Lay the cast iron skillet right-side up in a large plastic container, keeping it level.
Fill the skillet with white vinegar.
Allow the skillet to soak for two hours to remove the rust. If the rust is still stubborn after two hours, leave it in for another two hours.
Put on a pair of dish washing gloves to protect your hands.
Run the skillet under clean water to rinse it and then dry the skillet with a clean towel.
Bake the skillet in an oven set to low for two to three minutes to dry.
Remove the skillet from the oven and allow it to cool completely.
Remove the fine layer of rust that has developed on the skillet, using 150-grit sandpaper.
Wipe off any iron dust, using a clean towel.
Season the skillet by applying vegetable oil to a clean cloth and wiping down the skillet.
Place the skillet upside down in the oven and bake it for 45 minutes at 375 degrees Fahrenheit. This protects the skillet from further rust and damage.
Repeat Steps 10 and 11 three to four times for the best results. After one seasoning, however, the cast iron skillet is ready for use.