Cleaning a new, unseasoned cast iron skillet can leave white marks due to a process called "white oxidation" or "white rust." This white oxidation occurs when the cast iron comes into contact with water or moisture without any protective seasoning layer. Here's why it happens:
Raw Iron Surface: A new, unseasoned cast iron skillet has a raw iron surface that is susceptible to oxidation. When the iron comes into contact with water or moisture, a chemical reaction occurs, forming iron oxide or rust. In the case of white rust, the oxidation process doesn't fully progress to the typical reddish-brown rust color because it is not yet deeply embedded in the iron.
Lack of Protective Seasoning: Seasoning is a process of applying a thin layer of oil to the cast iron skillet and heating it to create a polymerized layer that acts as a natural non-stick coating. Seasoning not only provides non-stick properties but also protects the iron from direct contact with moisture, preventing rust formation.
When you clean a new, unseasoned cast iron skillet with water, the moisture comes into direct contact with the raw iron surface, leading to the formation of white marks, which are essentially the early stages of rust.
To prevent white marks or white rust on a new, unseasoned cast iron skillet:
Prevent Moisture Exposure: Avoid exposing the skillet to water or moisture. If you rinse it with water, dry it thoroughly and immediately after cleaning.
Seasoning: Properly season the cast iron skillet before use. Seasoning creates a protective layer that helps prevent rust and promotes a non-stick cooking surface.
If your new cast iron skillet has developed white marks, you can follow these steps to address the issue:
Scrubbing: Gently scrub the white marks with a stiff brush or steel wool to remove the oxidation. Rinse the skillet with water and dry it thoroughly.
Seasoning: Apply a thin layer of vegetable oil or flaxseed oil to the skillet's surface, including the handle, and bake it upside down in an oven at 375°F (190°C) for about an hour. This will create a new seasoning layer that protects the cast iron from further oxidation.
By properly seasoning and caring for your cast iron skillet, you can enjoy its excellent cooking properties and prevent rust or white marks from forming.