Copper Pot on Glass Cooktop w/electric element not working
It was a time for a new pot and after reading a hymnal praise to copper cookware everywhere, what we have here is small copper Bourgeat 2.5 mm (!) stainless-lined pot on older (15 yrs?) GE Radiant Range - glass (ceramic) cooktop with electric coils underneath.
The problem is that instead of expected fast heat response in copper pot, I get exactly opposite in ridiculous magnitude.
Boiling water in copper pot took >40 mins (that's for a few quarts, and only to simmerish boil, not real boil) - a feat achievable by old enameled pot in about 15 mins with the same water temperature on the same unit. While this was not totally fair comparison (I dared not crank heat all the way on copper and it had a bit more water) - given that copper is copper I expected it to work so much better.
Yes, bottom of the pot is quite flat (I have a straigthedge - this is the flattest pot my kitchen have seen apparently), and it matches size of surface unit perfectly.
My attempts to come up with a sound physics explanation for the phenomena failed so far. Even given higher heat capacity of copper pot, it should still overtake regular pot in case of full water load.
And if cooktop is not running hot enough, then 'lesser' pots should take forever+.
I have searched this forum and internet in general, and there seems to be people having no issues with copper on ceramic cooktops and then there are occasional mentions of copper not working just like my case (unable to boil a pot of water).
Anybody has a rationale explanation? Anybody figured it out? Or did I get a defective pot?
Thanks for your help!
"GE Radiant Range - glass (ceramic) cooktop with electric coils underneath"
This is because the copper surface is probably reflecting quiet a bit of light/radiation. Like you said, this is a radiant range, not a conductive range. Copper is known to conduct heat fast within the metal itself. No one said it is super fast to absorb the light (radiation). I would expect a shiny stainless steel pot will also has a similar challenge, while a black cast iron or black carbon steel pan will do better. As such, a radiant range has much more similarity with an oven. This is why you rarely hear people argue for copper bakeware. It is not necessary better.
"I dared not crank heat all the way on copper and it had a bit more water"
Why not? The copper pan should be more durable than the enameled cast iron pot. So if you can crank the heat up for the enameled cast iron pot, then you should do the same for the copper pot. It is just very difficult to compare the two pots if they are put on different heat settings. Reflectivity is one of the issues, but if the heat settings are different, then it is just impossible to compare.
Thanks for quick reply and correct physics explanation. Mirror-shiny copper bottom reflecting IR crossed my mind, but then I thought it would end up heating up burner and glass anyhow (with it having nowhere to go), but experiment showed you were correct.
I had been buzy and pot been sitting in a box for a week or more. When I got around to playing with it again, bottom was not all that mirror shiny anymore - I have not cleaned it after first attempt.
With pot half-full of water, on highest heat - roiling boil in 7 minutes! (full pot boiling time was also reasonable - can't remember what it was though) Mystery solved. I plan to fight the urge to ever clean the bottom - so performance should improve even more over time.
Once an object equilibrates with its environment, then its emissivity will become one, or in other words, becoming a blackbody (my advanced degree is actually closely related to blackbody radiation and boltzmann distribution). However, we are not talking about a blackbody here. Thus, like you nicely explained, the emissivity of a brand new polished copper or electroplated copper is very low, whereas copper with an layer of oxidized layer increases the emissivity by more than 20 folds. A big difference -- so this may very well explains the phenomena.
Regardless, it is working for the original poster, VirtualDestructor, so this is good. Interestingly, VirtualDestructor wouldn't have noticed this major difference if he was using say an electric coil stove.
Hmmm... First things first, since your Bourgeat (nice pan, BTW) is bimetal, fear thee not over high heat. Boil away.
Then... if indeed your newborn pan is flat and lidded and still taking ages to boil, I would wonder whether the mirror polish on its baby bottom might be the culprit. The emissivity will change markedly with use and patina.
Still... I am a bit puzzled because I also have a Frigidaire radiant glasstop at my beach house and have never had a slow race with even newly-polished copper. In fact, several of my boil speed tests posted here were run on that 'top.
Curiosity tempts me to suggest you blacken your baby's bottom with stove paint and try again, but you would never forgive me. Instead, I'll suggest that you heat-force a little patina by getting the empty pan nice and hot, until the color changes. This will spoil your polish, but if it works, you will be forever spared the task of polishing the bottom.
Another suggestion: Take your flattest, stoutest, non-aluminum pan into which your Borgeat will comfortably sit, and try again. You should beat 40 minutes by a mile, in which case I believe emissivity/reflection is guilty beyond a reasonable doubt.
Let us know what you find out.
I did find out mirror bottom was the culprit - see my reply to CK. It is working like a champ now :)
Couple of subjective observations about Bourgeat copper pot - hope this helps others to learn from my experience:
* The best looking/better made pot in my subjective opinion :) at least compared to mauviel copper @ store (though that might have been 150) and all-clad lines
* mirror-polished inside -- I love it, my wife hates that (makes water level difficult to see for her)
* correctly done lip - steel covers the lip, other pots I seen have copper lip -- might not matter to you, matters to me :)
* you might find some pots (like mine) are relatively "cheaper" than mauviel/falk - mostly due to more sizes available so you do not have to upsize (not sure if that was isolated phenomena with my pot or there is a theme there)
* handles on a pot are very small -- think sized for 10 yr old europeoid child -- if you are adult, pincer grasp only
* marketed to restaurants, not consumers - so not consumer-friendly purchase experience - you get stuck with dinged-up pots (mine had a lid with a deep (1/16" ?) scratch that was obvious mishandling @ warehouse, not manufacturing defect) and if you do not like it then it is 25% return restocking fee mandated by bourgeat (at that point selling it on e-bay might get you more $$$)
* beware of spouses not used to copper/cast iron handles combo: my wife bawled for half an hour about having to tolerate 'that medieval thing' in the kitchen. Literally. Now I do not think that pot leaves the stove, and it is not me cooking :)
* Very flat bottom as shown by my straightedge.
* Tolerates full heat on my radiant stove. Stove element does not cycle on full heat - copper pot is able to channel away all heat it gets so heating element never gets too hot.
* Need to patiently wait for patina on the bottom to develop for pot to work on radiant stove top. Took about a week for me after first use and forget.
* If you have radiant stove top, you got to be brave enough to ignore all warnings in the manual about dangers of using copper pots on it - problem being melting copper to bond to glass permanently ruining cooktop (i.e. no dry boiling or dragging hot pots)
* best/proper fitting lid I have seen
* somehow it just looks right to me proportions-wise
Have not cooked enough in it to figure out if food tastes better out of it. That's next science project :)
The water should dominate the performance, not the pot. Several quarts of water will soak up a lot of energy getting to the boiling point, then at the boiling point even more energy just changing phase to steam. Meanwhile, as you are putting energy into the pot at the bottom, heat will radiate from the sides of the pot, so that lost energy must be replaced. I expect a pot with lower thermal conductivity in the sidewalls, and the same bottom, would reach a boil faster because of the lower heat loss. You can test this effect by wrapping some sort of insulating layer around the pot.
Edit: After looking up the emissivity numbers, I agree that a shiny copper pot will reflect a significant amount of radiant energy, which will slow the heating.