finally generates resistive heating

                                                    So it is almost like the resistive electric coil, except your pan is the coil. It is almost like plugging electricity to each of your pans, except without the wire.

                                                    :)

                                                    Now to quote wikipedia :P

                                                    "Induction heating is the process of heating an electrically conducting object (usually a metal) by electromagnetic induction, where eddy currents (also called Foucault currents) are generated within the metal and resistance leads to Joule heating of the metal."

                                                    1. re: Chemicalkinetics
                                                      dcrb Nov 4, 2011 12:09 PM

                                                      I was joking about cancelling. PM has a tradition of publishing the salient points in most of its articles, and on occasion, as in a letter to the editor, will back up what it says with empirical data or an apology.

                                                      I think most folks come here to learn, or get approval for something they are about to purchase. Or maybe even encouragement.

                                                      I guess that is all from me for this post. Thanks.

                  2. o
                    oooYUM Nov 2, 2011 05:52 PM

                    Hey, Y'all, thanks so much for the replies and reassurances !
                    Also for the chemistry lessons !
                    It takes me back :-)

                    I will go forth and use my cookware with cautious abandon, then !!!!
                    (and Chem, I am just giving examples of the cookware I already have and use,
                    Copper is new for me, and not cheap. I just didn't want to risk doing something silly
                    with, for example, a metal whisk or spoon, or a quick pop into the oven.
                    That's all :-)

                    1 Reply
                    1. re: oooYUM
                      Chemicalkinetics Nov 2, 2011 06:29 PM

                      No problem. Again, normal searing is fine. You just don't want to heat an empty pan too hot and split the cladding. Oh one more thing, you don't want to suddenly cool it too fast either.

                    2. f
                      freia Nov 2, 2011 06:24 PM

                      Here's something with respect to induction cooking and ss lined copper pots:
                      http://www.e-dehillerin.fr/en/cuprino...
                      To quote: thier ss lined professional quality cuprinox are NOT suitable for induction hobs.
                      I bought my entire cookware line from Dehillerin, I have the Induc'Inox pro series, and I love love LOVE it. They wouldn't steer you wrong.
                      So no matter what the technical reason, at the end of the day, they state the ss lined copper pots are NOT suitable for induction cooking.

                      In any event, the OP I don't think mentions an induction cooktop? So it really kinda off topic with respect to the OP's inquiries...
                      :)

                      1. o
                        oooYUM Nov 2, 2011 07:11 PM

                        Hey no worries, but nope, no induction here.
                        I have a gas cooktop and I like it !
                        Again, thanks for all the advice, it's much appreciated :-)

                        1 Reply
                        1. re: oooYUM
                          f
                          freia Nov 3, 2011 07:50 AM

                          Then for gas, your copper clad is going to be amazing! It looks great, and if a nice weight and all, you'll love it. The thing that shies me away from it is the maintenance of the copper (if shiny copper is a priority for you LOL). i recall neighbors of ours who were quite well off had a cleaning lady come in once a week specifically to polish their copper cookware. Seriously!
                          Anyways, if you do check out the Dehillerin site (they're a primo cookware vendor in Paris), they deal in this type of cookware and sell it to pro kitchens, which tells me that it can take a fair amount of intense kitchen use.
                          :)

                        2. tim irvine Nov 3, 2011 04:37 PM

                          This is all convincing me even more firmly of the immense benefit of blissful ignorance. Ah, the glories of being an English lit. major! You had me at "ferric."

                          Show Hidden Posts