By Harold McGee
Iron was a relatively late discovery because it exists in the earth’s crust primarily in the form of oxides, and had to be encountered in its pure form by accident, perhaps when a fire was built on an outcropping of ore. Iron artifacts have been found that date from 3000 BCE, though the Iron Age, when the metal came into regular use without replacing copper and bronze (a copper-tin alloy) in preeminence, is said to begin around 1200 BCE. Cast iron is alloyed with about 3% carbon to harden the metal, and also contains some silicon; carbon steel contains less carbon, and is heat-treated to obtain a less brittle, tougher alloy that can be formed into thinner pans. The chief attractions of cast iron and carbon steel in kitchen work are their cheapness and safety. Excess iron is readily eliminated from the body, and most people can actually benefit from additional dietary iron. Their greatest disadvantage is a tendency to corrode, though this can be avoided by regular seasoning (below) and gentle cleaning. Like aluminum, iron and carbon steel can discolor foods. And iron turns out to be a poorer conductor of heat than copper or aluminum. But exactly for this reason, and because it’s denser than aluminum, a cast iron pan will absorb more heat and hold it longer than a similar aluminum pan. Thick cast iron pans provide steady, even heat.