Inspired by my muse and scourge Caroline, today I ran the first of what I hope to be a series of stovetop experiments designed to test heat "eveness" in pans of different materials and compositions. Today's bout was between 8-inch skillets (both pans having 7" diameter bottoms), one a black-enameled cast iron Le Creuset, the other a non-stick aluminum one by Swiss Diamond. Both pans' bottoms measured about 4mm thick
The test went as follows. I first cut 7" circles of cooking parchment, and placed them in the bottoms of the dry pans. Then I weighted them down by means of the clear glass beans I use for pie weights. The gas hob is a 2.25"-diameter ring, from which--on the dial marker "low"--flames extend to 3 inches overall. Everything started at room temp. My intent was to heat each pan to the point where dark scorching appeared anywhere on the parchment, then remove the beads and see how even any pattern was.
First I tried the aluminum pan. NOTHING for 5, 10, 15 minutes. At about 16 minutes, I could smell some definite toasting. By about 16:30 there was some browning, but only detectable by holding a fresh piece of white parchment up to it for reference. When I stopped the test at 20 minutes, there was NO SCORCHING WHATSOEVER, just a uniform browning across the parchment circle. There was a slight variegation, attributable to the parchment wrinkling as it cooked.
Next up, the Le Creuset. At only SIX minutes, there was darkening in a ring that perfectly matched the 3" flame diameter, which darkening was visible through the glass beans. White in the center and at the periphery. At 10:00, I had a bona fide black scorchspot, friable in the "ring", that was a solid 4" in diameter, but the outer 1.5" of the circle remained quite white. I ended the test at that point out of concern that the parchment might ignite.
My conclusions: (1) The aluminum pan showed no evidence at all of hot-spotting even after 20 minutes, and all signs were that, if it EVER completely scorched, it would be the entire 7" circle uniformly. In other words very even heat. (2) The cast iron pan hot-spotted very quickly at 6 minutes, scorched very strongly at 10 minutes, and never did even brown at the periphery. My sense was that the center of the cast iron parchment would have been ashes before the periphery scorched. (3) To cook evenly in the aluminum pan, you can pretty much leave it be; in cast iron, you have to watch it closely and move/stir your contents back and forth over the hot spot frequently. (4) The cast iron's hot-spotting problem would be even worse in a larger-bottomed pan, which means only a dependable 4" spot for searing, REGARDLESS OF PAN SIZE.
I will post photos of the tests and prints sometime in the next few days. And thyen hopefully repeat the experiment with copper and clad pans.