Questions have been raised about cast iron cookware, whether it can heat evenly or always exhibits hot spots.
Questions have been raised about induction energy sources, whether they are capable of supplying even heat on the insides (the food side) of vessels used on induction cooktops and ranges.
This post will not provide a definitive answer to either question. However, it offers a data point or two that may advance the knowledge base.
The test instruments were our LG LCE30845 induction cooktop and a Nambutetsu (Iwachu brand) pot, a bail-handle cauldron that is about 8" in diameter at the top rim, and has a rounded bottom. We previously have posted photos of the same pot on Chowhound. http://www.chow.com/photos/318806 The rounded bottom of the pot does not actually touch the cooktop, as the pot has three nub feet on which it rests, leaving the bottom of the pot maybe one millimeter above the surface. This pot has worked well as a cooking vessel in the past, not only on induction, but on a ribbon radiant Ceran-top cooking surface. Our sister-in-law in Japan has the same pot, and there she cooks with it on a gas range.
In common with cutipie721 as posted at http://chowhound.chow.com/topics/7418... we have only politically correct, environmentally friendly, unbleached, and therefore natural ecru, parchment paper in our household. So we attempted the "Arnold method" of sprinkling flour in the pot for the scorch test. This introduced some complications to the test, as will be discussed below.
It has been a very long time since we did any baking in which the recipe called for sifted flour, and along the way, our flour sifter has got misplaced. I looked for it, but could not find it. So I attempted manually to sprinkle flour evenly across the bottom of the pot, not very successfully. To even out the distribution of the flour, I used the bottom of a large soup ladle to spread out the flour, which made the thickness of the flour look pretty even in the fairly bright light of our kitchen, but which proved to be the source of the most striking feature of the test.
The four photos below (if they get uploaded properly) show the flour at the bottom of the pot in various stages of heating. In the first photo, taken before the induction burner was turned on, the instantaneous illumination from the camera's flash, combined with the format's inherent contrast, show much more clearly than the naked eye saw with fairly bright ambient illumination the variations in thickness of the flour layer at the bottom of the pot. The dark areas at 3:00 to 7:00, at 9:00 to 10:00, and at 12:00, are nearly vertical sidewalls of the pot that either never were touched with flour at all or from which the flour slid right down toward the floor of the pot. There is a ridge of fairly thick concentration of flour from about 11:00 toward the center of the pot, and a valley of very thin coverage just inside the bare spot on the walls at 9:00 to 10:00. There is a thick concentration around the edge of the floor of the pot from about 11:00 to 3:00, and again, around 7:00, with fair dollops of flour closer to the center at about 2:30 and 7:00.
The second photo shows the pot as the flour just began to scorch; it also shows that I had failed to center the pot on the burner. There is a very even circle of scorch, about 7" in diameter, but an unscorched crescent near the sidewall at the bottom of the photo, where the pot was beyond the burner's circle (on the cooktop); the width of the crescent is slightly exaggerated by the inverted keystoning caused by perspective distortion with close-up photography. Within the browning 7" circle, the degree of browning is completely congruent with, and inversely proportional to, the thickness of the layer of flour. From this, I derive the conclusion that flour is a lousy heat conductor, and it would be unwise to construct cooking vessels entirely of flour.
The third photo shows the pot after the flour had got pretty deeply browned. The 7" evenly browned circle is even more evident in the third photo, as is the fact that the unevenness in the degree of browning on the floor of the pot coincides pretty much exactly with the thickness of the layer of flour being browned: the thicker the layer of flour, the whiter, and he thinner the layer of flour, the deeper brown. The flour piled up along the vertical sides of the pot has barely browned at all, suggesting that there had been little heat conduction up the sides of the pot.
The fourth photo is a closer photo of just the left center of the floor of the pot, in an area where the elevation gradient between a thin layer of flour and an adjacent much thicker layer of flour is steepest. At the upper left of the fourth photo, you can even see a bit of the cast iron surface of the pot itself peeking through the very thin coating of flour at that spot. Were this a photo of the surface of Mars, we might be speculating whether that was snow on the mountain peaks.
There you have it. Another data point.