I've read several different recommendations for seasoning iron skillets and woks. Is there one way that's best?

Iron skillets and woks take to seasoning differently because they're usually made of different metals. They're both essentially iron, but the skillets are made of cast iron, while woks are usually made of spun carbon steel. A cast-iron pan is made by pouring molten metal into a mold, while a spun-steel wok is shaped out of thin sheet metal.

First, let's take a look at that classic, old black iron skillet that has been a kitchen standby for centuries, valued by grandmas and chefs alike for its remarkable ability to hold a uniform temperature.

Many books attribute that ability to the "fact" that cast iron is a good conductor of heat. But the truth is exactly the opposite. The reason it holds its heat so well is that cast iron is a relatively poor conductor of heat: one-third as good as aluminum and only one-fifth as good as copper.

Its low heat conductivity means that a cast-iron skillet will be slow to get hot, because the stovetop burner heats only the bottom surface and the heat is then only slowly transferred to the other parts of the pan. That may sound like a disadvantage, but it's not, because along with its reluctance to get hot comes a reluctance to cool down. So once the pan is heated, you can count on it to remain at a uniformly high temperature for even cooking, without any hot or cold spots. That's just great for making fried chicken and corn bread, as anyone below the Mason-Dixon line will tell you.

On the other hand, iron skillets are a bad choice for sauteing, where you often need to adjust the temperature quickly up or down. Copper, the best heat conductor, is best for that because it can change its temperature on a dime.

Cast iron's other unique property is that, unlike aluminum, copper and stainless steel, it is actually porous. That's because as the liquid metal solidifies in the mold, it shrinks and if more liquid isn't fed in fast enough to make up for the shrinkage, the lost volume shows up as internal pores. Again, that may sound like a disadvantage, and indeed it would be if you tried to use a new cast-iron skillet straight from the store. Foods would stick to it like crazy, because microscopic threads of food would get caught in the holes. But it is cast iron's porosity that allows it to develop a smooth, black, nonstick, "seasoned" surface.

Seasoning Reasoning

Recommendations for seasoning, including those from the two major manufacturers of cast-iron cookware, Wagner and Lodge, vary. The general idea is to coat the surface of the pan with a fat and heat it in a 300- to 350-degree oven for one or two hours, during which the fat seeps into the iron's pores and, after several repetitions, becomes a slick, dark coating that resists sticking.

Most advocate vegetable oil, but John "Hoppin' John" Martin Taylor, Southern culinary expert and author of "The Fearless Frying Cook book" (Workman, 1997), swears you must use only lard or bacon fat. So, which is it? My chemical guess is that it's mostly the unsaturated fats that turn into the varnishlike coating that we're trying to build up. (Techspeak: They oxidize, cross-link and polymerize more easily.) That would argue in favor of using the more unsaturated vegetable oils. But there are enough unsaturated fats even in lard to do the job, so I don't think it matters much which fat you use.

All things considered, then, here's the "best way" to season a new iron skillet, adapted from the recommendations of Lodge Manufacturing Co.: First, scrub off the manufacturer's anti-rust wax coating with a hot, soap-filled steel-wool pad. Rinse with plenty of hot water and dry thoroughly over a slow burner. From that moment on, it must never again see soap or detergent. After all, you're patiently building up an oil-based coating, and you don't want detergent to "clean up" your handiwork. After use, just scrub it with a brush or nylon pad and hot water and dry thoroughly.

Next, melt some Crisco -- a compromise containing both saturated and unsaturated fats -- and wipe it onto all surfaces of the skillet, inside and out, with a paper towel. Place the skillet upside down in a preheated oven at 350 degrees for two hours, letting any excess fat drip off onto a baking sheet or aluminum foil on the rack below. Turn off the oven and let the pan cool inside. Repeat the oiling and heating twice on a new pan and every once in a while thereafter, to build up the patina. The more it's seasoned and used, the better its nonstick properties will be.

Seasoning a Wok

Woks are a slightly different case. Classic Chinese woks were made of cast iron, thinner than our Western cast-iron skillets, but seasonable in much the same way. Today, most good woks are made of thin, spun carbon steel. I'm not talking about those fancy wok-shaped "stir-fry pans," which may be made of anodized aluminum, stainless steel or sandwiches of bonded metals and may even be nonstick coated or, heaven forbid, electrically heated. (My reason for invoking heavenly intervention here is that genuine wok stir-frying is accomplished at very high temperatures over a hot-as-Hades flame, and an electric heating element just won't cut it. Instead of being stir-fried, your food would be stir-steamed.)

Carbon steel is not porous, so its seasoning must take place entirely on the surface. And that happens only a little at a time; it's not a one-shot deal. In fact, the best way to season a wok is to use it daily for a lifetime. But if you're irretrievably middle-aged, do this: Wash off the anti-rust coating on a new wok, dry it thoroughly and start cooking. According to Grace Young in "The Wisdom of the Chinese Kitchen" (Simon & Schuster, 1999), it will acquire a rich mahogany patina after about six months of regular use. And she means regular. "The more you use it," she says, "the more it becomes like a nonstick pan, requiring less and less oil for stir-frying."

Robert L. Wolke (www.professor science.com) is professor emeritus of chemistry at the University of Pittsburgh. His latest book: "What Einstein Told His Barber: More Scientific Answers to Everyday Questions" (Dell, $11.95). Send your questions to wolke@pitt.edu.