been on my mind for a while and not been able to un puzzle it.

some pans don't caramelise - my wok and Zaal omelet pan being examples. both are thin steel. the wok will rust the omelet pan wont - so different steels

my curry pan and balti karahi(2) caramelise easily - these are thick, i dont think the karahi rust even though they are heavy iron. the curry pan is black steel (similar to ali which actually caramelise quicker). so different steels.

the question is whats going on. gut feeling is that it must be to do with the temperature in side the pan. to the eye all feel equally smooth - they may not be under cooking conditions - hence the question.

there may be nothing to learn - probably just peace of mind that i've missed nothing that could improve the cooking or pan selection

any thoughts appreciated

A really late reply to Jerry's question above and I realise he may not even see it, but it's a good topic for discussion I think.

My answer to the question posed would be it must be due to the heat conduction provided by thicker aluminium or iron pans. Iron especially is known as a great and efficient conductor of heat. Thin pans like a wok might seem like they would let the heat through quicker but I think the thinness actually works against you in that the surface of the pan which touches the hob heats up so quickly that the rate at which the pan can conduct heat energy will be lower than for a thicker pan made with a good conductor like iron.  For heat to flow there has to be a temperature difference, and the bigger the difference, the faster the flow. A pan which takes the heat away from the hob quicker is therefore going to be conducting more heat to the contents of the pan.

Thicker pan, better conductor (iron or copper), ergo better heat conduction and higher temps at the inside surface of the pan which the curry is in contact with.  This assumes a heat source which relies on conduction through the pan. Of course induction is different in that it heats the pan itself, so the thinner pans might work very well on induction.

This is my top-of-the-head theory, but I don't know of course. Interested to hear other views.

It all comes down to science. Physics and chemistry. Most good conductors of heat are also good conductors of electricity. This property is directly related to the nature of the metallic bonding and the atomic structure as well as the macro structure.
Iron is actually a poor conductor, due to the presence of free carbon. Due to iron cookware being generally heavy it is however a good heat battery. It takes a while to heat up, won't get so hot to burn stuff easily (using a stove this is) and retains what heat it does have. Stainless steel is a poor conductor of heat due to the tight and complex metallic bonding of multiple alloying elements. Copper and aluminium are known good conductors so the heat transfer is noticeably better. Hence copper bottom SS pots. Energy transfer requires the ability of sub atomic particles to move about freely outside the bonding structure.
But physics also tells us that once a pan reaches temperature then all further energy in should be delivered to the food. Why doesn't this actually happen? The opposite of conductivity is insulation. The pan with poor conductivity is actually insulating or protecting the food from heat transfer.. This is a desired feature for some cooking.
Then there is shape. The wok would definitely caramelise food (mine does) as long as it is not overloaded. Just as the material is heating from the bottom the large surface area up top is acting as a heat sink. Woks get pretty hot and caramelisation requires heat but they don't work if overloaded.
Having recently tried my newly acquired aluminium curry pan the noticeable increase in caramelisation was far more than I'd expected.

. I bet if you looked at cast iron under a microscope, the surface would be quite pitted and rough which I would imagine would make food stick to it more readily. It would also have a greater surface area because of that and would increase the chance of the curry caramelising/burning. Dont know what Jerrys currry pan was made off but if its aluminium I would imagine its spun aluminium which again wont that smooth a finish.

Just my thoughts - thats all

There isn't only 1 cast iron material and there are multiple methods of casting within a foundry. The surface finish of a cast iron material is widely variable.

Thanks for setting me straight on the thermal conductivity of iron Livo. Not sure where I got that idea from, probably placing too much faith in the advertising claims of lidl's iron Karahi dish which I was checking out recently.

Rankings of thermal conductivity are measurable. Cast iron still gets hot as do all metals. It's just that they aren't the same and there are well studied scientific and metalurgical explanations. Just as metals have a place on the galvanic scale for corrosion or the scales of hardness, they also vary in all other properties as well. Then you need to take into account the influence of even tiny amounts of alloying other metals, the inclusion of impurities as well as the forming processes and heat treatments used.
There are things that cast iron cookware is brilliant for. It is great for cooking thick steak, whereas the use of an aluminium curry pan would not work so well.

All good scientific stuff, Livo.  A pleasant change from some of the folk myths that abound here.  Thank you.
** Phil.

I am far from a metallurgist Phil but I have some knowledge in basic metallurgy from a previous life.