To remove rust from an old cast-iron skillet that has been seasoned but not used for years or decades, you can follow these steps:
Scrub the rust: Start by scrubbing the skillet with a stiff brush or steel wool to remove any loose rust particles. Make sure to scrub the affected areas thoroughly.
Create a vinegar soak: Fill a sink or basin with equal parts of water and white vinegar. Submerge the cast-iron skillet in the vinegar solution, ensuring that the rusty areas are fully immersed. Let it soak for 2 to 3 hours or overnight.
Scrub with vinegar and salt: After soaking, drain the vinegar solution and sprinkle a generous amount of coarse salt onto the rusty areas. Use a cloth or sponge to scrub the skillet, using the salt as an abrasive. The salt will help remove the remaining rust.
Rinse and dry: Rinse the skillet thoroughly with warm water to remove the salt and vinegar solution. Make sure to remove all the residue. Dry the skillet completely using a clean towel or by placing it on low heat on the stovetop.
Re-season the skillet: Once the skillet is rust-free and dry, it's important to re-season it to restore its protective coating. Apply a thin layer of vegetable oil or melted shortening to the entire skillet, including the inside, outside, and handle. Use a paper towel to evenly spread the oil, then wipe off any excess. Place the skillet in an oven preheated to around 375°F (190°C) and let it bake for about an hour. Turn off the oven and let the skillet cool inside before removing it.
Regular use and proper maintenance, such as drying the skillet thoroughly after each use and occasionally applying a light coat of oil, will help prevent rust from recurring in the future.