The brownish-gray patina that develops on old cast iron pans is a result of the seasoning process and the accumulation of oils and fats over time. Seasoning refers to the process of applying a thin layer of oil or fat to the cast iron and heating it to create a polymerized coating on the surface. This coating enhances the nonstick properties and protects the cast iron from rust.
With regular use and proper maintenance, the seasoning on a cast iron pan builds up and becomes darker, resulting in the characteristic patina. The patina forms as the oils and fats bond with the iron, creating a smooth, nonstick surface. The repeated heating and cooking process helps in the development of this coating.
New cast iron pans typically come with a factory pre-seasoning, which is a thin layer of oil or wax applied during the manufacturing process to protect the pan from rust before it reaches the consumer. However, this pre-seasoning is often not as robust as the seasoning that develops over time with regular use.
When you first acquire a new cast iron pan, it's recommended to season it before use to improve its nonstick properties and create a protective layer. This involves coating the pan with a thin layer of oil and baking it at a high temperature. Through repeated cooking and oiling, the pan will gradually develop its patina, similar to the older cast iron pans.
The patina not only enhances the nonstick surface but also helps in preventing rust and improving the overall performance of the cast iron pan. It's a sign of a well-seasoned and well-used cast iron cookware.