In the previous scorchprint thread, the Testmaster employed a Nambutetsu (Japanese cast iron from near Morioka) footed cauldron on an LG induction cooktop burner. The material to be scorched was King Arthur All Purpose flour, inartfully sprinkled by hand onto the dry surface of the interior of the cauldron, then smoothed, not entirely successfully, with the bottom of a large soup ladle. See http://chowhound.chow.com/topics/7544...
Caroline1 suggested that the flour might have spread more evenly had the Testmaster sprayed the interior of the cauldron with PAM first, then discarded the excess flour after sprinkling it over the oiled surface. kaleokahu wondered about how a flatter bottomed piece of cookware might have fared in the same test. The Testmaster has performed a further experiment to address both of those suggestions.
The pan in this second test is a Kuhn-Rikon frypan/sauté pan, which was not purchased as part of the Kuhn-Rikon Duromatic Duo set, but which is, nevertheless, identical to one of the two pans in that set. http://www.kuhnrikon.com/products/pre... A close up photo of the underside of our copy of the pan -- with a ruler to show its diameter at the base -- is the first image accompanying this post. The third image is a photo from above of the naked interior of the pan.
The pan in this test has a completely different construction from the Nambutetsu cauldron used in the prior test. The body of the Kuhn-Rikon is composed entirely of a single layer of heavy gauge NONmagnetic 18/10 stainless steel. A magnet is not attracted at all to the sidewall of this pan. Fused (or bonded) to the base of the pan is a very thin profile aluminum disk. The aluminum layer appears to be at most 1/16" (1.5 mm) thick, and could be a bit thinner than that. Fused (or bonded) to the bottom of the aluminum disk, in turn, is an even thinner disk of magnetic stainless steel of the same diameter; that bottom disk is the only magnetic material in the pan. Despite the predominance of materials that are poor heat conductors and the thinness of the heat-distributing aluminum disk, we have found the pan to be a very satisfactory tool on both induction and noninduction energy sources for a variety of cooking tasks, and I have recommended it as a fine starter pan in a few Chowhound threads.
Because the body of the pan is nonmagnetic, when used on an induction hob all heat that gets to the inside of the pan is generated in the thin disk at the very bottom and must make its way to the interior by heat conduction through the aluminum disk and then through a thick layer of 18/10 stainless steel, which is a poor heat conductor.
The second image in the series is of the induction burner on which the test was conducted. The ruler shows that the burner's diameter closely matches the diameter of the base of the Kuhn-Rikon.
Caroline1, no can of PAM has ever entered our home in the three decades plus that we have lived here. Lacking PAM, the Testmaster dribbled a few drops of Saffola oil into the bottom of the Kuhn-Rikon pan, then, using a paper towel, spread the oil around the bottom of the pan and soaked up all but a very thin film of oil. Flour then was sprinkled as evenly as possible all around the pan's interior, then the pan shaken and jiggled to get flour to every corner of the floor of the pan before the excess was poured out and discarded. Even with this procedure, there was some unevenness to the coating, as may be seen in the fourth of the accompanying photos, taken before the burner was turned on.
Do you see the lunar landscape of the topic line? That really is a photo of the floured Kuhn-Rikon and not a photo of the far side of the moon during a lunar eclipse on earth.
The induction burner was then turned on to 4. (four-dot), roughly the midpoint of the burner's levels. The fifth image shows the beginning of the scorching process about three minutes into the burn. The identical "map of the surface of the moon" shows as when the flour was unscorched. As was the case with the Nambutetsu cauldron, there is scorching all the way across the bottom of the pan, and the variations in the degree of scorching are almost exactly inversely proportional to the very localized thickness of the layer of flour. The "white stripe" from 7:00 to 1:00 is entirely specular reflectons from the on-camera flash. As if it required any proof, we have proved once more that King Arthur flour is a very good insulator.
The sixth image shows the "final" scorch, after about seven or eight minutes. The dimensions of the aluminum disk on the other side of the thick layer of stainless steel are sharply and distinctly outlined, and the scorching is uniform across the entire diameter. The area towards 4:00 in the photo appears to be less scorched than the area around 10:00, but the difference was much less pronounced in person than it appears in the photo, and may be more (though not entirely: see below) an artifact of the angle of incidence of the on-camera flash (see the specular highlights in the 4:00 region) than of differences of degree of scorching.
The seventh and final photo was taken from a different angle and a slightly greater elevation above the pan and more faithfully than the sixth photo represents the in-person appearance. In the final photo, what had been the 4:00 position of the fourth, fifth, and sixth photos now appears at 1:00, and (as in the earlier photos) that area is somewhat less darkly scorched than the area diametrically opposite on the floor of the pan. However, again specular highlights in the (new) 4:00 position show that it probably is the angle of light incidence from the flash that makes the portion of the scorch around 3:00 look lighter, relative to the darker-appearing scorch in the area opposite it at 9:00.
It is not possible with the data available to us at this time to evaluate whether the difference in degree of scorching between the 7:00 and the 1:00 positions in the final image trace to differences in the intensity of the magnetic field from the induction inverter or to differences between the rate of heat conduction from the bottom steel disk through the intermediate aluminum disk through the stainless floor of the pan.
One more data point.