In 1921, a woman in rural Arkansas received a cast iron skillet as a wedding gift. It cooked every meal on a wood stove for forty years, then on a gas range for thirty more. Her granddaughter uses it today. It has been seasoned by a century of lard, bacon fat, and use. It is not a sentimental object. It is a better pan than anything made last year.
Cast iron is an alloy of iron and carbon, with the carbon content between 2% and 4%. That carbon content is what makes it different from steel. It is what gives cast iron its thermal mass: the ability to absorb heat slowly, hold it evenly, and release it consistently across the cooking surface. A cast iron skillet on a gas burner takes five minutes to come to temperature. It then holds that temperature through contact with cold food -- something no thin aluminum pan can do.
The seasoning is polymerized fat. When you cook with fat in cast iron at high heat, the fat molecules bond to the iron surface and to each other, forming a layer of carbonized polymer. Each layer is microscopically thin. Over years of use, these layers build into a smooth, nearly non-stick surface that no commercial coating replicates. The cooking surface of a hundred-year-old cast iron pan is not iron -- it is a century of polymerized fat, impervious to cleaning, immune to scratching, and improving with every meal.
A modern non-stick pan has a polymer coating applied at the factory. That coating degrades with heat, abrades with metal utensils, and eventually flakes. The pan is then discarded. A cast iron pan has no factory coating to degrade. It has whatever seasoning its owners built over its lifetime. The longer it is used, the better it gets. The relationship between a cast iron pan and its cook is the opposite of every disposable product in the kitchen.
The manufacturers who make cast iron well today are the same ones who made it well a hundred years ago. Lodge in South Pittsburg, Tennessee has been pouring iron since 1896. The process is essentially unchanged: molten iron at 2600 degrees Fahrenheit poured into a sand mold, cooled, extracted, cleaned, and seasoned. The machinery is more precise. The iron chemistry is more consistent. The fundamental act of making a cast iron pan is the same as it was in 1896.
If you own a cast iron pan that has been poorly cared for -- rusty, gummy, uneven -- know that it is not ruined. Cast iron is essentially indestructible. Strip it with oven cleaner, sand the rust, season it with flaxseed oil at 500 degrees for an hour, and repeat three times. The pan that emerges is not restored to a previous condition. It is starting over, with a new seasoning built on iron that has been made denser and more refined by decades of heat cycling. The worst thing that can happen to a cast iron pan is being thrown away.